Motion Of Polymer Research Articles

Fingerprinting Brownian Motions of Polymers under Flow.

We present a quantitative approach to the self-dynamics of polymers under steady flow by employing a set of complementary reference frames and extending the spherical harmonic expansion technique to dynamic density correlations. Application of this method to nonequilibrium molecular dynamics simulations of polymer melts reveals a number of universal features. For both unentangled and entangled melts, the center-of-mass motions in the flow frame are described by superdiffusive, anisotropic Gaussian distributions, whereas the isotropic component of monomer self-dynamics in the center-of-mass frame is strongly suppressed. Spatial correlation analysis shows that the heterogeneity of monomer self-dynamics increases significantly under flow.

Polymer-ion interactions in PVDF@ionic liquid polymer electrolytes: A combined experimental and computational study

Polymer electrolytes based on poly (vinylidene fluoride) (PVDF) with different concentrations (40, 55, 65, and 75 wt.%) of 1-methyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide [EMIM][FSI] were investigated by experimental and molecular dynamics (MD) simulation techniques. The addition of ionic liquid (IL) slightly decreases the electrochemical stability window, as estimated by linear scanning voltammetry. For the neat PVDF, the simulated glass transition temperature (Tg) was obtained at 233.1 K, which is in good agreement with experimental data. Higher contents of IL promoted an increase of the glass transition temperature of the system, indicating a reduction of the polymer segmental mobility, possibly due to the increase of the interactions with the ions. Ionic conductivities were obtained through experimental measurements and MD simulations, which were calculated by Nernst-Einstein and Einstein-Helfand methods. The MD simulation results reproduced the general trend of the experimental ionic conductivities for the GPEs. The studied GPEs systems present an ionic conductivity that obeys a linear Arrhenius behavior, confirming that the ionic mobility is not dependent on the polymer motion.

Simulating wet active polymers by multiparticle collision dynamics.

The conformational and dynamical properties of active Brownian polymers embedded in a fluid depend on the nature of the driving mechanism, e.g., self-propulsion or external actuation of the monomers. Implementations of self-propelled and actuated active Brownian polymers in a multiparticle collision (MPC) dynamics fluid are presented, which capture the distinct differences between the two driving mechanisms. The active force-free nature of self-propelled monomers requires adaptations of the MPC simulation scheme, with its streaming and collision steps, where the monomer self-propulsion velocity has to be omitted in the collision step. Comparison of MPC simulation results for active polymers in dilute solution with results of Brownian dynamics simulations accounting for hydrodynamics via the Rotne-Prager-Yamakawa tensor confirm the suitability of the implementation. The polymer conformational and dynamical properties are analyzed by the static and dynamic structure factor, and the scaling behavior of the latter with respect to the wave number and time dependence are discussed. The dynamic structure factor displays various activity-induced temporal regimes, depending on the considered wave number, which reflect the persistent diffusive motion of the whole polymer at small wave numbers, and the activity-enhanced internal dynamics at large wave numbers. The obtained simulation results are compared with theoretical predictions.

The role of conformational dynamics in the activity of polymer-conjugated CalB in organic solvents

Perennial interest in enzyme catalysis has been expanding its applicability from aqueous phases where enzymes are naturally evolved to organic solvents in which the majority of industrial chemical syntheses are carried out. Although conjugating an enzyme with a soluble polymer has been attempted to enhance enzyme activity in organic solvents, the underlying mechanism remains poorly understood in terms of the conformational dynamics and enzyme activity. Herein, we combine LF-NMR measurements and MD simulations to investigate the effects of polymer grafting on the conformational dynamics of CalB in organic solvents and the consequential impacts on the catalytic kinetics, using the lipase-catalyzed transesterification reaction as a model system. LF-NMR measurements confirm that conjugation with a soluble polymer improves the enzyme flexibility in organic solvents, leading to an increase in the catalytic efficiency of up to two orders of magnitude. MD simulations suggest that the conjugated enzyme samples a larger conformational space, compared to its native counterpart, validating the hypothesis that polymer motion enhances enzyme dynamics. These experimental and simulation results provide new insights for enhancing enzyme conformational dynamics and thereby catalytic kinetics in organic solvents.

Unconventional Approaches to Light-Promoted Dynamic Surface Morphing on Polymer Films

Abstract Recent progress in research of light-promoted surface morphing on polymer materials is reviewed. Photoinduced mass transport motions in azobenzene polymers leading to surface relief gratings (widely called SRGs) formation are well-known and extensively discussed. Among many efforts, this article focuses on unconventional approaches, most of which are seemingly less highlighted. The first part introduces investigations using azobenzene polymers; introducing supramolecular approaches with tunable and removable azobenzene units, self-structuring of surface morphology upon single laser beam irradiation, photo-triggered migration via Marangoni flow, SRG formation and other functions of polymer brushes etc. The second part overviews the mass transport motions driven by other photoreaction classes such as photopolymerization, photocrosslinking, and photoisomerization of non-azobenzene components. The final part describes new dynamic surface morphing processes observed in fingerprint texture of liquid crystals and liquid crystal polymer networks, which can be applied to reversible friction control and self-cleaning. These uncommon attempts at photo-assisted dynamic morphing extend the possibilities of microfabrication on polymer films and are expected to find new opportunities to create new surface functions in soft materials.

Structural and Dielectric Properties of Polyvinyl Alcohol‐TiO2 Doped Thin Films

AbstractPolyvinyl alcohol(PVA)‐titanium dioxide(TiO2) polymer composite films are synthesized by well‐recognized and low cost method of solvent casting. The prepared composite films are characterized by FTIR, XRD, and FESEM. The real electric modulus (M’) spectra show large increment with frequency for 5wt% of TiO2 as compared to other compositions. The appearance of peaks for each concentration of TiO2 in M” spectra specifies that strong coupling in the movement of polymer motion and ions. The impedance plots of real impedance (Z’) versus imaginary impedance (Z”) shows semicircles, which diameter and thereby bulk resistance (Rb) is decreased with the loading of TiO2. AC conductivity (σAC) obeys the universal power law. The prepared PVA/TiO2 films can be used in a direct methanol fuel cell, and in optoelectronic devices.

Unravelling Main- and Side-Chain Motions in Polymers with NMR Spectroscopy and Relaxometry: The Case of Polyvinyl Butyral.

Polyvinyl butyral (PVB) is an amorphous polymer employed in many technological applications. In order to highlight the relationships between macroscopic properties and dynamics at a microscopic level, motions of the main-chain and of the propyl side-chains were investigated between Tg − 288 °C and Tg + 55 °C, with Tg indicating the glass transition temperature. To this aim, a combination of solid state Nuclear Magnetic Resonance (NMR) methods was applied to two purposely synthesized PVB isotopomers: one fully protonated and the other perdeuterated on the side-chains. 1H time domain NMR and 1H field cycling NMR relaxometry experiments, performed across and above Tg, revealed that the dynamics of the main-chain corresponds to the α-relaxation associated to the glass transition, which was previously characterized by dielectric spectroscopy. A faster secondary relaxation was observed for the first time and ascribed to side-chains. The geometry and rate of motions of the different groups in the side-chains were characterized below Tg by 2H NMR spectroscopy.

Interfacial Molecular Motion and Chemical Characteristics of Polymer Jointed to Metal by Chemical Bonding

Interfacial Molecular Motion and Chemical Characteristics of Polymer Jointed to Metal by Chemical Bonding

Movement of polymers in an asymmetric nano-channel under various parameters

Separation is an important process in various fields in science and technology, and nano-structures are now being widely used to improve the resolution and speed of separation processes. Continuous separation occurs when the components of a mixture separate at different locations in a device; this makes it possible to inject a new sample into the device at any time during an on-going separation process. Continuous separation of nano-particles in a nano-channel composed of consecutive cones has been shown previously, while this study investigates whether a nano-channel can perform continuous separation of polymers such that polymers of different lengths are separated at the two sides of the channel. For this purpose, the motion of a charged polymer in an asymmetric nano-channel under constant and alternating applied electric fields was studied theoretically and by applying computer simulations. Theoretical formalism was used to determine the situation under which the channel could perform continuous separation, with computer simulations used to check the theoretical results. The effect of different channel parameters on the performance of the nano-channel, as a device for continuous separation, was thus determined.

Probing the Structural Dynamics of the Coil-Globule Transition of Thermosensitive Nanocomposite Hydrogels.

Nanocomposite hydrogels have emerged to exhibit multipurpose properties, boosting especially the biomaterial field. However, the development and characterization of these materials can be a challenge, especially stimuli-sensitive materials with dynamic properties in response to external stimuli. By employing UV-vis spectroscopy and NMR relaxation techniques, we could outline the formation and behavior of thermosensitive nanocomposites obtained by in situ polymerization of poly(N-vinylcaprolactam) (PNVCL) and mesoporous silica nanofibers under temperature stimuli. For instance, inorganic nanoparticles covalently linked to PNVCL changed the pattern of temperature-induced phase transition despite showing similar critical temperatures to neat PNVCL. Thermodynamic parameters indicated the formation of an interconnected system of silica and polymer chains with reduced enthalpic contribution and mobility. The investigation of water molecule and polymer segment motions also revealed that the absorption and release of water happened in a wider temperature range for the nanocomposites, and the polymer segments respond in different ways during the phase transition in the presence of silica. This set of techniques was essential to reveal the polymer motions and structural features in nanocomposite hydrogels under temperature stimuli, demonstrating its potential use as experimental guideline to study multicomponent nanocomposites with diverse functionalities and dynamic properties.

Loads transfer behavior of graphene oxide/halloysite organic-inorganic hybrid aerogel: Motion of polymer ‘bridge’

Loads transfer behavior of graphene oxide/halloysite organic-inorganic hybrid aerogel: Motion of polymer ‘bridge’

Effect of POSS-PEG on ionic conductivity and relaxation of solid polymer electrolytes

Nanocomposite polymer electrolytes (NCPE) have been prepared by blending poly (ethylene oxide) (PEO) and polyhedral oligomeric silsesquioxane-functionalized with poly (ethylene glycol) (POSS-PEG) with lithium tetrafluoroborate (LiBF4). NCPE has been characterized by DSC and impedance analyzer. POSS-PEG was highly compatible with PEO up to 50 wt% and resulted in single Tg and increased ionic conductivity. The ionic conductivity of the nanocomposites increased to 4.02 × 10−6 S/cm at POSS-PEG 50 wt% by more than 2 orders of magnitude. POSS-PEG nanoparticles sustainably increased ionic conductivity without impeding chain motion of polymer and were highly compatible with PEO up to POSS-PEG 50 wt%, which can mitigate the restriction of the amount of nanoparticles introduction. Also, the stable POSS core structure supplements the mechanical properties of polymer electrolytes. To understand ion transport behaviors, the segmental relaxation times (τs) of nanocomposites were studied by dielectric spectroscopy as function of POSS-PEG loading. τs decreased to −1.54 from −1.01 at POSS-PEG 5 ∼20 wt%, but it slightly increased to −1.28 from −1.54 at POSS-PEG 40 ∼ 50 wt%, which could be attributed to bridged complex formed between PEO and POSS-PEG through Li+.

Diffusion Spectrum of Polymer Melt Measured by Varying Magnetic Field Gradient Pulse Width in PGSE NMR.

The translational motion of polymers is a complex process and has a big impact on polymer structure and chemical reactivity. The process can be described by the segment velocity autocorrelation function or its diffusion spectrum, which exhibit several characteristic features depending on the observational time scale—from the Brownian delta function on a large time scale, to complex details in a very short range. Several stepwise, more-complex models of translational dynamics thus exist—from the Rouse regime over reptation motion to a combination of reptation and tube-Rouse motion. Accordingly, different methods of measurement are applicable, from neutron scattering for very short times to optical methods for very long times. In the intermediate regime, nuclear magnetic resonance (NMR) is applicable—for microseconds, relaxometry, and for milliseconds, diffusometry. We used a variation of the established diffusometric method of pulsed gradient spin-echo NMR to measure the diffusion spectrum of a linear polyethylene melt by varying the gradient pulse width. We were able to determine the characteristic relaxation time of the first mode of the tube-Rouse motion. This result is a deviation from a Rouse model of polymer chain displacement at the crossover from a square-root to linear time dependence, indicating a new long-term diffusion regime in which the dynamics of the tube are also described by the Rouse model.

Consequences of Chirality in Directing the Pathway of Cholesteric Helix Inversion of π-Conjugated Polymers by Light.

Control over main-chain motion of chiral π-conjugated polymers can lead to unexpected new functionalities.Here, it is shown that by combining photoswitchable azobenzene units in conjugation with chiral fluorene comonomers and appropriate plasticizers, the polymer organization and chiroptical properties of these alternating copolymers steered by light and its state of polarization can be dynamically controlled. The configuration of the stereogenic centers in the side chains of the fluorene units determines the handedness of the cholesteric organization in thermally annealed films, indicating cooperative behavior. The polymer alignment and helicity of the supramolecular arrangement can be switched by irradiating with linearly and circularly polarized light, respectively.Intriguingly, when switching the handedness of thermally induced cholesteric organizations by illuminating with circularly polarized light that is opposite to the handedness of the cholesteric phases, a nematic-like intermediate state is observed during helix interconversion. By the sequence of irradiation with left and right circularly polarized light followed by thermal annealing, an asymmetric motion, reminiscent of that seen in molecular motors is observed. These findings suggest that functional conjugated polymers can exhibit emergent properties at mesoscopic scale.

Distinct Viscoelasticity of Hierarchical Nanostructures Self-Assembled from Multiblock Copolymers

We employed a nonequilibrium dissipative particle dynamics method to study viscoelastic properties of hierarchical lamellar structures self-assembled from heptablock copolymers. Three ways of shearing with respect to lamellar planes, including parallel, vertical, and transverse shearing, were imposed to study the viscoelasticity of ordered systems. In parallel shear, with the morphology transformation from disorder to general lamellae to parallel lamellae-in-lamella, both the storage and loss moduli of multiblock copolymer melt show a remarkable improvement. In addition to the parallel lamellae-in-lamella, the multiblock copolymers can form perpendicular lamellae-in-lamella with different viscoelastic behaviors. In vertical shear, parallel lamellae-in-lamella shows terminal behavior, while a low-frequency plateau in the storage modulus exists for the perpendicular lamellae-in-lamella. In transverse shear, the storage moduli for both perpendicular and parallel lamellae-in-lamellae with strong separation of small-length-scale structure exhibit a solid-like plateau at low frequency. The physical origin underlying the distinct viscoelasticity of various hierarchical lamellae was revealed by monitoring the motions of polymer blocks at different length scales. The present work could provide information for preparing advanced materials based on packed lamellae.

(Invited) Solvate Ionic Liquids and Their Polymer Electrolytes: Possible Beyond LIB Electrolytes

Certain molten solvates of Li salts can be regarded as solvate ionic liquids (SILs). A typical example is equimolar mixtures of glymes (G3: triglyme and G4: tetraglyme) and Li[TFSA]([TFSA]=[NTf2]) ([Li(glyme)][TFSA]). The amount of free glyme is a trace in [Li(glyme)][TFSA], and thereby can be regarded as solvate ionic liquids. Unlike conventional electrolytes, the solvation of Li+ by the glyme forms stable and discrete solvate ions ([Li(glyme)]+) in the solvate ionic liquids. The electrochemical oxidation of glyme in [Li(glyme)][TFSA] is greatly enhanced due to the donation of lone pairs of ether oxygen atoms to the Li+ cation, resulting in the HOMO energy level lowering of a glyme molecule. This anomalous Li+ solvation induces interesting transport properties when interfacial electrochemical reactions proceed, which is not transport of solvated ions based on Stokes’ law but a ligand (solvent)-exchange transport. Li+-intercalated graphite was electrochemically formed in [Li(G3)1][TFSA]. In contrast, the cointercalation of G3 and Li+ (intercalation of solvate [Li(G3)1]+ cation) into graphite occurred in [Li(G3) x ][TFSA] electrolytes containing excess G3 (x > 1). In the solvate ionic liquid, the activity of the free solvent is very low, which would make the solvate ion unstable and the desolvation possible at the interface. Another intriguing aspect of the solvate ionic liquids is unusual solubility, which leads to the stable operation of the Li–S battery due to very low solubility of the discharge products (Li2S x ). The theoretical capacity of the S cathode is 10 times higher than that of conventional cathode materials used in current Li–ion batteries. However, Li–S batteries suffer from the dissolution of lithium polysulfides, which are formed by the discharge reaction of the S cathode. In the SILs, [Li(glyme)][TFSA], both cations and anions are weakly coordinating ions with low Lewis acidity and basicity, respectively. The [Li(glyme)][TFSA] molten complexes do not readily dissolve other ionic solutes due to the weak coordinating nature of the cation and anion, which leads to the stable operation of the Li–S battery.Furthermore, polymer electrolytes composed of ABA-triblock copolymers and [Li(glyme)][TFSA] SILs are proposed to simultaneously achieve high ionic conductivity, thermal stability, and a wide potential window. Different block copolymers, consisting of a SIL-incompatible A segment (polystyrene, PSt) and SIL-compatible B segments (poly(methyl methacrylate) (PMMA) and poly(ethylene oxide) (PEO)) are utilized. The SILs can be solidified with the copolymers through physical crosslinking by the self-assembly of the PSt segment. The thermal and electrochemical properties of the polymer electrolytes are significantly affected by the stability of the [Li(glyme)]+ complex in the block copolymer B segments, and the preservation of the SILs contributes to their thermal stabilities and oxidation stabilities greater than 4 V vs. Li/Li+. The [Li(glyme)]+ complex cation is unstable in the PEO matrix, whereas the complex structure of [Li(glyme)]+ is stable in the PMMA-based polymer electrolyte. Intriguing points of the PMMA-based polymer electrolytes are decoupled ion transport from segmental motion of the matrix polymer. By using the PMMA-based polymer electrolytes, a 4-V class Li batteries with a LiCoO2 cathode and a Li metal anode can be stably operated; in contrast, this is not possible using the PEO-based electrolyte.Recently, we find that Li+ hopping conduction, which cannot be explained by conventional Stokes law, emerges in certain highly concentrated molten solvate electrolytes. Li+ diffuses faster than the solvent and anion, and thus the evolution of Li+ hopping conduction is confirmed, which leads to a higher Li+ transference number. Possible application of these new electrolytes will also be discussed.

Light-Driven Continual Oscillatory Rocking of a Polymer Film.

Achieving oscillatory motion in polymers without requiring on/off switching of stimuli is a current challenge. Hereby, a free‐standing liquid crystal polymer (LCP) is demonstrated to undergo a sustained oscillatory motion when triggered by light, moving back and forth, resembling the motion of a rocking‐chair. Two polymer films having different azobenzene photo‐switches have been studied, revealing photoswitch requirements as well as illumination conditions necessary to sustain oscillations. The motion presented here shows how feedback loops involving light‐triggered actuation, self‐shadowing and a shifting center of gravity can be utilized to achieve self‐sustained motion in free‐standing polymers.

The two-state reversible kinetics of a long polymer molecule in solution with a delocalized coupling term. An exact analytical model

We develop a mathematical recipe for calculating the exact delocalized rate constant, for the end loop motion of a long polymer. It undergoes reversible reaction between two disjunct states, the open and the closed state, due to the effect of the surrounding solvent. The Smoluchowski-like equation mathematically represents the diffusion of the end monomers of the open polymer chain and the closed chain in terms of a free particle performing random motion under different harmonic potentials. The coupling term between the two potentials is assumed to be represented by a delocalized coupling term. For a favorable disposition towards the more realistic experimental behavior, the rate constant have effect incorporated from all the bond making and bond breaking phenomenon of the chemical reactions different from the end loop formation. It not only involves the end looping but can evaluate for reactions where only one of the ends of the open-chain is involved.

Model for athermal enhancement of molecular mobility in solid polymers by light.

Molecular motion in polymers is frozen below the glass transition temperature T_{g} and changes of viscoelastic functions are most spectacular near T_{g}. Exceptional enhancement of molecular mobility and a decrease of polymer viscosity, by several orders of magnitude, down to the viscous flow regime, are observed way below T_{g} by light absorption. Relaxation processes, which take decades to centuries in some high-T_{g} polymers, are reduced to minute timescales by sub-T_{g} light absorption. Here we develop a model for this intriguing albeit spectacular action of light on glass forming materials and we propose experiments to relate light absorption to materials properties. The model provides a solution to a long-lasting problem of how molecular mobility is enhanced in solid polymers by photoisomerization and provides a tool for a better understanding of the relationship between light absorption and material properties and developing photosensitive polymers for light to mechanical energy transduction.

A review on the relaxation dynamics analysis of unentangled polymers with different structures

ABSTRACT Relaxation dynamics of unentangled polymer melts (with a chain length below N = 100 for polyethylene) can be studied by performing either Rouse mode or relaxation mode analysis, such as proper orthogonal decomposition. The former mode analysis can be derived analytically from the linear equation of motion of polymers with the inclusion of inertia term, whereas the latter is designed for the case when the numerical solution to a highly nonlinear equation of motion is known, such as MD simulation data. This article presents a summary of both approaches and their applications in the evaluation of zero-shear viscosity of polymer melts.