Scaling of high-pressure viscosity data in low-molecular-weight glass-forming liquids

We discuss the phenomenology related to the pressure behavior of viscosity in low-molecular-weight glass-forming liquids. We show that the effect of p ressure on viscosity in two examined glass-forming systems, salol and ortho -terphenyl, can be satisfactorily described, over considerable ranges of pr essure (up to 1 GPa) and temperature (300-425 K), by the two-parameter pres sure law which has been proposed previously for the relaxation time shift. The presented analysis indicates that one of the parameters (the pressure c ounterpart of the Vogel-Fulcher-Tammann law parameter D, which accounts for the fragility of a glass former) is independent of temperature in salol an d ortho-terphenyl. As a consequence, the scaling plot which normalizes data collected for different temperatures can be constructed for a given glass former. On the basis of the presented considerations, a general form of the temperature-pressure viscosity "equation of state'' is proposed. [S0163-18 29(99)14329-7].