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High-performance piezoelectric polymers are promising for a broad range of practical applications, such as sensors, actuators, and energy generators in medical devices, wearable electronics, and so...

Rapid and reliable processing methods for forming ordered block copolymer (BCP) materials with low defect density in a thin film geometry are required for many nanotechnology applications. Vertical...

Electrostatic interaction is widely considered to be the main driving force of the adsorption of polyelectrolytes (PEs) on an oppositely charged surface. Therefore, the alteration of charge distribution as a result of varying PE chain structures will directly affect the performance of the adsorption behaviors in the system at a certain monomer concentration. In this work, we studied the effects of chain structure (chain length, Nₘ) as well as sequence variables including charge fraction and blockiness on the adsorption behaviors of block-PEs on an oppositely charged planar surface in the salt-free system using PE-Poisson–Boltzmann equations. Due to the complicated competitions among the translational entropies of PEs and counterions, the conformational entropy of PEs, and the surface attractive interactions, we find that the adsorption amounts show rich behaviors. First, the adsorption amounts of charged ζc and neutral ζₙ monomers both show two-stage behaviors, that is, ζc and ζₙ drastically increase with Nₘ for short chains but moderately increase to an asymptotic value for relatively long chains. Second, the adsorption amounts of charged monomers show non-monotonic behaviors (increase first then decrease) with charge fraction. However, the adsorption amounts of neutral monomers monotonically decrease with charge fraction. Finally, when chain length and charge fraction are unchanged, the adsorption amounts of both neutral and charged monomers are independent of blockiness. Moreover, we find that overcharging can only appear when the bare surface charge density is low enough, while charge reversal and inversion can be observed in the entire range of the bare surface charge density with appropriate conditions. Additionally, our results indicate that the strength of charge reversal and inversion increases monotonically with chain length and charge fraction, while it changes non-monotonically with blockiness.

The spontaneous association of oppositely charged natural or synthetic polyelectrolytes in solution has evoked a great deal of interest from chemical, physical, and biological perspectives. The polymer-dense phases resulting from this phase separation are termed polyelectrolyte complexes or coacervates, PECs. PECs exhibit a range of properties and morphologies, from liquidlike to solidlike states. Though PECs have high water contents, a few of them are known to exhibit a glass transition near room temperature. In this work, the library of glassy PECs is substantially expanded with compositions that exhibit glass transition temperatures, Tg, over the entire working range of aqueous solutions between 0 and 100 °C. A radiochemical method of measuring the volume of pores that usually form in glassy PECs enabled a comparison of Tg with PEC phase water volume fraction, ϕH₂O,PEC. Tg correlated weakly with ϕH₂O,PEC only for a series of PECs in which one of the polyelectrolytes was held constant. In general, Tg was poorly correlated with ϕH₂O,PEC. On the other hand, time–temperature superposition of linear viscoelastic responses provided a classical estimate of fractional free volume of PECs, which correlated well with Tg.

A facile one-step approach for the synthesis of physically and chemically anisotropic polymer particles with tunable size, shape, composition, wettability, and functionality is reported. Specifically, dynamically reconfigurable oil-in-water Janus emulsions containing photocurable hydrocarbon or fluorocarbon acrylate monomers as one of the droplet phases are used as structural templates to polymerize them into precision Janus particles with highly uniform anomalous morphologies including (hemi-) spheres, lenses, and bowls. During polymerization, each interface is exposed to a different chemical environment, yielding particles with an intrinsic Janus character that can be amplified via side-selective postfunctionalization. The fabrication method allows to start with various common emulsification techniques, thus generating particles in the range of 200 nm –150 μm, also at a technical scale. The anisotropic shape combined with the asymmetric wettability profile of the produced particles promotes their directed self-assembly into colloidal clusters as well as their directional alignment at fluid interfaces. We foresee the application of such Janus particles in technical emulsions or oil recovery, for the manufacturing of programmed self-assembled architectures, and for the engineering of microstructured interfaces.

We report direct measurements of interactions, dimensions, and solution behavior of adsorbed nonionic and zwitterionic triblock copolymers as a function of aqueous [NaCl] and [MgSO4] in the range 0...

Polymers in the nanoscale vicinity of interfaces exhibit a broad range of alterations in their dynamics and glass-formation behavior. A major goal in the study of these effects is to understand the...

A simple strategy is presented to achieve well-ordered nanostructures in microphase-separated diblock bottlebrush copolymers (dbBB) for potential opportunities in nanotechnology that require large ...

The static and dynamic properties of a range of molecular weights (2 × 104 to 1.6 × 105 g/mol) of poly(benzyl methacrylate) have been assessed in four different imidazolium- and pyrrolidinium-based...

X-ray photon correlation spectroscopy and small-angle X-ray scattering were used to study the thermally driven motion and hierarchical structure of palladium (Pd) nanoparticles (NPs) in the concentrated solutions composed of polymers with different molecular weights. The Pd NPs were formed by in situ reduction of palladium(II) acetylacetonate (Pd(acac)2) in the solution of poly(2-vinylpyridine) (P2VP) and benzyl alcohol which acted as the reduction agent and solvent. Below the entanglement molecular weight (Me) of P2VP, a diffusion mode was found together with a fractal structure built up by the primary particles spanning over a broad range of length scales. Above Me, a subdiffusive motion was identified along with diffusive motion, and the hybrids formed a fractal structure built by the local clusters assembled by primary particles. The structural differences were attributed to different kinetic pathways of NP organization mediated by attractive interaction between P2VP and Pd NPs as well as the viscosit...

The behavior of polymer melts under planar confinement was investigated using molecular dynamics simulations. Polymers with a range of lengths, from unentangled to highly entangled (N = 25–400), we...

Despite a broad range of commercial applications, polyolefins, including polyethylene (PE) and polypropylene (PP), are not recommended for applications that require long-term exposure to elevated t...

Among numerous research studies focusing on macromolecular crowding and confinement, few are concerned with the medium at a broad range of concentrations, let alone the interplay between the crowdi...

Using molecular dynamics simulations, we study the response of a polymer brush exposed to co-nonsolvent (CNS), which acts as a preferential solvent for the polymer. We investigate a broad range of ...

Using the Poisson–Boltzmann–Flory approach and a cell model, we examine the properties of dendritic polyelectrolytes and counterions in a broad range of molecular weights under variation of dendrim...

Small-angle neutron scattering is used to measure the infinite dilution radius of gyration (Rg,0) for a range of molecular weights (10–250 kg/mol) of perdeuterated poly(ethylene oxide) (d-PEO) in v...

We aim to clarify how the chain length influences the critical flow rate (qc) for flexible linear chains translocating through cylindrical nanopores in the whole length range (9.5 > R/r > 1.0), where R and r represent the chain size and the pore size, respectively. By studying the translocation behavior of both mono- and polydisperse polystyrenes through 20 nm nanopores, we have, for the first time, experimentally revealed that there exist two different translocation regimes, i.e., strong and moderate confinement regimes. In the strong confinement regime (R/r > λ*), qc is found to be independent of the chain length, consistent with the prediction by classical theories, while in the moderate confinement regime (R/r < λ*), qc increases with the chain length significantly, where λ* represents the critical relative chain length. Theoretically, λ* is determined by the critical penetration length (l*), at which the free energy change (ΔE) of a translocating chain reaches its maximum value (ΔE ∼ kBT). For longer...

The microscopic structure of module-assembled thermoresponsive conetworks was systematically investigated as a function of both temperature T and the mole fraction of the thermoresponsive modules r using small-angle neutron scattering (SANS). The conetworks were prepared by end-linking of hydrophilic modules and LCST-type thermoresponsive modules in water by the molar ratio of (1 – r):r. When the hydrogels with 0.02 ≤ r ≤ 0.10 were heated above certain T, nanometer-scale spherical domains were formed by aggregation of several prepolymer modules, whereas for the hydrogel with r = 0.01 such domain formation was not detected in the T range investigated. The size of spherical domains increased with increasing r and T. The observed r dependence of the domain size was theoretically explained by considering the free energy of domain formation, from which we concluded that the equilibrium domain size was determined mainly by the balance between two free energy contributions: the interfacial free energy of domain–...

The self-diffusion of a single large particle in a fluid is usually described by the classic Stokes–Einstein (SE) hydrodynamic relation. However, there are many fluids where the SE prediction for nanoparticles diffusion fails. These systems include diffusion of nanoparticles in porous media, in entangled and unentangled polymer melts and solutions, and protein diffusion in biological environments. A fundamental understanding of the microscopic parameters that govern nanoparticle diffusion is relevant to a wide range of applications. In this work, we present experimental measurements of the tracer diffusion coefficient of small and large nanoparticles that experience strong attractions with unentangled and entangled polymer melt matrices. For the small nanoparticle system, a crossover from suppressed to enhanced diffusion is observed with increasing polymer molecular weight. We interpret these observations based on our theoretical and simulation insights of the preceding article (paper 1) as a result of a ...

We investigate the dynamics of nanoparticles in semidilute polymer solutions when the nanoparticles are comparably sized to the polymer coils using explicit- and implicit-solvent simulation methods. The nanoparticle dynamics are subdiffusive on short time scales before transitioning to diffusive motion on long time scales. The long-time diffusivities scale according to theoretical predictions based on full dynamic coupling to the polymer segmental relaxations. In agreement with our recent experiments, however, we observe that the nanoparticle subdiffusive exponents are significantly larger than predicted by the coupling theory over a broad range of polymer concentrations. We attribute this discrepancy in the subdiffusive regime to the presence of an additional coupling mechanism between the nanoparticle dynamics and the polymer center-of-mass motion, which differs from the polymer relaxations that control the long-time diffusion. This coupling is retained even in the absence of many-body hydrodynamic interactions when the long-time dynamics of the colloids and polymers are matched.

Single-molecule tracking was used to characterize the mobility of poly(ethylene glycol) chains at a solid–liquid interface over a wide range of surface coverage. Trajectories exhibited intermittent motion consistent with a generalized continuous time random walk (CTRW) model, where strongly confined “waiting times” alternated with rapid flights. The presence of three characteristic regimes emerged as a function of surface coverage, based on an analysis of effective short-time diffusion coefficients, mean-squared displacement, and CTRW distributions. The dilute “site-blocking” regime exhibited increasing short-time diffusion, less confined behavior, and shorter waiting times with higher surface coverage, as anomalously strong adsorption sites were increasingly passivated. At intermediate values of surface coverage, the “crowding” regime was distinguished by the exact opposite trends (slower, more confined mobility), presumably due to increasing intermolecular interactions. The trends reversed yet again in ...

Molecular weight distribution plays an important role by giving specific properties to polymeric materials. Despite the recent progress in controlled/“living” radical polymerization, polymer chemists do not have the ability to tune and manipulate the shape of molecular weight distributions (MWDs) (except for a few recent examples). In this article, new synthetic procedures have been developed for controlling MWDs using photoinduced electron/energy transfer–reversible addition-fragmentation chain transfer (PET-RAFT) polymerization, in conjunction with flow processes. By adjusting the pump flow rates, the chemical concentrations and residence times of the reactant streams were tailored throughout the polymerization, leading to control over the MWD. Changes to the intensity and wavelength of the light source also induced changes in the polymerization, allowing alteration of the MWD. The protocols described here should be amenable to a range of polymerization techniques and reaction setups.

Soft materials under geometrical confinement are ubiquitous and known to exhibit fascinating properties, sometimes even antagonistic to their bulk counterpart. Here, we explore the structural relaxation dynamics (α-relaxation) of the biopolymer gelatin dissolved in water (bulk form) and under soft spatial confinement using dielectric relaxation spectroscopy over a wide frequency range starting from 1 Hz up to 2 GHz. The gelatin–water mixture (hydrated gelatin) is geometrically restricted by the soft fluctuating surfactant monolayer of water–AOT (sodium bis(2-ethylhexyl)sulfosuccinate)-n-decane reverse microemulsions (MEs), where the core size of microemulsion droplets varies from 3.7 to 5.0 nm. The stability of the droplet phase of microemulsion after the incorporation of gelatin is confirmed by the small-angle neutron scattering (SANS) experiment. Notably, the hydrated gelatin in soft confinement exhibits faster relaxation dynamics in comparison to its bulk counterpart, and it further gets accelerated wi...

The significance of conjugated polymers for sensing applications stems from the intrinsic amplification of analyte binding events which is related to the efficient excitation energy migration in the polymers. Within the framework of conventional design of amplifying sensory polymers, interaction with an analyte creates a lower energy gap site within the conjugated backbone which acts as a trap for randomly migrating excitons typically producing a fluorescence quenching effect (turn-off sensors). Herein, we describe an alternative “higher energy gap” paradigm, a general design concept surprisingly overlooked so far. Within this paradigm, reaction with an analyte generates a higher energy gap site in the conjugated backbone. This higher energy gap site diminishes exciton migration length and causes pronounced enhancement of the polymer fluorescence (turn-on response). This effect benefits from the signal amplification and therefore can be used universally to design a wide range of fluorescent sensors. To de...

Aiming to understand the inversion of crystallization kinetics observed by DSC, detailed SANS investigations of the melt structure of a broadly distributed ethylene–1-hexene copolymer have been undertaken in a wide range of temperatures that were reached either by heating the solid or cooling from the homogeneous melt state. In both cases, the observed SANS signal transitions from a scattering cross section consistent with a homogeneous melt state (high temperature range) to an intensity that in the low Q region displays the characteristics of the Porod region for particles dispersed in a homogeneous matrix (low melt temperature range). The latter structure is consistent with demixing of the highly branched molecules and corroborates the postulated liquid–liquid phase separation (LLPS) as an explanation for the peculiar crystallization kinetics observed by DSC. The solution temperature is found at 160 °C by heating the solid and at 150 °C when cooling from the one-phase melt, thus denoting the effect of c...

We analyze the structural behavior of isolated semiflexible polymers grafted to an impenetrable surface. Employing a parallel multicanonical algorithm, we find a rich phase behavior for both purely entropic and attractive surface–polymer interactions. The corresponding conformations range from very compact ones, to folded bundles, to adsorbed and desorbed weakly bent rods. The case of a polymer grafted to a flat, noninteracting surface differs only marginally from the case of a completely free and isolated polymer. Introducing surface attraction, we find that below the adsorption transition temperature stiffer polymers are completely adsorbed and confined to an effectively two-dimensional conformation space. This ultimately holds true over the full range of semiflexibility for increasing surface attraction, in accordance with recent experimental findings.

Structural relaxations of a substance quenched to a temperature Tage below its glass transition temperature Tg enable the structure of the substance to approach equilibrium. This phenomenon, also known as physical aging, has been studied for many decades in bulk linear-chain polymer systems, where the aging rates are generally, to first order, independent of chain length. More recently, the phenomenon has been of keen interest in thin films, where the aging rate is shown to be film thickness H dependent, for films in the thickness range of nanometers to a few hundred nanometers. We show here, based on a study of polystyrene star-shaped polymers of a wide range of functionalities 2 ≤ f ≤ 64 and arm molecular weights Marm, that in the limit of sufficiently large values of Marm the aging behavior is similar to that of linear chains—independent of Marm and f. More importantly, in the limit of sufficiently small Marm and large f, the aging rate is independent of film thickness. Otherwise, the rate is a nonmono...

The sol–gel transition of tetrafunctional polymers with mutual reactive end-groups was investigated by analyzing the dynamics of probe particles via dynamic light scattering. The dynamics of probe particles was exclusively observed by matching the refractive index of the solvent and the polymers. The sol–gel transition point, decreasing of sol fraction and increasing of gel fraction with the reaction, the onset of formation of closed structure inside branched polymer clusters, and a piece of evidence for the decrease of the local viscosity in postgel regime were observed via the dynamics of probe particles. In addition, a scaling relationship ηeff ∼ e–1.13±0.06 was found in a wide range of cross-linking conversion (p) before the gel point, where ηeff is the effective viscosity estimated from probe particles’ dynamics and e ≡ |p – pc|/pc is the relative distance from the sol–gel transition point (pc is the cross-linking conversion at gel point).

Given the exceedingly high interfacial area-to-volume ratios in polymer nanocomposites and the ability to manipulate the polymer/nanoparticle interfacial interactions, manipulating the chain dynamics at these interfaces has immense potential for impacting macroscopic properties. There, the polymer center-of-mass tracer diffusion coefficient (D) from attractive (hydroxyl-terminated) and athermal (phenyl-terminated or polymer-grafted) substrates was measured over a range of temperatures and tracer molecular weights using elastic recoil detection. The tracer polymer diffusion slows significantly relative to the bulk when polymers are in direct contact with an attractive substrate and exhibits a weaker molecular weight dependence, D ∼ M–1.4. For polymers without direct contacts on the attractive substrates and for athermal substrates, the diffusion coefficients are similar to the bulk case. The temperature dependence of these diffusion coefficients indicates that the slower diffusion at the interfaces is coup...

We investigate the thermodynamic and dynamic properties of a model unentangled glass-forming polymer melt over a wide range of pressures (P) and temperatures (T) using molecular dynamics simulation. We show that the T dependence of the reduced thermal expansion coefficient and isothermal compressibility becomes weaker for higher P. Based on the generalized entropy theory, these trends suggest that the isobaric fragility of glass formation decreases with increasing P, consistent with our analysis from the structural relaxation time (τα). Moreover, we confirm previous findings that the onset and end of the glass formation process in our model can be estimated solely based on the static structure factor. We then provide a detailed analysis for the T and P dependence of τα as well as other quantities characterizing the dynamic heterogeneity of glass-forming liquids. In particular, we discuss how T and P influence the average extent L of the stringlike cooperative motion of monomers in our model polymer melt, ...

We used differential scanning calorimetry and spectroscopic ellipsometry to measure the molecular weight (MW) dependence of bulk fragility (mbulk) and spectroscopic ellipsometry to measure the thickness dependences of the glass transition temperature (Tg) and fragility (m) in supported thin films of low MW cyclic or ring polymer. The effects of confinement on Tg and m of thin polymer films are important in a range of advanced technology applications, including nanoimprinting. It has previously been shown that nanoconfined films of high MW linear polystyrene (PS) exhibit major Tg- and m-confinement effects whereas films of low MW cyclic PS (c-PS) show at most a very weak Tg-confinement effect. In the absence of chain ends, c-PS exhibits very weak Tg,bulk– and mbulk–MW dependences compared to linear PS. Despite low MW c-PS having mbulk values similar to that of high MW linear PS, we found that low MW c-PS films show a very weak m-confinement effect because of a weak free-surface effect; e.g., m for a 27 nm ...

We examine the role of molecular connectivity and architecture on the complexation of ionic macromolecules (polyelectrolytes) of finite size. A unified framework is developed and applied to evaluate the electrostatic correlation free energy for point-like, rod-like, and coil-like molecules. That framework is generalized to molecules of variable fractal dimensions, including dendrimers. Analytical expressions for the free energy, correlation length, and osmotic pressure are derived, thereby enabling consideration of the effects of charge connectivity, fractal dimension, and backbone stiffness on the complexation behavior of a wide range of polyelectrolytes. Results are presented for regions in the immediate vicinity of the critical region and far from it. A transparent and explicit expression for the coexistence curve is derived in order to facilitate analysis of experimentally observed phase diagrams.

The wide range of chemical compositions exhibited by polymers enables the fabrication of materials having highly tunable cohesive energy strength ϵ, and many of the properties that make polymers so useful as structural and responsive materials in both manufacturing and living systems derive from the variability of this basic property. The design and characterization of polymer materials then inevitably leads to a consideration of how ϵ impacts the thermodynamic and relaxation properties of polymer liquids. Our prior paper uses molecular dynamics simulations of a model coarse-grained polymer melt to systematically investigate the dependence of commonly measured thermodynamic properties on ϵ, while the present work focuses on the relaxation dynamics of the same molecular model. After demonstrating, as expected, that ϵ greatly influences the segmental relaxation time, we obtain a universal reduction of all our data for relaxation in terms of an activated transport model in which the activation free energy is...

The thermally sensitive charged poly(N-isopropylacrylamide-co-methacrylic acid) (P(NIPAM-co-MAA)) spherical microgel was prepared and their temperature-dependent volume phase transition behavior was systematically studied by analyzing the dielectric spectroscopy theoretically over a frequency range from 40 Hz to 110 MHz. It was found that the dielectric relaxation of the charged P(NIPAM-co-MAA) microgel drastically changed between 30 and 35 °C, and was significantly different from that of neutral PNIPAM microgels recently published in Soft Matter. The relaxation mechanism was speculated and the relaxation parameters were fitted after successfully eliminating the electrode polarization at low-frequency. On the basis of this, the differences in the structure, swelling ability and dehydration dynamics between charged P(NIPAM-co-MAA) and neutral PNIPAM microgels were compared. Although both of the two microgels showed the same changing trend around the volume phase transition temperature (VPTT), VPTT of charg...

We use molecular dynamics simulations to study mechanical properties of polymeric nanocomposites of liquid inclusions in polymeric network matrix. The shear modulus of nanocomposite is shown to be a universal function of the elastocapillary number γNL/(GNR0), where γNL is the surface tension of the liquid/network interface, GN is the shear modulus of the network and R0 is the initial size of liquid inclusions. First, in the range of elastocapillary numbers, γNL/(GNR0) GN. In such composites, the surface energy of the deformed liquid inclusions stiffens the composite. When the elastocapillary number increases further, γNL/(GNR0) ≫ 1, the interfacial energy of network/l...

The frequency ω dependent storage G′(ω) and loss G″(ω) moduli of star-shaped polystyrene (SPS) molecules of a range of functionalities f and molecular weights per arm Ma were measured under small amplitude oscillatory shear conditions. Star-shaped macromolecules are composed of an inner region, core, where the chain segments are stretched and the “packing” density is higher than that of the outer region, corona. The frequency dependencies of G′(ω) and G″(ω) for low functionality molecules (f < 8) with long arms Ma are well described by the model of Milner and McLeish, indicating that the translational dynamics are facilitated by an arm retraction mechanism. With increasing values of f and decreasing Ma the model fails—the arm retraction process is no longer valid—due largely to the increasing size of the core in relation to the overall size of the molecule. The molecules exhibit evidence of spatial structural order due to entropic, intermolecular interactions, and the translational dynamics of these molec...

Soft colloidal particles with multiple surface patches of differing composition are critical to the development of complex macroscopic structures that can serve as interfacial catalysts, macroscale surfactants, electronically responsive materials, and drug delivery vehicles. Here, we present a continuous process for the scalable formation of soft colloidal particles with multiple surface domains that employs well-established principles of polymer precipitation and phase separation to controllably shape particle architectures. Our results illustrate the broad range of particle morphologies, including Janus and Cerberus structures, and surface compositions accessible to our versatile solution-based assembly system. We also identify polymer diffusion, precipitation, and vitrification as the primary determinants of particle structure for the first time.

Confining DNA molecules with high throughput and structural integrity is an important challenge in nanochannel-based genomic mapping technology. Here we demonstrate dynamic confinement and linearization of DNA polymers within an embedded nanogroove array with 95% channel occupation. In standard nanofluidic technology, the free energy of confinement experienced by the DNA molecules increases strongly with decreasing device dimensions, leading to a suppression of molecule concentration in nanoconfined spaces. We overcome this limitation by combining “convex lens-induced confinement” (CLiC) geometry with in situ electrophoresis, simultaneously establishing gentle and continuously adjustable nanoconfinement and precise electrokinetic control. Together, these capabilities enable trapping and visualization of extended DNA molecules with high yield over an extended range of conditions. We demonstrate 10-fold increased DNA concentration in a confined region from 10 to 500 nm. Moreover, we develop and validate a p...

We revisit the nonuniversal aspect of polymer dynamics by considering both new and existing data on the zero-shear viscosity and linear viscoelastic response of various polymers, each with a wide range of molecular weights. Analysis of the zero-shear viscosity data in terms of the packing length p, whose role in entanglements has been discussed previously by Fetters and co-workers, reveals a behavior that is irreconcilable with our current understanding based on the tube model. Specifically, we find that the transition regime between Rouse and pure reptation dynamics, currently understood as the regime where contour length fluctuations are active, systematically shrinks as the packing length of the polymer increases. Further, we find that the slope of the loss moduli in the high-frequency wing of the terminal peak of well-entangled systems also decreases from the common −0.25 to −0.125 with increasing p. This is contrary to the single expected value of −0.25 from tube models which include contour length f...

Polymer nanocomposites for optical applications require high optical transparency at high filling ratios of nanoparticles. The nanoparticles provide optical functionality but unfortunately have a strong tendency to aggregate in polymer matrices leading to strong turbidity and reduced optical transmission, particularly at high filling ratios. We report a general route to nonaggregated highly filled, optically transparent polymer nanocomposites. It is based on using nanoparticles that have been coated with polymers forming spherical brushlike layers providing thermodynamic miscibility with the polymer matrix over the complete range of nanoparticle volume fractions. The polymers are attached via a versatile ligand exchange procedure which enables to prepare a wide range of optically transparent polymer nanocomposites up to weight fractions of 45%. This is demonstrated for a broad range of metal and semiconductor nanoparticles in optically transparent polymer matrices relevant for selective light/UV absorptio...

Recent literature has shown that the thickness of dip-coated films has a V-shaped dependence on dip-coating rate when very slow rates are included. For supramolecular block copolymer films, small molecule (SM) uptake and film morphology are also rate-dependent, as shown previously for a poly(styrene-b-4-vinylpyridine) (PS–P4VP) block copolymer in THF solutions containing naphthol (NOH) and naphthoic acid (NCOOH). Here, these investigations are extended to p-dioxane, toluene, and CHCl3 solutions. The V-shaped thickness dependence is validated for each solvent, but with the V minimum displaced to lower dip-coating rates and thicknesses for the solvents with lower vapor pressures (p-dioxane, toluene), thereby decreasing the dip-coating rate range of the “capillarity regime” (slow side of the V) and consequently extending that of the “draining regime” (fast side of the V). The SM/VP uptake ratio varies with the nature of the solvent, particularly in the capillarity regime, where it is higher for solvents that...

A series of weak donor-strong acceptor polymers containing two different electron-deficient units (diketopyrrolopyrrole and thienoisoindigo) are synthesized and used in broad-response and high-detectivity polymer photodetectors. By adjusting the composition ratio of the two acceptors, the absorption spectra, energy levels, molecular stacking, and film morphology are affected, which in turn influence the photodetector performance. With increased thienoisoindigo component, the HOMO energy levels shift from -5.41 to -4.76 eV, and the LUMO energy levels are nearly unchanged, corresponding to reduced bandgaps and red-shifted absorption spectra. 1,8-Diiodooctane additive shows greatly impact on the film morphology, which affects the photodetector performance significantly. Going from P1 to P5, the detectivity decreases, but the response range increases. The photodetector based on P4 exhibits detectivity of greater than 10(11) Jones in a broad spectral region of 300-1200 nm, which is really promising for UV-vis-NIR light detection.

The efficient hierarchical amplification of macromolecular helicity has been achieved through the long-range transfer of chiral information in polymer brushes consisting of a dynamically racemic helical poly(phenylacetylene) backbone and poly(phenyl isocyanate) pendants. The partial introduction of an optically active group at the pendant terminus, which was situated approximately 27 bond lengths (ca. >4 nm) away from the polyacetylene backbone, allowed for the transmission of stereochemical information to the polyacetylene backbone. This transfer of information induced a helical chirality in the polyacetylene backbone, which biased the helical handedness of the polyisocyanate pendants devoid of an optically active terminal group.

We use a numerical implementation of polymer self-consistent field theory to study the effective interactions between two spherical particles in polyelectrolyte solutions. We consider a model in which the particles possess fixed charge density and the polymers contain a prespecified amount of dissociated charges. We quantify the polymer-mediated interactions between the particles as a function of the particle charge, polymer concentrations and particle sizes. We study the interplay between depletion interactions, which arise as a consequence of polymer exclusion from the particle interiors, and the electrostatic forces which result from the presence of charges on the polymers and particles. Our results indicate that for weakly charged and uncharged particles, the polymer-mediated interactions predominantly consist of a short-range attraction and a long-range repulsion. When the particle charge is increased, the interactions become purely repulsive. A longer range, albeit weaker, bridging attraction was al...

We describe quasi-elastic neutron scattering measurements of polymer backbone dynamics in PEO-based single ion conductors with varying morphologies. These morphologies include aggregates, multiplets and ion pairs, where the dominant ion state varies with cation identity: Li+ samples are mostly aggregates, Cs+ samples are mostly ion pairs, and Na+ samples contain a range of ion states. The conductivities of these samples are roughly equivalent, suggesting that ion state does not have a large impact on conductivity. Because conductivity is connected to polymer dynamics, we use quasi-elastic neutron scattering to assess polymer dynamics in all three samples. In all three ionomers, the motion of the PEO spacer is slower near the ionic comonomer [anchor atoms] than it is in the spacer midpoint [bridge atoms], leading to two fractions in the measured dynamics. Anchor atom dynamics depend on cation content but not on the different morphologies associated with cation identity. We thus conclude that for this syste...

Two series of highly charged linear aliphatic polymers—sodium polystyrene-4-sulfonate and random copolymer of N-methyl-N-vinylacetamide and N-methyl-N-vinylamine hydrochloride—were studied in water solution without added salts and in solutions containing up to 5 M NaCl. Intrinsic viscosity in salt-free solutions was estimated by a method proposed earlier [Pavlov et al. Russ. J. Appl. Chem. 2006, 79, 1407–1412]. Molecular characteristics were obtained in 0.2 M NaCl. The polyelectrolytes were studied in more than 10-fold range of molar mass. Qualitatively, the conformational status of the polyelectrolyte chains in different ionic strength was defined with the Kuhn–Mark–Houwink–Sakurada plots normalized by the value of linear chain density. In salt-free solution both polyelectrolytes could be attributed to extra rigid chains with the statistical segment length of 650 nm for sodium polystyrene-4-sulfonate and 100 nm for copolymer chains. Such statistical segment lengths are provided by short-range electrostat...

Single particle tracking (SPT) microscopy is a powerful experimental technique for characterizing mobility within complex media. In this paper, we study the motion of single core/shell CdSe/ZnS quantum dots (QDs) within synthetic polyacrylamide (PAAm) hydrogels to provide insight into the structure of these heterogeneous gel networks. Subdiffusive mean-square displacements (MSD) and non-Gaussian van Hove functions are observed for gels with a range of cross-linker contents, which we interpret in terms of transient caging events of QDs due to the presence of denser regions of the network. Experimentally determined caging time distributions follow power-law behaviors for short times, consistent with the predictions of a simple random trap model for the confining energy landscape. Over the range of composition studied, greater cross-linker concentrations are found to yield an increase in the frequency of long trapping events, corresponding to larger characteristic trapping energies and therefore a lower over...

Nanoscale confinement alters the dynamics of glass-forming liquids in films of order 100 nm in thickness. A common hypothesis for the origin of this long range posits that interfacial dynamics prop...

We investigate, using theory and simulations, the role of the short and long grafted chains in polydisperse polymer grafted nanoparticles in stabilizing particle dispersion in a chemically similar polymer matrix in the presence of particle–particle attractions. The effect of the short and long chains in a polydisperse or bidisperse graft length distribution on the potential of mean force between the polymer grafted nanoparticles is coupled and distinct from their role in the corresponding deconstructed short and long monodisperse distributions. At high grafting density, the increased monomer crowding near the particle surface from both short and long chains maximizes shielding of particle–particle attraction, while the length and crowding of long chains away from the particle surface determine the location, range, and strength of the steric repulsion and midrange attraction. We find that to maximize grafted nanoparticle dispersion, it is best to synthesize grafted particles at high grafting density with p...

A model for heterogeneous nucleation of isotactic polypropylene in terms of a “cylindrical cap” with the critical size and barrier set by a contact angle is described. Quiescent crystallization data for bulk samples of isotactic polypropylene are analyzed to extract a contact angle in the range of 40° to 70° with a mean value of 56°, which corresponds to a factor of 6 decrease in the critical barrier from the homogeneous case. This value is in reasonable agreement with the contact angle of 79° ± 3° estimated from molecular scale theory (DOI 10.1021/ma400703m). This model could be combined with calculations from melt rheology of entropy reduction due to flow to frame discussions of flow-induced crystallization.