The Structure of the Free Volume in Poly(styrene-co-acrylonitrile) from Positron Lifetime and Pressure Volume Temperature (PVT) Experiments

✍ Scribed by Günter Dlubek; Vladimir Bondarenko; Ilham Y. Al-Qaradawi; Duncan Kilburn; Reinhard Krause-Rehberg

• Publisher: John Wiley and Sons
• Year: 2004
• Tongue: English
• Weight: 199 KB
• Volume: 205
• Category: Article
• ISSN: 1022-1352
• DOI: 10.1002/macp.200300104

✦ Synopsis

Abstract

Summary: The structure of the free volume and its temperature dependence between 25 and 190 °C of copolymers of styrene with acrylonitrile, SAN (0 to 50 mol‐% AN), is studied by pressure volume temperature (PVT) experiments and positron annihilation lifetime spectroscopy (PALS). In this second part of the work, PALS data are reported from which the temperature dependence of the mean size and size distribution of local free volumes (subnanometer size holes) is analysed. The mean hole volume, v~h~, varies in PS between 105 Å^3^ (27 °C) and 220 Å^3^ (190 °C), and shows a systematic decrease with increasing AN content, at T~g~ from 121 Å^3^ for PS to 102 (±2) Å^3^ for SAN50. The specific number of holes, $N_{\rm h} '$, estimated from a comparison of PVT and PALS results, is independent on the temperature and the composition of SAN, $N_{\rm h} '$ = (0.56 ± 0.02) × 10^21^ g^−1^ which corresponds to N~h~(T~g~) = $N_{\rm h} '$/V(T~g~) = 0.59 nm^−3^ and 1/N~h~(T~g~) = 1.7 nm^3^ for the volume which contains one hole. The analysed size distributions of the holes above T~g~ follow the compressibility of the free volume as it is predicted by the theory of thermal volume fluctuation. Moreover, we showed that the bulk elasticity modulus follows mastercurves as a function of v~h~ above and below T~g~.

Free volume hole radius distribution n(r~h~) in PS for three different temperatures.

magnified imageFree volume hole radius distribution n(r~h~) in PS for three different temperatures.