Characteristic Glass Transition Temperature Research Articles

Interaction between synthetic elastin-like polypeptide and collagen: Investigation of miscibility and physicochemical properties

Poly(GVGVP), where G-Glycine, V-Valine, and P-Proline, is a synthetic elastin-like polypentapeptide that has been studied for its interaction with collagen in blends using viscometry, Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), and X-ray diffractogram (XRD) techniques. Additionally, the thermal characteristics such as glass transition temperature (Tg) and thermal stability of the blends were studied respectively by Differential Scanning Calorimetry (DSC) and Thermogravimetric analysis (TGA). The results showed that amide A and B band's positions in FTIR spectra of collagen were shifted correspondingly to higher and lower wavenumbers after blending with polypentapeptide. DSC study unveiled characteristic glass transition temperatures (Tg) for the blends and the particular components. All the blends show thermal stability in between the pure polymers. Viscosity evaluations also showed a strong association between collagen and poly(GVGVP). Collagen and poly(GVGVP) together may provide the opportunity to assemble novel, promising materials for biomedical purposes.

The Thermal Characteristics, Sorption Isotherms and State Diagrams of the Freeze-Dried Pumpkin-Inulin Powders.

Powders based on plant raw materials have low storage stability due to their sorption and thermal properties and generate problems during processing. Therefore, there is a need to find carrier agents to improve their storage life as well as methods to evaluate their properties during storage. Water adsorption isotherms and thermal characteristics of the pumpkin powder with various inulin additions were investigated in order to develop state diagrams. Differential scanning calorimetry (DSC) was used to obtained glass transition lines, freezing curves and maximal-freeze-concentration conditions. The glass transition lines were developed using the Gordon–Taylor model. Freezing data were modeled employing the Clausius–Clapeyron equation and its development–Chen model. The glass transition temperature of anhydrous material (Tgs) and characteristic glass transition temperature of maximum-freeze-concentration (Tg′) increased with growing inulin additions. Sorption isotherms of the powders were determined at 25 °C by the static-gravimetric method and the experimental data was modeled with four different mathematical models. The Peleg model was the most adequate to describe the sorption data of the pumpkin–inulin powders. Guggenheim-Anderson-de Boer (GAB) monolayer capacity decreased with increasing inulin concentration in the sample.

Effect of cold rolling on the pressure coefficient of glass transition temperature in bulk metallic glasses

Vitreous alloys exhibit changes in the specific heat capacity (Δcp) as well as configuration at the characteristic glass transition temperature (Tg). A wide variety of bulk metallic glasses (BMGs) such as, Zr47.5Cu47.5Al5, Zr55Cu30Ni5Al10, Zr52.5Cu17.9Ni14.6Al10Ti5 and Zr41.2Ti13.8Cu12.5Ni10Be22.5 were rolled at room temperature, and the variation of Tg, Δcp at Tg, configurational entropy (ΔSconf.), pressure coefficient of Tg (dTg/dP) and bending strength were measured to understand the configurational change in BMGs upon cold rolling. The normalized bending moment during yielding of a cold rolled Zr55Cu30Ni5Al10 has increased by 43.4% than the as-cast specimen. The ΔSconf. of the Zr55Cu30Ni5Al10 plate increased upon rolling from 0.537±0.041 J/mol∙K for as-cast to 0.654±0.032 J/mol∙K for 70% cold rolled sample. A relaxed glassy state with low Tg exhibits high dTg/dP value and vice versa.

Molecular orientation and thermal stability of thin-film organic semiconductors

Molecular orientation in organic semiconductors plays a critical role in maximizing external quantum efficiencies of organic light-emitting diodes. It was generally believed that the molecular packing of organic semiconductors is either amorphous or liquid-crystal-like with a preferred molecular orientation distributed uniformly throughout the film. In this paper, however, we report that the orientation of organic molecules in physical-vapor deposited films varies drastically depending on thickness. The thermal stability of the molecular network, measured by its characteristic glass transition temperature, also varies as a function of the film thickness. Based on a two-layered film-structure model, we propose a simple function to quantify the molecular dipole orientation S parameter as a function of film thickness. This function describes well experimental data. In addition to contributing to external quantum efficiency, the molecular orientation parameter S is found to have a strong impact on disruptive change in material density after thermal anneal and glass transition.

Sorption properties, glass transition and state diagrams for pumpkin powders containing maltodextrins

The state diagrams of freeze-dried pumpkin powders with different maltodextrin additions were developed using glass transition line, freezing curve and maximal-freeze-concentrations conditions. The freezing curve was plotted employing Clausius – Clapeyron equation and glass transition lines were developed using Gordon – Taylor model. The ultimate maximum-freeze-concentration conditions of the powders were observed in range from 0.685 to 0.745 g solids/g sample. Characteristic glass transition temperature of maximum-freeze-concentration (Tg’) of the pumpkin was equal to - 83.7 °C and was increase with increasing maltodextrin addition. Adsorption isotherms of pumpkin – maltodextrin powders were determined at 25 °C by static - gravimetric method and the experimental data was modelled with BET and GAB equations. Monolayer moisture content of the pumpkin powder decreased with increasing maltodextrin additions. The state diagram and water adsorption isotherms of the pumpkin – maltodextrin powders are useful for predicting suitable storage and processing conditions.

Effect of CeO2 and Eu2O3 on the calorimetric behavior of Si–Al–Zn–K–Ti oxide glass

Glasses and glass-ceramics based on SiO2 have attracted a large attention. In this work, the thermal properties and crystallization kinetics of Si–Al–Zn–K–Ti glasses are investigated. Based on the thermal parameters derived from the differential scanning calorimetry technique ran upon various heating rates, the characteristic glass transition temperature, onset crystallization temperature and crystallization temperature were extracted. The crystallization peaks are carefully investigated by Kissinger, Ozawa and modified-Kissinger methods. Avrami index and the dimensionality of the crystal growth vary from 2 to 4 at the same time that crystallization activation energy decrease from 177.80 kJ/mol to 145.40 kJ/mol in Ozawa method and the thermal stability reaches to 177.20 ΔC° by doping with 0.5 wt% of CeO2 and 0.5 wt% of Eu2O3, both in excess. Our results confirm the role of rare earth ions in the crystallization kinetics, as well as improvement in the glass thermal stability.

The Role of Glass Transition Temperatures in Coamorphous Drug-Amino Acid Formulations.

The improved physical stability associated with coamorphous drug-amino acid (AA) formulations may indicate a decrease in mobility of the amorphous drug molecules, compared to the neat amorphous form of the drug. Since the characteristic glass transition temperatures ( Tgα and Tgβ) represent molecular mobility in amorphous systems, we aimed to characterize Tgα and Tgβ and to determine their role in physical stability as well as their potential usefulness to determine the presence of an excess component (either drug or AA) in coamorphous systems. Indomethacin (IND)-tryptophan (TRP) and carvedilol (CAR)-TRP were used as model coamorphous systems. The analytical techniques used were X-ray powder diffractometry (XRPD) to determine the solid-state form, dynamic mechanical analysis (DMA) to probe Tgα and Tgβ, and differential scanning calorimetry (DSC) to probe thermal behavior of the coamorphous systems. Tgα analysis showed a gradual monotonous increase in Tgα values with increasing AA concentration, and this increase in the Tgα value is not the cause of the improved physical stability. The Tgβ analysis for the IND-TRP sample with 10% drug had a Tgβ of 226.8 K, and samples with 20-90% drug had similar Tgβ values around 212.5 K. For CAR-TRP, samples with 10-40% drug had similar Tgβ values around 230.5 K, and samples with 50-90% drug had similar Tgβ values around 223.3 K. The similar Tgβ values in coamorphous systems at different drug ratios indicate that they in fact are the Tgβ of the component that is in excess to an ideal drug-AA coamorphous mixture. DSC and XRPD analysis showed that for IND-TRP, IND is in excess if the drug concentration is 30% or above and will eventually recrystallize. For CAR-TRP, CAR is in excess and recrystallizes when the drug concentration is 50% or above. We have proposed a means of estimating, on the basis of Tgβ, which drug to AA ratios will lead to optimally physically stable coamorphous systems that can be considered for further development.

Sorption isotherm and state diagram for indica rice starch with and without soluble dietary fiber

Moisture sorption isotherms and state diagrams for indica rice starch (IRS) and indica rice starch-soluble dietary fiber (IRS-SDF) were developed to investigate the effect of SDF on the stability of IRS. Sorption isotherms of IRS and IRS-SDF were determined by the static gravimetric method and the data were modeled by Guggenheim–Anderson–de Boer (GAB) model. The GAB monolayer moisture contents were calculated to be 7.43 and 8.37 g/100g (dry basis) for IRS and IRS-SDF, respectively. The state diagram was composed of the glass transition line and freezing curve, which were fitted according to Gordon–Taylor and Chen models, respectively. The ultimate maximum-freeze-concentration conditions were calculated as characteristic glass transition temperature (Tg’) of −42.5 °C and −31.5 °C with characteristic solids content (Xs') being 0.71 and 0.72 g/g (wet basis), and characteristic temperature of end point of freezing (Tm’) being −18.2 °C and −13.8 °C for IRS and IRS-SDF, respectively. The state diagrams and sorption isotherms of IRS and IRS-SDF have great significance for evaluating storage stability, optimizing drying and freezing processes.

A Study of Thermal Stability And Crystallization Kinetics of SbSeGe Glassy Alloys

Alloys of Sb10Se90-xGex (x = 0, 19, 21, 23, 25, 27) have been prepared using melt quenching technique. Differential thermal analysis has been used to determine the three characteristic temperatures, glass transition (Tg ), glass crystallization (Tc ) and melting temperature (Tm ), at four heating rates 5, 10, 15 and 20 K/min. The thermal stability and ease of glass formation have been evaluated in terms of Hruby parameter and reduced glass transition temperature respectively. The activation energy for glass crystallization (Ec ) has been calculated using Kissinger's method and Marseglia theory. The composition dependence of Tg and Ec has also been discussed.

Glass transition and state diagram for freeze-dried Lentinus edodes mushroom

Glass transitions of freeze-dried Lentinus edodes mushroom were determined using differential scanning calorimetry (DSC) as a function of water contents. Freeze-dried L. edodes containing unfreezable and freezable water were examined to explore the state diagram of L. edodes. The state diagram included the freezing curve, glass transition line, and ultimate maximal-freeze-concentration condition. The freezing curve and the glass transition line were fitted according to Clausius-Clapeyron model and Gordon-Taylor model, respectively. The ultimate maximal-freeze-concentration conditions were calculated as solid content of 0.81g solid/g (w.b.) with the characteristic glass transition temperature (Tg′) being −53.2°C, and characteristic temperature of end point of freezing (Tm′)u being −33.4°C. The other characteristic glass transition temperature Tg″ was −42.4°C. The state diagram of Lentinus edodes can be used in determining the storage stability as a function of temperature and water content, and optimizing drying and freezing processes.

Thermally Sprayed Y2O3-Al2O3-SiO2 Coatings for High-Temperature Protection of SiC Ceramics

The suitability of certain glass compositions in the Y2O3-Al2O3-SiO2 (YAS) system as protecting coatings for silicon carbide components has been prospected. One particular YAS composition was formulated considering its glass formation ability and subsequent crystallization during service. Round-shaped and homogeneous granules of the selected composition were prepared by spray drying the corresponding homogeneous oxide powder mixture. Glassy coatings (197 µm thick) were obtained by oxyacetylene flame spraying the YAS granules over SiC substrates, previously grit blasted and coated with a Si bond layer (56 µm thick). Bulk glass of the same composition was produced by the conventional glass casting method and used as reference material for comparative evaluation of the characteristic glass transition temperatures, crystallization behavior, mechanical, and thermal coating properties. The mechanical properties and thermal conductivity of the coating were lower than those of the bulk glass owing to its lower density, higher porosity, and characteristic lamellar structure. The crystallization of both bulk glass and coating occurred during isothermal treatments in air at 1100-1350 °C. Preliminary data on ablation tests at 900 °C using the oxyacetylene gun indicated that the YAS glassy coating was a viable protective shield for the SiC substrate during 150 s.

Thermal characteristics and state diagram of extruded instant artificial rice

Instant artificial rice was developed by extrusion method using corn flour, glycerol monostearate (GSM), and glucomannan and guar gum. Moisture sorption isotherm and thermal characteristics of the artificial rice with glucomannan and guar gum were measured and modeled to develop different regions of a state diagram. The freezing point, glass transition, and solids-melting were measured and modeled by Chen’s model, modified Gordon–Taylor model, and Flory–Huggins model, respectively. The ultimate maximal-freeze-concentration conditions were found as (Tm′)u (i.e., annealed end glass transition temperature for the sample with moisture 0.40g/g sample) equal to −8.3°C and (Tg‴)u (i.e., annealed onset glass transition temperature for the sample with moisture 0.40g/g sample) equal to −8.4°C, and the characteristic solids content, Xs′ as 0.76g/g sample (i.e., un-freezable water, Xw′ equal to 0.24g/g sample). Similarly the characteristic glass transition temperature, Tgiv (i.e., intersection of vertical line passing through Tm′ and glass transition line above Xs′) was estimated as 29.8°C.

Optical, physical and structural studies of vanadium doped P2O5–BaO–Li2O glasses

Glasses in the compositions (Li2O)25–(BaO)25–(P2O5)50−x–(V2O5)x (with x=0.5,1.0,1.5,2.0,2.5, and 3.0mol%) have been prepared by the conventional melt quenching technique. X-ray powder diffractrogram show broad peaks which conforms glassy nature of the sample. Differential scanning calorimetry (DSC) thermograms show characteristic glass transition temperature (Tg) and it increases with increasing substitution of V2O5 for P2O5. The measured physical parameters like density, refractive index, ionic concentration and electronic polarizability are found to vary linearly with increasing x. Infrared spectra exhibits few bands, which are attributed to (P=O)AS, (P=O)S, (V=O), (P–O–P)AS,P–O–V, (P–O–P)AS and O–P–O vibrations. The optical absorption spectra of VO2+ ions in these glasses show three bands and are assigned to the 2B2→ 2E,2B2→ 2B1 and 2B2→ 2A1 transitions. Electron paramagnetic resonance spectra of all the glass samples exhibit resonance signals characteristic of VO2+ ions. The values of Spin-Hamiltonian parameters indicate that the VO2+ ions are present in octahedral sites with tetragonal compression and belong to C4V symmetry.

Stability of Anthocyanins in Frozen and Freeze‐Dried Raspberries during Long‐Term Storage: In Relation to Glass Transition

Anthocyanins, natural plant pigments in the flavonoid group, are responsible for the red color and some of the nutraceutical benefits of raspberries. This study explores anthocyanin degradation in frozen and freeze-dried raspberries during storage in relation to glass transition temperatures. Frozen raspberries were stored at -80, -35, and -20 °C, while freeze-dried raspberries were stored at selected water activity (a(w)) values ranging from 0.05 to 0.75 at room temperature (23 °C) for more than a year. The characteristic glass transition temperatures (T'(g)) of raspberries with high water content and glass transition temperature (T(g)) of raspberries with small water content were determined using a differential scanning calorimeter. The pH differential method was used to determine the quantity of anthocyanins in frozen and freeze-dried raspberries at selected time intervals. The total anthocyanins in raspberries fluctuated during 378 d of storage at -20 and -35, and -80 °C. Anthocyanin degradation in freeze-dried raspberries ranged from 27% to 32% and 78% to 89% at a(w) values of 0.05 to 0.07 and 0.11 to 0.43, respectively, after 1 y. Anthocyanins were not detectable in freeze-dried raspberries stored at a(w) values of 0.53 to 0.75 after 270 d. First order and Weibull equations were used to fit the anthocyanin degradation in freeze-dried raspberries. The 1(st)-order rate constant (k) of anthocyanin degradation ranged from 0.003 to 0.023 days⁻¹ at the selected water activities. Significant anthocyanin degradation occurred in both the glassy and rubbery states of freeze-dried raspberries during long-term storage. However, the rate of anthocyanin degradation in freeze-dried raspberries stored in the glassy state was significantly smaller than the rate of anthocyanin degradation in the rubbery state.

Assessment and Formation Mechanism of Laser-Induced Periodic Surface Structures on Polymer Spin-Coated Films in Real and Reciprocal Space

In this work we evaluate the potential of grazing incidence X-ray scattering techniques in the investigation of laser-induced periodic surface structures (LIPSSs) in a series of strongly absorbing model spin-coated polymer films which are amorphous, such as poly(ethylene terephthalate), poly(trimethylene terephthalate), and poly(carbonate bisphenol A), and in a weaker absorbing polymer, such as semicrystalline poly(vinylidene fluoride), over a narrow range of fluences. Irradiation was performed with pulses of 6 ns at 266 nm, and LIPSSs with period lengths similar to the laser wavelength and parallel to the laser polarization direction are formed by devitrification of the film surface at temperatures above the characteristic glass transition temperature of the polymers. No crystallization of the surface is induced by laser irradiation, and crystallinity of the material prevents LIPSS formation. The structural information obtained by both atomic force microscopy and grazing incidence small-angle X-ray scattering (GISAXS) correlates satisfactorily. Comparison of experimental and simulated GISAXS patterns suggests that LIPSSs can be well described considering a quasi-one-dimensional paracrystalline lattice and that irradiation parameters have an influence on the order of such a lattice.

Novel polystyrene bearing highly branched hexafluoropropene trimer pendants

A novel styrenic monomer having hexafluoropropene trimer on the benzene ring was prepared. The highly fluorinated monomer was polymerized to yield a white powdery polymer, which was soluble in fluorinated solvents and had resistance to usual organic solvents, good water repellency, and low refractivity. In contrast to common fluoropolymers having linear-fluorinated side-chains, the polymer has a characteristic high glass transition temperature. Thus, the fluorinated polymer and copolymer with styrene are suitable for applications at elevated temperature. The polymers can replace the conventional fluorinated polyacrylates, which are used in large quantity as repellents with potentially generating perfluorooctanoic acid in the environment.

Water sorption and glass transition temperatures in red raspberry ( Rubus idaeus)

Water sorption isotherms and glass transition temperatures of raspberries were determined to understand interactions between water and biopolymers. Water adsorption and desorption isotherms of raspberries were determined with an isopiestic method. Thermal transitions of raspberries equilibrated at selected water concentrations using adsorption and desorption were determined by differential scanning calorimetry (DSC). The sorption isotherm data were modeled by BET and GAB equations, while the plasticizing influence of water on glass transition was modeled by the Gordon–Taylor equation. Equilibrium water concentrations varied at equivalent water activities during adsorption and desorption indicating occurrence of hysteresis and irreversibility of thermodynamic processes. The monolayer water concentrations of 0.099 and 0.108 kg water/kg dry raspberry solids obtained by BET and GAB models during desorption were larger than those during adsorption (0.059 and 0.074 kg water/kg dry raspberry solids). The glass transition temperature of raspberries decreased with increasing water concentrations. The Gordon–Taylor parameters T gs and k obtained for raspberries during adsorption were 42.6 °C and 4.73 and during desorption were 44.9 °C and 5.03, respectively. The characteristic glass transition temperature of the maximally freeze concentrated solution T ′ g was −63.1 ± 5 °C and the onset of ice crystal melting temperature T ′ m was −32.3 ± 0.4 °C. Although the water activity differed significantly at equivalent water concentrations obtained using absorption or desorption, the glass transition temperatures of raspberries were dependent on the concentration of water present not the method of equilibration.

Ion transport processes at polymer/oxide/metal interfaces under varying corrosive conditions

Cathodic delamination and interfacial ion transport processes were studied to analyse the stability of polymer/substrate interfaces at artificial Fe–Zn and Fe–SiO 2 cut edges. In-situ Scanning Kelvin Probe (SKP) measurements showed that a kinetic stabilisation of the material transitions could be achieved when they were coated with latex polymers of characteristic glass transition temperatures ( T g). A polarisation of the defect area with a potentiostat or by zinc accelerated cathodic delamination processes but also increased their susceptibility towards kinetic inhibitions. These conclusions were confirmed by Scanning Kelvin Probe–Blister Test (SKP-BT) experiments at epoxy amine/zinc oxide/zinc interfaces under controlled atmospheric conditions.

The Composition, Rheological and Thermal Properties of Tajonal (Viguiera Dentata) Mexican Honey

Samples of Tajonal honey (Viguiera dentata) from Yucatan, Mexico with different moisture contents were studied for their physicochemical, crystallization, rheological, and thermal characteristics. The presence of crystals changed the flow behavior from Newtonian to non-Newtonian. A characteristic glass transition temperature (Tg') was found for each sample, and it was observed to be dependent of the initial moisture content but independent of the storage period. The temperature and latent heat of fusion were not affected by the crystallization phenomenon, while both the moisture content and the glucose/water ratio were useful indexes for crystal growth in honey. Crystallization process can be controlled by harvesting the product with higher moisture contents without exceeding the limits established by international regulations.

Nanohole volume dependence on the cure schedule in epoxy thermosetting networks: A PALS study

A systematic study on the dependence of the volumes at nanoscale in epoxy systems cured with two selected aminic hardeners at different pre-cure temperatures is presented. Nanohole volumes were measured by positron annihilation lifetime spectroscopy. Additional information regarding the structure of the thermosets was obtained using dynamic mechanical analysis. Volume results obtained are discussed in terms of the cure schedule applied to the epoxy systems, their characteristic glass transition temperatures and their crosslink density. The pre-cure temperature and the structure of the hardeners govern the packing of the molecular chains of the epoxy network. Using together positron and mechanical experimental techniques allows to conclude that a strong change in the volume and number density of the nanoholes takes place when the pre-cure temperature crosses the glass transition temperature of the systems.