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Many industrial scale water treatment processes depend on ultrafiltration polymer membranes fabricated through highly nonequilibrium methods. Facile control over these nonequilibrium processes has remained elusive, constraining manufacturing facilities and experimentalists alike to rely on trial and error to construct a suitable membrane. Nonsolvent-induce phase separation (NIPS) is a common fabrication technique whereby the immersion of a polymer solution into a nonsolvent bath induces phase separation that ultimately forms the membrane matrix and pores. Although NIPS yields a favorable asymmetric structure, the broad pore size distribution at the surface leaves much to be desired. Addressing this issue, much effort has been devoted to coupling the self-assembling nature of block copolymers with NIPS (SNIPS) to produce next-generation integral-asymmetric membranes with an isoporous surface. The work of this thesis aims to provide insights into both NIPS and SNIPS that serve as guidance for future fabrication efforts. We accomplish this by leveraging dynamical field-theoretic simulations to model membrane morphology formation via NIPS and SNIPS. In a collaboration with experimentalists, we demonstrate that the influence of solvent and nonsolvent variation on morphology and kinetics during NIPS can be tied to changes in the size of the two-phase region. To model SNIPS, we developed a novel workflow using equilibrium self-consistent field theory (SCFT) to approximate an isoporous surface that is stitched onto a film prior to employing dynamical SCFT (DSCFT). Based on results obtained by varying several formulation parameters, we present guidelines for membrane preparation such that the resulting morphology retains an isoporous surface and forms a connection between the surface and substructure throughout the NIPS process.We conclude our work by addressing the question of \textit{which} block copolymer membrane morphologies are ideal for water filtration. To this end, we develop a multiscale workflow that allows us to determine the diffusivity of solute throughout a given block copolymer morphology. Solvated morphologies generated using SCFT are input into a kinetic Monte Carlo scheme that simulates the diffusion of solute through the pores. Our workflow serves as a tool for screening a wide array of structures to aid in the inverse design of desirable membrane morphologies.

Upon cooling below the order-disorder transition temperature, block polymers self-assemble into a wide variety of nanostructured morphologies. When paired with advances in synthetic chemistry that allow unprecedented control over the size and architecture of these block polymers, these self-assembly characteristics make block polymers excellent candidates for use in specialty materials with highly tunable properties. Potential applications of block polymers range from filtration membranes to photonic crystals. As it happens, however, the source of this exemplary potential is also one of the great barriers to its realization. The vast design spaces available for block polymers (through numbers and permutations of chemistries, and architectural features) make possible a potentially limitless variety of morphologies. At the same time, these design spaces combined with the subtlety of mechanisms driving morphology selection make finding systems which adopt those morphologies a daunting task.In this dissertation, we take a computational approach to address the challenge of designing block polymer specialty materials through two broad approaches. First, we directly address the challenges posed by these vast design spaces by developing an open-source software to automate the exploration of polymer parameter space. This software uses a particle swarm optimization algorithm to guide a search through polymer parameter space for positions where self-consistent field theory predicts a targeted morphology will be most stable compared to a set of competing phases. Second, we use computational studies of two classes of diblock blends seeking to understand the mechanisms that stabilize the low-symmetry Frank-Kasper phases in block polymers with the goal of improving the intuition that guides future efforts to design block polymer materials. In the first of these studies, we use an AB/B`C diblock ``alloy'' with miscible corona and immiscible core blocks to probe the effect of conformational asymmetry on the stability of Frank- Kasper Laves phases when the conformational asymmetry is confined to only particular particle positions. This study finds that conformational asymmetry can be either stabilizing or destabilizing for the Laves phases, depending on which particles are impacted. In the second of these studies, we attempt to identify the balance of core and corona bidispersity in AB/A`B` blends which can still enable formation of Frank-Kasper phases. Unfortunately, this latter study was complicated by a series of methodological flaws limiting its utility in the furtherance of block polymer design. Regardless, the flawed study serves as a lesson in proper study design, and the importance of carefully considering complicating factors.

Complex micellar packings which mimic transition-metal alloy crystal structures known as Frank Kasper phases have been serendipitously identified in a range of soft matter since the early 1990s. The set of known soft Frank Kasper (FK) phases presently includes A15, σ, C14, C15, and one instance of Z alongside closely related dodecagonal quasicrystals (DDQCs). These structures boast low symmetry unit cells containing ≥ 7 particles of ≥ 2 distinct shapes and sizes– a notable deviation from the two particles of a single type populating the canonical body centered cubic (BCC) lattice. The discovery of Frank Kasper phases in ostensibly simple diblock copolymer melts cemented the universality of this behavior across soft matter and triggered widespread reevaluation of the phase behavior of particle-forming diblock copolymers aimed at establishing far-reaching geometric principals underlying the formation of these low symmetry phases. This work addresses these concerns from two directions. First core-homopolymer/diblock (A′/AB) blends where diblock particle cores are swollen with core-block homopolymer were demonstrated to form thermodynamically stable Frank Kasper phases, even in diblock systems that do not form them in the bulk. These ideas were subsequently expanded towards low-molecular weight A′/AB blends, where A′ molecular weight was tuned to dictate AB diblock chain packing in the blend, and thus the ensuing impact on particle packing lattice symmetry. These works established simple A′/AB blending as a general strategy for forming Frank Kasper phases. Notably, these experiments were originally designed in analogy to a surfactant system, underscoring the universality of the geometry of complex phase formation across different types of system. The second thrust of this work focused on the nature of the metastable DDQC, which often forms in advance of equilibrium Frank Kasper phases– hence many Frank Kasper phases are known as quasicrystalline approximants. Initially, this involved establishing the conditions for DDQC formation in a crystalline amorphous poly(ethylene oxide)-block-poly(2-ethylhexyl acrylate) OA diblock copolymer with a minority poly(ethylene oxide) fraction. The OA diblock was demonstrated to undergo breakout crystallization at sufficiently low temperatures, erasing the melt particle-packing microstructure. Melting the semicrystalline state below the order-disorder transition of the diblock enable direct access to a supercooled glass-like packing of particles, which offered a platform from which a DDQC could nucleate. Quenching to the same temperature from the thermally disordered state (above the order-disorder transition) instead BCC to nucleate, which directly transitioned to σ, underscoring the requirement of disorder for the formation of the DDQC. Last, X-ray photocorrelation spectroscopy (XPCS) experiments were performed on a binary blend of a pair of poly(styrene)-block-poly(1,4-butadiene) diblock copolymers which forms DDQC at short anneal times, before ultimately transitioning to σ. These XPCS measurements revealed a wealth of dynamic information wherein σ apparently displays faster grain dynamics compared to DDQC at the same temperature in the same system, attributed to the differing grain structures of each phase.

In molecular dynamics (MD) simulations, coarse grained force fields significantly reduce the computational burden when predicting the structural properties of materials, but negatively impact the resulting transport property predictions, typically accelerating the dynamic evolution of the system. Using the methods of equilibrium and non-equilibrium MD simulations, the nanoscale structure of neat polymer grafted-nanoparticle (PGN) assemblies deposited on a smooth surface, and the transport properties of simple linear ethers are explored. Specifically, generic coarse grained bead-spring models are used to reach the time and length scales associated with entanglements, and to isolate the effect of architecture on the nanoscale structure and chain conformations of entangled and hexagonally packed PGN monolayers, which consist solely of nanoparticles (NPs) protected by grafted polymer chains. At increased graft densities brushes are dryer and more aligned, with decreased interpenetration between chains on neighboring canopies. This leads to fewer interparticle entanglements per chain, which are increasingly localized to interstitial regions. Chains also have increased alignment normal to the NP surface at high graft density, and increased intraparticle entanglement density near the surface. The inverse relationship between graft density and the degree of interparticle entanglement of the brush suggests that higher graft density monolayers will have reduced toughness and robustness under strain. Understanding these relationships, and generally connecting experimentally tunable parameters to molecular-scale structure and overall material properties, will provide insight into optimal design of future materials.In the second part of the thesis, finer transferable atomistic and united atom force fields are used to better capture trends in diffusivity and apparent viscosity across a range of temperatures and shear rates for a series of linear ethers. Specifically, trends in zero-shear viscosity with chain length, and force field performance relative to experiments are measured. Furthermore, there are consistent trends in activation energy barriers associated with diffusion and momentum transport across these models and experiments, as well as clear relationships between diffusive time scales, and rotational relaxation times, which are found to be inversely proportional to zero-shear viscosity. These time scales are explored as a means to gauge characteristic time scales of the system’s underlying dynamics, and are used to discuss whether the coarser united atom model can be treated as an accelerated version of its atomistic counterpart. Many transport properties, obtained by integrating equilibrium time correlation functions, are plagued by poor statistics. The relationships identified in this work may enable predictions of poorly behaved collective properties of the system, such as viscosity, from better behaved per-molecule properties, such as diffusion time and rotational relaxation time. Finally, by explicitly including the details of molecular conformations and intramolecular interactions, this work may help toward understanding the properties of fluids at a molecular level.

The current study probes the structure, dynamics, and rheological behavior of associating polymers including ionomers in melts and solutions as well as conjugated polymers confined into nanoparticles, using molecular dynamics (MD) simulations and neutron scattering techniques. The study focuses on two families of associative polymers, ion containing macromolecules and conjugated polymers. Polymers that consist of ionizable groups along their backbone found uses in a broad range of applications. Examples include light weight energy storage and generation systems, and biomedical applications, where the polymers act as ion exchange membranes, and actuators. The ionic groups tend to form clusters that are in the core of many of the applications. Understanding the relationship of cluster properties and the structure and dynamics of ionizable polymers is crucial to optimize current applications and develop new materials with controlled transport, mechanical stability, and desired response to external stimuli. The first part of the study focuses on understanding the structure and dynamics of polystyrene sulfonate melts as the distribution of the ionizable groups varies with random, precise (number of carbons between ionizable groups is exact), and blocky distributions along the backbone, using atomistic MD simulations. We find that the shape and size distribution of clusters as well as the number of unique chains associated with each cluster are affected by the distribution of the ionic groups. The dynamics of the polymer and the mobility of the counterions are affected by both the number and size of the clusters as well as the number of polymer chains associated with each cluster. Following the understanding of the effects of the clusters on polymer melts, the study proceeds to probe the effects of nonlinear elongational flow on associating polymer melts, which are processed into viable materials under elongational flows. This effort contains two components a coarse grain, and an atomistic MD studies. We find that the response of the melts to elongational flows results from the evolution of both the ionic clusters and Van der Waals domains. The coarse grain study shows that clusters break and reform continuously as the chain stretches heterogeneously in the presence of elongational flow. The atomistic study provides details regarding the effect of chain and cluster rearrangements on the response to the flow. Following melts studies, the work probed the segmental motion of slightly sulfonated polystyrene in cyclohexane solutions using the quasi-elastic neutron scattering technique. We find constraint dynamics at larger length scales however the polymer remains mobile on smaller length scales. Adding a small amount of alcohol is enough to release the constraints within the ionic clusters and results in an increase in segmental polymer motion on all length scales. The last part of the study focused on understanding the effects of the number of rigid luminescent polymer molecules, their chemistries, and initial orientation, on the structure and dynamics of soft nanoparticles (referred to as “polydots”). We find that increasing the number of chains confined affects the internal conformation of the polymer chains where side chains substituting the polymer backbone affect the polydots’ shape and stability. Similar to a single macromolecule polydots, these NPs exhibit a glass-like dynamics with relaxation times in a range of microseconds.

The intracellular environment is crowded with macromolecules that can occupy a significant fraction of the cellular volume. This can give rise to attractive depletion interactions that impact the conformations and interactions of biopolymers, as well as their interactions with confining surfaces. We used computer simulations to study the effects of crowding on biologically-inspired models of polymers. We showed that crowding can lead to attractive interactions between two flexible ring polymers, and we further characterized the adsorption of both flexible and semiflexible polymers onto confining surfaces. These results indicate that crowding-induced depletion interactions could play a role in the spatial organization of biopolymers in cells, and they also suggest that macromolecular crowding could be used to alter the spatial organization of cell-free synthetic systems. A major limitation of cell-free expression systems, which are widely used to study gene expression, is the lack of means to achieve spatial control of gene expression components. With a coarse-grained model of DNA plasmids and crowders, we showed that plasmids were uniformly distributed at low levels of crowding but, due to depletion interactions, became strongly adsorbed to confining surfaces at high levels of crowding. These results were experimentally validated by our collaborators using DNA and crowders in cell-sized vesicles. We used kinetic Monte Carlo simulations to study the effect of crowding and confinement on gene expression dynamics and noise, giving insight into experiments. Our work provides insights into the role of crowding and confinement on the spatial organization and dynamics of gene expression in cellular and cell-free systems.

Knots are intriguing topological objects and ubiquitous in biopolymers such as DNA molecules. The occurrence of knots in DNA confounds the accuracy of genomics technologies, such as nanochannel-based genome mapping and nanopore sequencing, that require uniformly stretching the DNA molecules. Knots existing in vivo also influence biological processes, such as DNA replication, and hence leads to cellular malfunction. The control of DNA knots is, thus, significant for genomics technologies and cell survival, which require first understanding the fundamental properties of knotted DNA in a crowded environment. The aim of this thesis is to address fundamental questions related to knot transport in nanochannel-confined DNA molecules, particularly the knot diffusion mechanism, the effect of knots on DNA diffusion in nanochannels and the interactions between two knots. We first determined the knot diffusive behavior along DNA confined in nanochannels to distinguish between two predicted knot diffusion mechanisms, self-reptation and knot region breathing. With a recently developed nanofluidic "knot factory" device, we generated knots in DNA molecules efficiently. The experimental results of knot motion along DNA chains show that knots undergo subdiffusion, i.e. their mean-squared displacement grows sublinearly with time, which supports the knot diffusion mechanism of self-reptation. We then investigated the effects of knots on DNA center-of-mass diffusion in nanochannels, thus resolving the open question which of these competing effects, the shortening of DNA chains or the increased DNA-wall friction, dominates knotted DNA diffusion in nanochannels. To address this question, we measured the diffusivity of DNA molecules before and after knot formation via a combination of the nanofluidic knot factory device for knot generation and laser-induced fluorescence microscopy for DNA observation. The experimental results show that the presence of knots decreases the diffusivity of DNA chains confined in nanochannels. The reduced diffusivity indicates that the DNA-wall friction, rather than the shortening of the confined chain size, dominates the friction of knotted DNA in nanochannels. Our previous work focused on the dynamical properties of single knots. Long DNA molecules are susceptible to form multiple knots in the chains. In the third research project, we investigated the interactions between two knots in nanochannel-confined DNA by analyzing the motion of the two knots along DNA chains. The free energy profiles of knot-knot interactions show that the separated knot state is more stable than the intertwined knot state, with dynamics in the separated knot state that are consistent with independent diffusion of the two knots. The thesis work provides deep insights into the dynamical properties of DNA knots under nanochannel confinement. We hope such fundamental knowledge gained in this dissertation could prescribe avenues for suppression and removal of knots under nanofluidic systems and crowded environments, thereby improving the genomic technologies and controlling knots in living cells.

Block polymers spontaneously self-assemble into a variety of morphologies upon cooling below their order-disorder temperature. Owing to this behavior, block polymers have various potential applications ranging from semiconductors fabrication to filtration devices. Recent discovery of the stable Frank-Kasper phases in diblock copolymer melts resulted in a shift of focus from high-symmetry morphologies to low-symmetry tetrahedrally close-packed phases. While experimentalists have been able synthesize block polymers that exhibit stable Frank-Kasper phases, they could not predictably determine the observed phases a priori. Computational tools can aid in prediction but are rooted in well-developed theories and experimental results. In this dissertation, we aim to develop theoretical understanding of the stability of Frank-Kasper phases that could aid in prediction through a computational study of block polymers guided by experimental data. To this end, we take a three-pronged approach in the dissertation. First, we examined an experimental diblock copolymer/homopolymer system which produces a variety of Frank-Kasper phases. Our computational study reproduced the salient behavior of the system and unveiled a new mechanism for the stabilization of Frank-Kasper phases. Next, we studied the disordered micelle regime, which has consequence in stabilizing metastable Frank-Kapser phases in thermal processing experiments, for conformationally asymmetric diblock copolymer melts. We uncovered a reduction in the window of stability for the disordered micelle regime with increasing conformationally asymmetric. Finally, we compared computational prediction of binary blends of high molecular weight diblock copolymer to experimental results and demonstrated their utility in accessing Frank-Kasper phases. Along with our analysis, we unveiled a potentially new mechanism that may be important in the stabilization of Frank-Kasper phases. We believe that our work in this dissertation provides additional understanding to the behavior of diblock copolymer, specifically in stabilizing Frank-Kasper phases. This work also opens up potential avenues of interest that may further our ability to tailor block polymers for specific applications.

Nature is a constant inspiration for us. The mechanisms on which life is based are, at the same time, incredibly complex and surprisingly harmonious; individual macromolecules interact in a seemingly chaotic dance, but which has an order and a melody. Amyloid fibrils are a class of bio-macromolecules that is being increasingly brought under the spotlight. In vivo, amyloids can be both pathological and functional. In fact, they are responsible of severely debilitating diseases, such as Alzheimer’s and Parkinson’s, but they also assume pivotal roles in key biological functions. In vitro, amyloid fibrils synthesized from food sources are more and more used as building blocks of innovative materials, the applications of which range from filtration of water pollutants to drug delivery. Consequently, extensive studies on how amyloid fibrils interact and how they form gels are pivotal, both for finding novel therapeutic approaches for the above-mentioned diseases, and for optimizing the synthesis of materials that meet human needs, while preserving the resilience of our Planet. Fibronectin is another important biomolecule, which is largely present in the extra-cellular matrix. The heparin-mediated conformational dance of fibronectin tunes its interactions with other key molecules, such as growth factors and, among these, the Vascular Endothelial Growth Factor (VEGF, the role of which is crucial for angiogenesis). A deeper understanding of how fibronectin and VEGF interact would lead to the possibility of synthesizing more effective drugs, the target of which is angiogenesis in pathological conditions (like cancer). This doctoral thesis contains studies on both the biomolecules mentioned above. Regarding amyloid fibrils, the aim of the studies we present is to characterize amyloid fibril gels (both over the course of their formation and structurally, when already formed), and to strengthen them through inclusion of polysaccharides. More in details, we show that in amyloid gels, the preparation of which is based on the passage of ions through a semipermeable membrane, the dynamic of the ions is non-diffusive but, instead, advective. This suggests the presence of a force that acts on the ions, that we hypothesize being arising from the Donnan effect. We also show that the ionic strength of the gels has a key role in tuning the entity and the frequency of restructuring phenomena, the role of which is to release the stresses accumulated by the fibrils over the gelation process. From a structural characterisation perspective, we show that the mesh size of amyloid networks can be measured through Dynamic Light Scattering (DLS) experiments, combining the theory of scattering from semi-flexible polymers together with a rigorous approach that takes the nonergodicity of the studied materials into account. Finally, with a more applied focus, we show an approach to strengthen amyloid fibril hydrogels and aerogels through inclusion of polysaccharides. The sugar chains improve the compression resistance of the materials, without interfering with the surface properties of the amyloid fibrils. In the case of fibronectin, we show how this molecule is able to bind not only with VEGF, but also with an important receptor of this growth factor (VEGFR2). More in detail, heparin has an important role in extending fibronectin molecules, exposing binding sites that can interact with both VEGF and VEGFR2. The interactions are favoured at acidic pH, due to modifications in the protonation state of the binding sites of the ligands: this piece of information deepens the understanding of how hypoxia and low extracellular pH are related to angiogenesis. Moreover, thanks to Surface Plasmon Resonance studies and their modeling, we show that not all the fibronectin molecules interact equally with VEGF and VEGFR2, and can instead be divided into two classes, with different kinetics and affinities. To resume, the presented studies broaden the actual knowledge on amyloid fibrils and fibronectin, and pave the way for synthesizing new functional materials and for facing severe diseases with novel therapeutic approaches.

Solid polymer electrolytes are attractive for use in batteries due to their ease of fabrication, electrochemical stability, and mechanical robustness. However, their low ion conductivity leads to insufficiently low charge/discharge rates for many applications. Our research employs coarse-grained molecular dynamics (MD) simulations to understand ion transport in both salt-doped homopolymers and block copolymers under different conditions, to aid the design of future materials with improved conduction. We first focused on how copolymer nanostructures affect particle diffusion using MD simulations and constrained random walk analysis. Diffusion through randomly oriented grains is 1/3 for cylinder and 2/3 for lamellar morphologies versus an homopolymer system, as previously understood. Diffusion in the double gyroid structure depends on volume fraction and is 0.47-0.55 through the minority phase at 30-50 vol.% and 0.73-0.80 through the majority at 50-70 vol.%. Thus, among randomly oriented standard minority phase structures with no grain boundary effects, lamellae is preferable for transport. Then, we applied a coarse-grained model that includes a 1/r4 potential form to represent ion solvation, allowing us to reproduce experimental behavior of ion diffusion in block copolymers and explore their molecular underpinnings. We show that the trend of increasing diffusion with molecular weight becomes more dramatic as ions are solvated in one polymer block more strongly or as the ion-ion interactions get stronger. In contrast to expectations, the interfacial width or the overlap of ions with the nonconductive polymer block do not adequately explain this phenomenon; instead, local ion agglomeration best explains reduced diffusion. Interfacial sharpening, controlled by the Flory parameter and molecular weight, tends to allow ions to spread more uniformly, and this increases their diffusion. To better understand correlated anion and cation motion, which can significantly reduce the overall ion conductivity, we calculate ion conductivity and the degree of uncorrelated ion motion (inverse Haven ratio) ion mobility under an applied electric field as a function of concentration and interaction strengths. In typical electrolytes, correlation in cation-anion motion is often expected to be reduced at low ion concentrations. However, for these polymer electrolytes with strong ion-polymer and ion-ion interactions, we find cation-anion motion is more correlated at lower concentrations when other variables are held constant. We show this phenomenon is related to the slower ion cluster relaxation rate at low concentrations rather than the static spatial state of ion aggregation or the fraction of free ions. Finally, we screen through salt-doped polymer systems with different ion sizes and polymer dielectric constants. We find that an increase in either polymer dielectric constant or ion size disparity reduces contact ion pairs and aggregates. However, cation conductivity (overall conductivity multiplied by cation transference number) does not always monotonically increase with polymer dielectric constant. At low ion size disparity, stronger polymer dielectric strength effectively reduces ion aggregation as well as the inverse Haven ratio, facilitating cation conduction. On the contrary, at high ion size disparity, increasing dielectric constant decreases cation mobility due to increased preferential solvation of cations versus the larger anion.

In this thesis, we examine a variety of engineered interfaces: polymer thin films—in the morphologies of brushes and LbL bilayers—and polymer membranes. First, this work investigates the swelling/de-swelling behavior of polyelectrolyte brushes of length 2 kDa–39 kDa of the weakly ionizable polyanion, poly(acrylic acid) (PAA) in the presence of KCl at concentrations from 0.1–1000 mM, at pH = 3, 7, and 9, and at grafting densities σ = 0.12–2.15 chains/nm2 using a Quartz Crystal Microbalance with Dissipation (QCM-D). After correcting our data for the effect of the solvent, we find that at pH 7 (above the pKa), at low and moderate grafting densities, our results in the high-salt “salted brush” (SB) regime (Cs > 10 mM salt) agree with the predicted scaling H~Nσ^+1/3Cs^-1/3 , where H is the brush height [1,2]. In the low-salt "osmotic brush” (OB) regime (Cs 0.45 chains/nm2) and in short chains (2 kDa), we see little or no hysteresis, and at an intermediate chain length (14 kDa) and grafting density (0.06 chains/nm2), hysteresis is observed at short timescales but is greatly reduced at longer timescales. We also observe hysteresis in swelling with a KCl cycle of 100-20-100-1000-100 mM at fixed pH=7 for a long chain brush (39 kDa) at low grafting density (0.023 chains/nm2), but not for a short chain brush (2 kDa) at a high grafting density (0.86 chains/nm2). We also revisit the discrepancies between our previous findings and scaling predictions1 for brush height with respect to grafting density. We find that for a standalone PAA brush of sufficient chain length at a pH value at which it is partially charged (4.2), the brush height decreases with increased grafting density in the OB regime in agreement with theoretical predictions [1]. Finally, this work describes the development of electrospun polyacrylonitrile (PAN) membranes featuring novel chemistry to immobilize the heterogenous alkaline catalyst CaO onto the membrane fibers using dopamine-catalyst coordination. The resultant membranes were found to successfully achieve biodiesel when used in the transesterification of crude canola oil. References: [1]Zhulina, E. B.; Birshtein, T. M.; Borisov, O. V. Theory of Ionizable Polymer Brushes. Macromolecules 1995, 28, 1491–1499. [2]Israels, R.; Leermakers, J. F. A. M.; Fleer, J.; Zhulina, E. B. Charged Polymeric Brushes: Structure and Scaling Relations. Macromolecules 1994, 27, 3249–3261.

It is becoming increasingly clear that the next generation of rechargeable batteries for the emerging clean energy landscape will require electrolytes that are fundamentally different from those used in today’s lithium-ion batteries. In addition, it has been shown that the most promising approach to significantly increase the energy density of rechargeable batteries is through the implementation of the Li metal anode. Current electrolytes consist of mixtures of organic carbonates and a lithium salt. They pose safety concerns due to their flammability and are also incompatible with Li metal. Polymer electrolytes, which are mixtures of polymers and a lithium salt, are both less flammable than the organic solvents used currently and have been shown to be compatible with Li metal. Although linear polymers are able to exert some stress on the battery electrodes, which is essential to enabling rechargeable batteries with Li metal anodes, their viscoelastic nature prevents them from enduring stress in the long-time limit. One approach to improving the mechanical properties of polymer electrolytes is to use microphase separated block copolymers, which allows for decoupling of the ionically conducting and mechanically reinforcing properties. The phase behavior of block copolymers, wherein two chemically distinct homopolymer chains are covalently bound, is dependent on two properties: segregation strength, χN, and copolymer composition, f_A. Segregation strength is the product of the Flory-Huggins interaction parameter, χ, and the overall chain length, N; it combines both enthalpic contributions from the monomer-monomer interactions, as well as entropic contributions which are directly related to chain length through the configurational entropy. The copolymer composition is measured in terms of the volume fraction of “block A”, f_A, and dictates the degree of curvature needed to minimize the areal contact between the unlike phases. For a given copolymer composition, when a copolymer has a segregation strength less than (χN)_odt, the copolymer melt will form a homogeneous disordered mixture. When the same copolymer has χN≥(χN)_odt, the copolymer will microphase separate into an ordered morphology such as body center cubic spheres, hexagonally packed cylinders, gyroid phases, or lamellae. The addition of salt to block copolymers allows them to conduct ions, but significantly alters their thermodynamics and resulting phase behavior. It is well-known for symmetric block copolymers, wherein the volume fractions of the two blocks are equal to 0.5, that the addition of salt will increase the segregation strength of the copolymer. For example, a copolymer that forms a disordered morphology in the salt-free state will undergo a disorder-to-order transition and form an ordered lamellar phase once a critical salt concentration is reached. In the simplest case, the increase in χ is linear with respect to salt concentration.It is well-known that ion transport in polymer electrolytes is linked to the segmental motion of the polymer backbone. At short times, the polymer repeat units can be modeled as beads linked together by springs that are characterized by a friction coefficient, ζ. Motion in this regime is known as Rouse dynamics. At longer times, the motion of a segment of a polymer chain is influenced by the presence of neighboring chains that form entanglement constraints represented by tubes of diameter, d. As time progresses, the polymer chain must reptate through the entanglement constraints until it is fully free of its tube and can undergo self-diffusion. The motion of the polymer chain while it is entirely or partially constrained by its tube is known as reptation. Previous studies of dynamics in the Rouse regime have shown that the monomeric friction coefficient decreases as salt concentration increases in polymer electrolytes due to the coordination between the polymer backbone and the cations. In fact, for some polymer electrolytes, the ionic conductivity can be explained entirely by the segmental motion of the polymer. However, no studies have been conducted on polymer electrolytes at time-scales that correlate with reptation. The block copolymer electrolyte used in this research is a well-studied model system: polystyrene-block¬-poly(ethylene oxide) mixed with lithium bis(trifluoromethanesulfonyl) imide (LiTFSI). SEO/LiTFSI was chosen as the model system because it is well-known that the Li salt preferentially segregates into the poly(ethylene oxide) (PEO) domains and the electrochemical properties of PEO/LiTFSI have been fully characterized. The objective of this dissertation is to develop a molecular-level understanding of the effect of salt on block copolymer self-assembly, thermodynamics, and dynamics. Specifically, I will use theories developed for salt-free polymer systems and apply them to data collected on block copolymer electrolytes to determine how the presence of salt changes polymer behavior. In cases where the original theories cannot explain the new data, I will derive new theories to describe the observed phenomenon. In order to conduct these studies, a library of SEO copolymers with precise molecular weights and a wide range of copolymer compositions was synthesized. The first section describes the methods used to synthesize the SEO copolymers with precise molecular weights and compositions and low polydispersities. The research in this dissertation covers a large area of polymer science; therefore, several different experimental techniques were used. Coincidentally, all experimental techniques were centered around scattering applications of both X-rays and neutrons. The second section provides an introduction to the fundamentals of scattering as well as a brief review on the specific techniques used in these studies. The phase behavior of SEO/LiTFSI was determined using small angle X-ray scattering (SAXS). We studied the effect of salt concentration, molecular weight, copolymer composition, and temperature on the morphology of SEO/LiTFSI in sections four and five. In SEO copolymers with a majority polystyrene phase, the addition of salt induced the formation of ordered morphologies. However, unique phase behavior was seen in one copolymer, with a PEO volume fraction, f_EO, of 0.20. In this sample, a reentrant phase transition was found such that the disordered copolymer first formed an ordered morphology, followed by a disordered morphology, followed by a different ordered morphology with increasing salt concentration. The first ordered morphology seen at a low salt concentration was a novel type of coexistence wherein two distinct lattices of the same lattice type was observed. The nature of this type of coexistence was further probed with electron tomography to visualize the lattice structure and resonant soft X-ray scattering (RSoXS) to quantify the volume of salt in each lattice. The goal of section five was to use the morphology data gathered from the SAXS experiments and assemble large experimental datasets of the phase behavior of SEO/LiTFSI. For simplicity, the phase diagrams were constructed at a single temperature of 100 °C. A simple framework based upon of mean-field theory developed for salt-free block copolymers was used to create a phase diagram plotting copolymer morphology as a function of χN and the volume fraction of the salt-containing phase, f_(EO,salt). It was found that the phase behavior of SEO/LiTFSI is qualitatively similar to that of salt-free block copolymer systems. In addition, the effect of copolymer composition and salt concentration was examined on the domain spacing of SEO mixed with two different Li salts. Expressions for the domain spacing as a function of copolymer chain length, composition and salt concentration were developed for both the weak (χN≤10) and strong segregation regimes (χN>10).The following section focuses on the quantification of the thermodynamics of SEO/LiTFSI. Through application of Leibler’s Random Phase Approximation, the Flory-Huggins interaction parameter of the neat, χ_(0,SC), and salt-containing, χ_(eff,SC), SEO copolymers were measured. An expression for χ_(eff,SC) was developed as a function of N,f_EO and salt concentration. It was then used in conjunction with mean-field theory to calculate the critical chain length for ordering, N_crit, as a function of copolymer composition and salt concentration. Two regimes of phase behavior emerged: at f_EO>0.27, the addition of salt stabilizes the ordered phase and at f_EO

Ultrathin films containing neat polymer-grafted nanoparticles (PGNs) show promise for designing next-generation printed electronics and energy storage devices. Our research utilizes molecular dynamics (MD) simulations to understand the structure, entanglements, and mechanical properties of adsorbed neat PGN particles with varying graft density and polymer length, to provide insight towards the rational design of robust materials with precise spacing of inorganic particles.We first simulate individual and pairs of PGNs adsorbed to a surface with varying monomer-surface interactions. For individual PGNs, increasing the monomer-surface adsorption strength causes the polymer chains to spread out to increase contact with the surface, which agrees qualitatively with recent experimental findings. 2D density profiles and radial distribution functions are used to show the combined effect of polymer length and graft density on the monomer packing and canopy shape at various adsorption strengths. A more detailed entanglement analysis is then developed to analyze interparticle entanglements. Pairs of PGNs show increasing particle spacing and decreasing interparticle entanglements with increasing monomer-surface interaction strength.Monolayers of PGNs in a hexagonal spacing are simulated at a favorable surface interaction strength. High graft density particles remain well-structured in the monolayer; however, the moderately grafted particles are less organized due to increased exposure of the nanoparticle surface and is more apparent at weaker monomer-surface interaction strengths. The extent of interpenetration is quantified and shows that moderately grafted PGN particles are more interdigitated than their high graft density counterpart, which results in an increase in interparticle entanglements. Uniaxial deformation of the monolayer displays an increase in strain at failure, and therefore robustness, for moderately grafted particles due to increased interdigitation and interparticle entanglements.Next, the hexagonally spaced PGNs in the monolayer are cooled below the glass transition temperature and uniaxial stretching is applied. Craze growth and behavior in PGN monolayers is compared to pure thin films and experimental TEM images of qualitatively similar systems. Images of the crazes show the craze structure is qualitatively different than bulk crazes and are characteristic of thin films. PGN crazes appear more like a perforated sheet. Density profiles and stress-strain curves are analyzed to characterize the craze formation and deformation behavior. Our work provides a molecular scale picture of how moderately grafted particles exhibit better interdigitation, interparticle entanglements, and increased toughness in the melt or glassy state.Lastly, we introduce a new coarse-grained mapping method to closely match our graft densities to polystyrene-grafted surfaces. We compare brush heights between our simulations of polymer-grafted brush surfaces to experimental data and find good agreement. We then apply this mapping method to PGNs, and simulate PGNs adsorbed to polymer-grafted surfaces at various graft densities. The structure of the PGN and surface chains are quantified, and we relate chain conformations and PGN-brush interdigitation to the mobility of the particle on the surface. These results are a first step in understanding adsorption properties of PGNs on brush surfaces, specifically PGNs adsorbed to a gradient brush surface, which have applications for controlling the spacing and organization of PGNs in thin films.

The main focus of this thesis lies on confining and/or pulling on two important biopolymers, i.e. cellulose nanofibrils (CNF) and amyloid fibrils. The results of these studies have implications for understanding in vivo biopolymer systems, improving the engineering of novel green materials, and furthering concepts in polymer physics. The first chapter introduces the reader to the motivations behind this work, as well as provides background information on CNF and amyloid fibrils and on the major polymer physics theories needed to devise experiments and simulations. In the second chapter, an experiment to study CNF under weak rectangular confinement is displayed. CNF were adsorbed into slits, previously obtained by thermal scanning probe nanolithography. Atomic force microscopy (AFM) coupled with single-molecule statistics allowed me to observe the alignment and self-folding of CNF under confinement. Simulations confirmed that the slits were not simply selecting a preexisting fibril population, but that the CNF were folding upon themselves as a result of the confinement. In addition, a kink preferential bending direction and an inverse correlation between kink angle and number of kinks, i.e. the fewer kinks the higher the angle, were noted. The combination of these observations provides further evidence that the kinks are a result of mechanical breaking. In the third chapter, an experiment to study subtle interplay between concurrent pulling and confinement of amyloid fibrils is explained. This was achieved by pulling the fibrils into a microcapillary device. AFM allowed a detailed single molecule statistics of the system. These results indicated that the extension of the fibrils was force- or confinement dominated at short and large length scales, respectively. This was in contrast to the order of the system, which was confinement-dominated at all length scales. Simulations both confirmed this result and brought to light the existence of other regimes. Therefore displaying the potential to tailor the system through the fine-tuning of the contribution of either effect. This data may in addition help understand in vivo amyloid phenomena in blood vessels, as well as other physiological occurrences involving the stretching and confining of semi-flexible biopolymers. The fourth chapter focuses on a technique to deposit gradients of amyloid fibrils from the liquid-liquid interface while under simultaneous compression, thus imposing macroscopic confinement. Orientation was induced perpendicularly to the compression, from isotropic to nematic. Reproducible transitions, from a monolayer to a bilayer and from a bilayer to a multilayer, were observed. This method brings forth an approach to overcome the engineering challenge associated with manipulating sticky amyloid fibrils. It further shows great potential for investigating amyloid aggregation at interfaces, which is of great relevance for understanding the propagation of certain amyloid fibril-related diseases. In conclusion, confinement successfully produced alignment, independently of the polymer and of the length scale. The effects of confinement can be modulated by adding a pulling force to the system. These experiments may not only be valid for CNF and amyloids, but show great potential for investigating divers biopolymers.

Polymeric materials that incorporate multiple functionalities are crucial in a variety of applications, from adhesives and membranes to thermoplastic elastomers and electrolytes. Control over the length scale of each component is key to designing the structure and resulting properties, driving efforts for greater control in copolymer systems. Controlling comonomer sequence is an attractive tool to reach this goal, as the length scales of assembly can be set by tuning the size and connectivity of different chemistries. However, materials systems that bridge the sequence-specificity of biopolymers and robustness of synthetic polymers are needed to experimentally understand the role of comonomer sequence in multicomponent polymer materials. This work utilizes versatile and scalable polypeptoid chemistry to install sequence-defined chains into traditional polymer systems, focusing on two potential applications. First, the roles of polymer sequence and functionality are investigated in a modular surface-active coating, achieving optimal marine antifouling and fouling release properties with finer length scales of amphiphilicity. Second, the role of comonomer sequence is investigated in self-assembling diblock copolymers, forming lamellae with tunable thermal and morphological properties based on sequence. The findings in this work emphasize the utility of comonomer sequence as a design tool to target both surface and bulk properties of multicomponent polymer materials.

Polymer nanocomposites are materials comprising of nanometer-sized particles embedded inside polymers. The study of dispersion and dynamics of nanoparticles in polymer matrices has important implications in the processing and long-term stability of polymer nanocomposite materials, which have found application in areas such as packaging, energy storage, and biomedical devices, among others. Another factor guiding our interest in such studies is the occurrence of noncontinuum dynamical behaviors as particle sizes become comparable or smaller than the radius of gyration (Rg) of the host polymers. In simple fluids such as polymer melts and solutions where the particle size is much greater than the radius of gyration of the host polymer, the long-time particle dynamics obeys random-walk statistics, and the bulk zero-shear viscosity of the material determines the drag experienced by the particle. In contrast, in polymer liquids (melts or solutions) where the particle size is smaller than the radius of gyration of the host, the effective frictional resistance to probe motion arises from the localized motion of polymer chain segments with size similar to those of the nanoparticle probes. We utilize a combination of theoretical and experimental techniques to examine the noncontinuum diffusion of nanoparticles in polymer nanocomposites. Through fluorescence microscopy we track the motion of nanoprobes in aqueous solutions of linear polyethylene oxide and probe particle dynamics in different regimes of particle diameter (d), with respect to characteristic polymer length scales, viz., the correlation length (ξ), the entanglement mesh size (a), and the radius of gyration (Rg). We show that in entangled polymer solutions when particle size becomes greater than the entanglement tube diameter, nanoparticle dynamics transition from diffusive to subdiffusive, reminiscent of particle transport in a field with obstructions. This last finding is in stark contrast to the nanoparticle dynamics observed in entangled polymer melts where X-ray photon correlation spectroscopy measurements reveal hyperdiffusive dynamics. The conventional wisdom surrounding hyperdiffusive processes calls for the presence of residual stresses or force fields that can bias particle motion. While this can explain the occurrence of hyperdiffusion in aggregating particles or materials close to their glass transition temperatures, this argument cannot explain the occurrence of hyperdiffusion in non-aging and uniform nanoparticle-laden polymer melts or solutions. We design a simple theoretical framework to understand the origins of diffusive and subdiffusive dynamics observed in entangled polymer solutions against the hyperdiffusive dynamics observed in entangled polymer melts and study the role of solvents in setting structural correlations in polymer nanocomposite systems.

Diblock copolymers are among the simplest amphiphilic molecules, and thus provide a model platform for understanding self-assembly in soft matter. The research presented in this work is broadly focused on the interplay between structure and dynamics in particle-forming diblock copolymer melts, motivated by a recent rise in the number of reports describing complex phase formation in these materials. Analogous complex, low-symmetry structures have been observed in hard materials, such as metals and metal alloys, pointing to the existence of underlying universalities within condensed matter physics. In this work, thermal processing methods commonly employed on hard materials are applied to short, compositionally asymmetric poly(1,4-isoprene)-block-poly(±-lactide) (IL) diblock copolymers. Two disordered IL samples exhibiting characteristic spherical micelle fluctuations above the order-disorder transition (ODT) were quenched in liquid nitrogen and reheated to target temperatures. This processing method lead to the formation of unconventional, low symmetry phases that were not otherwise formed by direct cooling from the disordered state, bearing similarities to metallurgy. However, unlike metals, the ordered states below the ODT imprinted particle densities onto the samples that persisted in the disordered state. This remarkable feature is a manifestation of the fluctuating disordered fluid in self-assembling soft materials. A recent report showed that conformational asymmetry in diblock copolymers, or the difference in space-filling capability between each block, is a key factor in complex phase formation. However, the most important parameter in polymer physics is the length of the polymer chain, which in a diblock copolymer may be represented by the invariant block degree of polymerization N ̅_b. In this work, the role of chain length on complex phase formation is investigated by probing the behavior of asymmetric poly(styrene)-block-poly(1,4-butadiene) (SB; N ̅_b ≈ 80) diblock copolymers. This system was devoid of complex phases, in contrast to previous results for short asymmetric poly(ethylethylene)-block-poly(±-lactide) (EL; N ̅_b ≈ 800) diblock copolymers with approximately the same conformational asymmetry. Differences in phase behavior associated with packing and entanglement theory and resulted in calculation of a universal crossover parameter, N ̅_x ≈ 400. In the case of SB, where N ̅_b > N ̅_x, asymmetry in space-filling capabilities are less important and the system exhibits phase behavior analogous to mean-field predictions. Conversely, the N ̅_b < N ̅_x regime places emphasis on conformational asymmetry and presumably other molecular factors that stabilize complex structures. In a diblock copolymer system, a dynamic constraint is imposed upon complex phase formation as mass (chain) exchange between particles is required to accommodate the multiple discrete particle shapes and sizes comprising these structures. In this work, the dynamics associated with particles below the ODT is investigated using dynamic mechanical spectroscopy (DMS) and X-ray photon correlation spectroscopy (XPCS). In the supercooled liquid prior to ordering, DMS and XPCS measurements conducted on a BCC-forming SB diblock copolymer revealed that particle dynamics are dependent on the ergodicity temperature, above which particle rearrangements are mediated by ergodic chain dynamics and below which non-ergodic ‘frozen’ particle motion becomes dominant. Additionally, a new analytical framework was developed to investigate the time evolution of particle dynamics via XPCS, which uncovered a wealth of dynamic features including time-resolved relaxation time and speed distributions associated with particles in grains.

The wide variety of phase behavior associated with polymer mixtures and block polymers enables unprecedented opportunities in developing novel polymeric materials with desired properties. However, the molecular design space of multi-component polymer systems is now so vast that guidance from theory and modeling is essential. The greatest challenge of predictive materials design is the lack of accurate and precise simulation methods in computing the phase diagram of polymer systems, due primarily to difficulties in (i) transferring polymer molecules between condensed phases and (ii) the sensitivity of phase diagram with respect to the interaction parameters used in the simulations. The overarching goal of this thesis is to address the above two problems. In this thesis, advanced sampling techniques of Monte Carlo simulations and accurate molecular models were developed to allow for the accurate and precise calculation of the mixing thermodynamics for binary mixtures. Furthermore, a case study of predictive materials design is presented, where molecular dynamics simulations were employed to explore the phase diagram of block oligomers with various chain lengths, volume fractions, and chain architectures, and thus, to guide the experimental synthesis for molecules with desired microphase morphologies. The work in this thesis lays a solid foundation for predictive materials discoveries using molecular simulations.

Block copolymers are composed of chemically distinct polymer chains that can be covalently linked in a variety of sequences and architectures. They are ubiquitous as ingredients of consumer products and also have applications in advanced plastics, drug delivery, advanced membranes, and next generation nano-lithographic patterning. The wide spectrum of possible block copolymer applications is a consequence of block copolymer self-assembly into periodic, meso-scale morphologies as a function of varying block composition and architecture in both melt and solution states, and the broad spectrum of physical properties that such mesophases afford. Materials exploration and discovery has traditionally been pursued through an iterative process between experimental and theoretical/computational collaborations. This process is often implemented in a trial-and-error fashion, and from the computational perspective of generating phase diagrams, usually requires some existing knowledge about the competitive phases for a given system. Self-Consistent Field Theory (SCFT) simulations have proven to be both qualitatively and quantitatively accurate in the determination, or forward mapping, of block copolymer phases of a given system. However, it is possible to miss candidates. This is because SCFT simulations are highly dependent on their initial configurations, and the ability to map phase diagrams requires a priori knowledge of what the competing candidate morphologies are. The unguided search for the stable phase of a block copolymer of a given composition and architecture is a problem of global optimization. SCFT by itself is a local optimization method, so we can combine it with population-based heuristic algorithms geared at global optimization to facilitate forward mapping. In this dissertation, we discuss the development of two such methods: Genetic Algorithm + SCFT (GA-SCFT) and Particle Swarm Optimization + SCFT (PSO-SCFT). Both methods allow a population of configurations to explore the space associated with the numerous states accessible to a block copolymer of a given composition and architecture.GA-SCFT is a real-space method in which a population of SCFT field configurations ``evolves" over time. This is achieved by initializing the population randomly, allowing the configurations to relax to local basins of attraction using SCFT simulations, then selecting fit members (lower free energy structures) to recombine their fields and undergo mutations to generate a new ``generation" of structures that iterate through this process. We present results from benchmark testing of this GA-SCFT technique on the canonical AB diblock copolymer melt, for which the theoretical phase diagram has long been established. The GA-SCFT algorithm successfully predicts many of the conventional mesophases from random initial conditions in large, 3-dimensional simulation cells, including hexagonally-packed cylinders, BCC-packed spheres, and lamellae, over a broad composition range and weak to moderate segregation strength. However, the GA-SCFT method is currently not effective at discovery of network phases, such as the Double-Gyroid (GYR) structure.PSO-SCFT is a reciprocal space approach in which Fourier components of SCFT fields near the principal shell are manipulated. Effectively, PSO-SCFT facilitates the search through a space of reciprocal-space SCFT seeds which yield a variety of morphologies. Using intensive free energy as a fitness metric by which to compare these morphologies, the PSO-SCFT methodology allows us to agnostically identify low-lying competitive and stable morphologies. We present results for applying PSO-SCFT to conformationally symmetric diblock copolymers and and a miktoarm star polymer, AB$_{4}$, which offers a rich variety of competing sphere structures. Unlike the GA-SCFT method we previously presented, PSO-SCFT successfully predicts the double gyroid morphology in the AB-diblock. Furthermore, PSO-SCFT successfully recovers the the A$_{15}$ morphology at a composition where it is expected to be stable in the miktoarm system, as well as several competitive metastable candidates, and a new sphere morphology belonging to the hexagonal space group 191, which has not been seen before in polymer systems. Thus, we believe the PSO-SCFT method provides a promising platform for screening for competitive structures in a given block copolymer system.

The generation of well-ordered complex structures from constituent block copolymeric building blocks by the spontaneous process of self-assembly is useful in various technologies. The well-defined 3D structures are dictated by complex energetic interplays and their shape is controllable by both preparative conditions and macromolecular design. This dissertation work aims at exploring the effect of chain flexibility and chain topology design changes on phase behavior of block copolymers in solution. Further, we exploit the tunable flexibility of the semiflexible polymers in studying dispersion and controlling macroscale thermal properties in polymer nanocomposites. The experimental design is based on two model systems: The first is based on polystyrene-b-poly1,3-cyclohexadiene (PS-b-PCHD). Here, the semiflexible nature of PCHD is tunable through alteration in the chain microstructure of the polymer backbone. As altered flexibility impacts the ability of chains to pack, which is shown to affect micelle morphology in solution. Further, we exploit the entropic contributions due to changes in chain configuration of PCHD (controlled through microstructure to control the dispersion of silica nanoparticles in matrices varying flexibility. Because we leave the monomer type unchanged, studying PCHD-based materials enables us to draw links between chain configuration and phase behavior. The second system is based on polystyrene-polyisoprene, (PS-PI), where multiple star copolymers were studied in a PI selective solvent. The study highlights how architecture and composition influence self-organization of the topologically-complex polymers in solution. The topological constraints introduced through architecture and composition were unable to induce any morphological changes, however design variation was successful in inducing changes in micelle size. These studies help understand the self-assembly properties of semiflexible and topologically-complex systems and provide means to control micelle properties through macromolecular design. Additionally, the macromolecular design changes also provide an opportunity to control and enhance desired properties in polymer nanocomposites. Thus, the work conducted as a part of this dissertation is very valuable to understand design-structure-property relationships by providing insights into the physics principles operating at the nanometer length scale.

Block polymers provide an accessible route to structured, composite materials by combining two or more components with disparate mechanical, chemical, and electrical properties into a single bulk material with nanoscale domains. However, the characteristic lengthscale of these systems is limited, and the choice of components is restricted to those that are able to undergo microstructural ordering at accessible temperatures. This thesis details routes to overcoming these limitations through the addition of a lithium salt, a blend of homopolymers, or both. Chapter 2 describes a study wherein complex sphere phases such as the Frank-Kasper sigma phase can be observed in otherwise disordered asymmetric block polymers through the addition of a lithium salt. Chapter 3 discusses the development and characterization of a ternary polymer blend of an AB diblock copolymer and A and B homopolymers doped with a lithium salt. Detailed characterization showed that doping blends that are otherwise disordered with lithium salt induced microstructural ordering and largely recovers the phase behavior of traditional ternary polymer blends. A systematic study of the ionic conductivity of the blends at a fixed salt concentration demonstrates that, at a given composition, disordered, yet highly structured blends consistently exhibit better conductivity than polycrystalline morphologies with long range order. Chapter 4 extends the methodology of Chapter 3 and details a systematic study of the effects of cross-linker concentration on the performance of polymer electrolyte membranes produced via polymerization-induced microphase separation that exhibit a highly structured, globally disordered microstructure. Finally, Chapter 5 details efforts to develop a water filtration membrane using a polyethylene template derived from a polymeric bicontinuous microemulsion. Throughout all of this work, the goal is to better understand structure-property relationships at the molecular level in order to ultimately inform design criteria for materials where simultaneous control over morphology and mechanical, chemical, or electrical properties is important.

Recent developments in next-generation sequencing (NGS) techniques have opened the door for low-cost, high-throughput sequencing of genomes. However, these developments have also exposed the inability of NGS to track large scale genomic information, which are extremely important to understand the relationship between genotype and phenotype. Genome mapping offers a reliable way to obtain information about large-scale structural variations in a given genome. A promising variant of genome mapping involves confining single DNA molecules in nanochannels whose cross-sectional dimensions are approximately 50 nm. Despite the development and commercialization of nanochannel-based genome mapping technology, the polymer physics of DNA in confinement is only beginning to be understood. Apart from its biological relevance, DNA is also used as a model polymer in experiments by polymer physicists. Indeed, the seminal experiments by Reisner et al. (2005) of DNA confined in nanochannels of different widths revealed discrepancies with the classical theories of Odijk and de Gennes for polymer confinement. Picking up from the conclusions of the dissertation of Tree (2014), this dissertation addresses a number of key outstanding problems in the area of nanoconfined DNA. Adopting a Monte Carlo chain growth technique known as the pruned-enriched Rosenbluth method, we examine the equilibrium and near-equilibrium properties of DNA and other semiflexible polymers in nanochannel confinement. We begin by analyzing the dependence of molecular weight on various thermodynamic properties of confined semiflexible polymers. This allows us to point out the finite size effects that can occur when using low molecular weight DNA in experiments. We then analyze the statistics of backfolding and hairpin formation in the context of existing theories and discuss how our results can be used to engineer better conditions for genome mapping. Finally, we elucidate the diffusion behavior of confined semiflexible polymers by comparing and contrasting our results for asymptotically long chains with other similar studies in the literature. We expect our findings to be not only beneficial to the design of better genome mapping devices, but also to the fundamental understanding of semiflexible polymers in confinement.

Mechanisms of equilibration in block copolymer micelles were investigated in detail using time resolved small angle neutron scattering (TR-SANS). The model polymers used in this study were polystyrene-b-polyethylenepropylene (PS-PEP) diblock copolymers and corresponding triblock copolymers (PS-PEP-PS, PEP-PS-PEP). When dissolved in squalane, the polymers self assembled into spherical micelles with the PEP blocks forming the solvated coronas, and undiluted PS blocks as the micelle cores. Normal and selectively deuterated equivalent polymers with controlled molecular weight, narrow molecular weight distribution and composition were synthesized by anionic polymerization of styrene and isoprene followed by the selective saturation of the polyisoprene blocks. The structure of polymer micelles were characterized using dynamic light scattering (DLS) and small angle X-ray scattering (SAXS). A contrast matching strategy was employed for the TR-SANS experiments, where separately prepared deuterated and protonated micelles were mixed at equal volume fractions in a solvent containing 42 vol% h-squalane and 58 vol% d-squalane. Chain exchange reduces the mean contrast of the micelle cores in the solvent mixture, thus reducing the SANS scattering intensity, providing a method to characterize the dynamics of the process as a function of time. In this thesis, several aspects of chain exchange mechanisms were investigated. The hypothesis of hypersensitivity of chain exchange rate to the core block length, and the single chain exchange mechanism, were first tested and confirmed in the PS-PEP model micelle system. The chain exchange mechanisms in PEP-PS-PEP and PS-PEP-PS micelles were then investigated, and a remarkable effect of molecular architecture on the chain exchange rate is documented. In addition, this study explores the facilitating role of the corona chains in molecular exchange. It was found that adding PEP homopolymers of size comparable to the PEP blocks into dilute PS-PEP micelle solutions can significantly retard the chain exchange rate. Decreasing the corona block fraction in the PS-PEP polymers also reduced the chain exchange rate, and the concentration dependence of the chain exchange relaxation time constant. Finally, we extended our scope to chain exchange between micelles away from equilibration, i.e., micelle hybridization of two populations of PS-PEP micelles of different sizes. The results of this work suggested quantitatively different mechanisms when the micelle systems are away from equilibration, and a concentration effect was found, even when the micelles are still dilute.

This research focuses on the computational modeling of fluctuations, interactions, phase behavior and structural characteristics of multicomponent polymeric systems. The role of fluctuations is studied in the context of block copolymer melts and polymer blends stabilized using copolymers exhibiting different sequence architectures. The relationship between interparticle interactions and structural characteristics of the aggregates formed in particle-polymer solutions is examined for charged nanoparticle-polymer and charged dendrimer-polyelectrolyte system. A hybrid Monte Carlo and self consistent field theory approach employed in single chain in mean field simulations (SCMF) is utilized in order to achieve the equilibrium morphologies/aggregates in such polymeric systems. We examine the effect of composition fluctuations on the phase behavior of polydisperse block copolymer melts quantified in terms of fluctuation-induced shift in the order-disorder transition temperature from the corresponding mean-field predictions. Fluctuation effects can also play an important role in stabilizing bicontinuous microemulsions phases. To study this effect, we examine polymer blend systems compatibilized by a copolymer having different sequence architectures such as monodisperse and polydisperse block copolymer, and gradient copolymer. We systematically assess the efficiency of such system in forming bicontinuous microemulsions phases. We also study the effect of sequence architecture on the phase behavior of gradient copolymer solutions. We extend above framework to account for electrostatic effects arising from charged polymers and dendrimers. Using such a framework, we characterize the clusters formed due to electrostatic binding between oppositely charged dendrimers and polyelectrolytes. Our results indicate that, the binding is maximum when the charge on dendrimers is balanced by the charge on the polyelectrolytes. We extend the above study to probe the phase behavior of charged nanoparticles suspended in polymer solutions. We examine the influence of polymer concentration, particle volume fraction, and particle charge on the structure and size of clusters. We also examine the influence of multibody effects on the resulting structure of nanoparticle clusters. The charged nanoparticle-polymer solution is seen to exhibit significant multibody effects and the effective two-body interparticle potentials are seen to be a function of nanoparticle density.

In general, the physical properties of polymers intimately depend on the morphology. In this dissertation we investigated the role of morphology on dynamic processes that occur in complex systems possessing appreciably different morphologies: (1) diblock copolymer/homopolymer blends; (2) miscible blends of linear chain polymers; (3) semicrystalline polymer. (i) A-b-B diblock copolymer chains form micelles of A-type coronas and B-type cores, in an A-type host. We investigated the segmental dynamics of polyisoprene (PI) chains in polystyrene-b-polyisoprene (PS-b-PI) melt as well as PS-b-PI/polystyrene (PS) blends. PS-b-PI forms micellar structures of varying geometries within PS hosts of different molecular weight. The glass transition temperatures and dynamics of PI were more strongly influenced by the local geometry than by the dimensions of confinement. The behavior is rationalized in terms of the notion of free volume. (ii) The segmental dynamics of poly(vinyl methyl ether) (PVME) chains in miscible blends of PVME/PS were investigated. These blends are known to be locally compositional heterogeneous. We showed, for the first time, the temperature dependence of the heterogeneity by measuring their dynamics: the PS and PVME chains are mixed more homogeneously at high temperatures, whereas at low temperatures the behavior is indicative of PVME chains relaxing in two distinctly local compositions. (iii) The effect of morphology of a hole-conducting semicrystalline polymer was studied. We showed that the out-of-plane hole transport in conjugated polymer films, poly(3-hexylthiophene) (P3HT), is very sensitive to the morphology of the polymer. Impedance spectroscopy conducted the measurement, which simultaneously extracted the dc conductivity, mobility and carrier density. The out-of-plane carrier mobility of P3HT increases with increasing thickness from 100 nm to ~700 nm, meanwhile the dc conductivity and the carrier density decrease dramatically with thickness in the same range. Such dramatic trends are due to the substrate induced orientation of the crystalline domains in P3HT; unlike the inorganic scenarios, in conjugated polymers the carrier mobility and density are no longer intrinsic properties and can be strongly influenced by the surrounding environment. The studies of these systems provide new insights into the role of morphology on diverse dynamic processes that occur in polymers.

Considerable effort has been given towards using polymers as active materials in many types of organic devices such as photovoltaics, active membranes and sensors as well as drug delivery. A number of the applications of polymeric materials involve thin film geometries; therefore the role of interfacial interactions has garnered a lot of interest of late. However, the influence of interfaces on the physical properties of polymer films in not well understood. One such property is physical aging, which leads to a time-dependence of many properties, including: increased brittleness, enhanced modulus and reduced permeability. Therefore, there is a strong technological and scientific importance to understanding the underlying phenomenon behind this process. In this dissertation three classes of polymers are used in order to investigate the role of interfaces on the dynamic properties of polymer thin films: (1) glassy structural relaxation in star-shaped polymers, (2) free surface dynamics of miscible A/B polymer/polymer blends, and (3) polymer nanocomposites. The structural relaxation rate of polystyrene in the bulk and micron thick films is strongly influenced by the chain architecture. Due to the decreased conformational freedom, and entropic constraints of the chains grafted to a central core exhibited by the star-shaped molecules, the stars exhibit up to a 40% reduction in the relaxation rate relative to their linear counterparts. In the case of supported thin films, the thickness dependence of the structural relaxation rate can be described with a universal model that accounts for to the temperature dependence of the structural relaxation rate as well as the distribution in local Tg throughout the film. In a miscible A/B polymer blend and miscible blend nanocomposites, the local surface composition can vastly differ from the bulk. The lower surface tension of the B component will lead to a surface excess. Because of the differences in the composition near the surface, and the reduced friction coefficient in the vicinity of a particle, the polymer chain dynamics near that interface can be vastly different from that of the bulk. All of these findings have implications in the processing and long term implementation of polymer films in many different applications.

Abstract: Electron beam lithography (EBL) is the leading technology for versatile two dimensional patterning at the deep (10-100 nm) nanoscale. In addition to its reputation as an enabling technology for next generation advances in industry, its ease of use, accuracy, and cost has made it the technology of choice for rapid sub-micron prototyping in academia and research institutes worldwide. Advances in EBL processing have enabled sub-10 nm fabrication using a variety of materials under limited conditions. Repeatable processing at the deep nanoscale, particularly for dense nanostructure fabrication, requires a systematic quantitative study of all processing steps and their intricate interdependencies. In addition, developing future nanofabrication strategies with features approaching molecular length scales, requires a thorough examination of the molecular interactions taking place in EBL processing. This research project investigates EBL processing using PMMA and ZEP resists through an in-depth quantitative study and analysis of process windows for dense grating fabrication. The effect of processing parameters from each EBL stage on process windows is thoroughly investigated. Through the study of process windows and contrast curves, EBL processing strategies are developed and high resolution processing limits in PMMA and ZEP resists are explored. Furthermore, the EBL development stage involving resist-solvent interactions is studied using molecular dynamics simulations in Accelrys Materials Studio software package, and analyzed using the Flory-Huggins polymer physics theory. Finally, optimized processing strategies for dense grating fabrication are demonstrated and techniques are employed for the fabrication of record ultra-narrow (8 nm) suspended SiCN cantilever structures and high aspect ratio polymer fabrication using novel SML resist.

Recent years have seen remarkable progress in our understanding of physical aging in nondisordered systems with slow, i.e. glassy-like dynamics. In many systems a single dynamical length L(t), that grows as a power-law of time t or, in much more complicated cases, as a logarithmic function of t, governs the dynamics out of equilibrium. In the aging or dynamical scaling regime, these systems are best characterized by two-times quantities, like dynamical correlation and response functions, that transform in a specific way under a dynamical scale transformation. The resulting dynamical scaling functions and the associated non-equilibrium exponents are often found to be universal and to depend only on some global features of the system under investigation. We discuss three different types of systems with simple and complex aging properties, namely reaction diffusion systems with a power growth law, driven diffusive systems with a logarithmic growth law, and a non-equilibrium polymer network that is supposed to capture important properties of the cytoskeleton of living cells. For the reaction diffusion systems, our study focuses on systems with reversible reaction diffusion and we study two-times functions in systems with power law growth. For the driven diffusive systems, we focus on the ABC model and a related domain model and measure two- times quantities in systems undergoing logarithmic growth. For the polymer network model, we explain in some detail its relationship with the cytoskeleton, an organelle that is responsible for the shape and locomotion of cells. Our study of this system sheds new light on the non- equilibrium relaxation properties of the cytoskeleton by investigating through a power law growth of a coarse grained length in our system.

In this dissertation, we have explored various aspects of polymer dynamics in dilute solutions, at equilibrium and non-equilibrium conditions, with computational models ranging over multiple length and time scales, using both molecular dynamics and Brownian dynamics (BD) simulations. Our investigations on equilibrium polymer dynamics helps resolve the puzzle of the absence of high frequency modes in the relaxation spectrum of the chain, reported decades ago by Schrag and coworkers. For this, we systematically introduce the various mechanisms acting on the atoms of a short polystyrene chain. Our simulations clearly show that, in terms of a re-scaled time that is based on the chain size and diffusivity of the center of mass, each additional detail causes a slow-down in the relaxation dynamics of the chain backbone bonds. Finally, when all mechanisms are present, including the explicit solvent molecules, the bond relaxation dynamics shows a single exponential decay for a short polystyrene chain with a time scale that is temporally indistinguishable from that of the end-to-end relaxation dynamics, in excellent agreement with the earlier experiments. Next, we investigate the conformational and dynamic behavior of polymer chains in shear flows using BD simulations with chain models encompassing widely varying resolutions. Our simulations reveal multiple regimes for chain deformation as the flow rates range from weak to ultra-high. We show that, in the absence of any excluded volume (EV), the chain compression obtained at high shear rates in several earlier simulations is an artifact of insufficient chain discretization. In the presence of EV, an orientational "locking" at the fully extended state is observed at extremely high shear rates. We show that the chain tumbling at strong shear rates occurs by the formation of loops whose length is limited by the time required to stretch them, and derive scaling laws from a balance of convection and diffusion of monomers in those loops. Our model and results presented here corrects the previously reported scaling laws obtained by using coarse-grained bead-spring models, which fails to capture the correct physics at strong shear rates that can excite a single spring away from equilibrium.

This research focuses on the modeling of surfaces decorated by grafted polymers in order to understand their structure, energetics, and phase behavior. The systems studied include flat and curved surfaces, grafted homopolymers and random copolymers, and in the presence of solvent conditions, homopolymer melt conditions, and diblock copolymer melt conditions. We use self-consistent field theory to study these systems, thereby furthering the development of new tools especially applicable in describing curved particle systems and systems with chemical polydispersity. We study a polymer-grafted spherical particle interacting with a bare particle in a good solvent as a model system for a polymer-grafted drug interacting with a blood protein in vivo. We calculate the energy of interaction between the two particles as a function of grafting density, particle sizes, and particle curvature by solving the self-consistent field equations in bispherical coordinates. Also, we compare our results to those predicted by the Derjaguin approximation. We extend the previous study to describe the case of two grafted particles interacting in a polymer melt composed of chains that are chemically the same as the grafts, especially in the regime where the particle curvature is significant. This is expected to have ramifications for the dispersion of particles in a polymer nanocomposite. We quantify the interfacial width between the grafted and free polymers and explore its correlation to the interactions between the particles, and use simple scaling theories to justify our results. In collaboration with experimentalists, we study the behavior of the glass transition of polystyrene (PS) films on grafted PS substrates. Using the self consistent field theory methods described above as well as a percolation model, we rationalize the behavior of the glass transition as a function of film thickness, chain lengths, and grafting density. Grafting chemically heterogeneous polymers to surfaces in melt and thin film conditions is also relevant for both particle dispersion and semiconductor applications. To study such systems, we model a random copolymer brush in a melt of homopolymer that is chemically identical to one of the blocks. We modify the self-consistent field theory to take into account the chemical polydispersity of random copolymer systems and use it to calculate interfacial widths and energies as well as to make predictions about the window in which perpendicular morphologies of diblock copolymer are likely to form. We also explore the effect of the rearrangement of the chain ends on the surface energy and use this concept to create a simple modified strong stretching theory that qualitatively agrees with our numerical self-consistent field theory results. We explicitly study the system that is most relevant to semiconductor applications - that of a diblock copolymer melt on top of a substrate modified by a random copolymer brush. We explore the morphologies formed as a function of film thickness, grafting density, chain length, and chain blockiness, and make predictions about the effect of these on the neutral window, that is, the range of brush volume fractions over which perpendicular lamellae are expected to occur.

This research presents the synthesis (by anionic polymerization and catalytic hydrogenation) and characterization of two types of block copolymers: CMC and XPX. In CMC, C is glassy poly(cyclohexylethylene) and M, the matrix, can be semicrystalline poly(ethylene) E, rubbery poly(ethylene-alt-propylene) P, or rubbery poly(ethylethylene) EE, or a combination to yield: CPC, CEEC, CEC, CPEEC and CEPC, with fC ≈ 0.18 – 0.30. XPX materials have X = CEC, fC ≈ fE, and fP ≈ 0.40 – 0.60. Block copolymer phase behavior and morphology were examined through a combination of DSC, rheology, SAXS, WAXS and TEM. CMC materials are meltordered due to block thermodynamic incompatibility with TODT > Tg (C) ≈ 147 °C and show lamellar or C cylinder morphologies. The design of XPX yields melt disordered materials up to high Mn with microphase segregation induced by E crystallization. Two high Mn XPX polymers are melt ordered above Tm(E) and show two correlation lengths in SAXS assigned to the C – E and X – P length scales. TEM images indicate that all XPX materials, irrespective of melt segregation, are characterized by composite glassy and crystalline hard domains dispersed in rubbery P at room temperature. Tensile and recovery testing at room temperature show that CMC and XPX materials, with the exception of plastic CEC, behave as thermoplastic elastomers with tunable properties. Interestingly, melt disordered XPX materials have competitive mechanical properties comparable to the strongest CMC polymers, but with advantageous processing. For melt ordered CMC, Tprocess > TODT, which is dependent on Mn, while for melt disordered XPX, Tprocess > Tm(E) ≈ 100 °C independent of Mn. The deformation of melt disordered XPX materials, probed by recovery studies and WAXS, suggests that deformation is first taken by P, then E and finally C, which causes ultimate failure, as agreed in the literature for conventional SBS and SIS thermoplastic elastomers. This implies that strain recovery in XPX materials can be comparable to that of CPC if materials contain low hard block content or are stretched to strains below the onset of E deformation. Finally, a collection of data of mechanical properties, namely modulus E, strain at break εb, tensile strength σTS and tension set εs, obtained from CMC, XPX and previously reported materials were examined. Most notably, E and εs were found to be strongly correlated with the volume fractions of C and E, as properties increase with (fC + fE)δ, where δ = 1 – 2.4. Ultimate properties such as σTS and εs are unaffected by changes in composition as failure is dictated by that of the hard domains and values are similar above a minimum amount of hard block. In addition, E, σTS, and εb are inversely correlated to rubber entanglement molecular weight Me, which implies that modulus and ultimate properties are affected by the ability of the rubber network to redistribute stress by entanglement slippage. However, εs is unresponsive to Me variations, which indicates that irrecoverable deformation in these materials results from deformation of the hard domains.

Graft polymers have polymeric side chains grafted onto a common backbone and exhibit extended conformations due to steric repulsion from densely grafted side chains. The ability to modulate conformation, and thus material performance, has made graft polymers a rich area of research in the last decade. This thesis expands the fundamental understanding of the physical properties of graft polymers in order to aid in the design of novel materials and focuses in three areas: rheology, thermodynamics, and mechanical properties. First, the effect of grafting density on the linear viscoelasticity of graft polymers is investigated. We demonstrate that graft polymers experience the same relaxational modes as linear polymers and their viscoelastic behavior can be described by the same Rouse and reptation theories. The experimental data is compared to scaling models to determine the conformation of the graft polymers, and a new model is proposed to better capture the behavior of experimentally relevant graft polymers. Next, the thermodynamics of densely grafted bottlebrush block polymers is explored. Bottlebrush block polymers were prepared with homopolymer side chains added in blocks along the backbone, varying side chain and backbone length. Their order-disorder transition temperatures were measured by temperature controlled small-angle X-ray scattering. The bottlebrush block polymers display a higher segregation strength compared to linear diblock polymers at the order-disorder transition, indicative of the shielding of the segments near the backbone. The segregation strength at the order-disorder transition decreased with increasing side chain and backbone length. Finally, the mechanical properties of graft polymers with diblock side chains are studied in an attempt to produce tough and sustainable polylactide plastics. The addition of a rubber domain initially toughens the polylactide but the polymers still undergo physical aging and become brittle over time; the time to brittle failure is found to be strongly dependent on the rubber content of the graft block polymers. Pre-straining of the polymers is used to produce stronger and tougher plastics that do not embrittle upon aging.