Free volume of molten and glassy polystyrene and its nanocomposites

Abstract

AbstractThe Pressure‐Volume‐Temperature (PVT) dependencies of polystyrene‐based clay‐containing nanocomposites (CPNC) were determined in the glassy and molten state. The PVT data in the melt were fitted to the Simha‐Somcynsky (S‐S) lattice‐hole equation‐of‐state (eos), yielding the free volume quantity, h = h(T, P), and the characteristic reducing parameters, P*, V*, T*. The data within the glassy region were interpreted considering that the latter parameters are valid in the whole range of independent variables, than calculating h = h(T, P) from the experimental values of V = V(T, P). Next, the frozen free volume fraction in the glass was computed as FF = FF(P). In the molten state the maximum reduction of free volume was observed at wsolid ≈ 3.6–wt % clay, amount sufficient to adsorb all PS into solidified layer around organoclay stacks. In the vitreous state FF increased with clay content from 0.6 to 1.6—this is the first time FF ≫ 1 has been observed. The highest value was determined for CPNC with the highest clay content, w = 17.1 wt %, thus well above wsolid. The derivative properties, compressibility, κ, and the thermal expansion coefficient, α, depend on T, P, and w. Plots of κ versus T indicate the presence of two secondary transitions, one at Tβ/Tg ≈ 0.9 ± 0.1 and other at TT/Tg = 1.2 ± 0.1. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2504–2518, 2008