Glass Transition Behavior Research Articles

Synthesis of well-defined di- and triblock acrylic copolymers consisting of hard poly(dicyclopentanyl acrylate) and soft poly(alkyl acrylate) segments by organocatalyzed group transfer polymerization and their glass transition behavior

Well-defined acrylic block copolymers with hard poly(dicyclopentanyl acrylate) and soft poly(n-alkylacrylate) blocks prepared by GTP are observed to undergo microphase separation by rheometry except for the crystallizable poly(n-dodecyl acrylate) series.

Mmolecular dynamics study of glass transition and nonlinear mechanical behavior of poly(methyl methacrylate)/carbon nanotubes nanocomposites

The glass transition temperature and nonlinear mechanics of polymer nanocomposites are strongly influenced by the short fibers. In this paper, coarse-grained molecular dynamics simulations are used to study the effects of single-walled carbon nanotube (CNT) content on the glass transition, diffusion coefficient, viscosity and nonlinear mechanical properties of poly(methyl methacrylate) (PMMA)/CNT nanocomposites. The glass transition temperature <i>T</i><sub>g</sub> is very important for the application of the materials. The <i>T</i><sub>g</sub> is related to the specific volume of the system. Generally, the location of the discontinuity on the curve of specific volume vs. temperature is the position of <i>T</i><sub>g</sub><i>.</i> Our simulation results show that the <i>T</i><sub>g</sub> of PMMA/CNT composite increases with CNT content, and the result is consistent with the experimental value (434 K). This increase of <i>T</i><sub>g</sub> is evidently due to the presence of CNTs, which imposes a limit on the mobility of the molecules of PMMA. For the free volume in the liquid state, recent experiments pointed out that the molecular mutation is relatively easy to occur because the unoccupied volume is large. Further analysis of the diffusion coefficient of the PMMA/CNT indicates that the difference in diffusion characteristic occurs above the glass transition temperature, and the diffusion coefficient of PMMA system and PMMA/CNT system are the same below the glass transition temperature. Polymer materials in the service process will inevitably suffer the deformation, and the modulus and toughness of material are inversely proportional. Based on this problem, the nonlinear mechanical properties of short CNTs added PMMA composite are studied by nonequilibrium molecular dynamics. Our results show that the yield modulus increases with the CNT content increasing. However, the toughness is almost unchanged. In order to further understand the origin of stress of PMMA/CNT nanocomposites, the stretch ratio and orientation parameters of MPPA chains are also investigated in the present work. According to the stretch ratio and orientation parameters, it is not difficult to conclude that the stress-strain curve is mainly the result of the synergistic effect of molecular chain stretching and orientation. This work provides a theoretical guidance for further experiments and processing at the atomic and molecular level.

Thermal properties and cold crystallization kinetics of deep eutectic solvents confined in nanopores.

Herein, the phase behaviors of both bulk and confined deep eutectic solvents in controlled pore glasses were first investigated. Glass transition, cold crystallization and melting behaviors alter significantly in the nanopores due to the size effect and interfacial interactions. Kinetic analysis of the crystallization reveals increased effective activation energies and pre-exponential factors under nanoconfinement.

Glass transition of ion-containing polymer melts in bulk and thin films.

Ion-containing polymers often are good glass formers, and the glass transition temperature is an important parameter to consider for practical applications, which prescribes the working temperature range for different mechanical and dynamic properties. In this work, we present a systematic molecular dynamics simulation study on the coupling of ionic correlations with the glass transition, based on a generic coarse-grained model of ionic polymers. The variation of the glass transition temperature is examined concerning the influence of the electrostatic interaction strength, charge fraction, and charge sequence. The interplay with the film thickness effect is also discussed. Our results reveal a few typical features about the glass transition process that are in qualitative agreement with previous studies, further highlighting the effects of counterion entropy at weak ionic correlations and physical crosslinking of ionic aggregates at strong ionic correlations. Detailed parametric dependencies are displayed, which demonstrate that introducing strong ionic correlations promotes vitrification while adopting a precise charge sequence and applying strong confinement with weak surface affinity reduce the glass transition temperature. Overall, our investigation provides an improved picture towards a comprehensive understanding of the glass transition in ion-containing polymeric systems from a molecular simulation perspective.

Mechanical reinforcement with enhanced electrical and heat conduction of epoxy resin by polyaniline and graphene nanoplatelets

Abstract In this study, the effects of polyaniline (PANI) incorporation (3 wt% of PANI) and graphene nanoplatelets (GNPs) loading (0.1–0.7 wt%) on the mechanical, thermal, and electrical performance of epoxy matrix were investigated. The incorporation of 0.3 wt% GNPs optimally enhanced the bending strength, bending modulus, tensile strength, tensile modulus, and impact strength (90 MPa, 1422 MPa, 63 MPa, 602 MPa, and 8.29 kJm−2, respectively). At 0.3 wt% GNPs, the hybridization effect optimally enhanced the glass transition behaviour of the epoxy nanocomposites. The electrical and thermal conductivities of epoxy were improved upon the inclusion of PANI, and this increase was further augmented when the GNPs content increased to 0.3 wt%. However, higher GNPs contents deteriorated the mechanical performance and electrical and heat conduction. Field emission scanning electron microscopy showed good filler distribution and effective interactions among the GNPs, PANI, and epoxy components with appropriate compositions.

Compression Effects on Structural Relaxation Process of Amorphous Indomethacin

Indomethacin is a common nonsteroidal anti-inflammatory drug, but its glass transition behaviors remain ambiguous. Here we present a simple theoretical approach to investigate the molecular mobility of amorphous indomethacin under compression. In our model, the relaxation of a particle is governed by its nearest-neighbor interactions and long-range cooperative effects of fluid surroundings. On that basis, the temperature and pressure dependence of the structural relaxation time is deduced from the thermal expansion process. Additionally, we also consider correlations between the activated dynamics and the shear response in the deeply supercooled state. Our numerical calculations agree quantitatively well with previous experimental works.

Probing the dynamical behavior in glass transition of PVPh-PEO blend

In this work, the dynamic behavior of glass transition in a miscible blend of Poly (vinyl phenol) (PVPh)/ Poly (ethylene oxide) (PEO) with a mass ratio of 3:1 (PVPh/PEO 75/25) were studied within a joint way of experimental and theoretical methods. The results showed the evidence for the influence of hydrogen bonding (HB) and Van der Waals (VdW) interaction between PVPh and PEO on the dynamic behavior in glass transition. The results reported here allows the opportunities for finding new blend dependent on this kind of interaction or design of special polymers to enhance such interactions.

The effects of different dopant on the optical parameters for selenium tellurium thin films

Glasses of (Se90Te10)95M5 (where M = Zn and Bi) were prepared using a melt–quench procedure. These incorporated elements were chosen as examples of transition metals and basic metal groups, respectively. Thin films of these glasses at a thickness of 100 nm were evaporated onto cleaned glass substrates. Structural investigations were studied using XRD, SEM, and DSC. The glass transition, Tg, and Onset crystallization behavior of glasses, Tc of (Se90Te10)95M5 (M = Zn and Bi) alloys were analyzed using DSC at a heating rate of 15 K min−1. XRD patterns confirmed the amorphous nature of the films. The absorption coefficient, α, and refractive index, n, were obtained for (Se90Te10)95M5 (M = Zn and Bi) films. The Eg values of Se90Te10 increase as dopant by Zn. Conversely, it decreases as dopant by Bi. Moreover, the optical constants of (Se90Te10)95M5 (M = Zn and Bi) films were estimated. The estimated results confirm the applicability of modifying samples to be used using in optoelectronics applications.

Synthesis and Swelling Behavior of Highly Porous Epoxy Polymers.

Many advantageous properties of cross-linked polymers relate to their network structures. In this study, network structures of three DGEBA-based epoxy systems at various DGEBA monomer sizes were investigated via equilibrium swelling and glass transition behavior. Each system was cured with a tetra-functional diamine, 4,4′-methylenebiscyclohexanamine, in the presence of a nonreactive solvent, i.e., THF at a solvent-to-monomer volume fraction ranging from 0 to 92%. Experimental results revealed that the conventional swelling model (the Dušek model) accurately calculates Mc values of the cured gels prepared in moderate dilute environments, up to approximately 60% by volume of THF. For gels cured in extreme dilute environments, i.e., in the presence of above 60% by volume of THF, the calculated Mc values using the Dušek model were found to increase sharply as a function of the initial solvent content. The observed dramatic increase in Mc values was not supported by the dry Tg of the identical polymer systems. In fact, the dry Tg values of the polymer systems were found to be relatively insensitive to the initial solvent content. A modification was proposed to the Dušek model that incorporates an additional term, which accounts for the probability of finding elastic chains in a polymer network. Using the modified equation, Mc values were varied as expected with the molecular weight of DGEBA and insensitive to the amount of the solvent initially used during cure. Furthermore, the modified Mc values were shown to be consistent with the dry Tg values in view of the Fox and Loshaek model.

(Invited) Partially Fluorinated Anion Exchange Membranes for Electrochemical Applications

There has been a considerable effort to develop high performance and durable anion exchange membranes (AEMs) for the electrochemical applications such as fuel cells, electrolyzers, and redox flow batteries. When these devices are operated under alkaline conditions, possible use of non-precious metal catalysts is advantageous. Although a number of AEMs have been proposed in the literature, chemical and mechanical stability in alkaline media still remains an issue for long-term, reliable operation of the devices. In the pursuit of more stable AEMs, we have recently reported some new polymer structures. Combination of absence of heteroatom linkages such as ether, sulfide, and sulfone in the main chain and employing pendant ammonium groups contributed to improvement of the alkaline and mechanical stability of AEMs. A typical example is QPAF-4 copolymers composed of perfluoroalkylene/phenylene main chain and hexylammonium head groups, which exhibited high hydroxide ion conductivity and alkaline stability.1 In the present paper, we report effect of other fluorinated components for our AEMs. We have developed a novel series of quaternized aromatic copolymers (BAF-QAFs) containing hexafluoroisopropylidene groups.2 Similar to QPAF-4 copolymer membranes, BAF-QAF copolymers had good solubility in polar organic solvents, membrane forming capability, and phase-separated morphology. Hexafluoroisopropylidene groups contributed to efficient anion transport as BAF-QAF membranes showed lower water uptake and higher hydroxide ion conductivity than those of QPAF-4 membranes. BAF-QAF membranes were thermally stable up to 95 °C and 90% RH with no obvious glass transition behavior in DMA analyses, while the elongation of BAF-QAF membranes were smaller than that of QPAF-4 membranes. BAF-QAF membranes were alkaline stable in 1 and 4 M KOH at 80 °C for 1000 h. A hydrogen/oxygen fuel cell with the BAF-QAF as a membrane and an electrode binder was successfully operated. The maximum power density reached 319 mW/cm2 at a current density of 702 mAcm2 with O2. The fuel cell with BAF-QAF copolymers were better in cathode performance than QPAF-4 cell most probably because of the higher hydroxide ion conductivity and better interfacial contact between the membrane and the catalyst layer. Acknowledgements This project was partly supported by NEDO through the Advanced Research Program for Energy and Environmental Technologies, JST through SICORP project, and JSPS/SNSF under the Joint Research Projects (JRPs) program. References Ono, T. Kimura, A. Takano, K. Asazawa, J. Miyake, J. Inukai, K. Miyatake, J. Mater. Chem. A, 5, 24804 (2017).Kimura, A. Matsumoto, J. Inukai, K. Miyatake, ACS Appl. Energy Mater., 3, 469-477 (2020). Figure 1

Molecular dynamics analysis of oxidative aging effects on thermodynamic and interfacial bonding properties of asphalt mixtures

Understanding the mechanisms of asphalt aging and aging related properties is of significant importance. In this paper, molecular dynamics (MD) simulation was employed to study the effects of asphalt oxidative aging on the thermodynamic and interfacial bonding properties of asphalt mixtures. The virgin and aged AAA-1 asphalt models, validated based on physicochemical properties, were constructed in this study. The glass transition behaviors of asphalt models were investigated by simulating a gradual cooling process. It is found that asphalt oxidative aging increases the intermolecular interaction, thus resulting in a higher glass transition temperature. Restrictions of dihedral torsion and non-bond interaction at a low temperature are primary reasons causing the glass transition behavior. The volumetric property, fractional free volume (FFV) among asphalt molecules was studied with an empirical calculation method. The results show that the FFV-temperature behavior for both virgin and aged asphalt models exhibits a glass transition phenomenon akin to the specific volume-temperature relationship. In addition, the asphalt diffusion behavior before and after oxidative aging was evaluated by their mean square displacements (MSD). The result indicates that oxidative aging causes a reduction of free volume, and thereby slows down asphalt molecular diffusion. Finally, the adhesion behavior and moisture susceptibility considering asphalt aging effects were investigated to provide a better understanding of the mechanism of asphalt oxidative aging and aging related phenomena.

Study on incorporating wattle tannin in polyvinyl acetate emulsion and its effect on properties for wood bonding application

Polyvinyl acetate emulsion (PVAc) is an essential class of adhesives for woodworking applications. However, it suffers from low water resistance. In the present research, wattle tannin was incorporated in synthesised PVAc emulsion at ratios ranging from 0 to 6 wt.% in PVAc emulsion. The study was carried out in two parts. The first part focuses on understanding the effect of the presence of tannin in PVAc emulsion on its adhesive performance. The second part deals with the study of the variation in adhesive properties of tannin PVAc emulsion adhesive by introducing isocyanate crosslinker in the system. DMA was employed to understand the glass transition and rheology behaviour. FTIR was used to assess the reaction of tannin with isocyanate crosslinker. Contact angle measurement was measured using goniometry to understand the surface wettability achieved by incorporating tannin in the PVAc emulsion system. Detail study on adhesive strength was carried out by bonding wood substrates followed by measuring bonding strength in wet conditions as per BS EN 204 and heat resistance as per DIN EN 14257 (WATT 91). The presence of tannin in the system enhances water and heat resistance property which gets further improved in the presence of isocyanate crosslinkers. The observed effect is due to better wetting of substrate by adhesive, hydrogen bonding between tannin and components in adhesive, and dense crosslinking formed by the reaction of isocyanate crosslinker.

Full-composition-range glass transition behavior of the polymer/solvent system poly (lactic acid) / ethyl butylacetylaminopropionate (PLA/IR3535®)

The polymer/solvent system poly (lactic acid)/ethyl butylacetylaminopropionate (PLA/IR3535®) is considered as a drug-delivery system, in which a polymer hosts a liquid with a functionality as insect repellent. Such devices require solubility of the components at high temperature and observation of crystallization-induced solid-liquid phase separation on cooling. Precise knowledge of the thermodynamic solubility of the components is then difficult to obtain due to possible superposition of liquid-liquid phase separation with polymer crystallization. Therefore, in the present study the miscibility of the polymer/solvent system PLA/IR3535® was explored by employing non-crystallizable PLA, by analysis of the glass transition behavior in the full composition range. The data revealed that the two components are miscible regardless the system composition, with the glass transition temperature of solutions showing a negative deviation from the linear mixing rule, suggesting rather weak enthalpic interactions of the system components. The study included application of conventional and fast scanning chip calorimetry, which allowed for controlled and stepwise evaporation of solvent by repeated exposing the system to elevated temperature and evaluation of the glass transition temperature during in-between cooling and reheating. This novel approach permits an efficient analysis of the glass transition temperature as function of the system composition in a single experiment in a wide range of solvent concentrations.

Dynamic coordination of miscible polymer blends towards highly designable shape memory effect

Miscible polymer blends offer great designability on shape memory effect (SME) with adjustable mechanical properties and stimuli-responsiveness, by simply changing the constituent compositions. However, the thermodynamics understanding behind those SMEs on miscible polymer blends are yet to be explored. This paper describes an approach to achieve highly designable SMEs with adjustable glass transition temperature (Tg) and width of glass transition zone by dynamically coordinating components in miscible blends. An extended domain size model was formulated based on the Adam-Gibbs theory and Gaussian distribution theory to study the synergistic coordination of component heterogeneities on conformational entropy, glass transition and relaxation behavior of the miscible blend. The effectiveness of model was demonstrated by applying it to predict dual- and triple-SMEs in miscible polymer blends, where the theoretical results show good agreements with the experiment results. We expect this study provide an effective guidance on designing advanced miscible polymer blends based on the SME.

Phosphonium‐based polythiophene conjugated polyelectrolytes with different surfactant counterions: thermal properties, self‐assembly and photovoltaic performances

AbstractPhosphonium‐based polythiophene conjugated polyelectrolytes (CPEs) with three different counterions (dodecylsulfate, octylsulfate and perfluorooctane sulfonate) are synthesized to determine how the nature of the counterion affects the thermal properties, the self‐assembly in thin films and the performance as the cathode interfacial layer in polymer solar cells (PSCs). The counterion has a significant effect on the thermal properties of the CPEs, affecting both their glass transition and crystalline behaviour. Grazing‐incidence wide‐angle X‐ray scattering studies also indicate that changing the nature of the counterion influences the microstructural organization in thin films (face‐on versus edge‐on orientation). The affinity of the CPEs with the underlying photoactive layer in PSCs is highly correlated with the counterion species. Finally, in addition to an increase of the power conversion efficiency of ca 15% when using these CPEs as cathode interfacial layers in PSCs, a higher device stability is noted, compared to a reference device with a calcium interlayer. © 2020 Society of Industrial Chemistry

Role of Interface Structure and Chain Dynamics on the Diverging Glass Transition Behavior of SSBR-SiO2-PIL Elastomers.

Intermolecular interactions between the constituents of a polymer nanocomposite at the polymer–particle interface strongly affect the segmental mobility of polymer chains, correlated with their glass transition behavior, and are responsible for the improved dynamical viscoelastic properties. In this work, we emphasized on the evolution of characteristic interfaces and their dynamics in silica (SiO2 NP)-reinforced, solution-polymerized, styrene butadiene rubber (SSBR) composites, whose relative prevalence varied with the phosphonium ionic liquid (PIL) volume fraction, used as an interfacial modifier. The molecular origins of such interfaces were examined through systematic dielectric spectroscopy, molecular dynamics (MD) simulations, and dynamic-mechanical analyses. The PIL facilitated H-bonding, cation−π, surface–phenyl, and van der Waals interfacial interactions between SSBR and SiO2 NP, thereby regulating the polymer chain dynamics, orientation, and mean-square displacement. Specifically, the mass density profiles from MD simulations revealed the dynamic gradient of polymer chains in the interfacial region as a function of radial distance from the center of mass of the SiO2 NP surface. The results showed a structuring effect to result in well-resolved density peaks at specific radial distances with the tangential orientation of styrene monomers in the vicinity of the SiO2 NP surface. These domino effects highlighted strong interfacial interactions to have an indispensable effect on the viscoelastic performance and thermal motion of SSBR molecular chains, leading to a higher glass transition temperature (Tg) by ∼15 K, validating the experimental data. More importantly, our results gave new insights into the fundamental understanding of the fact that the strength of intermolecular interactions induced by PIL at the polymer–particle interface is the key to control the α-relaxation dynamics and Tg optimization, desired for specific applications.

The rejuvenation and relaxation around the glass transition of a Ce-based metallic glass controlled by annealing, quenching and cryogenic treatments

Ce69Al10Cu20Co1 bulk metallic glass (BMG) samples were annealed at different temperatures ranging from sub-Tg to super-Tg. Some of the samples were cooled to room temperature in air to obtain the relaxed ones, while the others were directly quenched in liquid nitrogen. Then the quenched samples were either withdrawn directly from the liquid nitrogen or subjected to cryogenic treatments (CTs) for different time intervals. The glass transition behaviors and heat flow of the samples in different states, including the as-cast, relaxed, quenched and Quenching+CT states, were investigated by using the differential scanning calorimeter (DSC). The work aims to study the tendency of the rejuvenation and relaxation behaviors of MG around the glass transition that were caused by the annealing, quenching and subsequent cryogenic treatments. The results show that the annealing temperature, cooling rate and cryogenic time play key roles in the rejuvenation and relaxation of MG around the glass transition.

Fluoride ion field emission from a ZBLAC glass emitter

F− ion conducting 60ZrF4·30BaF2·LaF3·2AlF3·7CsF (mol%) with outer mol% of xIn2O3 (x = 0, 5, 10) glasses were prepared using a conventional melting method, and structure and glass transition behavior were investigated using X-ray diffraction (XRD), differential scanning calorimetry (DSC) and Raman spectroscopy. Impedance measurement reveals the glass with x = 10 shows F− ion conductivity of 5 × 10−6 S/cm at 200 °C. F− ion emission measurement was carried out for the first time using a sharpened glass tip, and the emission current was observed above the acceleration voltage of 2.5 kV at 200 °C and 1 × 10−4 Pa. After the F− emission measurement, fluorine was detected on a Cu target substrate by using an energy-dispersive X-ray spectrometer. However, a small amount of glass component was also detected on the target substrate, suggesting the glass tip may also decompose. A good linear correlation is obtained between log(current) and the square root of the voltage, suggesting the emission current of F− ion from the tip of glass is expressed by Schottky model.

Volatile Organic Compound Sensing Properties of Parylene E: Thermal Transition and Sorption Kinetics

The material properties of parylene E from chemical vapor deposition (CVD) have been characterized in the pursuit of gas sensing applications. First, the glass transition behavior and viscoelastic ...

Cryo-Transferred Ultrathin and Stretchable Epidermal Electrodes.

A simple cryo-transfer method to fabricate ultrathin, stretchable, and conformal epidermal electrodes based on a combination of silver nanowires (AgNWs) network and elastomeric polymers is developed. This method can temporarily enable the soft elastomers with much higher elastic modulus and dimensional contraction through exploiting their glass-transition behaviors. During this process, a much higher Von Mises stress can be loaded on AgNWs than usual, and the generated strong grip force can facilitate the complete transfer of AgNWs. Afterward, the thawed AgNWs and elastomer composites quickly recover to their soft state at room temperature. The obtained ultrathin and soft electrode with a thickness of 8.4 µm and transmittance of 90.8% at a sheet resistance of 13.2 Ω sq-1 can tolerate a stretching strain of 70% and 50 000 repeated bending cycles, which meets rigorous requirements of epidermal applications. The as-prepared epidermal electrodes are effective and comfortable for electrophysiological signal monitoring, and while showing excellent performance exceeding the commercialized gel electrodes.