A comparison of concentration-glasses and temperature-hyperquenched glasses: CO 2 -formed glass versus temperature-formed glass Mataz Alcoutlabi, Lameck Banda, Gregory B. McKenna * Department of Chemical Engineering, Texas Tech University, MS-3121, Lubbock, TX 79409-3121, USA Received 10 February 2004; accepted 2 April 2004 Available online 19 June 2004 Abstract Prior work from this laboratory has reported anomalous differences in the viscoelastic responses between temperature-jump formed glasses and carbon dioxide pressure-jump or relative humidity formed glasses. In the present work, we investigate the anomalous behaviour further by examining the structural response of an epoxy resin after pre-annealing treatments. In particular, we have measured the volume change of amine-cured diglycidyl ether of bisphenol A after thermal and carbon dioxide pressure (PCO 2 ) treatments. Our results show that contrary to prior interpretations in the literature, a plasticizer quench is different from a temperature hyperquench. Consistent with our prior work, the CO 2 -formed glass is more stable than the temperature-formed glass in spite of the former having a higher excess volume. Our new results show that the stability persists to above the nominal glass temperature, contrary to what happens in a temperature hyperquench. q 2004 Elsevier Ltd. All rights reserved. Keywords: Structural relaxation; Hyperquenched glass; Glass transition 1. Introduction In prior extensive calorimetric studies of enthalpy recovery in poly (vinyl chloride) (PVC), Berens and Hodge [1–5] reported that vapor quenched samples exhibited behaviors similar to those of hyperquenched glasses. The authors observed that the enthalpy recovery exhibited a typical delayed approach towards equilibrium from the nonequilibrium condition produced by the thermal, solvent vapor or mechanical histories used to traverse the glass transition. Similar findings have also been reported by Chan and Paul [6]. Based on differential scanning calorimetry (DSC) results (Fig. 1(a)), Berens and Hodge constructed an enthalpy–temperature diagram, shown in Fig. 1(b), which they interpreted to imply that the vapor- quenched glass is the same as a temperature-hyperquenched glass. We show in the present work that the schematic for the vapor-quenched glass shown in Fig. 1(b) is only partially correct. We show that the vapor-quenched glass is, in fact, different from the temperature hyperquenched glass and part of the misinterpretation in the Berens and Hodge work arises from the fact that the DSC measurements provide only second derivative information C P ¼ ›H ›T   P ¼ › ›T ›ðG=T Þ ›ð1=T Þ   P   P ; and a direct measurement of the first derivative of the free energy, i.e. volume, V ¼ ›G ›P   T results in a clearer picture of the differences in the temperature-hyperquench formed glass and the vapor- quench formed glass. In the following, we discuss more fully the results of the work of Berens and Hodge and follow this with our results, discussion and conclusions. We start by focusing on the enthalpy recovery results reported by Berens and Hodge [1] and particularly on the vapor- and temperature-hyperquenched PVC. Fig. 1(a) and (b) show the results of Berens and Hodge [1] in which they created glasses by vapor quenching and interpreted the results as similar to a thermal-hyperquench. The tempera- ture-hyperquenched PVC glass was created by cooling through T g at a high cooling rate of 320 8C/min. Fig. 1(a) shows the DSC curves obtained for free-cooled PVC powders which were subsequently treated overnight with CH 3 Cl vapor at 30 8C and 0.5 MPa pressure, evacuated and 0032-3861/$ - see front matter q 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymer.2004.04.004 Polymer 45 (2004) 5629–5634 www.elsevier.com/locate/polymer * Corresponding author. Tel.: þ 1-8067423553; fax: þ 1-8067423552. E-mail address: greg.mckenna@coe.ttu.edu (G.B. McKenna).