ACTA

Relaxation of Free Volume in Polycarbonate andPolystyrene Studied by Positron Annihilation Lifetime Spectroscopy

D. Cangialosi^a, M. Wübbenhorst^a, H. Schu^bt and S.J. Picken^a
^aDept. of Polymer Materials and Engineering, Delft University of Technology, Julianalaan 136, 2628 BL, Delft, The Netherlands
^bInterfaculty Reactor Institute, Delft University of Technology, Mekelweg 15, 2629 JB, Delft, The Netherlands

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Received: 20 09 2004;

We present the time evolution of polycarbonate and polystyrene free volume probed by positron annihilation lifetime spectroscopy, which occurs after thermal rejuvenation above the glass transition temperature (T_g) and after plastic deformation via cold rolling. The ortho-positronium (τ_o-Ps) lifetime and its intensity (I_o-Ps) are used to characterise, respectively, size and concentration of the free volume holes. Our results suggest that the effect of plastic deformation on the polymer microstructure is far different from that of a thermally rejuvenated sample contrarily to common beliefs. In particular, plastic deformation results in an increase inτ_o-Ps and a decrease in I_o-Ps, whereas rejuvenation above T_g results in an increase in I_o-Ps whileτ_o-Ps remains unchanged. In addition, physical aging below T_g after plastic deformation manifests as a reduction of τ_o-Ps, whereas a decrease in I_o-Ps is observed after thermal rejuvenation. These results corroborate the idea of an amorphous-amorphous transition induced by plastic deformation.

DOI: 10.12693/APhysPolA.107.690
PACS numbers:78.70.Bj, 82.35.Lr, 64.70.Kb