Segmental Mobility of Polymers Near Their Glass Temperature

Abstract

Glass forming polymers exhibit a rapid rise of activation energy for molecular motion as T is lowered through the glass temperature. This phenomena is explained here in two different but largely equivalent ways. The first method assumes that in order for a polymer segment to move (i.e., rotate or jump) an energy greater than a critical energy E must be localized on it and its neighbors. The second approach stipulates that a segment may not move unless more than a certain critical amount of free volume is associated with it and its neighbors. Both approaches lead to good agreement with experimental data available for polystyrene and polyisobutylene. The critical values of E and the free volume for these polymers are found and shown to be reasonable. Conclusions are drawn concerning factors influencing the glass temperature.

Do MELT or CONTIN Programs Accurately Reveal the o-Ps Lifetime Distribution in Polymers? Analysis of Simulated Lifetime Spectra

“…Investigating amorphous polymers, Liu et al [21] analysed asymmetrical o-Ps lifetime distributions from which an asymmetrical hole size distribution, correlating well with the free-volume theory of Simha and Somcynsky [22], was estimated. Other authors [23] present more symmetrical o-Ps lifetime distributions, the hole size distributions derived from which agree well with the free-volume theory of Bueche [24], who predicted a Gaussian hole size distribution. Recently, Dai and Jean [18] showed that the asymmetry in analysed distributions is due to the mathematical method used in CONTIN.…”

Transport Properdines of Gases in Polymers: Bibliographic Review

“…Cohen and Turnbull (1959) considered the diffusion of hard spheres in a liquid as the result of a redistribution of the free volume inside the liquid with no energy variation associated. Besides, in 1953, Bueche gave an analysis of the segmental mobility in polymers which was based on the theory of free volume fluctuations (Bueche, 1953;Slater, 1939).…”

Free-volume change during the volume phase transition of polyacrylamide gel studied by positron annihilation: Solvent-composition dependence

“…To compare the relative free-volume fraction deduced from these experimental data to that estimated from a free-volume theory, a theoretical free-volume fraction was calculated from viscosity data according to the Doolittle equation, 46 ln ϭ C 1 ϩ C 2 /f, where is the viscosity and C 1 (ln 0 ) and C 2 are constants. ln is plotted versus a reciprocal relative free-volume fraction, 1/f s , and is shown in Figure 4 Buchue 47 and Fox and Flory 48 suggested that the temperature dependence of the free-volume fraction for a polymer system is the difference between the thermal expansion coefficient above and below the glass-transition temperature, T g , as shown below:…”