Effect of Pressure on the Dielectric Spectra of Polymeric Systems

Pressure is one of the essential thermodynamic variables that control the structure and the associated dynamics of polymers and glass-forming systems. The pressure dependence of the viscoelastic relaxation times is of paramount importance because hydrostatic pressure is encountered in the extrusion and molding processes [1]. Dielectric spectroscopy was among the first dynamic techniques to take advantage of pressure through the recognition of the fact that the dynamic state of a glass-forming system can only be completely defined if T and P are specified [2]. This observation motivated studies of the effect of pressure on the dielectric α- and β-processes in a number of systems in the early 1960s [3]–[6]. The main concern in these pioneering studies was to unravel the effect of pressure on separating mixed processes. Since then, there have been reports on the effect of pressure on the relaxations of oxidized polyethylene [7],on the plasticization of poly(ethyl methacrylate) by sorbed carbon dioxide [8] and on the dynamics of a liquid crystalline siloxane polymer [9].