Glass, transition physical states

Despite its apparent simplicity, the operational definition of Tg given above comprises both of the key aspects of the physics of the glass transition. It states that, when a solid is heated up to Tg, it acquires enough thermal energy to be able to overcome the superposition of two different types of resistance to the large-scale motions of its components ... 

As appHed to hydrocarbon resins, dsc is mainly used for the determination of glass-transition temperatures (7p. Information can also be gained as to the physical state of a material, ie, amorphous vs crystalline. As a general rule of thumb, the T of a hydrocarbon resin is approximately 50°C below the softening point. Oxidative induction times, which are also deterrnined by dsc, are used to predict the relative oxidative stabiHty of a hydrocarbon resin. 

T and are the glass-transition temperatures in K of the homopolymers and are the weight fractions of the comonomers (49). Because the glass-transition temperature is directly related to many other material properties, changes in T by copolymerization cause changes in other properties too. Polymer properties that depend on the glass-transition temperature include physical state, rate of thermal expansion, thermal properties, torsional modulus, refractive index, dissipation factor, brittle impact resistance, flow and heat distortion properties, and minimum film-forming temperature of polymer latex... 

This difference in spatial characteristics has a profound effect upon the polymer s physical and chemical properties. In thermoplastic polymers, application of heat causes a change from a solid or glassy (amorphous) state to a flowable liquid. In thermosetting polymers, the change of state occurs from a rigid solid to a soft, rubbery composition. The glass transition temperature, Tg, ... 

The physical properties (7-10) of our E-V copolymers are sensitive to their microstructures. Both solution (Kerr effect or electrical birefringence) and solid-state (crystallinity, glass-transitions, blend compatibility, etc.) properties depend on the detailed microstructures of E-V copolymers, such as comonomer and stereosequence distribution. I3C NMR analysis (2) of E-V copolymers yields microstructural information up to and including the comonomer triad level. However, properties such as crystallinity depend on E-V microstructure on a scale larger than comonomer triads. 

The presence of a solvent, especially water, and/or other additives or impurities, often in nonstoichiometric proportions, may modify the physical properties of a solid, often through impurity defects, through changes in crystal habit (shape) or by lowering the glass transition temperature of an amorphous solid. The effects of water on the solid-state stability of proteins and peptides and the removal of water by lyophilization to produce materials of certain crystallinity are of great practical importance although still imperfectly understood. 

Figure 5. Logarithm of the retractive force at 49% strain (lower curve) and sample temperature (upper curve) plotted against logarithm of time reduced to 263 K. Cross-links are introduced at log t/aT is 3 in the glassy state where the spike on the force curve is due to thermal contraction upon cooling below the glass transition temperature. Equilibrium force at 263 K after cross-linking is feQ. (Reproduced, with permission, from Ref. 27. Copyright 1981, Journal of Chemical Physics.)...

The effect of physical aging on the crystallization state and water vapor sorption behavior of amorphous non-solvated trehalose was studied [91]. It was found that annealing the amorphous substance at temperatures below the glass transition temperature caused nucleation in the sample that served to decrease the onset temperature of crystallization upon subsequent heating. Physical aging caused a decrease in the rate and extent of water vapor adsorption at low relative humidities, but water sorption could serve to remove the effects of physical aging due to a volume expansion that took place in conjunction with the adsorption process. 

Everything discussed in the present paper shows that the free-volume concept, although very useful from the qualitative point of view, cannot be used for the quantitative description of many properties of polymer systems. This is especially clear when we consider glass-transition phenomena using the idea of the iso-free-volume state. Many experimental data, discussed above, show that this concept cannot be applied even to polymer materials having the same chemical nature but a different physical structure. From the experimental results Goldstein104 had already concluded that the concept of free-volume cannot be correct. These conclusions were carefully discussed later105. ... 

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