Influence of temperature and pressure on the dynamics of glass formers explored by dielectric spectroscopy

The dynamics of the epoxy compound polyphenyl-glycidyl-ether-coformaldehyde was investigated by wideband dielectric spectroscopy (10(-2) to 10(10) Hz) by varying either pressure or temperature. The measurements were undertake n in two different conditions: under isobaric condition (atmospheric pressu re) varying temperature down to the supercooled and glassy phases and under isothermal conditions by changing the pressure from 0.1 to 270 MPa. The an alysis of the structural relaxation time behavior either varying the temper ature or the pressure was found to agree well with a previously derived exp ression for tau (T, P) based on a cooperative model. In particular it was f ound that with a unique set of parameters it is possible to describe the 2- dimensional surface tau-(T, P) over a wide range of temperature and pressur e. This result agrees well with the observed independence of the fragility in both isothermal and isobaric conditions.