Free volume in two differently plasticized poly(vinyl chloride)s: a positron lifetime and PVT study G. Dlubek a, * , V. Bondarenko b , J. Pionteck c , M. Supej b,1 , A. Wutzler d , R. Krause-Rehberg b a ITA Institut fu ¨r innovative Technologien GmbH, Ko ¨then, Außenstelle Halle, Wiesenring 4, D-06120 Lieskau (bei Halle/S), Germany b Martin-Luther-Universita ¨t Halle-Wittenberg, Fachbereich Physik, D-06099 Halle/S, Germany c Institut fu ¨r Polymerforschung e.V., Hohe Strasse 6, D-01069 Dresden, Germany d Institut fu ¨r Polymerwerkstoffe e.V., Geusaer Straße, Geba ¨ude 131, D-06217 Merseburg, Germany Received 6 January 2003; received in revised form 6 January 2003; accepted 23 January 2003 Abstract The temperature dependence of the specific volume, V ; and of the mean size of local free volumes (holes), v h ; of poly(vinyl chloride) containing 10 wt% (PVC-h) and 30 wt% (PVC-s) of the plasticizer di-n-butyl phthalate (DBP) were studied by pressure – volume – temperature (PVT) and positron annihilation lifetime spectroscopy (PALS) experiments. Using the Simha – Somcynsky equation-of-state, the hole fraction h was calculated from the PVT data. It was found that the thermal expansivity of the specific volume V ; the specific free volume V f ¼ hV ; and v h increase with the content of plasticizer. From the comparison of V and V f with v h the hole number per gram N 0 h is estimated. Other than v h ; N 0 h does not depend on the temperature nor on the content of plasticizer. q 2003 Elsevier Science Ltd. All rights reserved. Keywords: Specific volume; Free volume; Positron annihilation 1. Introduction Positron annihilation lifetime spectroscopy (PALS) provides unique information about the properties of subnanometer size local free volumes (holes) appearing due to the structural (static or dynamic) disorder in amorphous polymers [1]. The holes form the (excess) free volume which effects thermal, mechanical, and relaxation properties of polymers. While PALS itself is only able to measure the mean volume, v h ; and the size distribution of these holes, the combination of PALS with the macroscopic volume, for example from pressure – volume – temperature (PVT) experiments, allows the number of holes and their entire volume fraction to be estimated [2–4]. In this way, all parameters of free volume, at least from volumetric point of view, can be determined. In the current work we studied, using PALS, the mean size of local free volumes in two types of poly(vinyl chloride) (PVC) containing different amounts of plasticizer. PVT experiments were performed and analysed by using the Simha – Somcynsky (S – S) equation of state (eos) (see Refs. [5,6] and references given therein). From our experiments we estimated characteristic parameters of the free volume, such as the S–S eos hole fraction, the specific free volume, the mean hole size, and the number density of holes. The main aim of our work is to study the temperature dependence of these parameters in PVC and the effect of plasticizer on them. 2. Experimental 2.1. Materials The materials under investigation were two different types of PVC both supplied by Chemische Werke Buna- Schkopau/Germany (now European Vinyl Corporation). The samples denoted by PVC-hard (PVC-h) and PVC-soft (PVC-s) have molecular weights of M w =M n ¼ 150; 000=65; 000 (g/mol) and M w =M n ¼ 193; 000=89; 500 (g/mol) determined by GPC using PS standards for 0032-3861/03/$ - see front matter q 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0032-3861(03)00056-9 Polymer 44 (2003) 1921–1926 www.elsevier.com/locate/polymer 1 On leave from: Department for Biomechanics, Faculty of Sport, University of Ljubljana, Gortanova 22, 1000 Ljubljana, Slovenija. * Corresponding author. Tel: þ 49-345-5512902; fax: þ 49-40- 3603241463. E-mail address: gdlubek@aol.com (G. Dlubek).