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/sup -2/ to 10/sup 10/ Hz) by varying either pressure or temperature. The measurements were undertaken in two different conditions: under isobaric condition (atmospheric pressure) varying temperature down to the supercooled and glassy phases and under isothermal conditions by changing the pressure from 0.1 to 270 MPa. The analysis of the structural relaxation time behavior either varying the temperature or the pressure was found to agree well with a previously derived expression for /spl tau/(T, P) based on a cooperative model. In particular it was found that with a unique set of parameters it is possible to describe the 2-dimensional surface /spl tau/(T, P) over a wide range of temperature and pressure. This result agrees well with the observed independence of the fragility in both isothermal and isobaric conditions.