Search

When cooled or pressurized, polymer melts exhibit a tremendous reduction in molecular mobility. If the process is performed at a constant rate, the structural relaxation time of the liquid eventually exceeds the time allowed for equilibration. This brings the system out of equilibrium, and the liquid is operationally defined as a glass - a solid lacking long-range order. Despite almost 100 years of research on the (liquid/)glass transition, it is not yet clear which molecular mechanisms are responsible for the unique slow-down in molecular dynamics. In this review, we first introduce the reader to experimental methodologies, theories, and simulations of glassy polymer dynamics and vitrification. We then analyse the impact of connectivity, structure, and chain environment on molecular motion at the length scale of a few monomers, as well as how macromolecular architecture affects the glass transition of non-linear polymers. We then discuss a revised picture of nanoconfinement, going beyond a simple picture based on interfacial interactions and surface/volume ratio. Analysis of a large body of experimental evidence, results from molecular simulations, and predictions from theory supports, instead, a more complex framework where other parameters are relevant. We focus discussion specifically on local order, free volume, irreversible chain adsorption, the Debye-Waller factor of confined and confining media, chain rigidity, and the absolute value of the vitrification temperature. We end by highlighting the molecular origin of distributions in relaxation times and glass transition temperatures which exceed, by far, the size of a chain. Fast relaxation modes, almost universally present at the free surface between polymer and air, are also remarked upon. These modes relax at rates far larger than those characteristic of glassy dynamics in bulk. We speculate on how these may be a signature of unique relaxation processes occurring in confined or heterogeneous polymeric systems.

The advancement of experimental methodologies to investigate chromatin spatial interactions has prompted the development of quantitative models from polymer physics to explore the underlying molecular mechanisms and to understand how the genome works. Here we review some development in the models used and their applications in different organisms.

Basic principles and sciences behind the biodegradable polymers are discussed. It starts with introduction of basic concepts on “soft” and “stiff” polymer chains and inter- and intra- molecular interactions. Based on the fundamental molecular mechanisms, polymer physics, mechanics and fracture are introduced. After that, two families of biodegradables, i.e. natural and synthetic polymers are generally discussed of their chemical structures and properties. Towards the end, guideline for selection of materials, basic criteria for design and development of medical devices and quality system regulation are introduced. Important new concepts and principles and materials chemistry and physics are generally covered in the chapter for knowledge-based educational learning and training to aid fundamental understanding of important biodegradable polymers.

We review the picture of chromatin large-scale 3D organization emerging from the analysis of Hi-C data and polymer modeling. In higher mammals, Hi-C contact maps reveal a complex higher-order organization, extending from the sub-Mb to chromosomal scales, hierarchically folded in a structure of domains-within-domains (metaTADs). The domain folding hierarchy is partially conserved throughout differentiation, and deeply correlated to epigenomic features. Rearrangements in the metaTAD topology relate to gene expression modifications: in particular, in neuronal differentiation models, topologically associated domains (TADs) tend to have coherent expression changes within architecturally conserved metaTAD niches. To identify the nature of architectural domains and their molecular determinants within a principled approach, we discuss models based on polymer physics. We show that basic concepts of interacting polymer physics explain chromatin spatial organization across chromosomal scales and cell types. The 3D structure of genomic loci can be derived with high accuracy and its molecular determinants identified by crossing information with epigenomic databases. In particular, we illustrate the case of the Sox9 locus, linked to human congenital disorders. The model in-silico predictions on the effects of genomic rearrangements are confirmed by available 5C data. That can help establishing new diagnostic tools for diseases linked to chromatin mis-folding, such as congenital disorders and cancer.

Gloss is a critical issue in many applications in the coating industry. Gloss depends on optical and rheological properties of complex mixtures, and estimating gloss from basic properties is still a challenge. In order to predict the gloss of an industrial thickened-to-application formulation this work presents a gloss-rheology semi empirical-modeling approach based on a gloss excess function and previous work from other authors. A new matt (low gloss) hybrid waterborne polyurethane dispersion composed out of a self-matting agent (A) and a traditional silica-based matting agent (B) has been studied, and the resulting gloss of the mixture has been correlated to pure component gloss values and dynamic viscosity at medium shear rate. Several modeling options have been tested and their goodness of fit has been determined. The most promising options have been selected and validated towards untrained data sets.

We have extended an existing hybrid MD-SCF simulation technique that employs a coarsening step to enhance the computational efficiency of evaluating non-bonded particle interactions. This technique is conceptually equivalent to the single chain in mean-field (SCMF) method in polymer physics, in the sense that non-bonded interactions are derived from the non-ideal chemical potential in self-consistent field (SCF) theory, after a particle-to-field projection. In contrast to SCMF, however, MD-SCF evolves particle coordinates by the usual Newton's equation of motion. Since collisions are seriously affected by the softening of non-bonded interactions that originates from their evaluation at the coarser continuum level, we have devised a way to reinsert the effect of collisions on the structural evolution. Merging MD-SCF with multi-particle collision dynamics (MPCD), we mimic particle collisions at the level of computational cells and at the same time properly account for the momentum transfer that is important for a realistic system evolution. The resulting hybrid MD-SCF/MPCD method was validated for a particular coarse-grained model of phospholipids in aqueous solution, against reference full-particle simulations and the original MD-SCF model. We additionally implemented and tested an alternative and more isotropic finite difference gradient. Our results show that efficiency is improved by merging MD-SCF with MPCD, as properly accounting for hydrodynamic interactions considerably speeds up the phase separation dynamics, with negligible additional computational costs compared to efficient MD-SCF. This new method enables realistic simulations of large-scale systems that are needed to investigate the applications of self-assembled structures of lipids in nanotechnologies.

The impact of organic compounds on the processing and reactivity of inorganic materials has been a source of inspiration for materials scientists for decades and continues to trigger novel and innovative applications in a broad range of disciplines. However, molecular design of such compounds to reach targeted properties remains challenging, particularly for reactive and multicomponent systems. This outstanding challenge is met here by combining a model cement, hosting different coupled reactions of dissolution, nucleation and growth, together with comb-copolymers that offer large and well-controlled variations of their molecular architecture. We show that silicate reactivity is affected by a combination of molecular and submolecular scale effects of these polymers. The first can be described by scaling laws from polymer physics, whereas the second involves specific chemical interactions. In particular, the ability of these polymers to hinder dissolution appears to be crucial, something for which strong experimental evidence is provided., Journal of the American Ceramic Society, 100 (3)

In mammalian cells, transcriptional regulation is intimately connected linked to three-dimensional structure of chromosomes. Methods based on chromosome conformation capture (3C) detect spatial proximity between genomic sequences in the context of cell nuclei and provide an invaluable a tool to investigate chromosome structure. 3C-based methods have revealed that chromosomes are folded in a complex hierarchy of structural layers, and particularly that regulatory sequences interact in the context of topologically associating domains (TADs), submegabase regions where the chromatin fiber preferentially interacts with itself. However, the information provided by 3C-based experiments is averaged over populations of millions of cells. Data-driven computational models based on polymer physics allow the single-cell information embedded within 3C data to be deconvolved, thus enabling study of the ensemble of conformations that give rise to the observed interaction patterns. Here we discuss how these physical methods can be implemented and what can be learned by applying such models, notably at the scale of TADs. We illustrate in particular how models revealed that TADs arise from highly fluctuating, although nonrandom structures of the chromatin fiber, which are predicted to arise from rapid formation and disassembling of unstable loops, and why this could be relevant for transcriptional regulation. Finally, we discuss how data-driven physical models relate to proposed biological and physical mechanisms of how chromosome structure is created.

Experimental evidence are collected together to show in general the viscoelastic mechanisms of low and high molecular weight polymers have different dependences on temperature T, pressure P, and the same scaling product variable, TVγ, where V is the specific volume and γ is a material constant. The viscoelastic mechanisms include the Johari–Goldstein β-relaxation, the segmental α-relaxation, the sub-Rouse modes, the Rouse modes, and the terminal relaxation if the polymer chains are entangled. Appropriately called the thermo-, piezo-, and TVγ-rheological complexity of polymers, these viscoelastic anomalies are fundamental and deserve attention from the polymer physics community. Although we show that the coupling model can rationalize the origin of the complexity and explain some of the data quantitatively, the objective of this paper is to stimulate others to construct a theory that can do even better.

The task of the polymer physics experiment course is using a certain percentage of nanocalcium carbonate (CaCO3) to composite polypropylene (PP) and using a twin-screw injection molding machine to inject the compound above into a standard sample. After that some mechanical properties test were made to get some nanocalcium carbonate data which may affect the mechanical properties of polypropylene.

Static laser scattering (SLS) is one of the most efficient techniques used for the molecular weight determination of polymer. Among of all polymers, polyvinyl alcohol (PVA) polymer was selected. A polystyrene (PS) was used as a standard polymer. A polyvinyl alcohol was investigated for its importance in pharmaceutical, biomedical, and industrial applications. Different concentrations in the range (3–9) × 10−3 g mL−1 were prepared. SLS data were obtained by using a self-built of the laser scattering system. The angular behavior of those selected polymer solutions with different concentrations were studied by plotting the intensity of the scattered light against the scattering angle in the range of 40–140°. By using Zimm plot the weight-average molecular weight Mw, radius of gyration RG, and second virial coefficient A2 of the standard PS and PVA were determined.

Clear organizational patterns on the genome have emerged from the statistics of population studies of fixed cells. However, how these results translate into the dynamics of individual living cells remains unexplored. We use statistical mechanics models derived from polymer physics to inquire into the effects that chromosome properties and dynamics have in the temporal and spatial behavior of the genome. Overall, changes in the properties of individual chains affect the behavior of all other chains in the domain. We explore two modifications of chain behavior: single chain motion and chain-chain interactions. We show that there is not a direct relation between these effects, as increase in motion, doesn’t necessarily translate into an increase on chain interaction.

Organic material characteristics of volume change and stress generation have attracted the attention of many researchers aiming to develop chemomechanical systems such as artificial muscles and polymer engines having the advantages of high energy density and silent operation. Although polymer gels offer a relatively large actuator stroke, their mechanical properties are relatively poor and the working temperature is relatively low, often limited by the evaporation of liquid if contained. We have developed an iodine-treated poly(vinyl alcohol) having extraordinarily large vapor-induced deswelling stress reaching 59 MPa, which is one to two orders of magnitude greater than those of ordinary polymer gels. Furthermore, this material has extremely large volumetric and gravimetric energy densities reaching 1.3 × 106 J m−3 and 9.6 × 102 J kg−1, respectively, and an elastic modulus of a few GPa and is heat-resistant to at least 200 °C. The high performance of this material can be demonstrated by a jump of a film. © 2014 The Authors. Journal of Polymer Science Part B: Polymer Physics published by Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 1357–1365

We have investigated the collapse transition of aqueous solutions of gradient copolymers from poly(iso-propyl-2oxazoline)s (PiPrOx), which contain few hydrophobic moieties (n-nonyl-2-oxazoline (NOx) monomers). We extend our previous investigations (Salzinger et al., Colloid Polym Sci 290:385–400, 2012), where, for the gradient copolymers, an intermediate regime right above the cloud point was identified where small aggregatesare predominant.Largeaggregatesare present in significant numbers only at higher temperatures. To investigate the stability of the intermediate regime, we performed time-resolved small-angle neutron scattering (SANS) experiments during temperature jumps starting below the cloud point and ending in the intermediate regime or in the high-temperature regime. We found that the intermediate regime is stable during the time investigated (∼1 h). Moreover, the collapse of the small aggregates and the surface structure of the large aggregates are related to the number of hydrophobic moieties and the quench depth. The present results elucidate the structural evolution of these polymers and relate them to their final state as well as to their macroscopic behavior.

The theoretical description of how entangled polymers undergo large deformation has been at the heart of polymer dynamics. Over the years, the polymer physics community has adopted the tube model as the standard paradigm for describing polymer deformation and flow in both the linear and nonlinear regimes. The tube model envisions an ensemble of chains that undergo reptation and fluctuation inside smooth confining tubes on time scales of the Rouse relaxation time. It provides a reasonable and appealing description of the equilibrium and near equilibrium dynamics of entangled polymer melts and concentrated solutions. Some of the predictions based on this paradigm are also in apparent agreement with macroscopic rheological measurements for large deformations. However, some discrepancies with the tube model have been noted in the literature. For example, the time for the onset of time-strain superposibility in experiments has been shown to be much longer than the Rouse time anticipated based on the tube model. More recently, S.-Q. Wang’s group using particle-tracking velocimetry reported a number of nonlinear rheological phenomena that questioned the validity of the tube-model assumptions. The theoretical implications of the reported phenomena have been controversial.

By the so-called wormlike chain (WLC) model in polymer physics envisioning an isotropic rod that is continuously flexible, the force-extension relations of semi-flexible polymer chains strongly constrained by various confinements are theoretically investigated, including a slab-like confinement where the polymer chains are sandwiched between two parallel impenetrable walls, and a capped nanochannel confinement with a circular or rectangular cross-section where the chains are bounded in three directions. The Brownian dynamics (BD) simulations based on the generalized bead-rod (GBR) model are performed to verify the theoretical predictions.

This article reviews current efforts towards quantitative prediction of rheological properties of industrial polymer resins, based upon their polydisperse branched molecular structure. This involves both an understanding of how reactor and reaction conditions influence the distribution of chain lengths and branch placement (which is the province of reactor engineering) and an understanding of how the molecular structures in turn give rise to the rheology (the province of polymer physics). Both fields are reviewed at an introductory level, focussing in particular on developments in theoretical prediction of rheology for both entangled model polymers and industrial polymers. Finally, we discuss three classes of reaction for which the fields of reactor engineering and polymer physics have been truly combined to produce predictions from reactor to rheology. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 123–141

Polydispersity plays an important role in polymer physics influencing both processing approaches and final properties. Despite the obvious physical importance of polydispersity, studies usually simulate monodisperse chains or occasionally, a few different chain lengths. This work presents a comprehensive methodology for mapping various molecular weight distributions onto a finite number of lattice chains. The use of a lattice in the present derivation enables a variety of lattice-based simulations to incorporate polydispersity. Examples are provided by extending the cooperative motion (COMOTION) algorithm for polydispersity to create the “polydisperse cooperative motion algorithm” (p-COMOTION). The dynamic version of p-COMOTION captures the dynamics of entangled polydisperse melts. For the same weight-averaged molecular weight, polydispersity gives a lower Rouse time and introduces a broadening of the reptation transition. In addition, when adapted into the cooperative motion with flow (COMOFLO) algorithm...

This article reviews the field of molecular simula- tions of thermoset polymers. This class of polymers is of inter- est in applications ranging from structural components for aerospace to electronics packaging and predictive simulations of their response is playing an increasing role in understanding the molecular origin of their properties and complementing experiments in the search for tailored materials for specific applications. It focuses on modeling and simulation of the pro- cess of curing to predict the molecular structure of these poly- mers and their thermomechanical response by all-atom molecular dynamics simulations. Results from Monte Carlo and coarse-grained simulations are briefly summarized. V C 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 00, 000-000

By performing molecular dynamics simulations, we investigate the structural and dynamical properties of polymer melts containing probe spherical nanoparticles. Generally speaking, the behavior of these polymer nanocomposites is strongly affected by the interaction strength established between the nanoparticles and the chain monomers and by the nanoparticle sizes. We highlight that this dependence is not always evident and some intriguing properties, such as the heterogeneous dynamics of both polymer chains and nanoparticles and their nonGaussian behavior at short and long timescales, are not particularly influenced by the degree of attraction between nanoparticles and polymer for the range of interactions we study (up to 6 kBT). We find the existence of weakly ordered interdigitated structures with sequential arrangements of particles and polymer chains, which separate each other and hence inhibit the formation of nanoparticle clusters. This is especially evident with big nanoparticles, being less prone to aggregate than small ones, even when their interaction with the polymer chain is as low as 0.5 kBT. Moreover, by integrating the stress-tensor autocorrelation functions, we estimate the shear viscosity and determine its dependence on the strength of the polymer-nanoparticle interactions and on the nanoparticle size. By acting as plasticizers, small nanoparticles decrease the viscosity, especially at low-to-moderate interactions with the polymer. By contrast, big nanoparticles that establish strongly attractive interactions with the polymer chains behave as thickening agents and significantly increase the viscosity. This complex and perhaps still scantily understood balance between the geometry of nanoparticles and their interaction with the polymer is key to predict and fully control the macroscopic response of nanocomposite materials and hence suitably tailor their mechanical properties.

Nowadays, achieving a uniform dispersion of rod-like molecules (like carbon nanotube) in a polymer matrix is still a complicated and unsettled issue in polymer physics and chemical physics. It is very significant to fully understand the effects of deterministic factors on dispersion and aggregation processes of nanorods in the polymer matrix. Here, we adopt a coarse-grained molecular dynamics simulation to investigate the nanorod- filled polymer nanocomposites. It is found that the characteristic relaxation time of the end-to-end vector correlation exhibits an Arrhenius-like temperature-dependent behavior and both the rotational and translational diffusion coefficients have a linear relationship with temperature. By tuning the polymer–nanorod interaction in a wide range, we obtain the spatial organization of nanorods and the best dispersion state at the intermediate interfacial interaction. Meanwhile, we observe that grafting polymer chains on the nanorod surface could promote the dispersion. Moreover, a lower or higher temperature than glassy transition temperature can prevent the nanorod aggregation. The aggregation of nanorods can be significantly accelerated by nanorod–nanorod attraction, while inhibited by cross-linking of polymer chains and external shear fields. In short, by tailoring the deterministic factors above, we can effectively control the dispersion or even spatial organization of one-dimensional nanorods in polymer nanocomposites.

One of the great goals in polymer physics is to relate the various macroscopic features of polymeric fluids with the microscopic behavior of single chains. Here, we directly visualize the conformational dynamics of individual semiflexible polymers in a semidilute solution above the overlap concentration under shear. We observe that the tumbling dynamics are significantly slowed down, in marked contrast to the case of a dilute solution, due to steric interactions with neighboring filaments. The observed macroscopic shear thinning effect can be rationalized by a simple model based on the single filament dynamics.

The β-nucleation behavior of isotactic polypropylene (iPP) is a fascinating and important issue in polymer physics; however, little about this phenomenon or its physical nature has been clearly understood. In the present study, by tuning the heating temperature (fusion temperature, Tf), the amount of ordered structures in iPP melt was controlled. In this way, the influence of five types of representative β-nucleating agents (β-NA) on the crystallization behavior of iPP with different melt structures (i.e. the amount of ordered structures) was comparatively studied by differential scanning calorimetry (DSC), polarized optical microscopy (PLOM), scanning electron microscopy (SEM), wide-angle X-ray diffraction (WAXD) and rheological measurement. A surprising synergetic effect was observed between β-NAs with α-/β-dual polymorphic selectivity (dual-selective β-NA) and the ordered structure of iPP, resulting in significant increases of the β-nucleation efficiency and the β-phase proportion of the sample. PLOM observation of the crystallization process confirmed that with the presence of ordered structures in iPP melt, a mass of dark, small crystal embryos derived from self-nuclei uniformly distributed in the melt and exhibited β-nucleation efficiency. This work provides the first evidence that for iPP nucleated with dual-selective β-NA, the ordered structures play a determining role in the β-nucleation of iPP. Under the influence of the dual-selective β-NA, the ordered structures exhibited β-nucleation efficiency and therefore encouraged β-nucleation. A possible mechanism was proposed.

International audience; Interfacial tension between immiscible phases is a well-known phenomenon, which manifests itself in everyday life, from the shape of droplets and foam bubbles to the capillary rise of sap in plants or the locomotion of insects on a water surface. More than a century ago, Korteweg generalized this notion by arguing that stresses at the interface between two miscible fluids act transiently as an effective, nonequilibrium interfacial tension, before homogenization is eventually reached. In spite of its relevance in fields as diverse as geosciences, polymer physics, multiphase flows, and fluid removal, experiments and theoretical works on the interfacial tension of miscible systems are still scarce, and mostly restricted to molecular fluids. This leaves crucial questions unanswered, concerning the very existence of the effective interfacial tension, its stabilizing or destabilizing character, and its dependence on the fluid's composition and concentration gradients. We present an extensive set of measurements on miscible complex fluids that demonstrate the existence and the stabilizing character of the effective interfacial tension, unveil new regimes beyond Korteweg's predictions, and quantify its dependence on the nature of the fluids and the composition gradient at the interface. We introduce a simple yet general model that rationalizes nonequilibrium interfacial stresses to arbitrary mixtures, beyond Korteweg's small gradient regime, and show that the model captures remarkably well both our new measurements and literature data on molecular and polymer fluids. Finally, we briefly discuss the relevance of our model to a variety of interface-driven problems, from phase separation to fracture, which are not adequately captured by current approaches based on the assumption of small gradients.

Based on the available experimental and theoretical data, the role of the α–Fe nanoparticles and higher metallic oxides in the structure of the EuO: Fe composite on the formation of a complex of inherent physical parameters is tracked. That along with the presence of a limited solid solution Eu1–xFex O in its structure contributes to the chemical stability of this high–temperature spin injector under normal conditions.

Lamellar thickening of semicrystalline polymers is a fascinating subject in the realm of polymer physics as lamellar thickness plays a vital role in deciding the performance of polymer products. Whereas, regarding the processing of semicrystalline polymers where both the flow and pressure exist, the mystery of lamellar thickening has not been revealed yet. Here, the lamellar thickening of isotactic polypropylene (iPP) crystallizing under flow (30 s−1) and pressure (100 MPa) is studied by using a custom pressuring and shearing device (PSD). IPP crystallizing under flow and pressure has manifested a large lamellar thickening rate, where the lamellar thickness increases from 24 to 31 nm within a very short period of time (3000 s). The increased portion of lamellar thickness (7 nm) is more than one quarter of the original lamellae. The fast lamellar thickening behavior of iPP is shown to be occurred only under the coexistence of flow and pressure. Conversely, the lamellar thicknesses for both the iPP crystallized under the sole effect of flow (7.0 nm) and pressure (7.5 nm) remain unchanged within the same period of time. Furthermore, the activation energy of lamellar thickening for iPP crystallizing under flow and pressure is 180.1 kJ/mol, substantially below that for iPP quiescently crystallizing at atmosphere pressure (460.7 kJ/mol). The fast lamellar thickening behavior for iPP crystallizing under flow and pressure is shown to be related with the flow-induced oriented α-parent lamellae, which are composed by regularly arranged polymer chains and have a low energy barrier for molecular chains translating along the chain axis. The current study pioneers the probing into lamellar thickening of iPP crystallizing under the coexistence of flow and pressure, and suggests a promising method to fabricate high performance polymer products with thick lamellae.

The pressure-specific volume-temperature (pvT) relationships of polymers are basic data for polymer engineering and polymer physics. The specific volume (vsp) is not only defined by the current value of pressure (p) and temperature (T) but is also dependent on the process history of p and T. The influence of measurement processes on the pvT relationships of a semi-crystalline polymer, polypropylene (PP), has been studied using a piston-die pvT testing device. Based on the isobaric cooling/heating processes and the isothermal compression/decompression processes, the specific volume was examined as a function of cooling, heating, compression, decompression, cooling/heating rates and compression/decompression rates. The specific volume increases with increasing cooling rates in the crystallization and solid state, and decreases with increasing heating rates in the crystallization and molten state. The decompression process causes lower specific volume than the compression process. The specific volume decreases with increasing compression rates but decreases then increases with increasing decompression rates.

Amyloid structures constitute a class of highly ordered nanomaterials formed by insoluble protein aggregates. These aggregates are characterized by a cross-β structural motif in which β-sheets are oriented perpendicular to the fibril axis and bound together by a dense hydrogen bonding network. Although they have been associated with several neurodegenerative disorders, such as Alzheimer's and Parkinson's diseases, amyloid fibrils have also been found in many physiologically beneficial roles, for instance in adhesives and hormone storage. Inspired by this natural occurrence of functional amyloid, the hierarchal self-assembly of these structures has recently been used to develop artificial biomaterials for applications in medicine and nanotechnology. In order to realize the full potential of amyloids as functional materials, it is important to understand their fundamental mechanical properties. This review explores a range of experimental strategies to determine the mechanical properties of amyloid fibrils and discusses the results in the context of polymer physics concepts. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 281–292

Glassy-state structural relaxation is a physical phenomenon that occurs in most amorphous and semicrystalline polymers after their melt-processing. As such, after these industrial conformation processes, polymers are usually found in a thermodynamic non-equilibrium state. Therefore, polymer chains undergo thorough conformational changes on their way towards a thermodynamically stable state. These molecular-level events involve macroscopic-level modifications, which are manifested as changes in physical properties. Here we propose a simple approach to monitor the physical aging in polymers by differential scanning calorimetry (DSC). Accordingly, the β H enthalpy relaxation rate is directly extracted from the DSC curves taking into account the enthalpy loss at different aging times. This method allows a simple quantification of the bulk aging dynamics in polymers, and can be extrapolated to systems containing reinforcing particles; i.e. composites and nanocomposites. This safe, low cost and simple experiment designed for undergraduate students of physical, chemical and engineering specialities serves as a guide to easily determine the physical aging suffered by polymeric materials during their storage and to understand its implications at macroscopic level, which is a relevant field in condensed-matter physics. Given the paramount relevance of physical aging in glassy materials, this experiment may also serve to raise awareness of the importance of the thermal history of materials on their resulting properties, which is overlooked too often.

Protein-based amyloid fibrils can show a great variety of polymorphic structures within the same protein precursor, although the origins of these structural homologues remain poorly understood. In this work we investigate the fibrillation of bovine serum albumin--a model globular protein--and we follow the polymorphic evolution by a statistical analysis of high-resolution atomic force microscopy images, complemented, at larger length scales, by concepts based on polymer physics formalism. We identify six distinct classes of coexisting amyloid fibrils, including flexible left-handed twisted ribbons, rigid right-handed helical ribbons and nanotubes. We show that the rigid fibrils originate from flexible fibrils through two diverse polymorphic transitions, first, via a single-fibril transformation when the flexible left-handed twisted ribbons turn into the helical left-handed ribbons, to finally evolve into nanotube-like structures, and second, via a double-fibril transformation when two flexible left-handed twisted ribbons wind together resulting in a right-handed twisted ribbon, followed by a rigid right-handed helical ribbon polymorphic conformation. Hence, the change in handedness occurs with an increase in the level of the fibril's structural organization.

In order to understand the moisture diffusion, we combine the obstruction-scaling model with the moisture clustering in confined spaces of the polymer hydrogel, with relevance to the performance of the super desiccant polymer. Special attention is focused on elucidating the effect of chain stiffness by considering the conformation of polymer chain on the basis of polymer physics. Relevant parameters for calculations are determined from literature information as well as the best fits for reported data performed with the copolymer. Our results exhibit the moisture diffusion decreases with increasing chain stiffness represented by the persistence length. Note that the larger persistence length provides smaller radius of openings in void spaces, resulting in the stronger hindrance effect on the moisture diffusion. Higher temperature makes the water molecules to be easier to form clusters, which provides the decrease in diffusivity. The increase of moisture diffusion at low humidity is attributed to the swelling of the chain, whereas its decrease at high humidity results from the water clustering.

Many papers have been published over the last decade on nanodielectrics. The results have sometimes proven to be inconsistent, and this is thought to be due to nonuniform dispersion of the nanophase. However, an increasing number of high-quality scientific contributions look specifically at how these novel materials should be assembled and processed, and at the various phenomena in the interphase region. Clive W. Reed published several interesting contributions on these topics [1]. Also, at a colloquium in January 2012, Alun S. Vaughan mentioned that many of the tools needed for the preparation of consistent and controlled nanodielectrics had already been considered in various areas, including polymer physics and colloids science [2].

Aligned multi-wall carbon nanotube (MWCNT)/polymer composite films were created in a one-step process. 5 wt% MWCNT/semi-crystalline polymer composite films of approximately 100 nm thickness were obtained by melt-drawing. The matrix polymers were isotactic polypropylene (iPP), poly(1-butene) (PB-1) and high density polyethylene (HDPE). Transmission electron microscopy (TEM) investigations revealed an exceptionally high degree of local MWCNT alignment with an angular deviation of 10 ° (HDPE) and 20 ° (iPP and PB-1) parallel to the films’ drawing direction for a broad range of drawing velocities. For HDPE, the lamellar polymer-crystals at the interface between the MWCNT and the polymer film were identified as the nano-hybrid shish-kebab morphology by selected area electron diffraction. Based on the direct visualization of the MWCNT disentanglement process in the TEM, a polymer physics-based model for the unraveling of MWCNT entanglements, a source of aligned MWCNTs, is proposed that explains differences in MWCNT alignment encountered for different matrix polymers. The melt-drawing mediated MWCNT alignment provides both an innovative approach for the fabrication of applicable MWCNT containing films and a versatile tool for studying the interface in MWCNT/polymer composites.

International audience; Biological functions including gene expression and dna repair are affected by the 3d architecture of the genome, but the underlying mechanisms are still unknown. notably, it remains unclear to what extent nuclear architecture is driven by generic physical properties of polymers or by specific factors such as proteins binding particular dna sequences. the budding yeast nucleus has been intensely studied by imaging and biochemical techniques, resulting in a large quantitative data set on locus positions and dna contact frequencies. we recently described a quantitative model of the interphase yeast nucleus in which chromosomes are represented as passively moving polymer chains. this model ignores the dna sequence information except for specific constraints at the centromeres, telomeres and the ribo-somal dna (rdna). despite its simplicity , the model accounts for a large majority of experimental data, including absolute and relative locus positions and contact frequency patterns at chromo-somal and subchromosomal scales. here, we also illustrate the model's ability to reproduce observed features of chromatin movements. our results strongly suggest that the dynamic large-scale architecture of the yeast nucleus is dominated by statistical properties of randomly moving polymers with a few sequence-specific constraints, rather than by a large number of dna-specific factors or epigen-etic modifications. in addition, we show that our model accounts for recently measured variations in homologous recombination efficiency, illustrating its potential for quantitatively understanding functional consequences of nuclear architecture.

We report a new methodology for studying diffusion of individual polymer chains in a melt state, with special emphasis on the effect of chain topology. A perylene diimide fluorophore was incorporated into the linear and cyclic poly(THF)s, and real-time diffusion behavior of individual chains in a melt of linear poly(THF) was measured by means of a single-molecule fluorescence imaging technique. The combination of mean squared displacement (MSD) and cumulative distribution function (CDF) analysis demonstrated the broad distribution of diffusion coefficient of both the linear and cyclic polymer chains in the melt state. This indicates the presence of spatiotemporal heterogeneity of the polymer diffusion which occurs at much larger time and length scales than those expected from the current polymer physics theory. We further demonstrated that the cyclic chains showed marginally slower diffusion in comparison with the linear counterparts, to suggest the effective suppression of the translocation through the threading-entanglement with the linear matrix chains. This coincides with the higher activation energy for the diffusion of the cyclic chains than of the linear chains. These results suggest that the single-molecule imaging technique provides a powerful tool to analyze complicated polymer dynamics and contributes to the molecular level understanding of the chain interaction.

DNA of eukaryotes is highly condensed in a nucleoprotein complex called chromatin. Both the spatial organization and the biochemical composition (“epigenomic” state) of the chromatin are fundamental for gene regulation. Remarkably, recent studies indicate that1D epigenomic domains tend to fold into 3D topologically associated domains (TADs) forming specialized nuclear chromatin compartments. In this thesis, we address the question of the coupling between chromatin folding and epigenome. We first built a software called IC-finder to segment HiC maps into interacting domains. We next used it to quantify correlations between the TADs and epigenomic partitions of the genome. This led us to develop a physical model of the chromatin with the working hypothesis that chromatin organization is driven by physical interactions between epigenomic loci. We modeled chromatin as a block copolymer where each block corresponds to an epigenomic domain. With this framework, we developed a method to infer interaction parameters between chromatin loci from experimental Hi-C map. An outcome of such inference process would be a powerful tool to predict chromatin organization in various conditions, allowing investigating in silico changes in TAD formations and long-range contacts when altering the epigenome.; L'ADN chromosomique des cellules eucaryotes est fortement condensé au sein d'un complexe nucléoprotéïque, la chromatine. Aussi bien l'organisation spatiale que la composition biochimique (état “épigénomique”) de la chromatine jouent un rôle fondamental dans la régulation des gènes. Grâce aux récents développements des techniques de séquençage à haut-débit, il est possible de déterminer l'état épigénomique local de la chromatine ainsi que la probabilité de contact entre deux sites génomiques (technique dite de “Hi-C”). Ces deux techniques ont permis de mettre en évidence l’existence de domaines d’interaction dont les positions corrèlent fortement avec la segmentation épigénomique de la chromatine. Cependant, les mécanismes responsables de ce couplage sont encore mal compris. L’objectif de cette thèse est de bâtir des modèles physiques permettant de valider l’hypothèse que l’épigénome est un acteur majeur dans le repliement 3D de la chromatine. Pour cela, nous avons tout d’abord développé “IC-Finder”, un algorithme permettant de segmenter les cartes Hi-C en domaines d’interaction. Nous avons alors pu quantifier précisément l’association entre épigénome et organisation de la chromatine. Les corrélations trouvées justifient l’idée de modéliser la chromatine par un copolymère par bloc dont les monomères ont chacun un état épigénomique. Dans ce cadre, nous avons développé une méthode d’inférence des potentiels d'interaction entre sites génomiques à partir des cartes Hi-C expérimentales. Ce travail permettra à plus long terme de prévoir l’organisation de la chromatine sous différentes conditions, ce qui permettra d’étudier en particulier les changements de structure résultant de l’altération de l’épigénome.

Steric repulsion between grafted side chains inhibits interpenetration of bottlebrushes, transforming them into flexible filaments., Bottlebrushes are fascinating macromolecules that display an intriguing combination of molecular and particulate features having vital implications in both living and synthetic systems, such as cartilage and ultrasoft elastomers. However, the progress in practical applications is impeded by the lack of knowledge about the hierarchic organization of both individual bottlebrushes and their assemblies. We delineate fundamental correlations between molecular architecture, mesoscopic conformation, and macroscopic properties of polymer melts. Numerical simulations corroborate theoretical predictions for the effect of grafting density and side-chain length on the dimensions and rigidity of bottlebrushes, which effectively behave as a melt of flexible filaments. These findings provide quantitative guidelines for the design of novel materials that allow architectural tuning of their properties in a broad range without changing chemical composition.

One of the most challenging problems in polymer physics is providing a theoretical description for the behaviour of rings in dense solutions and melts. Although it is nowadays well established that the overall size of a ring in these conditions scales like that of a collapsed globule, there is compelling evidence that rings may exhibit ramified and tree-like conformations. In this work I show how to characterise these local tree-like structures by measuring the local writhing of the rings' segments and by identifying the patterns of intra-chain contacts. These quantities reveal two major topological structures: loops and terminal branches which strongly suggest that the strictly double-folded "lattice animal" picture for rings in the melt may be replaced by a more relaxed tree-like structure accommodating loops. In particular, I show that one can identify hierarchically looped structures whose degree increases linearly with the size of a ring, and that terminal branches are found to store about 30% of the whole ring mass, irrespectively of its length. Finally, I draw an analogy between rings in the melt and slip-linked chains, where contact points are enforced by mobile slip-links and for which a field-theoretic treatment can be employed to get some insight into their typical conformations. These findings are ultimately discussed in the light of recent works on the static structure of rings and on the existence of inter-ring threadings., Comment: Accepted version. To appear in RSC Soft Matter. Suppl. Movie can be found at http://www2.ph.ed.ac.uk/~dmichiel/