Dynamics Of Polymer Chains Research Articles

Plasticization of NaX-PEO solid polymer electrolytes by Pyr13X ionic liquids

Addition of moderate contents (≤20wt%) of ionic liquids (ILs) to binary solid polymer electrolytes (SPEs) is made to alter the overall SPE properties, foremost to increase the room temperature ionic conductivity. Sodium conducting ternary electrolytes, based on sodium salts; NaTFSI and NaFSI, the polymer poly(ethylene oxide) (PEO), and pyrrolidinium ILs; Pyr13TFSI and Pyr13FSI, with different compositions: NaX(PEO)n – Pyr13X (X=TFSI, FSI), have been prepared. Raman and dielectric spectroscopy as well as differential scanning calorimetry have been used to evaluate the plasticizing effect of the Pyr13 IL cation and the accompanying TFSI and FSI IL anions via changes in ionic association, crystallinity, polymer chain dynamics, and total ionic conductivity. While all the TFSI based systems seem rather insensitive to the addition of IL with respect to speciation, the situation is much less clear for the FSI based systems. Furthermore, the addition of ILs seems beneficial for inhibiting PEO crystallization, especially for the FSI anion, and also for enhancing the polymer chain dynamics, but yet the FSI based ternary electrolytes show lower ion conductivities as compared to the analogous TFSI based systems.

Modeling and fundamental aspects of structural relaxation in high-solid hydrocolloid systems

The structural relaxation properties of high-solid gelling polysaccharides, gelatin and whey protein with small-molecule co-solute have been reviewed focusing on the glass transition region and glassy state of the mechanical master curve. Compliance with the principle of thermorheological simplicity is established allowing horizontal superposition of viscoelastic functions in the form of small-deformation stress relaxation or dynamic oscillation modulus. Numerical calculations via the Tikhonov regularization yield smooth stress relaxation spectra over a broad timescale that encompasses the isothermal process of vitrification in these systems. Next, the molecular coupling theory addressed the polymer chain dynamics of the local segmental motions that determine the glass transition temperature (Tg) of condensed matrices. Thus a more complete picture of the physics of intermolecular interactions in the short-time region of the glass dispersion has emerged. It allows estimation of the relaxation time for local segmental motions at Tg, and the extent of cooperativity between adjacent chemical moieties governing kinetics of viscoelastic relaxation in hydrocolloid based systems at the glass transition region.

Infrared spectroscopic study on electric-field-induced dynamics of polymer chains in a ferroelectric melt-quenched cold-drawn film of nylon-12

We studied the intensity changes of the infrared bands of a ferroelectric melt-quenched, cold-drawn film of nylon-12 as a function of an external cyclic stepwise electric field with the polarization perpendicular to the draw direction. The infrared bands assigned to the NH stretching and amide I modes exhibited butterfly-shaped hysteresis loops characteristic of ferroelectric materials, whereas the intensity changes of the infrared bands assigned to the CH2 antisymmetric and symmetric stretching modes were small and showed no butterfly-shaped hysteresis loops. These results indicate that only the amide groups were inverted under the external electric field. We proposed a molecular mechanism explaining the ferroelectric properties of nylon-12: the amide groups in the antiparallel β-sheet structure are inverted by the external electric field to form new hydrogen bonds, generating two stable states in a nearly double-minimum potential.

Effects of temperature and CO2 pressure on the emission of N,N′-dialkylated perylene diimides in poly(alkyl methacrylate) films. Are guest-host alkyl group interactions important?

Static and dynamic fluorescence measurements have been made on four N,N ′−dialkylated perylene diimides in films of poly(alkyl methacrylate)s (PAMAs) with 5 different alkyl groups and in a ‘model solvent’, n-butyl acetate, over wide temperature ranges. The results indicate that the excited singlet states of the perylene guest molecules are controlled primarily by chain relaxations rather than hole free volumes in the polymer matrixes. The short singlet lifetimes of the perylene molecules require that the guest molecules respond primarily to the environments experienced by their ground states within the PAMA matrixes; each of the PAMAs offers slightly different locations in which the guest molecules can reside as a result of interactions between the N−alkyl substituents on the imide groups of the perylenes and the alkyl groups on the PAMA side chains. PAMAs with branched side chains were found to have a larger influence than PAMAs with linear side chains on the fluorescence properties of the guest molecules. The results are compared to those employing pyrenyl derivatives (with much longer excited singlet lifetimes) in the same PAMA films. The overall results indicate that the perylenes can be used as a complementary probe of local polymer chain dynamics, but they are less sensitive to their environments than are pyrenyl groups. However, they offer some distinct advantages: (1) a much wider range of N,N ′−disubstituted perylene diimides can be synthesized easily; (2) those substituents can be designed to allow a greater or lesser interaction with an anisotropic host matrix. Also, rapid conformational changes of a bis-perylene derivative appear to be restricted in the polymer matrixes. Those restrictions appear reduced when the polymer films are placed under high pressures of the plasticizing gas, CO2, but not when they are under equal pressures of a much less intervening gas, N2. Experiments with four perylene diimide derivatives in five poly(alkyl methacrylate)s over wide temperature ranges and varying CO2 or N2 pressures indicate that fluorescence changes of the guest molecules are controlled primarily by chain relaxations rather than hole free volumes in the polymer matrixes.

Molecular‐level structures at poly(4‐vinyl pyridine)/acid interfaces probed by nonlinear vibrational spectroscopy

ABSTRACTThe molecular structures of the interfaces between a solid poly(4‐vinyl pyridine) (P4VP) surface and poly(acrylic acid) (PAA) as well as hydrochloric acid (HCl) solutions were probed using sum frequency generation (SFG) vibrational spectroscopy in situ in real time. Spectroscopic results clearly reveal that the PAA molecules are adsorbed onto the P4VP surface via hydrogen bonding at the P4VP/PAA solution interface while the P4VP surface is protonated at the P4VP/HCl solution interface. Consequently, the water molecules near the interfaces are strongly perturbed by these two interactions, exhibiting different orderings at the two interfaces. This work clearly demonstrates the power of studying the interfacial molecular‐level structures via nonlinear vibrational spectroscopy when molecular adsorption happens at the solid–liquid interface and paves a way for our future study on tracing the adsorption dynamics of polymer chains onto solid surfaces. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 848–852

Chain Dynamics and Segmental Orientation in Polymer Melts Confined to Nanochannels

We study changes in the dynamics of polymer chains confined to cylindrical nanochannels within aluminum oxide membranes. Specifically, a proton time-domain NMR technique is used to assess the effect of transient wall contacts on the time-averaged orientational order of poly(butadiene) segments in melts with different molecular weights (MW). Previous work has evidenced that the weakly interacting polymer, residing in ∼100 μm long, 20 and 60 nm wide channels, shows no significant confinement-related changes in the segmental (α) relaxation time and only weak (less than a factor of 2) changes in the micrometer-scale diffusivity. In the relevant temperature range above 340 K, we here use samples with pores oriented at different angles with respect to the main magnetic field to study the macroscopic anisotropy of segmental rotations and the effect of slower motions in regimes III and IV of the tube model up to the milliseconds time scale. We show that the pore walls exert a significant orientation effect on the chains, measured in terms of a time-averaged order parameter with a related length scale of one to a few nanometers, coexisting for high molecular weight (MW) inhomogeneously with bulk-like behavior in the pore center. Low MW with fewer than about 10 entanglements as well as low MW liquids exhibit a homogeneous response, with an overall residual orientation that represents a diffusively averaged quantity reflecting the pore geometry. We support our findings by a simulation model based upon one-dimensional curvilinear chain diffusion along the primitive path. The study is complemented by deuterium NMR experiments on a labeled poly(dimethylsiloxane) sample, in which strong surface contacts prevent full diffusive averaging.

Dynamics of a polymer in an active and viscoelastic bath.

We study the dynamics of an ideal polymer chain in a viscoelastic medium and in the presence of active forces. The motion of the center of mass and of individual monomers is calculated. On time scales that are comparable to the persistence time of the active forces, monomers can move superdiffusively, while on larger time scales subdiffusive behavior occurs. The difference between this subdiffusion and that in the absence of active forces is quantified. We show that the polymer swells in response to active processes and determine how this swelling depends on the viscoelastic properties of the environment. Our results are compared to recent experiments on the motion of chromosomal loci in bacteria.

Association Behavior, Diffusion, and Viscosity of End-Functionalized Supramolecular Poly(ethylene glycol) in the Melt State

In this work we present a combined analysis of small-angle neutron scattering, linear rheology and pulsed field gradient nuclear magnetic resonance spectroscopy experiments on the supramolecular association and chain structure of well-defined telechelically modified poly(ethylene glycol) (PEG) in the bulk. Oligomeric PEG was functionalized with directed heterocomplementary hydrogen-bonding end-groups, thymine (Thy) and diaminotriazine (DAT). The polarity of the backbone polymer is comparable to the end groups and avoids clustering of the groups basing on energetic arguments. Their linear association behavior in the ideal melt state was investigated on the microscopic/molecular level as a function of temperature. By means of a selective labeling scheme, which should ideally lead to the formation of alternating hydrogeneous-deuterated building block sequences if the hydrogen bonding reaction is exclusively heterocomplementary, we showed that the Thy–DAT association is dominant and a Thy–Thy homoassociation is approximately three times less probable. Latter nondirected association gives rise to a considerable amount of random-copolymerization without affecting seriously neither the macroscopic melt viscosity nor the diffusivity of the supramolecular associates. From the q-dependence of a multiblock RPA structure factor, the linear association in the melt is confirmed. Furthermore, this diffusion and viscosity study reveals simple Rouse dynamics of supramolecular polymer chains with molecular weight much larger than the entanglement mass Me. The Rouse-like dynamics of long supramolecular chains indicates short lifetime hydrogen bonds of the end groups. Our results are in excellent agreement with the related polycondensation theory.

Edge-Functionalized Graphene as a Nanofiller: Molecular Dynamics Simulation Study

In the present simulation work we study graphene-based polymer nanocomposites composed of hydrogenated and carboxylated graphene sheets dispersed in polar and nonpolar short polymer matrices (i.e., matrices containing chains with low molecular weight). The aim of our work is to examine spatial and dynamical heterogeneities of such systems and to provide a compact picture about the effects of the edge group functionalization of graphene sheets on the properties of hybrid graphene-based materials. We perform atomistic molecular dynamics simulations of edge-functionalized graphene sheets embedded in poly(ethylene oxide) (polar matrix) and polyethylene (nonpolar matrix). We choose a low loading of the graphene nanofiller (from 1.7% to 3.6%) in agreement with experimental data. We further implement a detailed analysis of static and dynamic properties of polymer chains on the level of both the entire hybrid material and the polymer/graphene interface through a new approach that is able to distinguish between the adsorbed and edge region around the nanofiller. At the local scale, strong structural and dynamical heterogeneities are observed; i.e., the behavior of the polymer matrix appears to be highly affected by the presence of the edge-functionalized graphene. Slow dynamics was detected in the adsorbed layers in all nanocomposites. Additionaly, interaction of grafted carboxylated groups with polar matrix led to a further delay in the segmental as well as the chain relaxation close to the graphene edges. This effect seems to slow down the chain dynamics even more than the actual adsorption of the chain on the surface. Overall average orientational dynamics of polymer chains in nanocomposites as well as the collective dynamics quantified through the single chain coherent structure factor reveal slight deviations from the bulk behavior in the terminal region, presumably due to the small percentage of the slow dynamic component at the given loading of the nanofiller. Enhancement of the rheological properties is not observed within the time window of our simulations. Our results emphasize the importance of the surface/polymer interactions in the graphene-based nanocomposites and suggest that by a proper choice of edge-grafted groups we can achieve better material performance.

Probing the effects of external species on poly(acrylate acid) chain dynamics by using cationic AIE-active fluorophore

We report here our results on the investigation of the chain dynamics of poly(acrylic acid) in aqueous solution. The concentration of poly(acrylic acid) was approximately 3.8×10−4 mol/L, two orders of magnitude higher than that reported in the literature. The pH value of the solution was 3.9, and the hydrogen bonds between the intrinsic and ionized carboxylic acid groups formed dynamic networks, which captured aggregation-induced emission-active molecules (a tetra-quaternary ammonium modified tetraphenylethene derivative) inside the polymer coils and induced fluorescence emission. The hydrogen bonds can be classified as intra- or intermolecular; both can be probed based on the emission change of the tetra-quaternary ammonium modified tetraphenylethene probes. The effects of different external stimuli on the polymer chain dynamics were investigated using different metal cations (including Na+, Li+, Zn2+, Ni2+, Ca2+, and Co2+), different cation concentrations (1×10−6 to 4×10−4 mol/L), different poly(acrylic acid) molecular weights (5, 240, and 450 kDa), and different copolymers. The experimental results indicate that the long poly(acrylic acid) chains (high molecular weight) tend to form dense globular coils and exclude the probe molecules outside, which are robust and unsusceptible to water-soluble metal cations. However, the shorter poly(acrylic acid) chains tend to form intermolecular hydrogen bonds, which are helpful in capturing more probe molecules inside the networks, thus inducing stronger emission. Because of the dual functions of forming hydrogen bonds with carboxylic groups and acting as an acceptor of protons from the carboxylic acid group to form cationic species, copolymerization with acrylate amide [poly(acrylic acid)-co-poly(acrylamide)] can greatly affect the chain dynamics of poly(acrylic acid) segments, which is reflected by the drastically decreased emission intensity from the fluorescent probes.

The Impact of Polymer Dynamics on Photoinduced Carrier Formation in Films of Semiconducting Polymers.

A better understanding of the carrier formation process in photosemiconducting polymers is crucial to design and construct highly functionalized thin film organic photodevices. Almost all studies published focus on the effect of structure on the photoinduced carrier formation process. Here, we study the dynamics of polymer chain impacts on the carrier formation process for a series of poly(3-alkylthiophene)s (P3ATs) with different alkyl side-chain lengths. The formation of polarons (P) from polaron pairs (PP) was accelerated at a temperature at which the twisting motion of thiophene rings occurs. Among all P3ATs employed, in P3AT with hexyl groups, or poly(3-hexylthiophene) (P3HT), it was easiest to twist the thiophene rings and generate P from PP. The activation energy for P formation was proportional to that of thiophene ring motion. This makes it clear that chain dynamics, in addition to the crystalline structure, is a controlling factor for the carrier formation process in photosemiconducting polymers.

Facilitation of polymer looping and giant polymer diffusivity in crowded solutions of active particles

We study the dynamics of polymer chains in a bath of self-propelled particles (SPP) by extensive Langevin dynamics simulations in a two-dimensional model system. Specifically, we analyse the polymer looping properties versus the SPP activity and investigate how the presence of the active particles alters the chain conformational statistics. We find that SPPs tend to extend flexible polymer chains, while they rather compactify stiffer semiflexible polymers, in agreement with previous results. Here we show that higher activities of SPPs yield a higher effective temperature of the bath and thus facilitate the looping kinetics of a passive polymer chain. We explicitly compute the looping probability and looping time in a wide range of the model parameters. We also analyse the motion of a monomeric tracer particle and the polymer’s centre of mass in the presence of the active particles in terms of the time averaged mean squared displacement, revealing a giant diffusivity enhancement for the polymer chain via SPP pooling. Our results are applicable to rationalising the dimensions and looping kinetics of biopolymers at constantly fluctuating and often actively driven conditions inside biological cells or in suspensions of active colloidal particles or bacteria cells.

Electric-Field-Induced Dynamics of Polymer Chains in a Ferroelectric Melt-Quenched Cold-Drawn Film of Nylon-11 Using Infrared Spectroscopy.

The changes in intensity of the infrared bands of a ferroelectric melt-quenched, cold-drawn film of nylon-11 were measured as a function of a cyclic external electric field of 1.4 MV/cm. The infrared bands assigned to the NH stretching, amide I, NH-vicinal, and CO-vicinal CH2 scissoring modes showed butterfly-shaped hysteresis loops that are characteristic of ferroelectrics; however, the intensity changes of the infrared bands assigned to the CH2 antisymmetric and symmetric stretching modes are small and showed no butterfly-shaped hysteresis loops. These results indicate that the amide groups are inverted, while the methylene groups are not inverted under the external electric field. We propose a new molecular mechanism that explains the ferroelectric properties of nylon-11. Only the amide groups in the antiparallel β-sheet structure are inverted by the external electric field to form new hydrogen bonds; these two states form a nearly double-minimum potential.

Lithography process simulation studies using coarse-grained polymer models

Lithography processes were modeled on the basis of coarse-grained polymer simulation techniques using OCTA, which is the simulation software for soft materials, and the simulations of these processes were performed to clarify the mechanism of the polymer chain dynamics in lithography processes. In the case of the top-down process, the development and rinse processes were modeled using a dissipative particle dynamics method. From our series of simulations, the line pattern constituted by resist polymers can be simulated as a result. In the rinse process, the reduction of line edge roughness (LER) can be found, and the importance of the rinse process to modify the LER was identified. The bottom-up process, which is called the directed self-assembly (DSA) process, can also be simulated. From our DSA process simulations, the polymer chain dynamics in the defect annihilation process can be analyzed. The lithography process simulations modeled by coarse-grained polymer techniques are reviewed. As a case of top-down process, development and rinse processes were simulated. From these simulations, line edge structure can be obtained to discuss the line edge roughness. As a case of bottom-up process, the directed self-assembly (DSA) process was simulated, and the polymer chain dynamics in the defect annihilation process can be analyzed.

Polymer chain dynamics in epoxy based composites as investigated by broadband dielectric spectroscopy

Epoxy networks of the diglycidyl ether of bisphenol A (DGEBA) were prepared using 3,3′- and 4,4′-diaminodiphenyl sulfone isomer crosslinkers. Secondary relaxations and the glass transitions of resultant networks were probed using broadband dielectric spectroscopy (BDS). A sub-Tgγ relaxation peak for both networks shifts to higher frequencies (f) with increasing temperature in Arrhenius fashion, both processes having the same activation energy and being assigned to phenyl ring flipping in DGEBA chains. A β relaxation is assigned to local motions of dipoles that were created during crosslinking reactions. 4,4′-based networks exhibited higher Tg relative to 3,3′-based networks as per dynamic mechanical as well as BDS analyses. The Vogel–Fulcher–Tammann–Hesse equation fitted well to relaxation time vs. temperature data and comparison of Vogel temperatures suggests lower free volume per mass for the 3,3′-based network. The Kramers–Krönig transformation was used to directly calculate dc-free ɛ″ vs. f data from experimental ɛ′ vs. f data. Distribution of relaxation times (DRT) curves are bi-modal for the 3,3′-crosslinked resin suggesting large-scale microstructural heterogeneity as opposed to homogeneity for the 4,4′-based network whose DRT consists of a single peak.

Interfacial effects on dielectric properties of polymethylmethacrylate‐titania microcomposites and nanocomposites

It is discussed that dielectric properties of polymethylmethacrylate (PMMA) composites are influenced by the particle size of titania as a result of changes in the structure and dynamics of polymer chains in the interphase regions around the particles. It is hypothesized that a loosely packed interphase layer, resulted from high stiffness and high cohesion energy of PMMA chains, provides enough free volume for segmental chain movements and dipole orientation along the applied electric field and causes an increase in dielectric properties of nanocomposites at low filler contents. It is shown that the attraction of PMMA toward micro‐titania and nano‐titania is similar by measuring the surface energy of fillers. Dynamics of polymer chains around fillers is investigated by dynamic‐mechanical‐thermal analysis and broadband‐dielectric spectroscopy, and presence of a loosely packed layer is confirmed by measuring thermal and mechanical glass transition temperature of composites. It is concluded that the anomalous enhancement in dielectric properties of 2 vol% nanocomposite, compared to the corresponding microcomposite, can be attributed to the higher volume fraction of loosely packed interphase layers in the nanocomposite. POLYM. COMPOS., 38:1158–1166, 2017. © 2015 Society of Plastics Engineers

Molecular Origins of Macroscopic Mechanical Properties of Elastomeric Organosiloxane Foams

Molecular compositions, structures, interactions, polymer chain dynamics, and micron-scale cell structures of elastomeric organosiloxane foams have been analyzed and correlated with their macroscopic mechanical properties. Open-cell organosiloxane foams were synthesized within a narrow range of relative densities (±5% relative uncertainty) and with similar micron-scale pore structures, as determined from quantitative analyses of micro-X-ray computed tomography (MXCT) images. Network cross-linking densities, polymer molecular weights, organic side-chain moieties, and inorganic filler contents were varied systematically, resulting in materials with significantly different mechanical properties. Solid-state single-pulse 1H and 29Si magic-angle-spinning (MAS), two-dimensional (2D) 29Si{1H} hetereonuclear correlation (HETCOR), and transverse 1H relaxation (T2) nuclear magnetic resonance (NMR) spectroscopy measurements establish significant differences in molecular and polymer network characteristics that are c...

Experimental evidence of ultrathin polymer film stratification by AFM force spectroscopy

By performing Atomic Force Microscopy measurements of pull-off force as a function of the temperature, we were able to probe the dynamic of supported thin polystyrene (PS) films. Thermal transitions induce modifications in the surface energy, roughness and surface modulus that are clearly detected by AFM and related to PS chain relaxation mechanisms. We demonstrated the existence of three transition temperatures that can be associated to the relaxation of polymer chains located at different depth regions within the polymer film. Independently of the film thickness, we have confirmed the presence of a region of high mobility for the polymer chains at the free interface. The thickness of this region is estimated to be above 7nm. The detection of a transition only present for film thicker than the gyration radius Rg is linked to the dynamics of polymer chains in a bulk conformation (i.e. not in contact with the free interface). We claim here that our results demonstrate, in agreement with other techniques, the stratification of thin polymer film depth profile in terms of relaxation behavior.

Impedance and dielectric spectroscopy of nano-graphite reinforced silicon elastomer nanocomposites

Impedance and dielectric spectra of silicone elastomer nanocomposites were used to study their secondary (α* or β) relaxation behavior as a function of nano-graphite loadings in the frequency range of 10−1 to 106 Hz. The effect of nano-graphite loadings on real and imaginary parts of complex impedance has been distinctly visible and explained on the basis of interfacial polarization of filler and relaxation dynamics of polymer chains. The effects of nano-graphite loadings on loss tangent, dielectric permittivity, complex dielectric modulus and electrical conductivity have also been studied. The dielectric permittivity of the composites strongly depends up on the extent of nano-graphite concentration and temperature. The conductivity and relaxation phenomenon have been investigated through dielectric modulus formalism. Nyquist plots, Cole-Cole plots and Argand diagram confirm the existence of non-debye relationship. The frequency dependence of ac conductivity has been investigated by using Percolation theory. The percolation phenomenon has been discussed from electrical conductivity and dielectric permittivity and percolation threshold was found at 6 phr nano-graphite loading. SEM photomicrographs shows well dispersion of nano-graphite.

Arrested Spinodal Decomposition in Polymer Brush Collapsing in Poor Solvent

We study the Brownian dynamics of flexible and semiflexible polymer chains densely grafted on a flat substrate, upon rapid quenching of the system when the quality of solvent becomes poor and chains attempt collapse into a globular state. The collapse process of such a polymer brush differs from individual chains, both in its kinetics and its structural morphology. We find that the resulting collapsed brush does not form a homogeneous dense layer, in spite of all chain monomers equally attracting each other via a model Lennard-Jones potential. Instead, a very distinct inhomogeneous density distribution in the plane forms, with a characteristic length scale dependent on the quenching depth (or equivalently, the strength of monomer attraction) and the geometric parameters of the brush. This structure is identical to the spinodal-decomposition structure, however, due to the grafting constraint we find no subsequent coarsening: the established random bundling with characteristic periodicity remains as the apparently equilibrium structure. We compare this finding with a recent field-theoretical model of bundling in a semiflexible polymer brush.