Glass Transition Region Research Articles

Release mechanism of omega-3 fatty acid in κ-carrageenan/polydextrose undergoing glass transition

A high-solid matrix of κ-carrageenan with polydextrose was developed to entrap α-linolenic acid, which is an omega-3 bioactive compound. Physicochemical analysis of this system utilised modulated DSC, dynamic oscillation in shear, ESEM, FTIR and WAX diffraction. The carbohydrate matrix was conditioned through an extensive temperature range to induce changes in molecular morphology and identify the network glass transition temperature. Thermally induced variation in phase morphology was employed to rationalise transportation patterns of the bioactive compound within the high-solid preparation. Thus, experimental observations using UV–vis spectroscopy modelled diffusion kinetics to document the mobility arresting effect of the vitrifying matrix on the micro-constituent. Within the glass transition region, results argue that free volume theory is the molecular process governing structural relaxation. Further, Less Fickian diffusion follows well the rate of molecular transport of α-linolenic acid as a function of time and temperature of observation in the condensed matrix.

Modified Adam–Gibbs models based on free volume concept and their application in the enthalpy relaxation of glassy polystyrene

Vogel–Fulcher–Tammann (VFT) equation based on free volume concept is used extensively to describe the temperature dependence of relaxation time of polymer above the glass transition temperature Tg, but failed in fitting the enthalpy relaxation data across the glass transition region. Under the line of the Adam–Gibbs theory on temperature dependence of cooperative relaxation property, two equations based on the free-volume theory of glass transition, free-volume (FV) and modified free-volume (FVM) equations, were proposed and applied to fit the enthalpy relaxation data of PS. Compared with the VFT equation, the fitting quality of FV equation is improved greatly and similar to that of the extensively used Tools–Narayanaswamy–Moynihan (TNM) and Adam–Gibbs (AG) models. The fitting quality of FVM equation is improved further and better than that of TNM and AG models, as well as Macedo model with the same number of fitting parameters, especially on the prediction of the limit fictive temperatures.

Temperature sensitivity and model of stress relaxation properties of cement and asphalt mortar

The stress relaxation properties of two types of cement and asphalt mortar (CA mortar) in the temperature range of −40 to 60°C and at the initial strain of 0.1% was studied by dynamic mechanical thermal spectrometer. The results show that the stress relaxation process of CA mortar can be divided into attenuation stress relaxation stage and steady stress relaxation stage. The lower the temperature is, the higher the initial stress and residual stress are. At the same temperature, the stress relaxation rate and specific stress relaxation of type I CA mortar are larger than that of type II CA mortar, while the initial stress, residual stress and stress relaxation modulus are relatively smaller. The glass transition region of type I CA mortar characterized by the isochronous stress–temperature curves is −20 to 0°C. The established model agrees well with experimental results, and φ, δ are dominated parameters affecting the stress relaxation of CA mortar. This indicates that the established model can effectively predict the time dependence and temperature sensitivity of stress relaxation of CA mortar. The results can provide reference for the calculation of temperature stress of CA mortar filling layer of ballastless slab track.

Structural relaxation time and cooling rate of a melt in the glass transition region

The nature of the parameter involved in the Bartenev equation qτg = C relating the cooling rate of a glass-forming melt to its structural relaxation time in the glass transition region is discussed on the basis of the Volkenshtein-Ptitsyn theory using a number of known relationships. It is established that parameter C for amorphous substances with the same fragility is linearly temperature dependent. This parameter is shown to equal the narrow temperature range δTg characterizing the liquid-glass transition region (by Nemilov); i.e., C = δTg. It is concluded that δTg for most glassy systems is only ∼0.7% of the glass transition temperature Tg. The narrowness of temperature range δTg is explained by the small fluctuation volume fraction fg “frozen” at the glass transition temperature. The concept of a close relationship between constant C and the structural order at Tg (i.e., the characteristic of the inner state of a nonequilibrium “frozen” amorphous system) is developed.

Long-Term Viscoelastic Response of E-glass/Bismaleimide Composite in Seawater Environment

The effect of seawater absorption on the long-term viscoelastic response of E-glass/BMI composite is presented in this paper. The diffusion of seawater into the composite shows a two-stage behavior, dominated by Fickian diffusion initially and followed by polymeric relaxation. The Glass transition temperature (Tg) of the composite with seawater absorption is considerably lowered due to the plasticization effect. However the effect of water absorption at 50 °C is found to be reversible after drying process. The time-temperature superposition (TTS) was performed based on the results of Dynamic Mechanical Analysis to construct the master curve of storage modulus. The shift factors exhibit Arrhenius behavior when temperature is well below Tg and Vogel-Fulcher-Tammann (VFT) like behavior when temperature gets close to glass transition region. As a result, a semi-empirical formulation is proposed to account for the seawater absorption effect in predicting long-term viscoelastic response of BMI composites based on temperature dependent storage modulus and TTS. The predicted master curves show that the degradation of storage modulus accelerates with both seawater exposure and increasing temperature. The proposed formulation can be applied to predict the long-term durability of any thermorheologically simple composite materials in seawater environment.

Preparation and characterization of poly(lactic acid)/poly(methyl methacrylate) blend tablets for application in quantitative analysis by micro Raman spectroscopy

Poly(lactic acid) (PLA) is a biodegradable polymer that has a variety of applications, one of which is as biomaterial in surgery or as functional layers on implants, due to its compatibility with living tissue.This paper reports the possibilities of quantification of poly(lactic acid) (PLA) in a polymer matrix such as poly(methyl methacrylate) (PMMA) by micro Raman spectroscopy (MRS). Blends of amorphous poly(DL‐lactic acid) with poly(methyl methacrylate) were prepared by the procedure of dissolution/precipitation. Thermal properties of the blends such as the glass transition temperature (Tg) were characterized by differential scanning calorimetry (DSC). The PLA/PMMA blends exhibited only a single glass transition region, indicating that this system is miscible. The PLA/PMMA system obeys the Gordon–Taylor equation (Tg versus PLA content). Various concentration ratios of PLA blends were prepared to use as a basis for quantitative analysis by MRS. Intensities of the characteristic bands at 813 cm−1 (νCOC of PMMA) and 873 cm−1 (νC―COO of PLA) were used for the calculation. The calibration graph showed a good linear correlation with an R2 value of 0.9985. On the basis of the calibration curve obtained, the determined content of several PLA/PMMA blends was in good agreement when compared with nominal contents. The limit of detection (LOD) and quantification (LOQ) were calculated by the calibration data set as signal‐to‐noise method. The relative standard deviation of this method was lower than 10% and the accuracy better than 4%. This study demonstrated that Raman spectroscopy provides an alternative non destructive method for quantitative analysis of PLA in a PMMA matrix. Copyright © 2015 John Wiley & Sons, Ltd.

Resolution and Characterization of Chemical Steps in Enzyme Catalytic Sequences by Using Low-Temperature and Time-Resolved, Full-Spectrum EPR Spectroscopy in Fluid Cryosolvent and Frozen Solution Systems.

Approaches to the resolution and characterization of individual chemical steps in enzyme catalytic sequences, by using temperatures in the cryogenic range of 190-250 K, and kinetics measured by time-resolved, full-spectrum electron paramagnetic resonance spectroscopy in fluid cryosolvent and frozen solution systems, are described. The preparation and performance of the adenosylcobalamin-dependent ethanolamine ammonia-lyase enzyme from Salmonella typhimurium in the two systems exemplifies the biochemical and spectroscopic methods. General advantages of low-temperature studies are (1) slowing of reaction steps, so that measurements can be made by using straightforward T-step kinetic methods and commercial instrumentation, (2) resolution of individual reaction steps, so that first-order kinetic analysis can be applied, and (3) accumulation of intermediates that are not detectable at room temperatures. The broad temperature range from room temperature to 190 K encompasses three regimes: (1) temperature-independent mean free energy surface (corresponding to native behavior); (2) the narrow temperature region of a glass-like transition in the protein, over which the free energy surface changes, revealing dependence of the native reaction on collective protein/solvent motions; and (3) the temperature range below the glass transition region, for which persistent reaction corresponds to nonnative, alternative reaction pathways, in the vicinity of the native configurational envelope. Representative outcomes of low-temperature kinetics studies are portrayed on Eyring and free energy surface (landscape) plots, and guidelines for interpretations are presented.

Exploring the glass transition region: crowding effect, nonergodicity and thermorheological complexity

Monte Carlo simulations performed on multiple polymer chains have produced accurate relaxation modulus Gs(t) curves which match the experimental G(t) curves of polystyrene reasonably well, over a wide temperature range around the glass transition region. The inter-segmental interactions, defined in terms of ε* (well depth) and σ (monomer size), exert a strong influence on the modulus, the length scale and the relaxation time scale of the system. Judicious selection of these interaction parameters has enabled us to create the whole range of temperature dependence of the thermorheological complexity, from ΔT = 40 °C to ΔT = 0 °C. Near the glass transition temperature, the development of nonergodicity vis-à-vis a crowding effect in the system emerges naturally from the analysis of the G(t) line shapes. The entropic slow mode is well described by the Rouse theory and the energetic fast mode shifts to longer time scales, revealing the generic behavior of the thermorheological complexity. Typical Gs(t) curves, when partitioned into glassy and rubbery components, are shown to obey Inoue-Okamoto-Osaki's modified stress-optical rule, with different stress-optical coefficients for each component. Closer to the glass transition temperature, the distance of the closest monomer shows a considerable increase, suggesting a penetrable resistance to the approach of another monomer. The parameter σ represents the characteristic length scale of the system in the glassy region. The thermorheological complexity incorporates the dynamic length scale of structural relaxation, increasing with the decrease of temperature towards the glass transition point.

Acetaminophen, Methocarbamol, Guaifenesin and Mephenesin in Propylene Glycol: Solubility and Phase Behaviour for Use in Medical Industry

Propylene glycol is generally used as inactive solvent for water-insoluble drugs in liquid form for administration orally and intravenously. The phase behaviour of these binary liquid mixtures is not known very well and this knowledge is desirable in the search for better drug design. In order to know the phase behavior, dielectric relaxation (10 -3 Hz – 2 MHz) and differential scanning calorimetry (DSC) measurements have been performed on binary liquid mixtures of propylene glycol with four drugs namely acetaminophen, methocarbamol, guaifenesin, and mephenesin. The glass transition temperature region is examined critically for a step like change in DSC scan at the heating rate of 10 K/min. The DSC scans are found to be unusually broad in the glass transition region, especially for intermediate concentrations. This together with the dielectric spectroscopic results, which revealed two liquid like processes, each following Vogel-Fulcher-Tammanns temperature dependence at all concentrations, point to microheterogeneity in these mixtures. The two processes are attributed to the separated liquid phases rich in pharmaceutical and propylene glycol respectively.

Peculiarities of structure relaxation of boric oxide in the glass transition region according to the light scattering data

The data describing the changes of the polarized component of the integral intensity of light scattering in the glass transition region of boric oxide at the observation angle of 90° obtained with the help of two experimental techniques—the temperature jump and continuous heating methods—are presented. It was established by the temperature jump method that the stabilization of the glass at 250°C resulted in the emergence of a maximum on the time dependence recorded at 290°C. It was shown that the change of value and position of the maximum with time was described by the empirical equation of the [1 − exp(−t/τ)] type, where t is the stabilization time and τ is the relaxation time, which was in agreement with the results obtained for other oxide glass. It was established that the temperature dependence of the light scattering intensity in the mode of continuous sample heating following stabilization at 225°C was also characterized by the presence of a maximum. It was found that the height of the maximum was represented by the monotonically increasing function of the time of preliminary stabilization at least for the realized stabilization times of the sample.

Tailoring the hard domain cohesiveness in polyurethanes by interplay between the functionality and the content of chain extender

Thermo-mechanical behavior of polyurethanes with diol/triol chain extension is reflected in a particular behavior in the glass transition and rubbery region and is ruled by the functionality and content of the chain extender.

Tannin-Ca Complex as Green Thermal Stabilizer Additive for PVC: Viscoelastic Properties

This study investigated the viscoelastic and rheometeric properties of PVC stabilized with tannin-Ca complex as totally bio-based thermal stabilizer. Dynamic mechanical thermal analysis (DMTA) used to characterize the viscoelastic properties of PVC samples obtained by thermal mixing of PVC with three composition percentages (1.0, 2.0, and 3.0) part per hundred ratios (phr) of tannin-Ca complex with this polymer. The torque rheometery test used to monitor the effect of tannins derivative on the thermal stability and mixing properties of PVC formulations during samples processing. For that purpose, PVC sample with 2 phr commercial thermal stabilizer (Reapak B-NT/ 7060) was used for comparison and considered as reference samples. Before the glass transition temperature of PVC at 30°C - 60°C, the DMTA curves show that the values of storage modulus and tan delta of PVC samples stabilized with tannin derivative were very similar with those of PVC sample stabilized with commercial thermal stabilizer. The glass transition temperature (Tg) of PVC stabilized with commercial thermal stabilizer and with tannin-Ca complex occurred at about 76°C. In a sequence, after the glass transition region of PVC samples, the DMTA scans confirmed that the PVC samples with 2 phr tannin-Ca complex have relatively longer flowing stage which occurs at lower temperatures by 18°C per that of PVC sample stabilized with commercial stabilizer. Global results of the torque rheometery which have suitable plateau stages and the DMTA show that the processing thermal stability and thermal flexibility of PVC are clearly increased with the incorporation of tannin-Ca complex. All the PVC formulations with tannins-Ca complex show excellent viscoelastic properties which were found to be slightly best or much closed to those obtained for PVC stabilized with commercial thermal stabilization.

Tribology of novel antibiocorrosion coatings

We have developed inorganic–organic hybrid bioactive composites and antibiocorrosion coatings based on epoxy or polyurethane matrices modified with varying amounts of a silicon organic oligomer. We have incorporated bioactive compound containing bis(η5-cyclopentadienyl) iron and spatial alicyclic fragment or its coordination compounds of Co and Ni. Glass transition regions located with differential scanning calorimetry (DSC) are above +50°C, so that our hybrids can be used for instance as coatings for museum exhibits. DSC shows also beta transitions in the glassy state around −50°C. Thermogravimetric analysis shows high thermal stability. We have also performed scratch resistance testing with linearly increasing load and sliding wear determination by multiple scratching along the same groove. Also here the hybrid formation enhances the scratch resistance. We observe the strain hardening in sliding wear that is the tendency towards a horizontal groove depth asymptote with increasing number of scratches. Water absorption in 720 h does not exceed 0·03 wt-% in all cases. Samples subjected to three months aging under normal temperature and pressure conditions were observed. The initial colours and optical transparency were preserved; no phase separation took place.

Preparation and dynamic mechanical properties of copolymers based on butadiene, isoprene, and styrene

The styrene-isoprene-butadiene terpolymers were prepared using n-butyl lithium as initiator, cyclohexane as solvent, tetrahydrofuran as structure modifier and tin tetrachloride as coupling agent by a method of the change addition time of structure modifier through the anionic polymerization technique. The polymerization rate of monomers, molecular weight, microstructure, tanδ and morphology of copolymers were investigated. The results showed that addition of THF had a great effect on the polymerization rate of three monomers, especially styrene, and could tune copolymer composition by using different addition time of THF; the copolymer composition could vary gradually along the chain from block copolymers (isoprene-butadiene) to gradient copolymers (isoprene-butadiene-styrene isoprene-butadiene). It resulted in broadening of glass transition region and damping range. The monomer ratio and molecular weight that affected the mechanical and dynamic mechanical properties of copolymers were also investigated. At the same time, the microstructure, morphology and mechanical properties were compared with random terpolymer and solution styrene-butadiene rubber/butadiene rubber/nature rubber blend.

Slow relaxations in semicrystalline poly(butylene succinate) below and aboveTg

The slow molecular mobility in the amorphous part of the semi-crystalline polymer poly(butylene succinate) (PBS) has been studied by the thermally stimulated depolarization current (TSDC) technique. Experiments were carried out in the temperature range, which includes the glassy state, the glass transformation region, and the rubber state. A broad and low intensity secondary relaxation was observed in the temperature region from −140°C up to the glass transition region; the activation energy of the motional modes of this secondary relaxation was in the range between 35 and 55 kJ mol−1. The glass transition temperature of PBS, provided by the TSDC technique, was Tg = −40 °C, and the fragility index was found to be m = 43. The aging behavior of the main and of the secondary relaxations was analyzed. A strong relaxation above Tg was observed, whose molecular origin was discussed. The thermal behavior of the PBS was also characterized by differential scanning calorimetry. POLYM. ENG. SCI., 55:1873–1880, 2015. © 2014 Society of Plastics Engineers

Acronitrile butadiene styrene/polycaprolactam/nano carbon black composites: Selective percolation, glass transition and temperature dependence of electrical conductivity

Preferential percolation is a promising strategy to develop conducting composites at lower loading of conducting filler; however, little information is available on temperature dependence of conductivity of such composites. This study reports synthesis and positive temperature coefficient (PTC) behavior of a novel multiphase polymer composite in which conducting filler preferentially percolates in a composite containing two incompatible polymers, both having glass transition in the temperature range of study. High electrical conductivity and good mechanical behavior was demonstrated by acrylonitrile butadiene styrene (ABS)/polycaprolactam (PCL)/nano carbon black (NCB) composites, which was dependent on blend composition as well as on the extent of NCB loading. PTC intensity was considerably less for ternary composites than it was for binary ABS/NCB or PCL/NCB composites. Theoretical analysis of the dispersion state of NCB in this phase separated system revealed preferential distribution of NCB at the interfacial region. PTC effect was also found to decrease significantly with increase in NCB content. ABS/PCL/NCB (1:1:2) composites showed no significant temperature dependence (zero positive coefficients) up to 413 K while ABS/NCB 30 wt% NCB composites showed highest PTC. A sudden rise was observed in the glass transition region of polymers for all composites; however, the effect was less pronounced for ternary composites. POLYM. COMPOS., 37:481–487, 2016. © 2014 Society of Plastics Engineers

Preservation of oleic acid entrapped in a condensed matrix of high-methoxy pectin with glucose syrup

This investigation deals with the diffusional mobility of essential fatty acids in triglyceride form (oleic acid) from a condensed matrix comprising 3% (w/w) high-methoxy pectin and 81% (w/w) co-solute (glucose syrup) to absolute ethanol. Work utilises rheological measurements in shear, differential scanning calorimetry, ESEM, FTIR and WAX diffraction to identify the molecular properties of the composite system. Results showed that the amorphous carbohydrate matrix underwent vitrification at −15 °C (mechanical Tg) calculated mathematically using the Williams, Landel and Ferry (WLF) and modified Arrhenius equations. Diffusion kinetics of the fatty acid (monitored via UV-vis spectroscopy) was combined with the newly introduced concept of spectroscopic shift factor to demonstrate that, although the increment of oleic acid mobility appeared to respond to the predicted glass transition temperature, this is distinct from the structural relaxation of the matrix. Experimental observations were further treated with the concept of diffusion coefficient to provide an estimate of the transport rate of the triglyceride as a function of time or temperature of observation within the glass transition region.

Diffusion kinetics of ascorbic acid in a glassy matrix of high-methoxy pectin with polydextrose

The relative mobility of ascorbic acid incorporated in a condensed matrix of high-methoxy pectin (HMP) and polydextrose is reported. Physicochemical and structural characterisation of the high-solid systems utilised modulated differential scanning calorimetry, small deformation dynamic oscillation in shear, scanning electron microscopy, Fourier transform infrared spectroscopy and wide angle X-ray diffraction. Theoretical modeling of the thermomechanical measurements demonstrated that the mechanism of free volume governs stress relaxation phenomena of the polymeric system through the process of vitrification yielding the mechanical glass transition temperature. Combination of UV-vis spectrophotometry and a vitamin-dye binding method was employed to follow for 60 min the diffusion process of ascorbic acid from the concentrated HMP/polydextrose matrix to the absolute ethanol phase throughout the temperature range of −30 to 20 °C. A relatively low estimate of activation energy for the diffusion of vitamin C reflects its freedom of mobility and high free volume, as compared to the relaxation of the polymeric system that exhibits strong temperature dependence in the glass transition region. Utilisation of the concept of diffusion coefficient sheds further light into the relationship between free volume of the polymeric system and diffusional mobility of the micronutrient.

Dual-phase glassy/nanoscale icosahedral phase materials in Cu–Zr–Ti–Pd system alloys

The present work is devoted to an investigation of the formation kinetics, stability and homogeneity area of the nanoscale icosahedral phase formed on heating in the dual-phase glassy/quasicrystalline phase Cu–Zr–Ti–Pd alloys. The data obtained indicate that the Cu–Zr–Ti–Pd icosahedral phase is not a Cu-rich part of the compositional homogeneity area of the Zr–Cu–Pd one. Moreover, Ti, as well as Pd, is found to be an important element stabilizing quasicrystalline phase in the Cu–Zr–Ti–Pd alloys. The formation criteria for Cu- and Zr/Hf-based icosahedral phases are discussed based on the quasilattice constant to average atomic diameter ratio. Deviation from a certain ratio leads to destabilization of the icosahedral phase. By using the isothermal calorimetry traces transformation kinetics above and below the glass-transition region was analyzed. Some difference in the transformation kinetics above and below the glass-transition region allows us to suggest that possible structure changes occur upon glass-transition.

The Slow Molecular Mobility in Semicrystalline Poly(Ethylene Oxide)

The thermally stimulated depolarization current (TSDC) technique has been used to study the slow molecular mobility in the amorphous part of the semicrystalline polymer, poly(ethylene oxide) (PEO). Experiments were carried out in the temperature range that includes the glassy state, the glass transformation region and the rubber state. The dipole moments in the polymeric main chain originated a broad and low intensity secondary relaxation in the temperature region from −130°C up to the glass transition region; the activation energy of the motional modes of this secondary relaxation was in the range between 35 and 100 kJ mol−1. The glass transition temperature of the PEO, provided by the TSDC technique, was Tg = −53°C, and the fragility index was found to be m = 43. A strong relaxation above Tg was observed, whose molecular origin was discussed. The thermal behavior of the PEO was also characterized by differential scanning calorimetry.