No abstract

Dielectric spectroscopy was used to follow the component dynamics in the miscible blend of poly-(vinyl methyl ether) (PVME) and poly(2-chlorosytrene) (P2CS). For the PVME component (which has the more intense loss peak due to its higher polarity), the shape of the segmental relaxation peak depends only on the relaxation time and is otherwise independent of thermodynamic conditions. This is in accord with the general behavior of neat materials. By measuring the spectra as a function of both temperature and pressure, the relative effect of temperature and volume on the segmental relaxation times was quantified from ratio of the isochoric and isobaric activation enthalpies. This ratio is essentially the same for the neat polymers, but blending has a disparate effect of the components: volume effects become stronger for the PVME but are diminished for P2CS. Similarly, the fragilities of the neat components are quite close but change markedly in the blend. The P2CS component has a fragility of 32, which is lower than found for any neat polymer. In comparison to the segmental dynamics, transport of mobile ions in the blend is relatively insensitive to volume (or pressure). These effects are reflected in the magnitude of the respective exponents of the scaling function, which enables collapse of the relaxation times onto single, component-specific master curves.

The role of jamming (steric constraints) and its relationship to the available volume is addressed by examining the effect that certain modifications of a glass-former have on the ratio of its isochoric and isobaric activation enthalpies. This ratio reflects the relative contribution of volume (density) and temperature (thermal energy) to the temperature-dependence of the relaxation times of liquids and polymers. We find that an increase in the available volume confers a stronger volume-dependence to the relaxation dynamics, a result at odds with free volume interpretations of the glass transition.