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Butyl acrylate polymer networks were synthesized to understand the effect of permanent cross-links on large, anisotropic dye diffusion. The average degree of polymerization between cross-links (Nx)...

The connection between slow activated relaxation in glass-forming liquids and various equilibrium thermodynamic properties remains intensely debated. The microscopic elastically collective nonlinea...

Hyaluronan is a biopolymer that is essential for many biological processes in the human body, like the regulation of tissue lubrication and inflammatory responses. Here, we study the behavior of hyaluronan at aqueous surfaces using heterodyne-detected vibrational sum-frequency generation spectroscopy (HD-VSFG). Low-molecular-weight hyaluronan (similar to 150 I(Da) gradually covers the water-air interface within hours, leading to a negatively charged surface and a reorientation of interfacial water molecules. The rate of surface accumulation strongly increases when the bulk concentration of low-molecular-weight hyaluronan is increased. In contrast, high-molecular-weight hyaluronan (>1 MDa) cannot be detected at the surface, even hours after the addition of the polymer to the aqueous solution. The strong dependence on the polymer molecular weight can be explained by entanglements of the hyaluronan polymers. We also find that for low-molecular-weight hyaluronan the migration kinetics of hyaluronan in aqueous media shows an anomalous dependence on the pH of the solution, which can be explained from the interplay of hydrogen bonding and electrostatic interactions of hyaluronan polymers.

The effects, that glycine (Gly) has on the local chain conformation and internal backbone dynamics (IBD) of polypeptides, were investigated by comparing the fluorescence response of a series of pyr...

The dynamics of adsorption and desorption of counterions on a polyelectrolyte chain in aqueous solution is studied at a single molecular level. The investigation is through the process of fluoresce...

It is now generally agreed that the most dramatic influence of a free surface on local relaxation dynamics occurs over the first 10 nm from the surface. Using the cooperative free volume (CFV) rate...

Although experimental evidence for shear-banding flows in concentrated polymer solutions has accumulated over the last 20 years, the origin of such shear-banding flows is still under heated debate....

We investigated the dynamics of the topological network formed by rotaxane-type movable crosslinks consisting of a poly(ethyl acrylate) backbone threaded through peracetylated cyclodextrins, which ...

Though the strong transformation in mechanical properties of glass-forming materials such as amorphous polymers near the glass transition, Tg, has long been recognized and exploited, efforts to und...

We present the results from an extensive atomistic molecular dynamics simulation study of poly(ethylene oxide) (PEO) doped with various amounts of lithium-bis(trifluoromethane)sulfonimide (LiTFSI) salt under the influence of external electric field strengths up to $1\,$V/nm. The motivation stems from recent experimental reports on the nonlinear response of mobilities to the application of an electric field in such electrolyte systems and arising speculations on field-induced alignment of the polymer chains, creating channel-like structures that facilitate ion passage. Hence, we systematically examine the electric field impact on the lithium coordination environment, polymer structure as well as ionic transport properties and further present a procedure to quantify the susceptibility of both structural and dynamical observables to the external field. Our investigation reveals indeed a coiled-to-stretched transformation of the PEO strands along with a concurrent nonlinear behavior of the dynamic properties. However, from studying the temporal response of the unperturbed electrolyte system to field application we are able to exclude a structurally conditioned enhancement of ion transport and surprisingly observe a slowing down. A microscopic understanding is supplied., Main manuscript comprises 30 pages and 13 figures, supplementary information section comprises 30 pages and 28 figures

Despite being the most ubiquitous compound on Earth, the fundamental properties of water are not fully understood, especially in nanoconfinement. Densely grafted polyelectrolyte (PE) molecules atta...

We employ molecular dynamics (MD) simulations to study the spreading and imbibition of a liquid drop on a porous, soft, solvophilic, and responsive surface represented by a layer of polymer molecul...

The dynamics of different blocks in block copolymers are expected to affect the other blocks due to compositional heterogeneity, thus influencing their bulk structure and performance. It is signifi...

Dendronized polymers (denpols) are thick polymers comprising a linear backbone with grafted treelike structures (dendrons). The latter give rise to a molecular thickness that is a function of dendr...

Well-dispersed polymer-tethered silica nanoparticles exhibit soft glassy rheology and caging behaviors due to chain interpenetration driven by entropic attraction and geometric confinement. In this...

The fluorescence blob model (FBM) was applied to analyze the fluorescence decays of a series of pyrene-labeled polypeptides to better understand how the amino acid (aa) composition of a polypeptide...

Recently, Hor et al. [Hor, J. L., Wang, H., Fakhraai, Z., & Lee, D. (2018). Macromolecules 51 (14), 5069–5078] reported a set of interesting results for the viscosity of unentangled polystyrene of ...

Ring polymers are a unique class of macromolecules that lack free ends and show qualitatively different dynamics compared to linear chains. Despite recent progress, the nonequilibrium flow behavior...

The acceleration of structural relaxation or physical aging by deformation, known as overaging, has been reported in experiments and simulations of polymer and colloid glasses, and correct accounti...

Three series of pyrene-labeled polypeptides, namely, poly(l-lysine) (Py-PLL), poly(l-glutamic acid) (Py-PLGA), and poly(d,l-glutamic acid) (Py-PDLGA), were studied in dimethyl sulfoxide (DMSO) by m...

The effects of interphase topology, entanglements, and chain dynamics on the mechanical response of semicrystalline polyethylene have been examined using atomistic simulations. In particular, the prevalence of the cavitation and melting/recrystallization mechanisms for yield and plastic flow were found to depend on both topological and dynamical properties of the molecular segments in the semicrystalline interphase. First, two different protocols were used during preparation of the interphase ensemble to modulate the distribution of (i) loops, bridges, and tails and (ii) entanglements within the noncrystalline domain. A protocol denoted “step-wise cooling” produced structures having a large fraction of long, entangled segments that yielded by the melting/recrystallization mechanism about 50% of the time. By contrast, the protocol denoted “instantaneous quench” produced structures that yielded by melting/recrystallization about 73% of the time. Second, two different united atom force fields, PYS and TraPPE-UA, that exhibit nearly identical topological characteristics of the noncrystalline domain but different mobilities were used to study the effect of chain dynamics on yield mechanisms. At the slower strain rate used in this work, yield and plastic flow proceeded exclusively via cavitation for the model using the TraPPE-UA force field, whereas both cavitation and melting/recrystallization were observed for the model using the PYS force field. The greater prevalence of melting/recrystallization in the latter case is attributed to faster chain-sliding dynamics in the crystalline domain. The dependences of the yield mechanism on topology and dynamics are found to be related. ISSN:1520-5835 ISSN:0024-9297

We investigate single chain dynamics of an entangled linear poly(ethylene oxide) melt in the presence of well-dispersed attractive nanoparticles using high-resolution neutron spectroscopy at partic...

We systematically investigate the effects of surface roughness on the static and dynamic properties of polymer chains in confined films by using molecular dynamics simulations, in which the roughne...

Processability of vitrimers strongly relies on the temperature dependence of viscosity. In this study, we analyzed temperature-dependent viscoelasticity of vitrimers based on the dioxaborolane meta...

The dynamics of polymer nanocomposites (PNCs) are dictated by two intertwining components, the polymer matrix and the nanoparticle network, whose characteristics have not been elucidated. Here, we ...

We combine 1H, 7Li, and 19F NMR methods to selectively investigate polymer, cation, and anion dynamics in polymer electrolytes on various length and time scales and over broad temperature ranges. B...

We analyze the dynamics from microsecond-long, atomistic molecular dynamics (MD) simulations of a series of precise poly(ethylene-co-acrylic acid) ionomers neutralized with lithium, with three diff...

The rotation of Ni nanorods, dispersed in dilute and semidilute poly(ethylene oxide) solutions, is investigated. Ni nanorods with similar diameter but different lengths are synthesized using the an...

Atomic force microscopy (AFM) imaging was used to study the in situ swelling of terraced poly(styrene-block-methyl methacrylate) (PS-b-PMMA) thin films under cyclohexane, a selective solvent for PS...

In this paper, we report comprehensive studies on the molecular dynamics of a series of poly(propylene glycol) (PPG) derivatives characterized by three different terminal groups and various molecul...

Polymerized ionic liquids (PILs) represent one class of promising candidates for self-healing materials because of the potential diffusion of ion pairs from one aggregation to another. Therefore, d...

The dynamics of critical clusters consisting of four-armed poly(ethylene glycol) (tetraPEG) was investigated by means of dynamic light scattering (DLS). The critical clusters were synthesized by cr...

Rotaxane is a topological supramolecule in which a ring molecule is threaded onto an axial chain. A unique feature of rotaxane is that the ring can slide along the chain. In this study, we investig...

Polymer–substrate interfaces are significant in determining the dynamics of nanoconfined polymers. In this study, an improved understanding of the interfacial effect was gained from the critical di...

Polymer segmental dynamics, center-of-mass chain diffusion, and nanoparticle (NP) diffusion are directly measured in a series of polymer nanocomposites (PNC) composed of very small (radius ≈ 0.9 nm...

Semicrystalline polymers have been classified into crystal-mobile and crystal-fixed polymers, depending on the existence or absence of intracrystalline chain dynamics. Although it was claimed that ...

Optical probe reorientation experiments and mechanical stress relaxation measurements in the linear response regime were performed on a polymer glass. Segmental dynamics of lightly cross-linked poly(methyl methacrylate) (PMMA) were monitored via both methods at temperatures between 9 and 24 K below the glass transition temperature (Tg) and over the course of 8 h of aging. Relaxation times from the two methods cover a range of ∼1.7 decades. Similar results were obtained from the two experiments other than a slight difference in the aging rate. A difference of ∼0.3 decades (a factor of ∼2) is observed between the optically and mechanically obtained relaxation times, related primarily to the size of the probe. Both experiments give a value near 0.3 for the Kohlrausch–Williams–Watts (KWW) β parameter. These results provide an important baseline for the interpretation of optical probe reorientation experiments during nonlinear deformation.

The mobility gradient of polymer chains near a solid interface plays an important role in explaining a complex behavior of relaxation dynamics and thermodynamic properties observed for various poly...

This report provides evidence that the blobs characterized through the application of the fluorescence blob model (FBM) to the analysis of the fluorescence decays acquired with pyrene-labeled polypeptides are equivalent to the foldons used in the study of protein folding. The FBM was applied to characterize the length and time scale over which pyrene excimer formation (PEF) took place between pyrene labels covalently attached onto α-helical and partially helical poly(l-glutamic acid) (Py-PLGA) in DMF and DMSO, respectively, and unfolded poly(dl-glutamic acid) (Py-PDLGA) in both DMF and DMSO. The blob size obtained for α-helical Py-PLGA in DMF and the characteristic time determined for the backbone dynamics of unfolded Py-PDLGA matched very closely the expected size of foldons and their characteristic folding times, respectively. In particular, the blob size was confirmed by conducting molecular mechanics optimizations (MMOs) with HyperChem. Furthermore, the level of pyrene clustering along the polypeptide...

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

We measure the dynamics of high molecular weight polystyrene grafted to silica nanoparticles dispersed in semidilute solutions of linear polymer. Structurally, the linear free chains do not penetrate the grafted corona but increase the osmotic pressure of the solution, collapsing the grafted polymer and leading to eventual aggregation of the grafted particles at high matrix concentrations. Dynamically, the relaxations of the grafted polymer are controlled by the solvent viscosity according to the Zimm model on short time scales. On longer time scales, the grafted chains are confined by neighboring grafted chains, preventing full relaxation over the experimental time scale. Adding free linear polymer to the solution does not affect the initial Zimm relaxations of the grafted polymer but does increase the confinement of the grafted chains. Our results elucidate the physics underlying the slow relaxations of grafted polymer.

The segmental relaxation times τA and τB of the A and B components, respectively, of an A/B polymer/polymer blend typically exhibit dissimilar temperature dependences and can differ by orders of magnitude, thereby manifesting the influence of spatial compositional heterogeneity. We show that for weakly miscible A/B blends the relaxations of the faster A component occur via separate and distinct mechanisms. In the melt state, τA increases in a nonlinear manner as temperature T decreases toward blend glass transition temperature Tg(blend) (or toward the local effective glass transition temperature of its component Tg(A)); this is the typical α relaxation process. For temperatures below the transition, 1/τA exhibits an Arrhenius temperature dependence; this is identified as the α′ process. A third relaxation process, a so-called α0 process, also occurs in the melt state; it is slower than the α process and exhibits a significantly stronger dependence on temperature. Each relaxation process, characterized by ...

A facile method was developed to measure the utmost distance of polymer dynamics suppressed by a solid substrate by investigating the diffusion of a fluorinated tracer-labeled polymer in the bottom layer of bilayer samples. Here, a labeled layer of fluorinated tracer-labeled at the polymer chain end of variable thickness was supported on a substrate, and the corresponding homopolymer layer of fixed thickness was deposited on top of the bottom layer. From the critical time (t*) required for the fluorinated component to diffuse from the bottom layer to the bilayer film surface as a function of the thickness of the bottom layer, a critical thickness of the bottom layer (hc*), corresponding to the thickness at which t* started to increase, was obtained. This thickness was related to the distance over which polymer dynamics were altered by the substrate. The results showed that hc* was very sensitive to the surface chemistry of the substrate and exhibited both molecular weight and temperature dependencies.

I corroborate an important experimental evidence reported by Schuldt et al. [Phys. Rev. Lett. 2016, 117, 197801] revealing the incapability of the current theoretical framework to fully describe the dynamics of semiflexible polymer solutions in the tightly entangled concentration regime. These results have been endorsed here by means of previously published, but overlooked, data by Tassieri et al. [Phys. Rev. Lett. 2008, 101, 198301; Biophys. J. 2008, 94, 2170]. The ensemble of information provides a strong evidence that the scaling law of the plateau modulus as a function of polymer’s concentration and persistence length, i.e., G0 ∝ cαLpβ, should have both the exponents positive, in contrast with all the existing predictions converging on similar values of α > 0 and β < 0—hence the need of new theoretical models able to better interpret the contribution of the polymer bending rigidity to the viscoelastic properties of the polymer network.

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