Glass Transition Temperature Measurements Research Articles

Correlating Ionic Conductivity to Structure and Dynamics of Li-Ion Battery Electrolyte Systems: Raman Spectroscopy, Dielectric Relaxation Measurements, and Streak Camera Solvation Data Analysis.

A correlation between ionic conductivity and electrolyte solution structure and dynamics was explored by performing electrolyte concentration- and temperature-dependent measurements of conductivity, viscosity, and dielectric relaxation (DR) in solutions of lithium bis(trifluoromethane)sulfonimide (LiTFSI) in triethylene glycol dimethyl ether (also known as triglyme, G3). In addition, an electrolyte concentration-dependent Raman spectroscopic study and ultrafast dynamic fluorescence Stokes shift measurements of solvation of a dissolved solute by employing a streak camera detection technique were carried out. Measured conductivities (σ) and the average DR times (⟨τDR⟩) were found to be partially decoupled from the solution viscosities (η) and obeyed the relation, σ or ⟨τDR⟩-1 ∝(η/T)-p, with p = 0.6-0.75 for σ and p = 0.2-0.45 for ⟨τDR⟩-1. Raman data indicated the formation of ion pairs and ionic aggregates in these solutions, while the measured glass transition temperature increased with LiTFSI concentration. Conductivities (σ) showed a nonlinear concentration dependence but increased linearly with the solution static dielectric constants (εs). The latter may be explained by considering the temperature effects on complex electrolyte species and the subsequent solution dielectric behavior. Interestingly, an inverse power-law dependence of σ on the measured DR or solvation time scales, σ ∝ (τx)-m, with m = 1.2-1.9, was observed. This dependence may be explained by considering that the same environmental friction regulates both the ion diffusion and the medium polarization relaxation. The control of a slow process (ion translation) by relatively faster medium dynamics (dipolar rotation), although quite fascinating for the present system, warrants further experimental scrutiny for other electrolyte systems relevant to battery applications.

Physicochemical Characterization and In Vitro Activity of Poly(ε-Caprolactone)/Mycophenolic Acid Amorphous Solid Dispersions.

The obtention of amorphous solid dispersions (ASDs) of mycophenolic acid (MPA) in poly(ε-caprolactone) (PCL) is reported in this paper. An improvement in the bioavailability of the drug is possible thanks to the favorable specific interactions occurring in this system. Differential scanning calorimetry (DSC) was used to investigate the miscibility of PCL/MPA blends, measuring glass transition temperature (Tg) and analyzing melting point depression to obtain a negative interaction parameter, which indicates the development of favorable inter-association interactions. Fourier transform infrared spectroscopy (FTIR) was used to analyze the specific interaction occurring in the blends. Drug release measurements showed that at least 70% of the drug was released by the third day in vitro in all compositions. Finally, preliminary in vitro cell culture experiments showed a decreased number of cancerous cells over the scaffolds containing MPA, presumably arising from the anti-cancer activity attributable to MPA.

Development and characterization of co-amorphous griseofulvin/L-leucin by modified solvent processing hot-melt extrusion

Co-amorphous systems (CAMS) were developed between griseofulvin (GRI) and L-leucine (LEU) at 2:1 wt ratio, by application of a novel solvent assisted hot-melt extrusion (HME) method that involved wet processing/drying of the feeds prior to extrusion. CAMS formation was confirmed by powder crystallography (pXRD) and thermal analysis (DSC). Intermolecular H-bonding between the carbonyl groups of GRI and the hydroxyl and amino groups of LEU were identified by vibrational spectroscopy (ATR-FTIR). The measured glass transition temperatures (Tg) of the extrudates from feeds processed with aqueous acetic acid (AcOH) were markedly lower than that of neat amorphous GRI and values predicted from Gordon-Taylor equation, indicating plasticizing action of AcOH. Drug concentrations during dissolution of CAMS under non-sink conditions (Sink Index 0.0115) were up to x82 higher at plateau compared to crystalline drug solubility. The degree of supersaturation lasted for at least 24 h. Plasticizer (Compritol®/Kolliphor® 75/25) added before extrusion did not impact significantly on CAMS formation but altered the dissolution profile from a spring-and-parachute profile to gradual rise to maximum. These findings reinforce the application of drug/amino acid-based CAMS in formulation, particularly for high-dose drugs, for which polymers are unsuited due to the required large proportions.

Influence of Epoxy Spray Binder on Infusion and Cure in Liquid Composite Molding Processes

Binders are known to influence the different steps in liquid composite molding process chains. Most reseach focuses on powder binder and veils. Spray binders are rarely studied. Therefore, the effect of an epoxy spray binder on the infusion and cure steps of liquid composite molding processes is studied in this paper. Permeability measurements, solubility tests and measurements of glass transition temperature, resin cure time and resin viscosity show a complex interaction between binder and resin depending on the process conditions. The binder mostly increased the permeability of the tested preforms. This effect increases with increasing binder loading. At low fiber volume fractions the binder had a positive effect on preform permeability, most likely by to delaying the closure of macro flow channels or textile inhomogeneity. The binder did not dissolve in the resin until temperatures of around 120 °C, while remaining as a separate phase at 22 °C, 40 and 80 °C. This has to be considered when defining the cure profile of the resin, as the binder is expected to participate in the cure reaction. The glass transition temperature remained unchanged for the binder-resin combination used. An increase in viscosity by a factor of 1.5-2 was observed when the binder was dissolved in the resin. Samples with dissolved binder cured slightly faster than pure resin. The experimental results were theoretically transferred to real infusion processes.

Measuring glass transition of a polymer coating layer over working fiber using forward Brillouin scattering.

The glass transition temperature is a key parameter of polymer coating layers that protect optical fibers, and it affects the proper function of the fibers in their service environment. Established protocols for glass transition temperature measurements are destructive, require samples of specific geometries, and may only be carried out offline. In this work, we report the nondestructive measurement of the glass transition temperature of an acrylate polymer coating layer over a working standard fiber. The method is based on forward stimulated Brillouin scattering. A large decrease in the modulus of the coating layer above the glass transition temperature manifests in the narrowing of the modal linewidths in the forward Brillouin scattering spectrum. The transition temperature agrees with the standard dynamic mechanical analysis of samples made of the same polymer. The protocol can be useful for coating materials research and development, production line quality assurance, and preventive maintenance.

Surface Pressure-Area Mechanics of Water-Spread Poly(ethylene glycol)-Based Block Copolymer Micelle Monolayers at the Air-Water Interface: Effect of Hydrophobic Block Chemistry.

Amphiphilic block copolymer micelles can mimic the ability of natural lung surfactant to reduce the air-water interfacial tension close to zero and prevent the Laplace pressure-induced alveolar collapse. In this work, we investigated the air-water interfacial behaviors of polymer micelles derived from eight different poly(ethylene glycol) (PEG)-based block copolymers having different hydrophobic block chemistries to elucidate the effect of the core block chemistry on the surface mechanics of the block copolymer micelles. Aqueous micelles of about 30 nm in hydrodynamic diameter were prepared from the PEG-based block copolymers via equilibration-nanoprecipitation (ENP) and spread on the water surface using water as the spreading medium. Surface pressure-area isotherm and quantitative Brewster angle microscopy (QBAM) measurements were performed to investigate how the micelle/monolayer structures change during lateral compression of the monolayer; widely varying structural behaviors were observed, including the wrinkling/collapse of micelle monolayers and deformation and/or the desorption of individual micelles. By bivariate correlation regression analysis of surface pressure-area isotherm data, it was found that the rigidity and hydrophobicity of the hydrophobic core domain, which are quantified by glass-transition temperature (Tg) and water contact angle (θ) measurements, respectively, are coupled factors that need to be taken into account concurrently in order to control the surface mechanical properties of polymer micelle monolayers; micelles having rigid and strongly hydrophobic cores exhibited high surface pressure and a high compressibility modulus under high compression. High surface pressure and a high compressibility modulus were also found to be correlated with the formation of wrinkles in the micelle monolayer (visualized by Brewster angle microscopy (BAM)). From this study, we conclude that polymer micelles based on hydrophobic block materials having higher Tg and θ are more suitable for surfactant replacement therapy applications that require the therapeutic surfactant to produce a high surface pressure and modulus at the alveolar air-water interface.

Machine-Learning-Enabled Framework in Engineering Plastics Discovery: A Case Study of Designing Polyimides with Desired Glass-Transition Temperature.

Great and continuous efforts have been made to discover high-performance engineering plastics with specific properties to replace traditional engineering materials in many fields. The utilization of machine learning (ML) has brought more opportunities for the discovery of high-performing engineering plastics. However, hindered by either the relatively small database or a lack of accurate structure descriptors with clear physical and chemical meanings relating to polymer properties, the current ML studies show some flaws in the accuracy and efficiency in polymer development. Herein, we collected a dataset of 878 polyimides (PI), one of the best engineering plastics, with experimentally measured glass-transition temperature (Tg) values, and developed a rapid and accurate ML approach to design PI candidates with the desired Tg value. After the conversion from PI structures into "mechanically identifiable" SMILES (Simplified molecular input line entry system) language, the eight most critical descriptors were ultimately obtained by multiple analysis methods. The physiochemical meaning of the key descriptors was further analyzed carefully to translate the implicit "machine language" to chemical knowledge. The artificial neural network (ANN)-based model gave the most accurate results with a root-mean-square error of ∼11 K among the studied ML methods. More importantly, three potential PI candidates with desired Tg (DPIs) were designed according to the chemical insight of the key descriptors, which were then verified by experiments. The experimental and predicted Tg values of DPIs have an acceptable average deviation of ca. 3.66%. This accuracy has reached the level of the traditional molecular simulation, but the time consumption and hold-up computing resource are tremendously reduced. Furthermore, the current ML approach could offer a scalable and adaptable framework in future engineer plastics innovation.

Nonlinear creep characteristics of extruded Poly (vinylidene fluoride-co-hexafluoropropylene) with high ß-phase content under extreme conditions: Design, characterization, and modeling

This study is concerned with the nonlinear creep characteristics of extruded Poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) dominated by β-phase polymorphs over the temperature range 40 °C − 80 °C and tensile stress levels between 5 MPa and 12.5 MPa. The measured data using the developed experimental setup as well as the dynamic mechanical analyzer invariably suggested a nonlinearity taking place at temperatures near to 60 °C, where αc-relaxation began corresponding to 100 °C above the measured glass transition temperature of PVDF-HFP. The results from accelerated testing conditions indicated the transition to tertiary creep stage at 24% to 28% strain, irrespective of test condition, referred to as critical strain range. Following the identification of Findley power law model constant at different test conditions, a generalized temperature- and stress-dependent model was developed with only 7 constants. The comparisons between the measured and modeled data conveyed the model effectiveness in describing the nonlinear creep characteristics of the polymer over the measured temperature and stress levels. Time-temperature-compliance master curves were consequently constructed using the developed generalized model, which in combination with the critical strain failure criterion, provided the essential design data including the maximum allowable ranges of stress and temperature for achievement of 20 years creep life.

Cold tolerance and mechanical properties of thermoplastic polymer based composite for the marine cables operating in polar regions

Cold tolerance of a thermoplastic polymer largely depends on the type and content of about 20 or more additives used to make the polymer. Observing the change of dynamic viscoelasticity as a function of the temperature change through glass transition temperature measurement is a representative method for evaluating cold resistance. In this study, mechanical properties of composite materials prepared by mixing various types of thermoplastic polymers and various additive components were evaluated to improve their cold tolerance performances. The cold tolerance was improved by blending resin having an embrittlement temperature lower than the operating temperature.

Investigation of Ga2O3-BaO-GeO2 glasses for ultrafast laser inscription

From the perspective of developing robust mid-infrared (mid-IR) integrated photonic devices, barium-gallium-germanium (BGG) oxide glasses are strong candidates among other mid-IR glasses. Indeed, compared to fluoride, tellurite or chalcogenide glasses, BGG glasses present the highest thermal and chemical stabilities, while transmitting light up to 6 µm. In parallel to this, technological advances in ultrafast direct laser writing (UDLW)-based devices are driving the development of novel photonic glasses. Specifically, there is a need to identify the most efficient mid-infrared transmitting BGG glass compositions for sustaining the UDLW process. In this article, we thoroughly investigate the BGG physicochemical properties through absorption and Raman spectroscopies, refractive index, density, and glass transition temperature measurements in two relevant glass series: one via a Ga3+/Ge4+ ratio fixed to 1 and a barium content varying from 25 to 40 cationic percent, the other via a 2Ba2+/Ga3+ ratio fixed to 1 and a germanium content varying from 20 to 80 cationic percent. In the meantime, we explore the photosensitivity of these glasses under UDLW. Our findings reveal the valuable role of both barium and gallium ions, notably through their concentration, structural stabilization sites and viscosity influence. Finally, we demonstrate the fabrication of an 8.2 cm-long UDLW-induced waveguide with propagation losses of < 0.3 dB.cm-1 at 1550 nm.

Material characteristics of WO3/Bi2O3 substitution on the thermal, structural, and electrical properties of lithium calcium borate glasses

Glasses belonging to the xWO3-(30-x) Bi2O3–15Li2O–15CaO–40B2O3 (0 ≤ x ≤ 10) have been obtained by melt-quenching technique. With increasing the concentration of WO3, an increase in the measured glass transition temperature {T}_{mathrm{g}} and crystallization temperature {T}_{mathrm{c}} are observed, while the values of the thermal expansion coefficient decrease. Due to the unpaired pentavalent ions, the electron spin resonance spectra of glasses doped with {mathrm{WO}}_{3} them show unique signals. The results of Raman spectra show that the glass network is mainly constituted by [{mathrm{BiO}}_{6}], [{mathrm{BO}}_{3}], [{mathrm{BO}}_{4}], and [{mathrm{WO}}_{4}] basic structural units. The activation energies for all studied samples were observed to range from 0.02 to 0.08 eV, and the dielectric constant and the conductivities of the investigated glasses increased with increasing temperature. The electrical behavior of the prepared samples revealed their semiconducting character. The prepared samples are being investigated as potential semiconductor material candidates for use in electronic devices.

Release Enhancement by Plasticizer Inclusion for Amorphous Solid Dispersions Containing High Tg Drugs.

Plasticizers are commonly used in the preparation of amorphous solid dispersions (ASDs) with the main goal of aiding processability; however, to the best of our knowledge, the impact of plasticizers on drug release has not been explored. The goal of this study was to evaluate diverse plasticizers, including glycerol and citrate derivatives, as additives to increase the drug loading where good drug release could be achieved from copovidone (PVPVA)-based dispersions, focusing on high glass transition (Tg) drugs, atazanavir (ATZ) and ledipasvir (LED). ASDs were prepared using the high Tg compounds, atazanavir (ATZ) and ledipasvir (LED), as model drugs. Release was evaluated using surface normalized dissolution testing. Differential scanning calorimetry was used to measure glass transition temperature and water vapor sorption was performed on select samples. The presence of a plasticizer at 5% w/w for ATZ and 10% w/w for LED ASDs, led to improved drug release. For ATZ ASDs, in the absence of plasticizer, release was very poor at drug loadings of 10% w/w and above. Good release was obtained for plasticized ASDs up to a drug loading of 25%. The corresponding improvement for LED was from 5 to 20% DL. Interestingly, for a low Tg compound, ritonavir, relatively smaller improvements in release as a function of drug loading were achieved through plasticizer incorporation. The use of plasticizers represents a potential new strategy to increase drug loading in ASDs for high Tg compounds with a low tendency to crystallize and may help improve a major limitation of ASD formulations, namely the high excipient burden.

On the bridge hypothesis in the glass transition of freestanding polymer films.

Freestanding thin polymer films with high molecular weights exhibit an anomalous decrease in the glass-transition temperature with film thickness. Specifically, in such materials, the measured glass-transition temperature evolves in an affine way with the film thickness, with a slope that weakly depends on the molecular weight. De Gennes proposed a sliding mechanism as the hypothetical dominant relaxation process in these systems, where stress kinks could propagate in a reptation-like fashion through so-called bridges, i.e. from one free interface to the other along the backbones of polymer macromolecules. Here, by considering the exact statistics of finite-sized random walks within a confined box, we investigate in details the bridge hypothesis. We show that the sliding mechanism cannot reproduce the basic features appearing in the experiments, and we exhibit the fundamental reasons behind such a fact.

Polymer-Supported Aqueous Electrolytes for Lithium Ion Batteries: II. Conductivity Gain Upon Polymerization and Double Glass Transition in LiTFSI + H2O + PDA Gels

Polymerization via ultraviolet irradiation of LiTFSI21mH2O + PDA liquid mixtures turned most of these liquids into gels or solids. Here, LiTFSI21mH2O denotes a 21 m aqueous solution of lithium bis(trifluoromethanesulfonyl)imide, and PDA stands for a monomer of poly(ethylene glycol) diacrylate of Mn 575. Systematic thermoconductometric measurement on these electrolytes, both before and after the polymerization, showed the gel electrolytes to be considerably more conductive than their precursor liquid mixtures, especially at lower temperatures. A parallel measurement of glass transition temperature, θ g, revealed in these gel electrolytes a unique double glass transition enveloping two sub-transitions each with its own θ g’s. These and a number of other related experimental observations can be consistently and clearly explained based on the existence of a solution and a polymer substructure in the polymerized electrolytes, and on these substructures becoming codominant in the gels. The exceptional conductivity in these gel electrolytes points to a promising direction to formulating a polymer-supported aqueous electrolyte with a set of desirable physical traits and an uncompromising conductivity.

Synthesis and characterization of a computationally predicted redox and radiation stable deep eutectic solvent

• DFT calculations towards finding suitable HBD and HBA for the formation of redox and radiation stable DES. • Phase diagram to depict the molar ratio of the constituents in the new DES. • Stabilization energy calculation of the predicted new DES. • Experimental synthesis and characterization of the DES predicted from computational calculations. • Radiation stability study and by-product analysis of the as synthesized DES under gamma irradiation. A redox and radiation stable DES has been predicted based on the fundamental electronic properties such as energy gap, ionization potential and electron affinity computed applying suitable density functionals in combination with 6-311++G(d,p) set of atomic basis functions. A selected series of optimized hydrogen bond donors (HBDs) and hydrogen bond acceptors (HBAs) has been screened using density functional theory (DFT). The long range corrected density functionals; ωB97XD and LC-BLYP are found to be cost effective and appropriate towards orbital energy gap calculations of such systems. Choline acetate and malonic acid appeared to be the most appropriate combination among those studied for formation of a chemical and radiation stable DES. Theoretically constructed phase diagram using Gibbs free energy minimization technique is applied to suggest the eutectic point and eutectic composition of the recommended DES. Stabilization energy calculations following electronic structure support the phase diagram data denoting formation of a stable eutectic with 1:2 stoichiometry. Density, viscosity, differential scanning calorimetry (DSC) and Fourier transform infra-red (FTIR) experiments have been carried out with this synthesized DES. Measured glass transition temperature (−75 °C) is observed to be lower than the theoretical eutectic point (−40 °C) indicating strong interspecies interaction within the medium. Experimental FTIR analysis gives an idea of the type and number of H-bonds present within the DES whereas computationally optimized 1:2 geometry identifies the specific H-bonds along with their distances. Irradiation of this new DES has been conducted at a constant dose of 100 kGy to observe the extent of degradation. UV–Vis and FTIR analysis does not denote generation of any new species within the liquid phase upon irradiation, however the yields of the gaseous by-products have been quantified by Gas Chromatography (GC).

Glass Transition Temperature Measurement of Polycarbonate Specimen by Dynamic Mechanical Analyser Towards the Development of Reference Material

Glass Transition Temperature Measurement of Polycarbonate Specimen by Dynamic Mechanical Analyser Towards the Development of Reference Material

Materials characterization of FRP composite seismic retrofits after long-term service in a subarctic Alaskan environment

This study assesses physical and chemical properties of fiber reinforced polymer (FRP) composite materials aged in Alaska’s subarctic climate. Carbon FRP (CFRP) and glass FRP (GFRP) samples were collected in 2019 from the exterior and interior of Ted Stevens International Airport (TSIA, retrofitted in 2008) and McKinley Tower (MKT, retrofitted in 2004). Differential scanning calorimetry (DSC) was used to measure glass transition temperature (Tg) and physical aging, FTIR and Raman spectroscopy were used to investigate potential chemical degradation and degree of cure, and scanning electron microscopy (SEM) to evaluate cross-sectional microstructure, respectively. The results indicate that exposure to the subarctic climate had minimal effect on the composites’ Tg and chemical properties. The variability in fiber content at MKT and thermal properties at TSIA suggest there were likely some inconsistencies in the FRP installation that may affect load-carrying capacity. Furthermore, some microcracks were observed in the FRP retrofits which may have resulted from a combination of poor fiber impregnation and thermal cycling.

An indirect approach to measure glass transition temperature in metallic glasses

Abstract Glass transition behavior of metallic glasses under some extraordinary conditions (such as under high pressures) remains unexplored. Conventional measurements of glass transition temperature, T g, are very difficult to perform under these extraordinary circumstances. In the present paper, we introduce an indirect approach to characterize glass transition, using enthalpy recovery experiments. With annealing deeply relaxed glassy samples and subsequent DSC measurements, a variation of enthalpy change upon heating with annealing temperature can be obtained. The variation of enthalpy change, a signature of glass transition, was found to correlate well with the directly measured DSC curves for the glass transition. This unique method was successfully applied in determining T g of several metallic glasses under hydrostatic high pressures and compression stresses.

Simultaneous Measurement of Glass-Transition Temperature and Crystallinity of As-Prepared Polymeric Films from Restitution

Simultaneous Measurement of Glass-Transition Temperature and Crystallinity of As-Prepared Polymeric Films from Restitution

Study of mechanical and rheological properties, morphology, and miscibility in polylactid acid blends with thermoplastic polymers

AbstractBlends of polypropylene, polystyrene (PS), polyethylene terephthalate (PET), and high‐, low‐ and linear low‐density polyethylene (LDPE and LLDPE) with different contents on polylactid acid (PLA) were prepared. Tensile and impact properties and melt flow rate (MFR) of the mixtures were determined. Morphology was analyzed through scanning electron microscopy (SEM) and interactions were studied by measuring glass transition temperatures (Tg) as well as applying a model to quantify the composition dependence of tensile strength. Results show that there are significant differences on structure and properties among the blends. Polyolefin based blends feature heterogeneous structures with big particle sizes, which translates to blend properties with high negative deviation from the rule of mixtures (ROM), especially for LDPE and LLDPE. Blends of PET and PS feature smaller dispersed particles, resulting in blends with mechanical properties close to those of ROM. Shifting in glass transition temperatures indicate interactions between these materials, which were quantitatively determined indicating the strongest interactions for the PS/PLA pair followed by the PET/PLA mixture.