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To increase their durability and reliability, the incorporation of self-healing capabilities into polymers and other materials is being studied extensively, aiming at increasing the life-time of, for example, bulk composites or coatings and at the reduction of the over-dimensioning often required for structural parts. There are two major approaches to achieve (autonomous) self-healing in polymers: extrinsic and intrinsic. For the extrinsic self-healing polymers, healing agents are pre-embedded in microcapsules, hollow fibers, or in a vascular network. These healing agents will be released and will autonomously react when a crack is produced in the material, stopping the progress of the crack before it leads to a complete failure of the material, or before an underlying substrate is attacked. In case of intrinsic self-healing materials, the ability to self-heal is inherent to the material, via physical interactions or chemical reactions. These intrinsic self-healing polymers often require an external stimulus such as heat or light to heal, making them non-autonomous. In our work, advanced thermal analysis methods combined with dynamic rheometry and (temperature-dependent) spectroscopy support the development of the structure-property relationships of self-healing polymer materials. In this contribution, the development of several extrinsic and intrinsic self-healing materials will be discussed, including nanovascular healing systems, thermo- and photoreversible network systems. Recently we successfully introduced thermoreversible materials into robotics to create self-healing actuators for self-healing robotics applications.

Incorporation of small reactive moieties, the reactivity of which depends on externally imposed load (so-called mechanophores) into polymer chains offers access to a broad range of stress-responsive materials. Here, we report that polymers incorporating spirothiopyran (STP) manifest both green mechanochromism and load-induced addition reactions in solution and solid. Stretching a macromolecule containing colorless STP converts it into green thiomerocyanine (TMC), the mechanically activated thiolate moiety of which undergoes rapid thiol-ene click reactions with certain reactive C=C bonds to form a graft or a cross-link. The unique dual mechanochemical response of STP makes it of potentially great utility both for the design of new stress-responsive materials and for fundamental studies in polymer physics, for example, the dynamics of physical and mechanochemical remodeling of loaded materials.

Sic1 is a cyclin-dependent kinase inhibitor which must be phosphorylated on at least six sites (termed Cdc4 phosphodegrons, CPDs) to allow its recognition by the WD40 binding domain of Cdc4. The highly-cooperative switch-like dependence on the number of phosphorylated sites on Sic1 cannot be accounted for by traditional thermodynamic models of cooperativity. Further experimental attention is necessary to determine the physicochemical/mechanistic basis of its highly cooperative binding.We used single molecule fluorescence techniques to study the dimensions and dynamics of Sic1's N-terminal targeting region (residues 1-90, henceforth Sic1), phosphorylated Sic1 (pSic1), and the pSic1-WD40 dynamic complex.Previous single molecule Fӧrster Resonance Energy Transfer (smFRET) measurements [Liu, 2014] observed end-to-end reconfiguration on timescales larger than ∼1ms; resulting in FRET histograms with multiple conformational sub-ensembles. Sic1, pSic1, and the pSic1-WD40 complex are examined using smFRET to study the dynamics and dimensions of the various sub-ensembles. In a refinement to the conventional approaches for inferring dimensions from smFRET experiments, we use distance distributions from Monte Carlo simulations which extensively sample coarse-grained protein conformations. The application of polymer physics theory/simulation towards smFRET data interpretation, and towards IDP binding, contributes to the growing toolkit for understanding the diverse behaviours of IDPs.

Protein fibrils resulting from assembly of proteins or peptides into long, insoluble, highly ordered fibrillar structures are emerging as one of the fastest growing scientific areas, since interest in these systems spans disciplines as broad and diverse as medicine, biology, soft condensed matter, nanotechnology, and materials science. Since the discovery of the implication of protein amyloid fibrils in neurodegenerative diseases, to their more recent applications in high-performance materials, the understanding of these intriguing macromolecular assemblies has been steadily widening and deepening. Thus, the precise characterization of structural, physical, and mechanical properties of protein fibrils is the first critical step toward our understanding of these systems not only in the context of biology and medicine but also in nanotechnology and advanced biomaterials applications. In this Perspective we wish to discuss how polymer and colloidal science concepts can be efficiently used to unravel very use...

Polymer solar cells (PSCs) have attracted much attention because of their potential application in flexible, light-weight, and low-cost large-area devices through roll-to-roll printing. The bulk heterojunction PSCs showed advanced features in realizing high efficiencies and solution-processible devices. The active layer in this kind of device consists of an interpenetrating network formed by an electron-donor material blended with an electron-acceptor material. 3] Typically, conjugated polymers are used as electron donors and fullerene derivatives are used as the electron acceptors in the PSCs. Recently, power conversion efficiencies (PCEs) of 6–7% have been realized by using new conjugated polymer donors or new fullerene-derived acceptors. Short circuit current density (Jsc), open circuit voltage (Voc), and fill factors (FF) are key parameters for a PSC device, because the PCE of the device is proportional to the values of the three parameters. To broaden the response wavelength range of a PSC device by using conjugated side chains or narrowband-gap conjugated polymers is an effective way to realize high Jsc values. Conjugated polymers with lower HOMO levels are helpful in realizing high Voc and PCE values, as the Voc value of PSCs is directly proportional to the offset between the HOMO level of electron donor and the LUMO level of electron acceptor. PSiFDTBT, PFDTBT, and PCDTBT are three excellent examples for this concept. Consequently, by using conjugated polymers with lower HOMO levels and also narrow band gaps, high PCEs were realized in different families of conjugated polymers. Conjugated polymers based on benzo[1,2-b :4,5-b’]dithiophene (BDT) units have attracted interest as electron donors in the PSC field in recent years, since the report of Hou and Yang et al. on the synthesis and photovoltaic properties of a series of copolymers based on BDT. Many copolymers of BDT with different conjugated units, such as thieno[3,4b]thiophene (TT), 4,7-dithiophene-2-yl-2,1,3-benzothiadiazole (DTBT), N-alkylthieno[3,4-c]pyrrole-4,6-dione (TPD), and bithiazole, etc. were synthesized, and the copolymers showed promising photovoltaic properties. In these BDT-based polymers, the alternative copolymers of BDT and TT, namely PBDTTTs, are an important family of photovoltaic materials. For additional improvements in the photovoltaic performance of the PBDTTTs, structural modifications brought about by using different substituents on BDT, or the copolymerized moieties is of great importance. For example, Liang et al. introduced a fluorine atom into the TT unit of the PBDTTTs, and the HOMO level of the resulting polymer was successfully lowered by approximately 0.12 eV, and thus a higher Voc value was achieved, resulting in a great improvement of PCE. Hou et al. optimized PBDTTTs further by replacing the alkoxycarbonyl group on the TT unit with the alkylcarbonyl groups. The structural modification can also be carried out on the BDT units. In this work, we designed an 5-alkylthiophene-2-yl-substituted BDT monomer and synthesized two new PBDTTT-based polymers having either the thienylsubstituted BDT with alkoxycarbonyl-substituted thieno[3,4b]thiophene (TT-E) or the alkylcarbonyl-substituted thieno[3,4-b]thiophene (TT-C); that is PBDTTT-E-Tand PBDTTTC-T, respectively (Scheme 1). To fully investigate the effect of the thienyl-substituted BDTon the photovoltaic properties of the polymers, two corresponding PBDTTT polymers based on the alkoxy-substituted BDT (BDT-O), PBDTTT-E and PBDTTT-C (Scheme 1), were also prepared. The synthetic route of the thienyl-substituted BDT monomer (BDT-T) is shown in Scheme 1. The branched alkyl group 2-ethylhexyl was employed as the side chain on the thiophene to guarantee high solubility of the target polymers. The TT-E and TT-C monomers are commercially available. The polymers were prepared through a Stille coupling reaction between the bis(trimethyltin) BDT monomers (BDT-T and BDT-O) and the bromides (TT-E and TTC) as shown in Scheme 1. All the polymers are soluble in chloroform (CHCl3), chlorobenzene, and dichlorobenzene. Thermogravimetric analysis (TGA) measurements were employed to evaluate the thermal stability of the polymers. We found that the two-dimentional (2D) conjugated polymers based on alkylthienyl-substituted BDTs are much more stable than their analogues, the alkoxy-substituted BDTs. The TGA plots of these four polymers are shown in Figure 1. It can be seen that the decomposition temperatures [*] Dr. L. Huo, S. Zhang, F. Xu, Prof. J. Hou State Key Laboratory of Polymer Physics and Chemistry Beijing National Laboratory for Molecular Sciences Institute of Chemistry, Chinese Academy of Sciences Beijing 100190 (China) E-mail: hjhzlz@iccas.ac.cn

The theory of multiphase polymer systems has a venerable tradition. The 'classical' theory of polymer demixing, the Flory-Huggins theory, was developed already in the forties of the last century. It is still the starting point for most current approaches -- be they improved theories for polymer (im)miscibility that take into account the microscopic structure of blends more accurately, or sophisticated field theories that allow to study inhomogeneous multicomponent systems of polymers with arbitrary architectures in arbitrary geometries. In contrast, simulations of multiphase polymer systems are relatively young. They are still limited by the fact that one must simulate a large number of large molecules in order to obtain meaningful results. Both powerful computers and smart modeling and simulation approaches are necessary to overcome this problem. This article gives an overview over the state-of-the art in both areas, theory and simulation. While the theory has reached a fairly mature stage by now, and many aspects of it are covered in textbooks on polymer physics, the information on simulations is much more scattered. This is why some effort has been invested into putting together a representative list of references in this area (up to the year of 2008) -- which is of course still far from complete., 63 pages, 11 Figures, 453 References

A suit of teaching exercises courseware of physics and chemistry of polymers is introduced, the characteristic of physics and chemistry of polymer is narrated. The advantages of the teaching exercises courseware is introduced too.

Macromolecular conformation dynamics, which span a wide range of time scales, are fundamental to the understanding of properties and functions of their structures. Here, we report direct imaging of structural dynamics of helical macromolecules over the time scales of conformational dynamics (ns to subsecond) by means of four-dimensional (4D) electron microscopy in the single-pulse and stroboscopic modes. With temporally controlled electron dosage, both diffraction and real-space images are obtained without irreversible radiation damage. In this way, the order-disorder transition is revealed for the organic chain polymer. Through a series of equilibrium-temperature and temperature-jump dependencies, it is shown that the metastable structures and entropy of conformations can be mapped in the nonequilibrium region of a “funnel-like” free-energy landscape. The T -jump is introduced through a substrate (a “hot plate” type arrangement) because only the substrate is made to absorb the pulsed energy. These results illustrate the promise of ultrafast 4D imaging for other applications in the study of polymer physics as well as in the visualization of biological phenomena.

Coating a spherical colloid with a nematic liquid crystal causes frustration-induced defects in the crystal. The thickness of this coating can be used to systematically control the number and orientation of these defects, which could be useful for engineering the microstructure of colloidal materials.

Investigation on compaction and decompaction of polymers is very important since it is a fundamental problem in polymer physics. With the aids of atomic force microscope (AFM) and dynamic light scattering (DLS) measurements in this contribution, the temperature-dependent compaction/decompaction transition process of water-soluble cationic polythiophene (PT) was investigated in the presence of KI. The above process is characterized by the red-to-yellow color change and fluorescence recovery and is reversible during the heating-cooling cycles in the range from 25 to 55 °C, indicating that the compaction and decompaction of polymer can be employed as a temperature indicator.

The past decade has seen a renaissance in the study of polymer solutions flowing in confined geometries, the renaissance driven in part by advances in visualization of large DNA molecules and the desire to manipulate DNA for genomic applications. This article summarizes the features of the fundamental polymer physics and fluid dynamics that are relevant to the flow of confined polymer solutions, then reviews the recent literature on the topic. Experiments have clarified and extended prior work showing that diffusion of confined flexible polymers is substantially altered by confinement and that, during flow, polymers exhibit substantial cross-stream migration. Simulation methods have been developed that have the capability of capturing both polymer and fluid motion in confined geometries and yield results that are in semiquantitative agreement with experiments in dilute solutions. Kinetic-theory treatments of simple polymer models have led to analytically tractable models that qualitatively encompass the key phenomena observed in experiment.

The ability to reproducibly load bioactive molecules into polymeric microspheres is a challenge. Traditional microsphere fabrication methods typically provide inhomogeneous release profiles and suffer from lack of batch to batch reproducibility, hindering their potential to up-scale and their translation to the clinic. This deficit in homogeneity is in part attributed to broad size distributions and variability in the morphology of particles. It is thus desirable to control morphology and size of non-loaded particles in the first instance, in preparation for obtaining desired release profiles of loaded particles in the later stage. This is achieved by identifying the key parameters involved in particle production and understanding how adapting these parameters affects the final characteristics of particles. In this study, electrospraying was presented as a promising technique for generating reproducible particles made of polycaprolactone, a biodegradable, FDA-approved polymer. Narrow size distributions were obtained by the control of electrospraying flow rate and polymer concentration, with average particle sizes ranging from 10 to 20 µm. Particles were shown to be spherical with a homogeneous embossed texture, determined by the polymer entanglement regime taking place during electrospraying. No toxic residue was detected by this process based on preliminary cell work using DNA quantification assays, validating this method as suitable for further loading of bioactive components.

There is rapidly growing evidence that folding of the chromatin fibre inside the interphase nucleus has an important role in the regulation of gene expression. In particular, the formation of loops mediated by the interaction between specific regulatory elements, for instance enhancers and promoters, is crucial in gene control. Biochemical studies that were based on the chromosome conformation capture (3C) technology have confirmed that eukaryotic genomes are highly looped. Insight into the underlying principles comes from polymer models that explore the properties of the chromatin fibre inside the nucleus. Recent models indicate that chromatin looping can explain various properties of interphase chromatin, including chromatin compaction and compartmentalisation of chromosomes. Entropic effects have a key role in these models. In this Commentary, we give an overview of the recent conjunction of ideas regarding chromatin looping in the fields of biology and polymer physics. Starting from simple linear polymer models, we explain how specific folding properties emerge upon introducing loops and how this explains a variety of experimental observations. We also discuss different polymer models that describe chromatin folding and compare them to experimental data. Experimentally testing the predictions of such polymer models and their subsequent improvement on the basis of measurements provides a solid framework to begin to understand how our genome is folded and how folding relates to function.

Flow-induced crystallisation (FIC) in polymers is simultaneously of great fundamental and practical importance. Current work on the molecular origins of FIC is providing insight into this fascinating, kinetically driven, non-equilibrium phase transition. This understanding also has the potential to be hugely beneficial to the plastics industry. In this article the main processes active during flow of crystallising polymers in complex geometries and the ways they are coupled are reviewed. Each of these processes individually presents a substantial modelling challenge, drawing on a diverse range of areas in polymer physics. Recent progress is reviewed and likely future directions indicated.

Picking up at the conclusion of Viovy's review of the physics of gel electrophoresis [J.-L. Viovy, Rev. Mod. Phys. 72, 813 (2000)], this review synthesizes the experimental data, theoretical models, and simulation results for DNA electrophoresis in microfabricated and nanofabricated devices appearing since the seminal paper by Volkmuth and Austin [Nature (London) 358, 600 (1992)]. Prototype versions of these devices separate DNA by molecular weight at a rate far superior to gel electrophoresis. After providing an overview of the requisite background material in polymer physics, electrophoresis, and microfluidic device fabrication, the focus is on the following three generic problems: (i) collision with an isolated post, (ii) transport in an array of posts, and (iii) entropic trapping and filtration in the slit-well motif. The transport phenomena are examined here in the context of the length and time scales characterizing the DNA, the device, and the applied electric field.

Efforts to study the polymer physics of DNA confined in nanochannels have been stymied by a lack of consensus regarding its wall depletion length. We have measured this quantity in 38 nm wide, square silicon dioxide nanochannels for five different ionic strengths between 15 mM and 75 mM. Experiments used the Bionano Genomics Irys platform for massively parallel data acquisition, attenuating the effect of the sequence-dependent persistence length and finite-length effects by using nick-labeled E. coli genomic DNA with contour length separations of at least 30 µm (88 325 base pairs) between nick pairs. Over 5 × 106 measurements of the fractional extension were obtained from 39 291 labeled DNA molecules. Analyzing the stretching via Odijk's theory for a strongly confined wormlike chain yielded a linear relationship between the depletion length and the Debye length. This simple linear fit to the experimental data exhibits the same qualitative trend as previously defined analytical models for the depletion length but now quantitatively captures the experimental data.

Biological polymers such as DNA, RNA, and proteins are essential parts of life on Earth from its very beginning. People started using biopolymers many centuries ago. For example, ancient Egyptians prepared ink by mixing carbon black with Arabic gum, whereas Amazon Indians made boots from unvulcanized natural rubber extracted from hevea trees more that 25 centuries ago. People started synthesizing polymers during the first half of the 19th century, but they understood that these molecules are long linear chains only in the beginning of the 20th century. Unfortunately, even now in the beginning of the 21st century, some physicists do not know that polymers exist, as polymer physics is still not a part of ‘‘proper’’ Physics education and culture. This situation with polymer physics hasn’t improved much either over the last 3 decades since the publication of de Gennes’ textbook ‘‘Scaling Concepts in Polymer Physics’’ or over the last 2 decades since his Nobel Prize in Physics. Personally, I do not recall seeing a polymer in any of the classes or seminars throughout my entire Physics education (B.S. from Caltech and Ph.D. from Harvard). Thus, according to my ‘‘proper’’ Physics education, polymers could not possibly be part of Physics.

Saito, Takahashi and Yunoki developed the continuous version of worm-like chain (WLC) model that is very suitable for description of the polymer conformational properties affected by chain rigidity. By adjusting persistence length directly, the WLC model can depict the extensive range of chain conformations from flexible chains to rigid chains. It is widely accepted that more physical properties of real polymer can be obtained by utilizing coarse-grained model than Gaussian chain (GSC). This paper reviews the applications of the WLC model in the framework based on self-consistent field theory, which is an efficient method of theoretical exploration of phase separation in polymer system. It is noticed that the development of numerical schemes is in favor of solving modified diffusion equation that adjusts the probability distribution of polymers. In addition, we conclude the recent applications of the self-consistent field theory based on the WLC model as the following three points: phase transitions of liquid crystal polymer; the influences of surface curvature on polymer system that involves the chain orientation effects; self-assembly of worm-like block copolymer. These researches have been out of the range of the self-consistent field theory based on GSC model that has been used in a large number of theoretical studies. Finally, we present ideas of theoretical development in field theory simulations based on the WLC model in the future. It is universally acknowledged that chain rigidity is a key factor that influences the properties of structural stabilities in the meso-scale in articles. Theoretical researches determine the key physical mechanisms that play crucial roles in many experimental systems with attractively promising applications in practice, for systems such as liquid crystalline polymers and organic solar cell based on the conjugated polymers.

Polymers in flow deform elastically as a result of reduced entropy stored in the distorted chain. Elastic stretching of the chains in flow is assumed; however, measurement of the deformation of individual chains in concentrated solution in flow has largely eluded experiment. Several recent simulations have shown that the chains may compress in flow to elastically deform. Here, we show that polymer chains compress in simple shear flow, using time-resolved fluorescence to measure changes in fluorescence resonance energy transfer of a tagged polymer molecule. Time resolved measurements allow quantitative determination of changes in polymer chain dimensions, and are free from potential artifacts that could affect steady-state fluorescence. Flow-induced chain compression is reconciled with the observed rheological behavior of polymers, namely, shear thinning and elasticity. The ability to understand the flow behavior and model these complex systems will evolve through this important finding. The implications f...

The aggregation of proteins is central to many aspects of daily life, including food processing, blood coagulation, eye cataract formation disease and prion-related neurodegenerative infections[1–5]. However, the physical mechanisms responsible for amyloidosis—the irreversible fibril formation of various proteins that is linked to disorders such as Alzheimer’s, Creutzfeldt–Jakob and Huntington’s diseases—have not yet been fully elucidated[6–9]. Here, we show that different stages of amyloid aggregation can be examined by performing a stat- istical polymer physics analysis of single-molecule atomic force microscopy images of heat-denatured b-lactoglobulin fibrils. The atomic force microscopy analysis, supported by theoretical arguments, reveals that the fibrils have a multistranded helical shape with twisted ribbon-like structures. Our results also indicate a possible general model for amyloid fibril assembly and illustrate the potential of this approach for investigating fibrillar systems. 1. Caughey, B. & Lansbury, P. T. Protofibrils, pores, fibrils and neurodegeneration: separating the responsible protein aggregates from the innocent bystanders. Annu. Rev. Neurosci. 26, 267–298 (2003). 2. Stradner, A. et al. Equilibrium cluster formation in concentrated protein solutions and colloids. Nature 432, 492–495 (2004). 3. Mezzenga, R., Schurtenberger, P., Burbidge, A. & Michel, M. Understanding foods as soft materials. Nature Mater. 4, 729–740 (2005). 4. Selkoe, D. J. Folding proteins in fatal ways. Nature 426, 900–904 (2003). 5. Chiti, F. & Dobson, C. M. Amyloid formation by globular proteins under native conditions. Nature Chem. Biol. 5, 15–22 (2009). 6. Knowles, T. P. et al. Role of intermolecular forces in defining material properties of protein nanofibrils. Science 318, 1900–1903 (2007). 7. Nelson, R. et al. Structure of the cross-beta spine of amyloid-like fibrils. Nature 435, 773–778 (2005). 8. Chiti, F. & Dobson, C. M. Protein misfolding, functional amyloid and human disease. Annu. Rev. Biochem. 75, 333–366 (2006). 9. Dobson, C. M. Protein folding and misfolding. Nature 426, 884–890 (2003).

This article focuses on the influence of the geometric structure of the polymer chain on the physical properties of polymers. It is shown that for polyheteroarylenes the Kuhn segment calculated based on the geometric structure of the polymer chain has a good correlation with the physical properties of those polymers. For aliphatic polymers, a volume factor is suggested that equals the ratio of the Van der Waals volume of pendant substitute to the volume of the whole polymer chain. It is shown that the properties of aliphatic polymers that depend on free volume are well described by this value.

This review concerns the rheological research related to compounds obtained using powder injection molding (PIM) technology. PIM is a process for making metallic and ceramic items using forming method for thermoplastics. This technique allows the large-number production of relatively small (corresponding to a weight of around 100 grams) parts of complex shapes with reduced cost comparing to traditional metallurgy and increased efficiency by avoiding the use of extra processes. On the other hand, the number of process variables is very high, and their interactions are only partially understood. The knowledge of the flow properties is the key factor for successful injection molding. Its novelty consists in the polymer physics aspects of the problem, considering the compounds obtained in PIM process as polymer melts highly filled with powder particles.

The applications of laser light scattering (LLS) to polymer physics and colloid science have been extensive and noteworthy, especially in particle-size analysis. The study presents an example of LLS application to the characterization of interpolymer complexation of poly(aspartic acid) with a vinylic polymer, by particle size and zeta potential evaluation. The LLS technique is complemented by oscillatory rheological data. The complexes have a potential biomedical application by bioactive substances attachment.

Laser-interferometric creep rate meter (LICRM) is the original high-resolution method developed in the Materials Dynamics Laboratory at Ioffe Physical-Technical Institute of the Russian Academy of Sciences (Saint-Petersburg). LICRM has been successfully applied to solving various problems of polymer physics and materials science, especially being combined with other techniques. LICRM setup allows to register precisely creep rates on the basis of deformation increment of 150–300 nm. This approach provided absolutely new experimental possibilities exhibiting the superiority in resolution and sensitivity to the conventional relaxation spectrometry techniques. Amongst such possibilities are creep studying on submicro-, micro- and meso-scale levels; revealing the connections between stepwise microplasticity and polymer morphology; getting kinetic information on creep at any temperature and deformation degree, the discrete analysis of dynamics within an each relaxation region; analyzing microplasticity, relaxations and phase transitions in brittle materials; using creep rate spectra for non-destructive prediction of the temperature anomalies in mechanical behavior of materials, etc. The report represents this method and some (not all) results of numerous studies performed with applying of LICRM setups for different polymeric materials in the form of bulk specimens, films or thin fibers.

Nuclear magnetic resonance (NMR) spectroscopy has been used effectively in the analysis of elastomeric, soft materials and has been proven to be both sensitive to micro- and macroscopic changes associated with “aging” mechanisms. Traditional analyses, however, rely on empirical formulae containing a large number of (often arbitrary) independent variables. The resulting ambiguity can be circumvented largely by developing models of NMR observables that are based on basic polymer physics. We compare two such models, one previously published and one derived herein, along with two empirical expressions that describe the proton transverse magnetization decay associated with complex polymer networks. One particular extracted parameter, the proton–proton residual dipolar coupling (RDC), can be directly related to network topology, and a comparison of the extracted RDCs reveals high consistency among the models. An expression derived from the properties of a static Gaussian chain can minimize the number of parameters necessarily to describe the solid-like, networked proton population to a single independent parameter, the average RDC, D avg . The distribution of RDCs derived via this methodology is qualitatively similar to those derived from previously published multiple quantum techniques, although quantitative differences between the derived RDCs persist, suggesting that further analysis is necessary.

A mesoscopic computational model for polymer networks and composites is developed as a very coarse-grained representation of the network microstructure. Unlike more complex molecular dynamics simulations, the model network is static unless undergoing deformation. The elastic modulus, which depends only on the crosslink density and parameters in the bond potential, is consistent with rubber elasticity theory, and the network response satisfies the independent network hypothesis of Tobolsky. The model, when applied to a commercial filled silicone elastomer, quantitatively reproduces the experimental permanent set and stress-strain response due to changes in the crosslinked network from irradiation.

Disordered Proteins Disordered proteins sample an ensemble of conformations, but it has remained unclear how compact these conformations are in water. Polymer physics relates the radius of gyration ( R g) to solvent quality, with more chain collapse occurring in poorer solvents. Riback et al. developed an analysis scheme that allows them to extract solvent quality and R g from a single small-angle x-ray scattering measurement. Applying this method, they found that even disordered proteins with low net charge and high hydrophobicity remain expanded in water. Science , this issue p. [238][1] [1]: /lookup/doi/10.1126/science.aan5774

We present a patch code for LAMMPS to implement a coarse grained (CG) model of poly(vinyl alcohol) (PVA). LAMMPS is a powerful molecular dynamics (MD) simulator developed at Sandia National Laboratories. Our patch code implements tabulated angular potential and Lennard-Jones-9-6 (LJ96) style interaction for PVA. Benefited from the excellent parallel efficiency of LAMMPS, our patch code is suitable for large-scale simulations. This CG-PVA code is used to study polymer crystallization, which is a long-standing unsolved problem in polymer physics. By using parallel computing, cooling and heating processes for long chains are simulated. The results show that chain-folded structures resembling the lamellae of polymer crystals are formed during the cooling process. The evolution of the static structure factor during the crystallization transition indicates that long-range density order appears before local crystalline packing. This is consistent with some experimental observations by small/wide angle X-ray scattering (SAXS/WAXS). During the heating process, it is found that the crystalline regions are still growing until they are fully melted, which can be confirmed by the evolution both of the static structure factor and average stem length formed by the chains. This two-stage behavior indicates that melting of polymer crystals is far from thermodynamic equilibrium. Our results concur with various experiments. It is the first time that such growth/reorganization behavior is clearly observed by MD simulations. Our code can be easily used to model other type of polymers by providing a file containing the tabulated angle potential data and a set of appropriate parameters. Program summary Program title: lammps-cgpva Catalogue identifier: AEDE_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEDE_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: GNU's GPL No. of lines in distributed program, including test data, etc.: 940 798 No. of bytes in distributed program, including test data, etc.: 12 536 245 Distribution format: tar.gz Programming language: C++/MPI Computer: Tested on Intel-x86 and AMD64 architectures. Should run on any architecture providing a C++ compiler Operating system: Tested under Linux. Any other OS with C++ compiler and MPI library should suffice Has the code been vectorized or parallelized?: Yes RAM: Depends on system size and how many CPUs are used Classification: 7.7 External routines: LAMMPS (http://lammps.sandia.gov/), FFTW (http://www.fftw.org/) Nature of problem: Implementing special tabular angle potentials and Lennard-Jones-9-6 style interactions of a coarse grained polymer model for LAMMPS code. Solution method: Cubic spline interpolation of input tabulated angle potential data. Restrictions: The code is based on a former version of LAMMPS. Unusual features.: Any special angular potential can be used if it can be tabulated. Running time: Seconds to weeks, depending on system size, speed of CPU and how many CPUs are used. The test run provided with the package takes about 5 minutes on 4 AMD's opteron (2.6 GHz) CPUs. References: [1] D. Reith, H. Meyer, F. Muller-Plathe, Macromolecules 34 (2001) 2335–2345. [2] H. Meyer, F. Muller-Plathe, J. Chem. Phys. 115 (2001) 7807. [3] H. Meyer, F. Muller-Plathe, Macromolecules 35 (2002) 1241–1252.

The translocation dynamics of a polymer chain through a nanopore in the absence of an external driving force is analyzed by means of scaling arguments, fractional calculus, and computer simulations. The problem at hand is mapped on a one dimensional {\em anomalous} diffusion process in terms of reaction coordinate $s$ (i.e. the translocated number of segments at time $t$) and shown to be governed by an universal exponent $\alpha = 2/(2\nu+2-\gamma_1)$ whose value is nearly the same in two- and three-dimensions. The process is described by a {\em fractional} diffusion equation which is solved exactly in the interval $0 $, and $ - < s(t)>^2$ which provide full description of the diffusion process. The comparison of the analytic results with data derived from extensive Monte Carlo (MC) simulations reveals very good agreement and proves that the diffusion dynamics of unbiased translocation through a nanopore is anomalous in its nature., Comment: 5 pages, 3 figures, accepted for publication in Phys. Rev. E

Research into polymers incorporating polyhedral oligomeric silsesquioxane (POSS) has intensified during the past several years, revealing new fundamental polymer physics, new synthetic routes, and unexpected applications. The present review article critically examines the recent scientific literature on POSS polymers with an emphasis on structure-property relationships. We conclude that it is an exciting time to work on such materials and we expect the field to continue to grow in the foreseeable future.

The current concepts concerning the structure of fibres and fibre materials were analyzed based on an examination of their morphological and energetic characteristics at four fundamental structural levels: molecular (chemical structure), supramolecular (nano-) level, microlevel (fibre) and macrolevel (fibre material). The features of the structural dependence of the mechanical properties and the structural mechanics of the oriented polymers (fibres) are discussed. The principles and methodology for predicting the properties of fibres and fibre materials with methods of polymer physics and physical chemistry are examined.

It is traced out a parallel between the cosmological constant problem and the polymer physics. The time evolution of the universe world line is compared with the growing of a polymer chain. An equivalent Flory free energy and a modification of it are used as a means to evaluate two versions for the radius of gyration of the universe. It is proposed a link between this radius of gyration and the cosmological constant parameter., Comment: 6 pages, no figures

Exciton binding energy (E b ) is a key factor for the polymer electronics as well as for the fundamental polymer physics, which has been controversial since long time. Light-emitting polymer requires a large E b so that the charge recombination dominates. But, the photovoltaic polymers need small E b to allow efficient charge separation. First-principles Density Functional Theory (DFT) is employed to calculate E b for polydiacetylene (PDA), trans-polyacetylene (PA), polythiophene (PT), poly(2,5-thienylenevinylene) (PTV), and poly(p-phenylene vinylene) (PPV). We find that the hybrid B3LYP, B972, PBE1PBE, and B1B95 functionals with 20–25% amount of exact HF exchange can give reasonable results and predict E b is around 0.1–0.6 eV for these π-conjugated polymers.

Our understanding of the rich and complex motion of macromolecules has developed rapidly in recent years, particularly in the entangled regime. In this paper we highlight examples of research that has exploited our detailed picture of macromolecular motion. These studies encompass a broad range of areas in polymer physics, including neutron scattering under strong flow, tear properties of oriented polymers, flow-induced crystallisation and single molecule rheology of biopolymers. In each case molecular modelling plays a key role in understanding the observed phenomena.

For chain-like polymers on surfaces, the relationship between chain topology and inherent physical properties has long been puzzling due to the lack of proper models and detection systems with ultrahigh sensitivity and high accuracy. Among various chain-like polymers, soluble organopolysilane is one suitable model for elucidating the uniqueness of chain-like polymers on surfaces because of its (1) controllable molecular length, polydispersity, stiffness, and terminal group by an adequate molecular design, a careful synthesis, and a precise purification, and (2) highly luminescent chromophore due to Siσ-Siσ* transition of the Si main chain. This review comprehensively covers the works on (i) molecular imaging with scanning probe microscopy, (ii) tethering on surfaces by a grafting-to approach, (iii) self-assembly, (iv) structural phase transition, (v) orientational phase transition, and (vi) chiroptical switching, memory and amplification in single and double layer films deposited on solid surfaces. This knowledge and understanding may stimulate advanced studies on polymer-based nanoscience, nanotechnology, and nanofabrication as well as in traditional surface chemistry and polymer physics.

In this work we used atomistic molecular dynamics simulations to examine different aspects of tubular nanostructures constructed using protein building blocks with a beta-helical conformation. Initially, we considered two different natural protein building blocks, which were extracted from the protein data base, to compare the relative stabilities of the nanotubes obtained made of self-assembled and covalently linked repeats. Results show nanotubes constructed by linking building blocks through covalent bonds are very stable suggesting that the basic principles of polymer physics are valid when the repeating units are made of large fragments of proteins. In contrast, the stability of self-assembled nanostructures strongly depends on the attractive nonbonding interactions associated to building blocks aligned in a complementary manner. On the other hand, we investigated the ability of a conformationally constrained synthetic amino acid to enhance the stability of both self-assembled and polymerized nanotubes when it is used to substitute natural residues. Specifically, we considered 1-aminocyclopentane-1-caboxylic acid, which involves strong stereochemical constraints produced by the cyclopentane side chain. We found that the incorporation of this amino acid within the more flexible regions of the beta-helical building blocks is an excellent strategy to enhance the stability of the nanotubes. Thus, when a single mutation is performed in the loop region of the beta-helix, the bend architecture of the whole loop is stabilized since the conformational mobility is reduced not only at the mutated position but also at the adjacent positions.

Intrinsically disordered proteins (IDPs) are unfolded under physiological conditions. Here we ask if archetypal IDPs in aqueous milieus are best described as swollen disordered coils in a good solvent or collapsed disordered globules in a poor solvent. To answer this question, we analyzed data from molecular simulations for a 20-residue polyglutamine peptide and concluded, in accord with experimental results, that water is a poor solvent for this system. The relevance of monomeric polyglutamine is twofold: It is an archetypal IDP sequence and its aggregation is associated with nine neurodegenerative diseases. The main advance in this work lies in our ability to make accurate assessments of solvent quality from analysis of simulations for a single, rather than multiple chain lengths. We achieved this through the proper design of simulations and analysis of order parameters that are used to describe conformational equilibria in polymer physics theories. Despite the preference for collapsed structures, we find that polyglutamine is disordered because a heterogeneous ensemble of conformations of equivalent compactness is populated at equilibrium. It is surprising that water is a poor solvent for polar polyglutamine and the question is: why? Our preliminary analysis suggests that intrabackbone interactions provide at least part of the driving force for the collapse of polyglutamine in water. We also show that dynamics for conversion between distinct conformations resemble structural relaxation in disordered, glassy systems, i.e., the energy landscape for monomeric polyglutamine is rugged. We end by discussing generalizations of our methods to quantitative studies of conformational equilibria of other low-complexity IDP sequences.

The micelle formation of five poly(2-oxazoline) diblock, triblock and gradient copolymers in water was investigated using fluorescence correlation spectroscopy. The polymers were synthesized by consecutive or simultaneous living cationic polymerization of 2-methyl-2-oxazoline for the hydrophilic and 2-nonyl-2-oxazoline for the hydrophobic polymer segments. Fractions of the polymers were fluorescence-labeled at the polymer termini with TRITC for the FCS measurements. The hydrodynamic radii of solubilized polymer unimers and of the aggregates (micelles) were determined in a concentration range of 10 -8 -10 -3 M and were found to depend in a characteristic way on the polymer architecture.

Recasting a many-particle problem in a field-theoretic formalism is nowadays a well-established theoretical tool used by scientists across a wide spectrum of research areas, ranging from polymer physics to molecular electronic structure theory. It has shown to provide useful results in many complex situations, where the physics of the system involves many degrees of freedom and a multitude of different length scales, generally rendering its numerical treatment on a detailed level computationally intractable. To reduce the computational burden, field-theoretic methodologies usually take advantage of the mean-field approximation. This approximation technique is known to give reliable information about the system in the high concentration regime, where the interactions are highly screened. However, it is well established that the ranges of physical interest in most biological and technological applications lie in the intermediate to low concentration regimes, where fluctuations beyond the mean-field level of approximation become important and dominate the overall physical behavior. In this work we introduce a new self-consistent field theory for flexible polyelectrolyte chains, in which the monomers interact via a pair potential of screened Coulomb type, and derive suitable thermodynamic expressions for all concentration regimes. Our approach combines the renormalization concepts of tadpole renormalization, which has recently been successfully employed in calculations of prototypical neutral polymer and polyelectrolyte solutions, with the Hartree renormalization procedure. By comparing our approach to experimental measurements as well as alternative theoretical approaches, we demonstrate that it provides useful osmotic pressure results for polyelectrolyte systems composed of sodium poly(styrene-sulfonate) without and with added salt over the whole range of monomer concentrations.

Ming Xiong, andHongxia Guo*State Key Laboratory of Polymer Physics and Chemistry,Joint Laboratory of Polymer Science and Materials,Institute of Chemistry, The Chinese Academy of Sciences,Beijing 100080, P. R. ChinaHiroshi Jinnai* and Takeshi KanekoDepartment of Macromolecular Science and Engineering,Graduate School of Science and Engineering,Kyoto Institute of Technology, Goshokaido-cho,Matsugasaki, Kyoto 606-8585, JapanReceiVed February 6, 2007ReVised Manuscript ReceiVed May 14, 2007Closure of block copolymer bilayer in the solution generatesthe so-called polymeric vesicles or polymersomes with thesolvent fills in their internal spaces. Recently, polymeric vesicleshave attracted a great attention not only from academia but alsofrom application field for drug delivery.

Spatially resolved and time-resolved understanding of complex fluid situations compose a new frontier in physical chemistry. Here we draw attention to the significance of spatially resolving systems whose ensemble average differs fundamentally from the spatially resolved individual elements. We take examples from the field of fluid phospholipid bilayers, to which macromolecules adsorb; the field of polymer physics, when flexible chains adsorb to the solid-liquid interface; and from the field of lubrication, when two solids are squeezed close together with confined fluid retained between them.

Using Monte Carlo simulations, we have found that there is a surprising non-monotonic dependence of a polymer's diffusion coefficient upon the degree of disorder of the surrounding environment. Starting with a two-dimensional periodic lattice of obstacles, we randomly displace obstacles to create a quenched gel system with a tunable degree of disorder. Very small displacements increase the diffusion coefficient of polymers since they increase the width of the tube through which the polymer chains reptate. As we displace the obstacles further, however, entropic trapping is observed and the diffusion coefficient of the polymer decreases dramatically. This is a striking example of the delicate balance between entropic and frictional effects for a polymer diffusing in a dense system.

Diffusion and sorption data of methanol and toluene in the ternary system methanol–toluene–poly(vinylacetate) (pvac) were measured by means of a magnetic suspension balance (MSB). Ternary diffusion coefficients were determined from sorption kinetics with a method of Crank [1975. The Mathematics of Diffusion, second ed. Claredon Press, Oxford] classically used for binary polymer solvent systems. Assumptions and limitations for this method are discussed. Sorption data of methanol and toluene in the ternary system were correlated with a modified Flory–Huggins theory taking four instead of three interaction parameters into account and compared with predictions of UNIFAC-FV. All four binary Flory–Huggins interaction parameters were correlated as a function of concentration, determined from binary polymer–solvent sorption measurements and from solvent–solvent equilibrium data. The modified Flory–Huggins approach for ternary systems predicts the two limiting cases for the binary polymer–solvent as well the two solvent–solvent equilibria. Diffusion coefficients determined from sorption kinetics measurements were correlated with free-volume theory predictions of Vrentas et al. [1984. Self diffusion in polymer–solvent–solvent systems. Journal of Polymer Science, Polymer Physics Edition, 22, 459–469] and compared with a few available literature data from Surana et al. [1998. Diffusion and equilibrium measurements in ternary polymer–solvent–solvent systems using inverse gas chromatography. Industrial and Engineering Chemistry Research, 37, 3203–3207]. Cross diffusion terms are not taken into account. Diffusion and sorption data, determined with this gravimetric method, were used in model simulations with modified Flory–Huggins and free-volume theory to predict drying curves of ternary methanol–toluene–pvac solutions. The results were compared with previously published experimental results performed by means of Inverse-Micro-Raman-Spectroscopy (IMRS) from Schabel [2004. Trocknung von Polymerfilmen - Messung von Konzentrationsprofilen mit der Inversen-Mikro-Raman-Spektroskopie. Ph.D. Thesis, Universitat Karlsruhe (TH), Germany].