Effect of water content on the glass transition and textural properties of hazelnut

This study is based on the assumption that the change in the texture of hazelnut, induced by water sorption or desorption, can be derived from the glass transition. No previous study has investigated the glass transition properties of hazelnuts. This study aimed to investigate the effect of water content on the glass transition and textural properties of a roasted hazelnut product. Water content of the sample was adjusted in various relative humidity conditions, and the mechanical glass transition temperature T_g was investigated using thermal rheological analysis (TRA), a type of thermomechanical analysis. The TRA curve exhibited a clear force drop induced by the glass transition, and mechanical T_g of the samples was determined. Water plasticizing effect caused mechanical T_g to decrease as the water content increased. The reduction in T_g was analyzed using the Gordon–Taylor equation and linear equation, and the critical water contents (water content at mechanical T_g?=?25 °C) were obtained. The fracturing properties of the hazelnut changed from brittle to ductile at the critical water contents. This suggested that the change in the texture of hazelnut can be characterized by the glass transition.

     

Preparation of polymer nanoparticles, and the effect of nanoconfinement on glass transition, structural relaxation and crystallization

In this review the preparation methods of polymer nanoparticles from chemical microemulsion polymerization to physical methods such as spray-drying, freeze-drying, freeze-extracting, fast evaporation and spreading evaporation have been summarized. The influence of nanoconfinement on glass transition temperature (T _g) variation from significant or slight decrease, no evident T _g deviation, to even T _g increase, as well as possible explanations of T _g deviations were discussed. The influences of nanoconfinement or entanglement on the other properties such as structural relaxation, crystallization in polymer nanoparticle samples were also reviewed in this article.     

Infrared spectroscopic studies of polymer transitions. III. Effects of sodium ion on glass transitions in styrene-based ionomers

The glass transition in styrene-based ionomers was investigated by means of infrared spectroscopy and differential scanning calorimetry (DSC). Transition temperatures were determined from the temperature dependence of the peak absorbances of the 1700 and 1745 cm^?1 bands. These transition temperatures agreed with glass transition temperatures (T_g) determined by DSC. With increasing degree of ionization, T_g and the enthalpy ΔH of the residual intermolecular hydrogen bonding increased. The values of T_g obtained were analyzed by the theory of Fox and Loshaek for the effect of crosslinks. It is concluded that sodium ions probably from ionic domains and act as crosslinks to reinforce the residual hydrogen bonding and may increase T_g. The absorbance at 1560 cm^?1 (ν_COO^?) did not change at T_g. This suggests that the glass transition observed here is not due to the onset of the mobility in ionic domains, as has been proposed for ethylene-based ionomers on the basis of dielectric measurements.     

Depression of the glass transition temperature of poly(methyl methacrylate) by plasticizers: Conformity with free volume theory

Mixtures of poly(methyl methacrylate) (PMMA) and plasticizer were made by γ-irradiation of mixtures of methyl methacrylate with diethyl phthalate or with dioctyl phthalate. The glass transition temperature T_g was determined by differential scanning calorimetry. Plots of T_g versus volume fraction of PMMA were found to conform to the simple free volume theory of Kelley and Bueche, using physical property values either reported in the literature or else calculated by Bondi's procedures.     

Thermal stability and crystallization kinetics of Pb and Bi borate-based glasses

Glasses with compositions 60B₂O₃–40PbO, 60B₂O₃–40Bi₂O₃, and 60B₂O₃–30Bi₂O₃–10PbO have been prepared and studied by differential thermal analysis. The crystallization kinetics of the glasses was investigated under non-isothermal conditions. From dependence of the glass transition temperature (T _g) on the heating rate, the activation energy for the glass transition was derived. Similarly the activation energy of the crystallization process was determined. Thermal stability of these glasses were achieved in terms of the characteristic temperatures, such as the glass transition temperature, T _g, the onset temperature of crystallization, T _in , the temperature corresponding to the maximum crystallization rate, T _p, beside the kinetic parameters, K(T _g) and K(T _p). The results revealed that the 60B₂O₃–40PbO is more stable than the others. The crystallization mechanism is characterized for glasses. The phases at which the glass crystallizes after the thermal process have been identified by X-ray diffraction.     

Phase separation and glass transition point versus composition diagrams of binary mixtures with covalent bond between components

The geometric thermodynamics approach has been used for investigation of the possible glass transition point versus composition curves and their dependence on various parameters for both mixtures and systems with covalent bond between the components (block-, graftand star-polymers) in which phase separation is possible. Predicted relationships are compared with the experiment. Conditions have been determined under which glass transition hinders the liquid-liquid separation.List of principle symbols and abbreviations T _ps phase separation (or annealing) temperature - T _ps1,T _ps2... two-phase region annealing temperature - T _{ps 0} one-phase region annealing temperature - T _g1,T _g2 glass transition temperature of the first and second component - T _g,T _g glass transition temperature of phases with the compositionx andx - T _g ⁰ glass transition temperature of one-phase system - T _b temperature bordering the two-phase region at which the glass transition affects the phase separation - T_bin temperature of the liquid-liquid phase transition - M ₁,M ₂ molecular mass of 1st (rigid) and 2nd (soft) components, correspondingly - x, x compositions (fraction of the second component) in the first and second phases - x_trunc the value of the fraction of the second component at which the concentration profile is truncated by the glass transition - x _ent,M _ent the composition and molecular mass of the entrance beneath the binodal surface - x _cr,M _cr the critical composition and molecular mass - x _ent,x _ent the compositions of the first and second phases at the point of the entrance of the composition curve beneath the binodal surface - x_ex M _ex the composition and molecular mass of the composition curve exit from under the binodal surface - volume fraction - CPC cloud point curve - GTD glass transition diagram - GTCSS glass transition curve of a single phase system - LCP lower critical point - UCP upper critical point     

Above,below, and in‐between the two glass transitions of ultrathin free‐standing polystyrene films: Thermal expansion coefficient and physical aging

In previous work we observed two simultaneous transitions in high molecular weight (MW) free‐standing polystyrene films that were interpreted as two thickness‐dependent reduced glass transition temperatures (T_gs). The weaker lower transition agreed well with the MW‐dependent T_g(h) previously reported, while the much stronger upper transition matched the MW‐independent T_g(h) previously observed in low‐MW free‐standing films. Here, we investigate the nature of these two transitions by inspecting the temperature dependence of the films' thermal coefficient of expansion (TCE) and present physical aging measurements using ellipsometry both below and in‐between the two transitions. TCE values indicate approximately 80 to 90% of the film solidifies at the upper transition, while only 10 to 20% remains mobile to lower temperatures, freezing out at the lower transition. Physical aging is observed at a temperature below the upper transition, but above the lower transition, indicative of the upper transition being an actual glass transition associated with the α‐relaxation. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 64–75     

A study of enthalpic relaxation of a liquid crystal

A liquid crystal, BL038, which was observed not to crystallize, has a glass transition at 215 K and a nematic to isotropic transition at 380 K. Samples aged below the glass transition at various temperatures T _a, exhibited an endotherm at the transition which developed with extent of ageing time, t _a. We attribute this endotherm to the relaxation of the glass towards the equilibrium liquid. The progress of the relaxation process was measured using differential scanning calorimetry. On subsequent reheating, the aged glass showed an apparent shift in the glass transition to higher temperatures. The endotherm was used to define the extent of enthalpic relaxation and the maximum value observed was found to increase initially then decrease, with the extent of undercooling from the glass transition temperature, Δ T, passing through a maximum for a Δ T = 15 K. From the temperature dependence of the relaxation times, an apparent activation enthalpy for the relaxation process of 85 ± 10 kJ mol^-1 was determined. The small value of the activation enthalpy compared with that found in the ageing of polymers reflects differences in the molecular species involved in relaxation processes.     

Effect of thermoplastic toughening agent on glass transition temperature and cure kinetics of an epoxy prepreg

The isothermal time–temperature-transformation (TTT) cure diagram is developed in this article to investigate the effect of thermoplastic toughening agent on glass transition temperature (T _g) and cure kinetics of an epoxy carbon fiber prepreg, Cycom 977-2 unidirectional (UD) tape. The glass transition temperature was measured using differential scanning calorimetry (DSC) over a wide range of isothermal cure temperatures from 140 to 200 °C. Times to gelation and vitrification were measured using shear rheometry. The glass transition temperature master curve was obtained from the experimental data and the corresponding shift factors were used to calculate the activation energy. The kinetic rate model was utilized to construct iso-T _g contours using the calculated activation energy. It was observed that the iso-T _g contours did not follow the behavior of the neat epoxy resin, since they deviated from the gel time curve. This deviation was believed to be the effect of the thermoplastic toughening agent. The behavior of the neat epoxy resin in 977-2 was shown by constructing the iso-T _g contours using the activation energy obtained from gel time modeling.     

Effect of sample preparation on the glass‐transition of thin polystyrene films

We have investigated the effect of sample preparation on the glass‐transition temperature (T_g) of thin films of polystyrene (PS). By preparing and measuring the glass‐transition temperature T_g of multilayered polymer films, we are able to assess the contribution of the spincoating process to the reduced T_g values often reported for thin PS films. We find that it is possible to determine a T_g even on the first heating cycle, and that by the third heating cycle (a total annealing time of 15 min at T = 393 K) the T_g value has reached a steady state. By comparing multilayered versus single layered films we find that the whole T_g depends only on the total film thickness, and not on the thickness of the individual layers. These results strongly suggest that the spincasting process does not contribute significantly to T_g reductions in thin polymer films. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4503–4507, 2004     

Effect of anisotropic deformation on the differential scanning calorimetry response of polymer glasses

Large anisotropic deformation affects the physical state of a polymer glass, where the changes in the state of material are revealed by performing a differential scanning calorimetry (DSC) experiment. Previously, the deformation was applied to polymers well below their glass transition temperatures, and it was found that uniaxial compressive loading–unloading resulted in a broad exothermic peak on the DSC trace. Here we report on the effect on the subsequent DSC response of a deformation experiment performed in uniaxial extension on a ductile 50:50 co-polymer poly(BMA-co-MMA) (PBMA/MMA). The deformation of up to 80% strain was applied at T_g − 30°C and T_g − 40°C, that is, closer to T_g than in the previous work. Unlike in the well below T_g deformation case, the DSC trace contains an endothermic peak followed by an exothermic peak. The magnitude of the endothermic peak as well as the asymptotic glassy heat capacity increase with the amount of mechanical work performed during the deformation cycle.     

Thermodynamic and kinetic behaviour of salicylsalicylic acid

The thermal behaviour of salicylsalicylic acid (CAS number 552-94-3) was studied by differential scanning calorimetry (DSC). The endothermic melting peak and the fingerprint of the glass transition were characterised at a heating rate of 10°C min^-1. The melting peak showed an onset at T _on = 144°C (417 K) and a maximum intensity at T _max = 152°C (425 K), while the onset of the glass transition signal was at T _on = 6°C. The melting enthalpy was found to be Δ_mH = 28.9±0.3 kJ mol^-1, and the heat capacity jump at the glass transition was ΔC _P = 108.1±0.1 J K^-1mol^-1. The study of the influence of the heating rate on the temperature location of the glass transition signal by DSC, allowed the determination of the activation energy at the glass transition temperature (245 kJ mol^-1), and the calculation of the fragility index of salicyl salicylate (m = 45). Finally, the standard molar enthalpy of formation of crystalline monoclinic salicylsalicylic acid at T = 298.15 K, was determined as Δ_fH_m ^o(C₁₄H₁₀O₅, cr) = - (837.6±3.3) kJ mol^-1, by combustion calorimetry. This revised version was published online in August 2006 with corrections to the Cover Date.     

Glass transition kinetics of some Se-Te-Ag chalcogenide glasses

Summary The present paper reports the Differential Scanning Calorimetric (DSC) study of some Ag doped Se-Te chalcogenide glasses. DSC runs were taken at different heating rates. Well-defined endothermic and exothermic peaks were obtained at glass transition and crystallization temperatures. The variation of glass transition temperature T_gwith Ag concentration has been studied. It has been found that T_gdecreases with increase in Ag concentration. The heating rate dependence of T_gis used to evaluate the activation energy of glass transition (DE_t). The value of<span style='font-size:10.0pt; font-family:"SymbolProp BT";mso-bidi-font-family:"SymbolProp BT"'>DE_thas been found to increase with increase in Ag concentration followed by nearly constant value at higher concentrations of Ag.     

Crossover in dynamics of polymeric liquids: Back to Tll?

Light scattering spectra of two polymers, polyisobutylene (PIB) and polystyrene (PS), were analyzed in the broad frequency range at temperatures above the glass transition (T_g ). At high temperatures, the spectra followed the qualitative scenario suggested by mode‐coupling theory (MCT) of the glass transition. The crossover temperature (T_c ) was defined to be approximately 1.35 T_g in PIB and approximately 1.15 T_g in PS. At lower temperatures (T < T_c ), the light scattering spectra deviated strongly from the idealized MCT scenario. Different signs of the dynamic transition around T_c are discussed. The difference between the suggested interpretation and an old idea of the liquid–liquid transition in polymeric liquids is stressed: we describe the transition as purely dynamic in nature. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2785–2790, 2000     

Preparation and properties of the polyester made from 2.2-bis(4-hydroxycyclohexyl)propane and adipic acid

Poly[2,2-bis(4-oxycyclohexyl)propane adipate] was formed by melt polymerizing adipic acid and 2,2-bis(4-hydroxycyclohexyl)propane in the presence of n-butylhydroxyoxostannane. This polyester possessed a melting temperature (T_m) of 200°C and a glass transition temperature (T_g) of 75°C. An excellent notched impact strength of 22 ft. lbs./in. was its best physical property.     

Glass transition temperatures of ABA poly(styrene-b-isoprene) block copolymers by differential scanning calorimetry

The glass transition behavior of two sets of ABA poly(styrene-b-isoprene) block copolymers was examined by differential scanning calorimetry. In one series, the triblock copolymers had different total molecular weights and the same (30 wt %) polyisoprene content, in the other, the molecular weight was constant (30,000 g/mol) and the elastomer content was the variable. For all triblock copolymers studied, the data show an inward shift for the glass transition temperatures T_g of the corresponding homopolymers. This shift increases for the rigid-phase T_g as the polystyrene block length decreases. Depending on their molecular characteristics, two, three, or only one T_g were found. The third T_g was interpreted in terms of the existence of an interphase. Some of these conclusions could be confirmed by transmission electron microscopy.     

Glass transition of crosslinked polystyrene shells formed on the surface of calcium carbonate whisker

Glass transition of core/shell capsules consisting of calcium carbonate whisker as a core and crosslinked polystyrene as a shell was studied by differential scanning calorimetry. The thickness of the crosslinked shell was in the range of 26–81 nm. The crosslinked shells were revealed to show higher glass transition temperatures (T_g) than the corresponding bulk values. It was revealed that a thicker shell exhibits a lower T_g than a thinner shell, and that capsules without core (hollow capsules) exhibit lower T_g's than the corresponding core/shell capsules. These results suggest that the interfacial molecular interaction plays a role in the segmental relaxation, which is responsible for the glass transition. The difference in T_g between the core/shell and hollow samples was reduced when a coupling agent, methacrylic acid 3‐(trimethoxysilyl)propyl ester, was not included. This also suggests the interfacial effect on T_g. However, the results still suggest that the enhancement of T_g for the present crosslinked shells is not only due to the interfacial effect but also to the effects of chain configuration and heterogeneous crosslink. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2475–2485, 2006     

Glass transition temperature for epoxy-diamine networks

The glass transition temperature of systems based on epoxy resin and a number of diamines has been determined by using a torsion pendulum. An equation relating composition and crosslink density with the glass transition temperature has been established which gives reasonable predictions of the glass transition temperatures for systems based on aliphatic or aromatic amines and methylated amines and for systems containing a monofunctional epoxy diluent. The equation may be used to predict T_g for systems with non-stoichiometric quantities of curing agent and blends of amines. Deviation of the predicted and observed values for T_g is interpreted in terms of differences between definitions of T_g used by other workers and, also the occurrence of competing side reactions during polymerization which lead to additional crosslinks.     

Challenge and Solution of Characterizing Glass Transition Temperature for Conjugated Polymers by Differential Scanning Calorimetry

Thermomechanical properties of polymers highly depend on their glass transition temperature (T _g). Differential scanning calorimetry (DSC) is commonly used to measure T _g of polymers. However, many conjugated polymers (CPs), especially donor–acceptor CPs (D–A CPs), do not show a clear glass transition when measured by conventional DSC using simple heat and cool scan. In this work, we discuss the origin of the difficulty for measuring T _g in such type of polymers. The changes in specific heat capacity (Δc _p) at T _g were accurately probed for a series of CPs by DSC. The results showed a significant decrease in Δc _p from flexible polymer (0.28 J g^?1 K^?1 for polystyrene) to rigid CPs (10^?3 J g^?1 K^?1 for a naphthalene diimide‐based D–A CP). When a conjugation breaker unit (flexible unit) is added to the D–A CPs, we observed restoration of the Δc _p at T _g by a factor of 10, confirming that backbone rigidity reduces the Δc _p. Additionally, an increase in the crystalline fraction of the CPs further reduces Δc _p. We conclude that the difficulties of determining T _g for CPs using DSC are mainly due to rigid backbone and semicrystalline nature. We also demonstrate that physical aging can be used on DSC to help locate and confirm the glass transition for D‐A CPs with weak transition signals. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1635–1644