Polymer Mobility Research Articles

Enhancement of molecular mobility in solid polymers by light: fundamentals and applications

Enhancement of molecular mobility in solid polymers by light: fundamentals and applications

Температурная эволюция взаимодействия релаксационных процессов с локальной динамикой на терагерцевых частотах в полимерах с водородными связями

At terahertz frequencies, the torsional-vibrational motion is associated with dielectric relaxation in disordered solids with hydrogen bonds. The interaction between these processes is still poorly understood, especially at temperatures below the glass transition temperature, which is especially important for molecular mobility in polymers. We have studied polymers with hydrogen bonds (polyamide-6 and polyvinyl chloride) at temperatures from 90 to 400 K in the range 0.25 - 4 THz using far-infrared spectroscopy. Three general features were observed in the spectrum of dielectric losses, ”(a) at temperatures well below the glass transition (Tg), these losses are represented by the low-frequency wing of the absorption peak due to the libration of polymer monomer units. (b) At 0.7Tg <T <Tg, additional temperature-dependent losses are observed, which can be associated with the manifestation of secondary relaxation processes. (c) At temperatures above Tg, primary α-relaxation processes become the dominant contribution to terahertz losses. The results obtained show that the evolution of terahertz losses with temperature is caused by a change in the structure of hydrogen bonds, which, apparently, is universal for systems with similar intermolecular interactions.

Temperature evolution of the interaction of relaxation processes with local dynamics at terahertz frequencies in polimers with hydrogen bonds

At terahertz frequencies, the torsional-vibrational motion is associated with dielectric relaxation in disordered solids with hydrogen bonds. The interaction between these processes is still poorly understood, especially at temperatures below the glass transition temperature, which is especially important for molecular mobility in polymers. We have studied polymers with hydrogen bonds (polyamide-6 and polyvinyl chloride) at temperatures from 90 to 400 K in the range 0.25-4 THz using far-infrared spectroscopy. Three general features were observed in the spectrum of dielectric losses, ε''(ν) (a) at temperatures well below the glass transition (Tg), these losses are represented by the low-frequency wing of the absorption peak due to the libration of polymer monomer units. (b) At 0.7Tg<T<Tg, additional temperature-dependent losses are observed, which can be associated with the manifestation of secondary relaxation processes. (c) At temperatures above Tg, primary α-relaxation processes become the dominant contribution to terahertz losses. The results obtained show that the evolution of terahertz losses with temperature is caused by a change in the structure of hydrogen bonds, which, apparently, is universal for systems with similar intermolecular interactions. Keywords: polymers, terahertz IR-spectra, temperature dependence, α- and β-relaxations, hydrogen bonding.

An anisotropic immerse precipitation process for the preparation of polymer membranes.

We study the immerse precipitation process in a ternary polymer/solvent/non-solvent system by numerically solving the two-dimensional Cahn-Hilliard phase field equation. In particular, we introduce anisotropic mobility, namely the mobility of a polymer varies over different spatial directions, and focus on the porosity morphology of the obtained polymer membrane. Simulations reveal that as the anisotropy increases in the polymer mobility, the polymer pattern changes from nearly isotropic and random voids to strips parallel to the direction with smaller mobility. The influence of anisotropy quickly saturates. The anisotropic mobility model is also applied to a ternary system mimicking the preparation of a hollow fiber membrane, and shows strong effects on the membrane porosity pattern.

A critical analysis on the effects of xanthan gum properties and its derivatives in enhanced oil recovery

Polymer flooding or mobility control techniques that focus on maintaining favorable mobility ratios can be used to improve volumetric sweep efficiency. The development of specialized polymer solutions optimizes the mobility ratio between the injected polymer solution and the oil or water bank being displaced in advance of the polymer. Because of its solid structure, lack of effect of salt on viscosity (unlike partially hydrolyzed polyacrylamide (HPAM), which has a salinity influence on viscosity), and lack of effect of high temperatures, xanthan gum, also known as polysaccharide biopolymer, is the most frequently utilized. This research investigates many properties of xanthan gum, as well as its effectiveness with other polymers and the modifications made to improve its performance.

Dielectric Manipulation of Polymer Translocation Dynamics in Engineered Membrane Nanopores.

The alteration of the dielectric membrane properties by membrane engineering techniques such as carbon nanotube (CNT) coating opens the way to novel molecular transport strategies for biosensing purposes. In this article, we predict a macromolecular transport mechanism enabling the dielectric manipulation of the polymer translocation dynamics in dielectric membrane pores confining mixed electrolytes. In the giant permittivity regime of these engineered membranes governed by attractive polarization forces, multivalent ions adsorbed by the membrane nanopore trigger a monovalent ion separation and set an electroosmotic counterion flow. The drag force exerted by this flow is sufficiently strong to suppress and invert the electrophoretic velocity of anionic polymers and also to generate the mobility of neutral polymers whose speed and direction can be solely adjusted by the charge and concentration of the added multivalent ions. These features identify the dielectrically generated transport mechanism as an efficient means to drive overall neutral or weakly charged analytes that cannot be controlled by an external voltage. We also reveal that, in anionic polymer translocation, multivalent cation addition into the monovalent salt solution amplifies the electric current signal by several factors. The signal amplification is caused by the electrostatic many-body interactions replacing the monovalent polymer counterions by the multivalent cations of higher electric mobility. The strength of this electrokinetic charge discrimination points out the potential of multivalent ions as current amplifiers capable of providing boosted resolution in nanopore-based biosensing techniques.

Asymmetric Hybrid Siloxane Side Chains for Enhanced Mobility and Mechanical Properties of Diketopyrrolopyrrole-Based Polymers.

High performance organic field effect transistor devices based on intrinsically scalable materials are of great significance in wearable electronics. In this work, an exclusive approach is reported to rationale the carrier mobility and stretchability of the conjugate polymers (CPs) by modifying the symmetry of the side chains species. Semiconductor CPs with symmetrical alkyl side chains (P(C-C)), symmetrical siloxane side chains (P(Si-Si)), and asymmetrical silicon-carbon side chains (P(C-Si)) are synthesized to investigate the influence of these side chains on the carrier mobility and mechanical behavior. The result shows that silicon-carbon asymmetric side chains can modulate the aggregation degree of polymer chains with a coherence length of 134 Å and maintain the mobility at 0.90 cm2 V-1 s-1 . P(C-Si) exhibits superior tensile properties that even elongation up to 100% the value of mobility retains a majority properties. The main reason is that the lowest coherence length of P(C-Si) polymer leads to an increased proportion of amorphous zones in its polymer film, which efficiently dissipates mechanical stresses. This study provides an efficient strategy for the design and synthesis of the CPs with high carrier transport properties-mechanical stability.

Probing Hydrophobic Interactions between Polymer Surfaces and Air Bubbles or Oil Droplets: Effects of Molecular Weight and Surfactants.

Hydrophobic interaction plays an important role in numerous interfacial phenomena and biophysical and industrial processes. In this work, polystyrene (PS) was used as a model hydrophobic polymer for investigating its hydrophobic interaction with highly deformable objects (i.e., air bubbles and oil droplets) in aqueous solutions. The effects of polymer molecular weight, solvent (i.e., addition of ethanol to water), the presence of surface-active species, and hydrodynamic conditions were investigated, via direct surface force measurements using the bubble/drop probe atomic force microscopy (AFM) technique and theoretical calculations based on the Reynolds lubrication theory and augmented Young-Laplace equation by including the effect of disjoining pressure. It was found that the PS of low molecular weight (i.e., PS590 and PS810) showed slightly weaker hydrophobic interactions with air bubbles or oil droplets, as compared to glassy PS of higher molecular weight (i.e., PS1110, PS2330, PS46300, and PS1M). The hydrophobic interaction between PS and air bubbles in a 1 M NaCl aqueous solution with 10 vol % ethanol was weaker than that in the bare aqueous solution. Such effects on the hydrophobic interactions are possibly achieved by influencing the structuring/ordering of water molecules close to the hydrophobic polymer surfaces by tuning the surface chain mobility and surface roughness of polymers. It was found that the addition of three surface-active species, i.e., cetyltrimethylammonium chloride (CTAC), Pluronic F-127, and sodium dodecyl sulfate (SDS), to the aqueous media could suppress the attachment of the hydrophobic polymer and air bubbles or oil droplets, most likely caused by the additional steric repulsion due to the adsorbed surface-active species at the bubble/polymer/oil interfaces. Our results have improved the fundamental understanding of the interaction mechanisms between hydrophobic polymers and gas bubbles or oil droplets, with useful implications on developing effective methods for modulating the related interfacial interactions in many engineering applications.

Optimization of polymer mobility control for enhanced heavy oil recovery: Based on response surface method

As an enhanced oil recovery (EOR) method, polymer flooding has been widely applied in heavy oil production. Polymer's viscosity and residual resistance factor (RRF) are the key parameters of mobility control, whose increment can both result in the increased oil recovery factor (RF) and worse injectivity. Aiming at oil with viscosities of 50–350 cP, recovery factor and injection pressure of polymer flooding are obtained in the reservoir numerical simulation model. Then we used response surface method to optimize the combination of viscosity and residual resistance factor. The results show that injecting polymer solutions can balance the injectivity gap among layers caused by permeability heterogeneity, while high permeability layers contribute most in oil recovery. For polymer solutions with different combinations of viscosity and RRF in research scope, analyses of growth rates of recovery factor and pressure show that increasing RRF is suitable for above three-fourths of polymers. In such a way, a greater incremental recovery can be achieved under a reasonable increased injecting pressure. This study indicates that polymer solutions with relatively low viscosity and high RRF are more applicable to heterogeneous heavy oil reservoirs.

Water Domain Enabled Transport and Enhanced Stability in Aqueous Solid Polymer-in-Salt Electrolytes for Lithium-Ion Batteries

As lithium-ion batteries (LIBs) continue to grow in use for energy storage applications, concerns over their safety have influenced research for alternative materials, particularly solid-state electrolytes to replace the highly flammable and electrochemically unstable liquid organic electrolytes used in commercial LIBs. Aqueous-based solid polymer electrolytes (SPEs) offer a safer approach by using water as an abundant, cheap, and non-toxic solvent in an inherently nonflammable polymer matrix. This class of electrolyte also offers decreased cost and weight, ease of processibility, and increased long-term chemical and mechanical stability. However, widespread commercial adoption of SPEs for lithium-ion batteries has been hindered by subpar transport properties, namely, ionic conductivities <1 mS/cm at room temperature and slower Li+ transport compared to anion transport due to slow polymer chain mobility. The use of water as a solvent also lends to restrictive electrochemical stability windows (ESWs) due to its nonideal redox properties that lead to minimal anodic and cathodic limits, dominated by hydrogen evolution at potentials beyond common anode materials (>2 V vs. Li/Li+).To combat these challenges, our work builds upon the concept of super-concentrated salt systems. In the solid-state regime, highly concentrated “polymer-in-salt” systems can exhibit an ion cluster effect allowing for fast cationic transport decoupled from polymer chain segmental motion. In the aqueous regime, highly concentrated “water-in-salt” systems exhibit the formation of a passivating solid electrolyte interphase (SEI) through reduction of TFSI- to form LiF on the anode surface. The presence of water in the “water-in-salt” system also gives rise to a disproportionation of Li+ solvation environments, namely TFSI-rich and water-rich domains, allowing for fast cationic transport through the water domains. By including a highly concentrated “water-in-salt” system into a polymer matrix, the unique aqueous solid polymer-in-salt electrolyte (ASPE) demonstrates preferential Li+ transport compared to anion transport, high ionic conductivity, and extended ESW. This system also exhibits unique stability in air that eliminates the need for meticulously dry environments and solution processing, which is desirable to manufacturers for substantial savings in productions costs.We demonstrate that the ASPE comprised of poly(ethylene oxide) (PEO), water, and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) salt can achieve a high room temperature ionic conductivity of >1.75 mS/cm. Pulsed field gradient NMR shows a lithium transference number of 0.66, which was corroborated with electrochemical impedance spectroscopy. Molecular dynamic simulations reveal that the exceptional transport properties of the ASPE are likely due to decoupling of ion conduction from the polymer-assisted transport seen in typical SPEs, instead being dominated by water-assisted vehicular transport. The system exhibits stability to ~1.5 V vs. Li/Li+, enabling access to anode materials like LTO and LVPF previously incompatible with aqueous electrolytes. Cycling performance was assessed using LTO/LMO, a ~2.8 V output, to demonstrate the capability of the ASPE to promote intercalation and deintercalation in these electrodes.Further work demonstrates improvement to the ESW of the ASPE by changing the composition of the “water-in-salt” electrolyte to a highly concentrated hybrid aqueous/ionic liquid electrolyte and changing the polymer matrix. The inclusion of ionic liquid as a second, non-aqueous solvating molecule reduces the amount of water needed in the system and provides an alternative pathway for quality SEI formation. High molecular weight polymer offers a solvating matrix to reduce the overall concentration of water while simultaneously reducing water activity through changes in the hydrogen bonding structure. Additionally, the new polymer matrix exhibits superior thermodynamic stability at high voltages and aids in decoupling ionic mobility from polymer mobility, making it a strong choice for highly concentrated systems without sacrificing transport properties. This new class of ASPE demonstrates a remarkable extended cathodic limit <1 V vs. Li/Li+ and overall ESW >4 V with minimal electrochemical activity up to 5.5 V vs. Li/Li+. Cyclic voltammetry demonstrates compatibility with commercial LTO and TNO anodes, which when paired with appropriate high voltage cathode material can enable fast-charging systems with increased energy density.

Carbon Dots Evoked Li Ion Dynamics for Solid State Battery

Solid composite electrolyte-based Li battery is viewed as one of the most competitive system for the next generation batteries; however, it is still restricted by sluggish ion diffusion. Fast ion transport is a characteristic of the polyethylene oxide (PEO) amorphous phase, and the mobility of Li+ is restrained by the coordination interaction within PEO and Li+ . Herein, the design of applying functionalized carbon dots (CDs) with abundant surface features as fillers is proposed. High ionic conductivity is achieved in the CD-based composite electrolytes resulting from enhanced ion migration ability of polymer segments and mobility of Li+ . Specially, the optimum effect with nitrogen and sulfur co-doped carbon dots (NS-CD) is a consequence of strong interaction between edge-nitrogen/sulfur in NS-CD and Li+ . Solid-state nuclear magnetic resonance results confirm that more mobile Li+ is generated. Moreover, it is observed that lithium dendrite is suppressed compared to PEO electrolyte associated with reinforced mechanical properties and high transference number. The corresponding all-solid-state batteries, with the cathode of LiFePO4 or high voltage NCM523, exhibit long cycling life and excellent rate performances. It is a novel strategy to achieve high ionic conductivity composite electrolyte with uniform lithium deposition and provides a new direction to the mechanism of fast Li+ movement.

Structure-Properties relationships in renewable composites based on polylactide filled with Tannin and Kraft Lignin - Crystallization and molecular mobility

Calorimetry and dielectric spectroscopy supplemented by polarized light microscopy, X-ray, infrared spectroscopy and scanning electron microscopy are employed here to assess the crystallization, interactions and molecular mobility in polylactide (PLA) filled with Tannin and kraft-Lignin prepared by melt extrusion. The direct and indirect effects of the fillers are investigated within two states of the polymer, namely, amorphous and semicrystalline (melt-crystallization annealed). The extremely slow and weak crystallization of PLA is enhanced by the fillers, mainly in the rate, via the combined effects of providing sites for crystallization and moderately enhancing polymer mobility (chains diffusion). Interestingly, the crystal structure and semicrystalline morphology were found altered in the composites as compared to the unfilled PLA. The effect on crystallization was found slightly stronger in PLA/Tannin, whereas the overall results were found in accordance to previously proposed models on the role of weak or absent interfacial interactions on promoting nucleation, such as in our case. Dielectric spectroscopy enabled the recording of the overall molecular dynamics mapping. Local dynamics was found to consist mainly of two individual processes. Regarding segmental mobility of PLA, the presence of tannin and lignin was found to impose moderate changes, namely, slight acceleration, narrowing of relaxation times range and suppression in fragility, however, not systematic changes in the calorimetric or dielectric strengths. The overall data could be rationalized exploiting known models involving as an indirect filler effect the increase in free volume. Despite the weak effects, Tannin was found again more effective and this seems to correlate with their smaller size and moderately better distribution as compared to lignin. The involvement of crystallization resulted in an expected blocking of ions transport, which, along the recorded potential for tuning semicrystalline morphology, make these materials interesting and worth to be further studied with regard to their permeation, mechanical and antioxidation performance.

Enhanced molecular selectivity and plasticization resistance in ring-opened Tröger's base polymer membranes

As a new class of membrane materials, Tröger's base (TB) polymers suffer from CO2-induced plasticization, which leads to a loss in their gas separation selectivity. To address this challenge, we describe a new approach for enhancing their plasticization resistance by ring-opening a TB polymer to establish hydrogen bonds between polymer chains. The ring-opened membranes, called TB-OR, exhibit H2/CO2 and H2/CH4 selectivities of 5.1 and 186.7, respectively. High-pressure CO2 feed measurements reveal that the TB-OR membranes possess better plasticization resistance than untreated TB polymers. The increased plasticization resistance is likely due to hydrogen bonds formed between –N-H groups and N atoms in TB-OR polymers, which reduce the polymer chain mobility and CO2-induced swelling of polymers. The design principles open a new route for making molecularly-selective membranes with significantly enhanced CO2 plasticization resistance that are potentially useful for CO2 separation and hydrogen purification.

Collagen and Carbon-ferrous Nanoparticles Used as a Green Energy Composite Material for Energy Storage Devices

Background:: Chrome shavings, a bioactive material, are generated from tannery as waste material. These chrome shaving can be used for the preparation of many value-added products. Objective:: One such attempt is made to use these chrome shaving wastes as a composite bio-battery to produce DC voltage, an alternate green energy source and cleaner technology. Methods:: Chrome shavings are hydrolyzed to make collagen paste and mixed with the ferrous nanoparticles of Moringa oleifera leaves and Carbon nanoparticles of Onion peels to form electrolyte paste as base. Then, the electrolyte base was added to the aluminum paste and conducting gel, and mixed well to form composite material for bio-battery. Results:: The composite material of bio-battery has been characterized using Scanning Electron Microscopy (SEM), Fourier-Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC) and Thermo Gravimetric Analysis (TGA). Series and parallel circuit testing were done using Copper and Zinc electrodes or Carbon and Zinc electrodes as the battery terminals in the electrolyte paste. The surface area of these electrodes needs standardization from bench to pilot scale. The power generated, for an AA battery size, using a single bio-battery cell has produced a DC voltage of 1.5 V; current of 900 mA. Circuit testing on 1 ml of 80 well-cells connected in series has produced DC output of 18 V and 1100 mA whereas 48 V and 1500 mA were obtained from a series-parallel connection. Conclusion:: The glass transition temperature (Tg) of electrolyte of the bio-battery at 53°C indicated that at this temperature, all the substances present in the bio-battery were well spread and consistently contributed to the electrolyte activity where Fe-C-nano-particles were able to form strong chemical bonds on the flanking hydroxyl group sites of the collagen leading to reduced mobility of polymers and increased Tg. The results instigate promising trends for commercial exploitation of this composite for bio-battery production.

Effects of Ag, ZnO and TiO2 nanoparticles at low contents on the crystallization, semicrystalline morphology, interfacial phenomena and segmental dynamics of PLA

Polymer nanocomposites, PNCs, based on polylactide (PLA, molar mass 75 kg/mol) reinforced with metal and metal oxide nanoparticles, commercial silver (Ag, ∼10 nm in size), zinc oxide (ZnO, <10 nm) and titania (TiO2, 3−5 nm), at small fractions (0.5, 1 and 2.5 wt%), are comparatively studied here. The main scope is the evaluation of the direct and indirect effects of the fillers on the in general slow crystallization rate of PLA, the latter being wanted in processing of this widely used renewable polymer. In addition, we explore the impact of the polymer-filler interactions on polymer mobility in connection to crystallizability. The following sum of complementary techniques are employed, attenuated total reflection Fourier transform infra red spectroscopy, X-ray diffraction (XRD) spectroscopy, differential scanning calorimetry (DSC), polarized optical microscopy (POM) and dielectric relaxation spectroscopy (DRS). Opposite to most cases of PLA-based PNCs, the fillers do not act as nuclei here and their role is indirect. The polymer seems to interact with the fillers resulting in the formation of an interfacial rigid amorphous fraction. Due to the presence of fillers surrounded by bound PLA, there seems to be an acceleration of the bulk-like chains diffusion (Tg slightly drops), most probably due to free volume increase. Subsequently, the easier chains diffusion leads free volume holes (defects) toward the polymer/nanoparticle interfaces, based on previously proposed model [Polymer 53 (2012) 1362–1372]. This leads to, in general, faster hot crystallization rate and thicker crystal lamellae (XRD). In the PNCs, quite larger however fewer spherulites formed in the PNCs as monitored by POM. DRS enabled the recording of segmental dynamics, which exhibits faster time scale and weakly improved cooperativity. Next to that, an additional molecular dynamics process was revealed to possibly arise from the polymer located around the nanoparticles. Finally, the overall data demonstrate the possibility to tune semicrystalline morphology and, indirectly, the mechanical performance and the diffusion of small molecules over the PNC volume, which is wanted in both applications and processing.

Effects of Expandable Graphite at Moderate and Heavy Loadings on the Thermal and Electrical Conductivity of Amorphous Polystyrene and Semicrystalline High-Density Polyethylene

In this work, we prepared and investigated two series of polymer composites, wherein the matrix was either an amorphous polystyrene (PS) or a semicrystalline high-density polyethylene (HDPE) filled with expandable graphite (EGr) at relatively high loadings within the range 5–55 wt %. For the investigation we employed a thermogravimetric analysis and differential scanning calorimetry to assess the thermal transitions and evaluate the various polymer fractions (crystalline (CF), mobile (MAF) and rigid amorphous (RAF)) in addition to broadband dielectric spectroscopy and a laser flash analysis to evaluate the EGr effects on electrical conductivity, σ, and thermal conductivity, λ, respectively. In PS, EGr was found to impose an increase of the glass transition temperature and a systematic decrease of the corresponding heat capacity change. The latter was rationalized in terms of the formation of an interfacial RAF. No glass transition was recorded for HDPE whereas the fillers increased the CF moderately. As expected, σ increased with the filler loading for both matrices, up to 10−3–10−2 S/cm, resulting in a conductive percolation threshold for electrons at &gt; 8 wt % EGr. Simultaneously, the λ of PS and HDPE were strongly increased, from 0.13 and 0.38 W·K–1·m–1 up to 0.55 and ~2 W·K–1·m–1, respectively. λ demonstrated an almost linear EGr loading dependence whereas the semicrystalline composites exhibited a systematically higher λ.

Electrically Conductive Coordination Polymers for Electronic and Optoelectronic Device Applications.

Electrically conductive coordination polymers (generally known as metal-organic frameworks, MOFs) are a class of crystalline hybrid materials produced by the reasonable self-assembly of metal nodes and organic linkers. The unique and intriguing combination of inorganic and organic components endows coordination polymers with superior optical and electrical properties, which have recently aroused much attention in several electronic and optoelectronic technological applications. However, there are many challenging obstacles and issues that need to be addressed in this burgeoning field. In this Perspective, we first provide a fundamental understanding about the electronic design strategies that provide better guidance for realizing high conductivities and good mobilities in coordination polymers. We then examine the current established synthetic approaches to construct high-quality working samples of electrically conductive coordination polymers for device integration. This is followed by a discussion of the current state-of-the-art progress toward the preliminary achievements in (opto)electronic devices spanning chemiresistive sensors, field-effect transistors, organic photovoltaics, photodetectors, etc. Finally, we conclude this Perspective with the existing hurdles and limitations in this area, along with the critical directions and opportunities for future research.

A Monte Carlo simulation of water + oil + ABA triblock copolymer ternary system II. Rheology under shear flow field by Monte Carlo Brownian Dynamics method

A water/oil/amphiphilic polymer ternary system is analyzed by Monte Carlo (MC) method using a lattice model to determine the thermal equilibrium distribution by changing the component ratio. Particularly the rheological properties such as shear stress and viscosity are evaluated via Monte Carlo Brownian Dynamics (MCBD) simulation, in which the flexibility of polymer movement is considered by the bond fluctuation model and the shear force is expressed by the Kramers potential. Our analysis on the micelle pattern for each concentration ratio shows that, the increase of polymer concentration decreases the solute (water, polymer) mobility, and exponentially increases the viscosity. These results in our simulation reflect general phenomena in concentrated colloid system. By assuming that the polymer orientation dominates the stress of system by the elasticity between polymer bonds, we newly find that from the polymer placement under the shear field, the shear stress itself exponentially increases while raising the concentration. Even in the category of lattice model, our study indicates the possibility of acquiring new knowledge on Dynamics by using a polymer model with specific consideration on flexible mobility and MCBD method.

On the Mutual Relationships between Molecular Probe Mobility and Free Volume and Polymer Dynamics in Organic Glass Formers: cis-1,4-poly(isoprene).

We report on the reorientation dynamics of small spin probe 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO) in cis-1,4-poly(isoprene) (cis-1,4-PIP10k) from electron spin resonance (ESR) and the free volume of cis-1,4-PIP10k from positron annihilation lifetime spectroscopy (PALS) in relation to the high-frequency relaxations of cis-1,4-PIP10k using light scattering (LS) as well as to the slow and fast processes from broadband dielectric spectroscopy (BDS) and neutron scattering (NS). The hyperfine coupling constant, 2Azz′(T), and the correlation times, τc(T), of cis-1,4-PIP10k/TEMPO system as a function of temperature exhibit several regions of the distinct spin probe TEMPO dynamics over a wide temperature range from 100 K up to 350 K. The characteristic ESR temperatures of changes in the spin probe dynamics in cis-1,4-PIP10k/TEMPO system are closely related to the characteristic PALS ones reflecting changes in the free volume expansion from PALS measurement. Finally, the time scales of the slow and fast dynamics of TEMPO in cis-1,4-PIP10k are compared with all of the six known slow and fast relaxation modes from BDS, LS and NS techniques with the aim to discuss the controlling factors of the spin probe reorientation mobility in polymer, oligomer and small molecular organic glass-formers.

Cellulose nanocomposite modified conductive self-healing hydrogel with enhanced mechanical property

Synthetic conductive materials capable of self-healing have attracted increasing attention and have been developing rapidly because of their potential applications. Despite great achievements, there is a need to advance mechanical properties and reduce the time for healing simultaneously since the branch functionalities are limited and the polymer mobilities are poor in current devices. In this work, we report an effective and simple free radical polymerization approach to synthesize hydrogel using multi-vinyl-modified reduced graphene oxide (rGO) and acrylate monomers containing abundant polar groups. After enhanced by polar groups modified Cellulose Nanocrystal (CNC), the hydrogel exhibits extremely fast electronic self-healing ability and excellent repeatable restoration performance at 25 °C. The stress of hydrogel reaches 2.5 MPa and 1600% of elongation. The hydrogel recovers to its original mechanical and conductive properties within 12 s after cutting and maintains efficiency of nearly 99.3% of its original mechanical and conductive properties after 5 times of cutting and self-healing processes. The design of this conductive, room-temperature self-healing hydrogel takes unique advantage of supramolecular chemistry and polymer nanoscience and shed light on promising applications for self-healing electronics, artificial skins, soft robotics, biomimetic prostheses, and energy storage.