Glass pressure densified

Naoki, M. Mori, H. Owada, A., "Equation of State of Pressure-Densified Glasses of Poly(vinyl chloride)," Macromolecules, 14, 1567 (1981). 

Kogowski, G. J., and FiUsko, F. E., Experimental-study of the density recovery of pressure-densified polystyrene glasses. Macromolecules, 19, 828-833 (1986). 

Schmidt, M., and Maurer, R H. J., Isotropic pressure-densified atactic poly(methyl methacrylate) glasses free-volume properties from equation-of-state data and positron annihilation lifetime spectroscopy. Macromolecules, 33, 3879-3891 (2000a). 

The experimental increase of T with pressure of polystyrene is indicated in Fig. 6.122 by line BE. The liquid D cooled at elevated pressure, freezes at the higher glass transition temperature E than liquid C cooled at atmospheric pressure (T = B). On releasing the pressure below T, the compressed sample F expands to G, not to the level A of a glass cooled at atmospheric pressure. The glass remains pressure densified by the amount AG FF, where F is the volume after isothermal compression from A. This densification corresponds to a volume strain. 

Figure 6.124 shows for polystyrene cooled at atmospheric pressure the typical DSC trace of enthalpy relaxation for a sample cooled slowly and heated fast. This experiment represents the typical hysteresis or enthalpy relaxation described in Fig. 6.6. Carrying out the same DSC experiments with a pressure-densified glass instead of a slowly cooled glass leads to the much different response of the upper curves in Fig. 6.124. The beginning of the glass transition is shifted considerably...

Thermal Analysis of Annealed Pressure-densified Polystyrene Glasses... 

Cooling microphase separated tr iblock copolymer melts of S/I/S under pressure in situations where large amounts of flow occur (thin bonds) and allowing them to solidify may produce behavior that is related to that observed in pressure densified homopolymer glasses. Thermal analysis supports this conclusion. 

Figure 1 Schematic representation of the preparation of pressure densified and stressed glasses.

Figure 2 The apparent heat capacity at 20K/min. of 110 day old pressure densified PVC glasses which had been prepared by cooling from 413 K under the indicated pressures.

The concept of a single structural transition in amorphous material, i.e., an amorphous-amorphous transition, was coined in 1985 by Mishima et al. [25] on the example of water. Today, in many respects the nature of pressure- and/or temperature-induced transformations in glasses and amorphous solids remains unclear. In most cases, the pressure treatment of glasses and amorphous solids results in residual densification. In the process, the densified glasses and... 

The maximum densification of 18-20% is achieved after a pressure of 16-20 GPa—room temperature treatment or after 5-8 GPa—800-1000 K treatment. The densified glasses have predominantly tetrahedral coordination of silica atoms, Z 4-4.5 [14, 71, 88], Elastic moduli and optical characteristics of densified glasses are distinctly different from those of pristine silica glasses. 

The corrected Raman spectra of nonnal and shock-densified Si02 glasses aie shown in Fig. 3.11. The Raman bands show significant pressure variations m frequency, bandwidth, and relative intensity (Fig. 3.12). The broad band iieai 455 cm t shows large variations of frequency and width. Generally, there is an inverse correlation between the frequency of this band and the Si O-Si ang.le... 

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