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Mechanophores are molecules that are incorporated into a host material and react to the local mechanical condition—the state of stress or strain—of that host material. Among their many purposes is that of a reporter: Mechanophores whose optical activity changes in response to mechanical cues can reveal bulk material processes that are ordinarily hidden, such as fatigue and fracture. Moreover, they may do so well before a material is fully fractured. To extract quantitative information from the optical signals from embedded mechanophores it is important that the mechanophores, which are generally a minority component of the material, report proportionally and unambiguously on the mechanical condition of the bulk. This is particularly important for early reporting of damage and wear, for which the optical signal from the mechanophore should accurately reflect bulk bond scission. In this article, we develop and analyze a general theory for the quality of optical mechanoreporting by mechanophores in soft materials, based on the Bell-Evans theory of bond breaking. We find, that at the typical low fractions in which mechanophores are incorporated the overall change in strength is limited, but that the proportionality of the reporting can be off by significant amounts, particularly at short times after loading but, for non-scissile bonds, at long times as well.

Despite their wide potential utility, the manufacture of polymer-nanoparticle (NP) composites with high filler fractions presents significant challenges because of difficulties associated with dispersing and mixing high volume fractions of NPs in polymer matrices. Polymer-infiltrated nanoparticle films (PINFs) circumvent these issues, allowing fabrication of functional composites with extremely high filler fractions (50 vol %). In this work, we present a one-step, room-temperature method for porous PINF fabrication through solvent-driven infiltration of polymer (SIP) into NP packings from a bilayer film composed of a densely packed layer of NPs atop a polymer film. Upon exposure to solvent vapor, capillary condensation occurs in the NP packing, leading to plasticization of the polymer layer and subsequent infiltration of polymer into the NP layer. This process results in a porous PINF without the need for energy-intensive processes. We show that the extent of polymer infiltration depends on the quality of solvent and the duration of solvent annealing as well as the molecular weight of the polymer. SIP can also be induced using a slightly poor solvent, which offers a great advantage of inducing SIP via liquid solvent annealing, eliminating potential hazards associated with solvent vapor annealing. The SIP process circumvents challenges associated with dispersing high concentrations of nanoparticles in a polymer matrix to prepare a nanocomposite film with high filler fraction. Thus, SIP is a potentially scalable method that can be used for the manufacturing of porous PINFs of a wide range of compositions, structures, and functionalities for applications in structural and barrier coatings as well as electrodes for energy storage and conversion devices.

The development of controlled/living polymerization has contributed significantly to the exploration of new phenomena and applications in polymer physics and materials science. This method has recently been translated into the supramolecular domain, where it is likewise expected to open the door to fruitful fields of research; however, the principles of monomer design remain elusive. In this focus review, I present a case study of a series of porphyrin-based monomers that we have investigated over the past 10 years. By systematically designing monomers, we have been able to gain deep insights into the mechanisms of controlled/living supramolecular polymerization, and we have even been able to apply the developed method to synthesize two-dimensional supramolecular nanosheets with controlled areas and aspect ratios. This case study provides evidence for how nanostructures with precisely defined dimensions and optimized properties can be created using appropriate monomer design. Recently, controlled/living supramolecular polymerization has been evolved by many research groups; however, the principles of monomer design remain elusive. In this focused review, I present a case study of a series of porphyrin-based monomers that we have investigated over the past 10 years. By systematically designing monomers, we have been able to gain deep insights into the mechanisms of controlled/living supramolecular polymerization, and we have even been able to apply the developed method to synthesize two-dimensional supramolecular nanosheets with controlled areas and aspect ratios.

Solvents have an essential association with polymer solution behavior. However, few researches have been deeply done on this respect. In recent years, our research group focus on the study on effect of solvent properties on solution behavior and film condensed state structure for semi-rigid conjugated polymer up till to apply for optoelectronic device. Herein, influence of solvent properties including solubility of solvent, aromaticity, polarity and hydrogen bonds on semi-rigid polymer chain solution behavior, i.e., single chain conformation, chain shape, size and chains aggregated density were studied by means of static/dynamic laser light scattering (DLS/SLS) and exponential law etc. Effect of solvent properties on condensed state structure of the semi-rigid conjugated polymer film was studied by UV absorption spectroscopy, PL spectroscopy and electron microscopy etc. The essential reasons for the influence were discovered and the mechanism was revealed. It was found that solution behavior with different solvent properties had an essential physical relationship with chains condensed state structure of the semi-rigid conjugated polymers. More importantly, there was a quantitative structure-activity relationship between solution and film. The key to this relationship depended on the interaction between solvent molecules and the semi-rigid conjugated polymer chains. This interaction could also affect optoelectronic devices performance. This study is of great significance to effectively control the condensed state structure of the semirigid conjugated polymers in the process of dynamic evolution from solutions to films. It not only enriches the knowledge and understanding of both semi-rigid conjugated polymer solution behaviors and film condensed state physics based on polymer physics, but also is meaningful to practical application for conjugated polymer and other traditional polymer systems.

Knowledge of interaction parameters and Kuhn length for a polymer/solvent pair is a foundation of polymer physics of synthetic and biological macromolecules. Here, we demonstrate how to obtain thes...

The exploration of macromolecular topology provides common ground amongst chemists, material scientists, mathematicians, and artists. Fascinating polymer architectures, ranging from linear to branched to cyclic to star, can be constructed from myriad building blocks; their topological-dependent properties merge the beauty of symmetry with the intricacies of polymer physics. Specifically in cyclic macromolecules, the lack of chain ends result in unique physical characteristics (e.g., smaller hydrodynamics volume, lower viscosity, and lack of chain entanglement) compared to their linear counterparts. In this review, developments in the synthesis of cyclic polymers will be addressed, with an emphasis of recent advances in the past five years.

Conformation and dynamical evolution of block copolymers in shear flow is an important topic in polymer physics that underscores the forming process of various materials. We explored deformation and dynamics of copolymers composed of rigid or flexible blocks in simple shear flow by employing multiparticle collision dynamics integrated with molecular dynamics simulations. We found that compared with the proportion between rigid and flexible blocks, the type of the central blocks plays more important role in the conformational and dynamical evolution of copolymers. That is, if the central block is a coil, the copolymer chain takes end-over-end tumbling motion, while if the central block is a rod, the copolymer chain undergoes U-shape or S-shape deformation at mid shear rate. As the shear strength increases, all copolymers behave similar to flexible polymers at high shear rate. This can be attributed to the fact that shear flow is strong enough to overcome the buckling force of the rigid blocks. These results provide a deeper understanding of the roles played by rod and coil blocks in copolymers for phase interface during forming processing.

One of the most celebrated achievements in polymer physics is the finding of simple scaling laws that correlate molecular behaviors with molecular size. Scaling relations of 2D macromolecules betwe...

Conformation statistics of macromolecules in dilute solution is one of the fundamental issues in polymer physics. Herein, we experimentally explore the average conformation of model randomly hyperb...

We study the phase behavior of a block copolymer and ionic liquid mixture using the Landau theory of Leibler and field-theoretic techniques in polymer physics. Our weak-segregation theory of microp...

The intrinsic coupling effect between the multiscale microstructure and macroscopic performance is a fundamental issue in polymer engineering and polymer physics. Combing the tensile testing and in...

Macromolecules in an entangled environment are constrained to wriggle predominantly along a confining tube, giving rise to the so-called reptation or tube-like motion. While the principles of polymer physics were well developed to understand its conformational dynamics, the quantitative characterization of the tube diameter and resulting reptation remains an open question. Here, using highly confined parallel plate geometry nanoslits down to sub-30 nm, we directly observe reptation in a one-dimensional (1D) confined nanoenvironment. We provide a quantitative analysis scheme, by introducing the segmental tangential vector and its associated correlation function, to characterize the strand reptation and connect it to the confinement degree. Our analysis shows that the amplitude of the transverse fluctuations (the virtual 2D "tube") exhibits the typical scaling of fluctuating interfaces, contact lines, or charge density waves, with a roughness exponent, which depends on the slit height. Our results are shown to lead to less rough DNA profiles in shallower nanoslits. We anticipate our analysis to be a starting point for a more detailed understanding of the relationship between polymer physics and other nonequilibrium physical systems.

Internal dynamics of polymer chains is one of the most important fundamental problems in polymer physics. This work reports the first example of a dynamic light scattering (DLS) study of internal m...

Herein, sequence-controlled polymerization and sequential Ugi-4CR/thiol–yne click reactions inspired a novel synthetic strategy for preparing a well-defined multigraft polymer in which the sequence-controlled amino-functionalized backbones were converted to mono- or di-modular alkynyl-functionalized main chains via an Ugi-4CR and clicked with well-defined thiol end-functionalized polystyrene branches through the “graft-onto” method. The Ugi-4CR showed high conversions (above 91%), while the efficiencies for the thiol–yne click reaction were above 97%. Meanwhile, an innovative concept of “polymeric topological isomers” that had similar molecular weights but different grafted structures was proposed for the first time. These four well-defined multigraft isomeric polymers (mono-brush polymer, double-brush polymer, mono-comb polymer and double-comb polymer) provide a high-level platform for polymer physics studies. Through preliminary measurements, the dilute solution properties were found to be significantly different and to change regularly with variations in the grafted structures.

This study aims to use molecular dynamics (MD) simulations of Kremer–Grest (KG) chains to inform future developments of models of entangled polymer dynamics. We perform nonequilibrium MD simulations, under shear flow, for well‐entangled KG chains. We study chains of 512 and 1000 KG beads, corresponding to 8 and 15 entanglements, respectively. We compute the linear rheological properties from equilibrium simulations of the stress autocorrelation and obtain from these data the tube model parameters. Under nonlinear shear flow, we compute the shear viscosity, the first and second normal stress differences, and chain contour length. For chains of 512 monomers, we obtain agreement with the results of Cao and Likhtman (ACS Macro. Lett. 2015, 4, 1376). We also compare our nonlinear results with the Graham, Likhtman and Milner‐McLeish (GLaMM) model. We identify some systematic disagreement that becomes larger for the longer chains. We made a comparison of the transient shear stress maximum from our simulations, two nonlinear models and experiments on a wide range of melts and solutions, including polystyrene (PS), polybutadiene, and styrene–butadiene rubber. This comparison establishes that the PS melt data show markedly different behavior to all other melts and solutions and KG simulations reproduce the PS data more closely than either the GLaMM or Xie and Schweizer models. We discuss the performance of these models against the data and simulations. Finally, by imposing a rapid reversing flow, we produce a method to extract the recoverable strain from MD simulations, valid for sufficiently entangled monodisperse polymers. We explore how the resulting data can probe the melt state just before the reversing flow. © 2019 The Authors. Journal of Polymer Science Part B: Polymer Physics published by Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1692–1704

Polyelectrolyte brushes are important stimuli-responsive materials in a variety of technological applications as well as in biological systems. Their small size, however, introduces characterization challenges, particularly in studying 3D structure and time-dependent behavior. In this Letter, we report on the polyelectrolyte brush behavior of extra-large hyaluronan brushes (∼15 μm) recently developed using an enzyme-mediated growth process. In response to increasing ionic strength, the brush displays the osmotic brush regime and the salted brush regime. We also show a collapse of 96% when the brush is placed in a poor solvent. This collapse is rapid when changing from a good to poor solvent, but re-expansion is slow when changing back to a good solvent. The observed brush behavior described in this Letter is similar to that seen for smaller polyelectrolyte brushes, indicating that these larger brushes may serve as model systems to study more complex phenomena through confocal microscopy.

Internal dynamics of flexible polymer chains is one of the most important fundamental problems in polymer physics. Although numerous efforts have been devoted to the understanding of internal dynamics for linear polymers, little attention was paid to branched systems. This work aims to elucidate how the branching effect quantitatively influences the internal motions of long-subchain hyperbranched polymers in dilute solution. By light scattering study of four hyperbranched polystyrene samples with controlled branching patterns and low polydispersities (Mw/Mn < 1.40 and Mw ∼ 107 g/mol), we quantified and analyzed the asymptotic behavior of the reduced first cumulant [Γ* = Γ(q)/(q3kBT/η0)], the value of Γ* at high q-regime [the approximate values of Γ*(∞)], the scattering vector (q) dependence of linewidth [Γ(q)], the number of relaxation modes in Γ(q)-distribution curves, the characteristic relaxation time (τ1) of the first internal mode, and the q-dependent relative strength of internal motions. Our result...

Significant parallels exist between the phase separation behavior of polymers in solution and the types of biomolecular condensates, or ‘membraneless organelles,’ that are of increasing interest in living systems. Liquid–liquid phase separation allows for compartmentalization and the sequestration of materials and can be harnessed as a sensitive strategy for responding to small changes in the environment. Here, I review many of the parallels and synergies between ongoing efforts to study and take advantage of phase separation in living versus synthetic materials.

Combining atomistic and coarse-grained (CG) models is a promising approach for quantitative prediction of polymer properties. However, the gaps between the length and time scales of atomistic and CG models still need to be bridged. Here, the scale gaps of the atomistic model of polyethylene melts, the bead&ndash, spring Kremer&ndash, Grest model, and dissipative particle dynamics with the slip-spring model were investigated. A single set of spatial and temporal scaling factors was determined between the atomistic model and each CG model. The results of the CG models were rescaled using the set of scaling factors and compared with those of the atomistic model. For each polymer property, a threshold value indicating the onset of static or dynamic universality of polymers was obtained. The scaling factors also revealed the computational efficiency of each CG model with respect to the atomistic model. The performance of the CG models of polymers was systematically evaluated in terms of both the accuracy and computational efficiency.

A sterically π-congested ortho-phenylated poly(p-phenylene) (PPP) has been synthesized with unprecedentedly high molecular weights up to 29 kDa after fractionation, as confirmed by gel permeation chromatography coupled with a multiangle laser light scattering detector. The chain translation diffusion coefficient obtained from dynamic light scattering experiments displayed strong scaling (∼Lw–0.8) to the chain contour length, indicating a rodlike shape with remarkably high rigidity of this novel PPP. These results provide an interesting insight into the relationship between the structure and the chain stiffness of PPP-based polymers and challenge the validity of the existing diffusion models in polymer physics.

Theoretical models of the conformational behavior of flexible polymer chains in mixed solvents enunciated in the world literature during the last decade are critically reviewed. Models describing different mechanisms of coil-to-globule transitions in a good solvent induced by cosolvent addition are highlighted. Special attention is given to the analysis of theoretical approaches to describing the collapse of polymer chains in binary mixtures of good solvents. The review addresses researchers engaged in polymer physics and chemistry and materials scientists involved in the design of smart polymers.

The bioactive additive toolbox to functionalize supramolecular elastomeric materials expands rapidly. Here we have set an explorative step toward screening of complex combinatorial functionalization with antifouling and three peptide‐containing additives in a bisurea‐based supramolecular system. Thorough investigation of surface properties of thin films with contact angle measurements, X‐ray photoelectron spectroscopy and atomic force microscopy, was correlated to cell‐adhesion of endothelial and smooth muscle cells to apprehend their respective predictive values for functional biomaterial development. Peptides were presented at the surface alone, and in combinatorial functionalization with the oligo(ethylene glycol)‐based non‐cell adhesive additive. The bisurea‐RGD additive was cell‐adhesive in all conditions, whereas the endothelial cell‐specific bisurea‐REDV showed limited bioactive properties in all chemical nano‐environments. Also, aspecific functionality was observed for a bisurea‐SDF1α peptide. These results emphasize that special care should be taken in changing the chemical nano‐environment with peptide functionalization. © 2019 The Authors. Journal of Polymer Science Part B: Polymer Physics published by Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1725–1735, Adhesion of endothelial and smooth muscle cells on supramolecular biomaterials is regulated via combinatorial functionalization with bioactive‐peptide and antifouling additives. The modularity in this material system allows for fast preliminary screening of material properties and corresponding functioning of the incorporated additives. Changes in the chemical nano‐environment of bioactive peptides prove to be important factors in bioactive peptide functionality.

Oxygen permeability (P), diffusivity (D) and solubility (S) properties are representative of gaseous diffusion in polymers and required for the understanding of polymer physics driven phenomena as well as the quantification of mass transport or polymer degradation processes when diffusion limited oxidation effects result in spatially dependent oxidation behavior. Precise P, D, S characterization data for O2 in polymeric materials at elevated temperatures have not been reported due to instrumental challenges and competitive reactively driven oxygen loss (oxidation reactions), although estimations have been accomplished from indirect measurements of oxidation depths when analyzed with theoretical degradation models. This study offers an overview on experimental approaches which have been applied to the characterization of a range of thin polymer films. As an overview, the O2 permeation features of three epoxy thermo-set materials, polyimides (Kapton and bismaleimides), and polypropylene for 25–140 °C were investigated with time-dependent flux measurements and yield permeation data which so far have not been available in the literature. Arrhenius plots of P for two epoxies (828/D230 and 828/D400) show the influence of the glass transition temperature, and intriguingly a transition originates mostly through noticeable changes in S but not D. Multiple material behaviors demonstrating the influence of reactive oxygen loss are discussed. Polymer oxidation chemistry will often interfere with physical permeation measurements at elevated temperatures, in conflict with perhaps the expectation for simple non-reactive O2 transport. Misleading data may result unless the underlying reactive oxidative loss is considered and compensated for, or permeation data are compared at multiple O2 partial pressures to validate non-reactive experimental conditions.

Synchrotron radiation (SR) provides highly brilliant light with tunable wavelength from hard X-ray to far infrared, on which scattering, spectroscopy and imaging techniques with high time and spatial resolutions have been developed for in situ study on biological system and materials like polymer. With examples on flow-induced crystallization of polymer, deformation of nanoparticle filler network in rubber composite and necking propagation in tensile stretch, current work attempts to demonstrate the advantages of in situ synchrotron radiation X-ray scattering, X-ray nano-CT and infrared imaging in the study of deformation-induced multi-scale structural evolutions of polymers. With time resolution up to sub-ms, synchrotron radiation is expected to play a great role in understanding non-equilibrium polymer physics under processing and service conditions, while high-throughput characterization platform based on synchrotron radiation opens the possibility to establish polymer Materials Genome database in processing parameter space within reasonable time, which can serve as the roadmap for industrial polymer processing and accelerate material innovation.

Much like our own body, our planet is a macroscale dynamic system equipped with a complex set of compartmentalized controls that have made life and evolution possible on earth. Many of these global autoregulatory functions take place in the ocean; paramount among those is its role in global carbon cycling. Understanding the dynamics of organic carbon transport in the ocean remains among the most critical, urgent, and least acknowledged challenges to modern society. Dissolved in seawater is one of the earth’s largest reservoirs of reduced organic carbon, reaching ~700 billion tons. It is composed of a polydisperse collection of marine biopolymers (MBP), that remain in reversible assembled↔dissolved equilibrium forming hydrated networks of marine gels (MG). MGs are among the least understood aspects of marine carbon dynamics. Despite the polymer nature of this gigantic pool of material, polymer physics theory has only recently been applied to study MBP dynamics and gel formation in the ocean. There is a great deal of descriptive phenomenology, rich in classifications, and significant correlations. Still missing, however, is the guide of robust physical theory to figure out the fundamental nature of the supramolecular interactions taking place in seawater that turn out to be critical to understanding carbon transport in the ocean.

The study of the conformation properties of macromolecules is at the heart of polymer science. Essentially all physical properties of polymers are manifestations of the underlying polymer conformations or otherwise significantly impacted by the conformation properties. In this Perspective, we review some of the key concepts that we have learned over nearly eight decades of the subject and outline some open questions. The topics include both familiar subjects in polymer physics textbooks and more recent results or not-so-familiar subjects, such as non-Gaussian chain behavior in polymer melts and topological effects in ring polymers. The emphasis is on understanding the key concepts, with both physical reasoning and mathematical analysis, and on the interconnection between the different results and concepts.

Owing to changes in their chemistry and structure, polymers can be fabricated to demonstrate vastly different electrical conductivities over many orders of magnitude. At the high end of conductivity is the class of conducting polymers, which are ideal candidates for many applications in low-cost electronics. Here, we report the influence of the nature of the doping anion at high doping levels within the semi-metallic conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) on its electronic transport properties. Hall effect measurements on a variety of PEDOT samples show that the choice of doping anion can lead to an order of magnitude enhancement in the charge carrier mobility > 3 cm2/Vs at conductivities approaching 3000 S/cm under ambient conditions. Grazing Incidence Wide Angle X-ray Scattering, Density Functional Theory calculations, and Molecular Dynamics simulations indicate that the chosen doping anion modifies the way PEDOT chains stack together. This link between structure and specific anion doping at high doping levels has ramifications for the fabrication of conducting polymer-based devices, The authors acknowledge the European Research Council (ERC-starting-grant 307596), the Swedish foundation for strategic research (project: “Nano-material and Scalable TE materials”), the Knut and Alice Wallenberg foundation (project “Power Paper” and “Tail of the Sun”), The Swedish Energy Agency (3833221), the Swedish Research Council via “Research Environment grant” on “Disposable paper fuel cells” (2016205990), and the Advanced Functional Materials Center at Linköping University. The authors thank Masatsugu Yamashita from the THz Sensing & Imaging Lab at RIKEN in Japan for conducting the THz reflectance spectroscopy experiments. D.R. Evans acknowledges the support of the Australian Research Council through the Future Fellowship scheme (FT160100300). J.W. Andreasen acknowledges the support of the European Research Council (ERC-consolidator-grant 681881). The computations were performed on resources provided by the Swedish National Infrastructure for Computing (SNIC) at NSC.

Revealing the nature of chain packing in conjugated polymer nanoparticles (CPNs) is one of the important issues to polymer physics research. Surfactant-stabilized CPNs in water show significantly enhanced luminescence intensity in comparison to small molecular organic dyes and single polymer chains dissolved in solvents. The importance of the conjugated polymer structure in nanomaterials is undoubted. However, details of the relationship between alignment of conjugated polymer backbone in CPNs and its luminescent property have not been established. Furthermore, there are yet no methods that can predict the atom-resolved structure of conjugated polymer in the CPNs. Herein, we employ coarse-grained (CG) molecular dynamic simulations to investigate the structure of phase-separated film and the film shattering process for a mixture of poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′]-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) and 1,2-dioctanoyl-sn-glycero-3-phosphocholine (D8PC). The π...

Understanding the conformational changes of polymeric chains in solutions is an essential and integral part of polymer physics. By increasing the concentration of polymer solutions from dilute to semidilute regime, the critical chain overlapping has been reported at the concentration termed as C*. In this study, the associated inter- and intrachain conformational transitions in polystyrene (PS) solutions are reported. By comparing the spectroscopic intensity ratio versus concentration for an intrachain PS system, a break point was observed in good solvent which coincided with the theoretically predicted C*. Moreover, the intrachain conformation showed no obvious change below C*, while significant collapse started to occur above C*. This result reveals a new insight in polymer physics, since traditionally the size of polymer chains is considered to decrease weakly regarding the concentration change in the semidilute regime. It is important to find such an abrupt intrachain conformational transition between the dilute and semidilute solutions and provide the first experimental observation that inter- and intrachain conformational transitions are correlated to one the other. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017

We study the hydrodynamic transport of knotted ring polymers through modulated channels, establishing that the transport velocity is strongly dependent on the ring topology for Peclet numbers smaller than unity. As soon as convection dominates, transport properties become insensitive to the presence and type of knots. We identify two distinct modes of transport, corresponding to the motion being led by the knotted or unknotted portions of the ring, most surprisingly without impact on separation efficiency. The modes can be selected by the channel geometry, and this could be harnessed to design nanofluidic devices for the continuous topological sorting of entangled biopolymers.

Polyelectrolyte complex micelles (PCMs, core-shell nanoparticles formed by complexation of a polyelectrolyte with a polyelectrolyte-hydrophilic neutral block copolymer) offer a solution to the critical problem of delivering therapeutic nucleic acids, Despite this, few systematic studies have been conducted on how parameters such as polycation charge density, hydrophobicity, and choice of charged group influence PCM properties, despite evidence that these strongly influence the complexation behavior of polyelectrolyte homopolymers. In this article, we report a comparison of oligonucleotide PCMs and polyelectrolyte complexes formed by poly(lysine) and poly((vinylbenzyl) trimethylammonium) (PVBTMA), a styrenic polycation with comparatively higher charge density, increased hydrophobicity, and a permanent positive charge. All of these differences have been individually suggested to provide increased complex stability, but we find that PVBTMA in fact complexes oligonucleotides more weakly than does poly(lysine), as measured by stability versus added salt. Using small angle X-ray scattering and electron microscopy, we find that PCMs formed from both cationic blocks exhibit very similar structure-property relationships, with PCM radius determined by the cationic block size and shape controlled by the hybridization state of the oligonucleotides. These observations narrow the design space for optimizing therapeutic PCMs and provide new insights into the rich polymer physics of polyelectrolyte self-assembly.

Large DNA molecules have been utilized as a model system to investigate polymer physics. However, DNA visualization via intercalating dyes has generated equivocal results due to dye-induced structural deformation, particularly unwanted unwinding of the double helix. Thus, the contour length increases and the persistence length changes so unpredictably that there has been a controversy. In this paper, we used TAMRA-polypyrrole to stain single DNA molecules. Since this staining did not change the contour length of B-form DNA, we utilized TAMRA-polypyrrole stained DNA as a tool to measure the persistence length by changing the ionic strength. Then, we investigated DNA stretching in nanochannels by varying the ionic strength from 0.06 mM to 47 mM to evaluate several polymer physics theories proposed by Odijk, de Gennes and recent papers to deal with these regimes.

One of the most intriguing properties of rod-like polymers is the ability to form a nematic phase. Among a broad variety of external stimuli to promote the isotropic (I)-nematic (N) transition, a shear-induced nematic phase represents one of the most fascinating phenomena in polymer physics. Here, after reviewing some relevant findings on quiescent and shear-induced nematics, we present the novel shear-induced isotropic-nematic transition exhibited by poly(ether ether ketone) (PEEK) melts of various chain lengths. The key factor is the significant rigidity of the PEEK chain that makes it a rod-like polymer. The molecular weight (Mw) dependence of the zero-shear viscosity ( η 0 ) of PEEK in the isotropic phase, follows the Doi-Edwards theoretical prediction for rod-like polymers in the entangled regime; η 0 ∼ M w 6 . The shear-induced I-N transition manifests in the apparent shear viscosity dependence on the shear rate (flow curves) with three regimes: I) an isotropic response with no measurable birefringence at low shear rates, II) an I-N transition with an isotropic-nematic biphase, two steady state values of apparent viscosity and mild birefringence at intermediate shear rates, and III) a continuous nematic phase with strong birefringence at high shear rates with η ∼ γ ˙ − 1 / 2 . Additionally, the observed threshold shear rates for regimes II and III for the four PEEK samples were used to construct a dynamic phase diagram of PEEK at 370°C, revealing that such a transition is stress-controlled.

A combination of nano-focus X-ray scattering and nanocalorimetry was used to re-explore the phenomenon of multiple melting behavior of a typical semirigid-chain polymer, poly(trimethylene terephthalate), PTT. The multiple melting of semirigid-chain polymers constitutes one of the long-standing issues in polymer physics. By using very high heating and cooling rates the micro-structure of PTT corresponding to different stages of melting has been arrested by quenching it to room temperature. Although the recrystallization of PTT can be largely precluded under these conditions, the nanocalorimetric curve exhibits two melting events. By employing an in-situ small-angle X-ray scattering, SAXS, it is observed that the low-temperature melting peak corresponds to formation of streaky SAXS patterns. At this stage, the crystalline lamellar stacks lose their long-range order due to melting of the crystals confined in the smallest amorphous gaps, which can be explained by the negative stresses imposed on these crystals. This low-melting crystal fraction can be selectively molten away by performing a fast heating just above the corresponding melting point, and the subsequent heating does not reveal the double-melting behavior anymore. Therefore the phenomenon of the double (or multiple) melting behavior is not necessarily coupled to the melting–recrystallization processes and can be observed even in the absence of any recrystallization.

We carry out simultaneous mechanical and IR-thermal-imaging-based temperature measurements of tensile extension on untreated, milled (mechanically “rejuvenated”) and melt-stretched bisphenol A-polycarbonate (PC). The extension is found to cause significant buildup of both excess internal energy u 2 and plastic dissipation. The magnitude of u 2 is one to two orders of magnitude higher than the energy involved in rubbery elastic deformation. While the ratio of u 2 to the mechanical work w decreases with increasing rate of extension for untreated PC, milled PC is found to be more dissipative at lower rates. Homogeneous extension of melt-stretched PC in the post-yield regime including strain hardening behavior reveals largely non-dissipative responses, emphasizing the plastic deformation of glassy polymer may not be fully dissipative. The experimental results clearly indicate that a significant component of stress can be intrasegmental leading to the observed buildup of internal energy by distortions of covalent bonds. The glassy polymer physics at the chain level complements the more familiar idea of inter-segmental dissipation as the dominant event during plastic deformation.

We present our personal appraisal of a few recent trends in polymer physics and theory. The four main themes discussed are crystallization and melting of polymers, memory in polymer systems, topologically frustrated polymer dynamics, and phase behavior of polyelectrolyte solutions.

This reactive molecular dynamics study explores the salt concentration dependence of the viscoelastic and mechanical failure properties of a poly(propylene glycol)/LiPF6‐based solid polymer electrolyte (SPE) at a graphitic carbon electrode interface. To account for the finite‐size effect of interface‐confined SPE films, the properties of two distinct film thicknesses are compared with the respective bulk properties. Additionally, the effect of uniaxial compression in the interface‐normal direction on free energy profiles of Li‐ion SPE‐desolvation is studied. © 2018 The Authors. Journal of Polymer Science Part B: Polymer Physics Published by Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 718–730

We report on a novel synthetic route to synthesize relatively large quantities of polystyrene (PS) star polymers with targeted arm functionality and molar mass and their theological properties in the molten state. The synthetic route involves grafting styrene monomers onto a modified (aliphatic, alternating) polyketone backbone with a specific number of initiating grafting sites using controlled atom transfer radical polymerization (ATRP). Several polyketone precursors were used. This resulted in a large array of star polystyrenes with nonspherical cores and varying average arm length and number of arms. Their linear viscoelasticity was investigated and discussed in the context of the known response of anionically synthesized stars. Using a powerful characterization toolbox, including state-of-the-art interaction chromatography, rheometry, and tube modeling via the branch-on-branch (BoB) algorithm, we have assessed the viscoelasticity of these star polymers quantitatively. In particular, we have demonstrated a variability in molecular structure, which differs substantially from their anionically synthesized counterparts. Hence, whereas this new family of star polymers is not recommended for fundamental studies of polymer physics such as the molecular origin of relaxation mechanisms without prior extensive fractionation, they could be used in studies of mixtures as well as industrially relevant processing operations that require large amounts of polymeric stars.

Azobenzene liquid-crystal networks (LCNs) are well known for their photo-deformation, shrinking in UV light, and reverting to their original shape in visible light. Such reversible deformation is due to trans-cis photoisomerization of the azobenzene monomer, which disturbs well-aligned order of nematic LCN. In order to predict the photo-strain of azobenzene LCNs in multiple conditions (light intensity, polarization angle, and temperature), we propose using a density functional theory (DFT)-based modeling approach, which integrates stimulated Raman adiabatic passage calculations (STIRAP), non-linear Beer's law, and polymer physics. The model predicts that as the azobenzene ratio increases, the penetration depth of photo strain decreases, whereas the shrinkage ratio of the LCN in the unit cell increases. We identify that this opposite tendency of change is the reason why there is bending limit during the photo bending of azobenzene LCN films when increasing the ratio of the azobenzene monomer, which was also measured in experimental data.

Summary Polymer Education is considered against a background of four questions. Why do we teach Polymer Science? To whom and by whom is Polymer Science taught? How can instruction in basic Polymer Science be related to capability in Polymer Technology? What aspects are important in developing countries? In developing countries innovative technological research and gathering “tacit knowledge” are needed if they are to break out of the “middle income trap”. So the education of researchers, mostly in universities, as well as of those who will enter industry directly must encourage holistic thinking. Polymer science is usually taught as polymer chemistry, polymer physics and polymer engineering with very little connection between them. This article suggests how a bridge of understanding, being a consideration of polymer molecular motion, can inter-relate them.

Polymer-solvent compound formation, occurring via co-crystallization of polymer chains and selected small-molecular species, is demonstrated for the conjugated polymer poly(9,9-dioctylfluorene) (PFO) and a range of organic solvents. The resulting crystallization and gelation processes in PFO solutions are studied by differential scanning calorimetry, with X-ray diffraction providing additional information on the resulting microstructure. It is shown that PFO-solvent compounds comprise an ultra-regular molecular-level arrangement of the semiconducting polymer host and small-molecular solvent guest. Crystals form following adoption of the planar-zigzag β-phase chain conformation, which, due to its geometry, creates periodic cavities that accommodate the ordered inclusion of solvent molecules of matching volume. The findings are formalized in terms of nonequilibrium temperature–composition phase diagrams. The potential applications of these compounds and the new functionalities that they might enable are also discussed., Journal of Polymer Science. Part B, Polymer Physics, 53 (21), ISSN:0887-6266, ISSN:0098-1273, ISSN:1099-0488

Solution-crystallization is studied for two polyfluorene polymers possessing different side-chain structures. Thermal analysis and temperature-dependent optical spectroscopy are used to clarify the nature of the crystallization process, while X-ray diffraction and scanning electron microscopy reveal important differences in the resulting microstructures. It is shown that the planar-zigzag chain conformation termed the β-phase, which is observed for certain linear-side-chain polyfluorenes, is necessary for the formation of so-called polymer-solvent compounds for these polymers. Introduction of alternating fluorene repeat units with branched side-chains prevents formation of the β-phase conformation and results in non-solvated, i.e. melt-crystallization-type, polymer crystals. Unlike non-solvated polymer crystals, for which the chain conformation is stabilized by its incorporation into a crystalline lattice, the β-phase conformation is stabilized by complexation with solvent molecules and, therefore, its formation does not require specific inter-chain interactions. The presented results clarify the fundamental differences between the β-phase and other conformational/crystalline forms of polyfluorenes., Journal of Polymer Science. Part B, Polymer Physics, 53 (21), ISSN:0887-6266, ISSN:0098-1273, ISSN:1099-0488

How a polymer chain translocates through a cylindrical pore with its pore size smaller than the chain size (ultrafiltration behavior) is a fundamental question in polymer physics. Answering this question can provide broader implications and lead to potential applications for many applicable processes, such as gene transfection, protein transportation, and separation of a mixture of polymer chains. In the process of an electroneutral polymer chain passing through a nanopore, generally, an external flow with a sufficient high shear stress is needed to apply at the entrance of pore to induce a conformation change from a coil-like to a rod-like shape which is referred to as the “coil-to-stretch” transition, to squeeze into the pore. Up to last decade, many theoretical models have been built and carried out to predict how polymer chains pass through a nanopore. By contrast, rather limited experimental investigations have been performed to validate these theoretical predications, which is mainly because this kind of experimental study demands polymer chains with explicit topologies and nanopores with well-defined structures. Namely, 1) the polymer samples with narrow molecular-weight distributions, well-defined chain configurations, as well as hydrodynamic sizes larger than the pore radii; and 2) membranes with well-defined pore structure and isolated pore channels to prevent possible interaction between neighboring shearing flows. In recent years, the development of polymer synthetic technology and the improvement of membrane manufacturing technology have stimulated a mass of research work on understanding the ultrafiltration behavior of polymer chains under an elongational flow field. In this feature article, the authors would like to mainly focus on the ultrafiltration behavior of flexible polymer chains with various topologies in dilute solution. More specifically, we will elucidate how the structural parameters of a polymer chain are related to the critical volumetric flow rate and the shape of polymer retention curve. Further application of this ultrafiltration method to the separation of polymer chain mixture and the rapid transformation among various polymer chain aggregated structures will be discussed. It is hoped that this perspective can provide a better view in understanding the translocation behavior of (bio)macromolecules in various practical processes and offer some guidance for the design and reality of commercially available ultrafiltration separation apparatus in the future.

Recent research on the stability of entanglements of polymer melts and on the correlation between viscosity improvement during processing and entanglement stability led to the discovery of a new property of the liquid state of polymers which is not explained by the current models in polymer physics: it is called “sustained orientation.” In simple terms, by manipulation of the stability of entanglements, it is possible to create and maintain quasi-stable at high temperature in an amorphous polymeric melt (say 120°C above Tg) a certain state of orientation that was induced by a mechanical deformation. The manipulation of entanglements was done by Rheo-Fluidification. In our experiments, the viscosity of a melt (e.g., PMMA) was measured at the exit of a Rheo-Fluidification treatment where the melt was submitted to a combination of shear thinning and strain softening via the use of cross-lateral shear vibration superposed on pressure flow (originated by an extruder feed). The exiting melt was frozen into pell...

Due to their inherent mechanical flexibility and stretchability, organic-based electronic devices have garnered a great deal of academic and industrial interest. Here, molecular-dynamics simulations are used to examine the molecular-scale details that govern the relationships among molecular weight, chain entanglement, persistence length, and the elastic characteristics of the widely studied π-conjugated polymer poly-(3-hexyl thiophene), P3HT. Oligomers containing at least 50 monomer units are required in the simulations to observe elastic behavior in P3HT, while much longer chains are required to ensure description of appropriate levels of entanglement: only when the molecular weight is greater than 50 kDa, that is, oligomers with approximately 400 monomer units, is truly entangled behavior observed. Interestingly, results from primitive path analysis of amorphous P3HT matches well with the observed onsets of inter-chain excitonic coherence with increased molecular weight. The simulations also indicate that the P3HT modulus saturates at 1.6 GPa for chain lengths of 50–100 monomers, a result that compares well with experimental results. This work highlights the care that needs to be taken to accurately model P3HT morphologies in relation to experimental measurements. © 2015 The Authors. Journal of Polymer Science Part B: Polymer Physics Published by Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 934–942

The statistical description of a polymer chain within the nematic system of many chains isconsidered. The chain entropy and free energy are numerically calculated on the basis offundamental definitions. No constraints are imposed on the elongation of the chain end-to-end distance, which can change from zero to a value formaximally stretched chains, or on the strength of theinternal nematic interactions within the system.Obtained results are compared with those calculatedby approximate formulas for varying strength ofinteractions and length of chains.