Fragility under pressure:: Diamond anvil cell viscometry of ortho-terphenyl and salol

Viscosities of the fragile glass-forming liquids ortho-terphenyl and salol have been measured in a diamond anvil cell for pressures up to 1 GPa and for temperatures 300 K < T < 425 K. Utilizing a rolling ball technique viscosities up to 10(8) mPas could be determined. From these data the pressure dependence of the fragility index, corresponding to a reference viscosity of about 10(8) mPas, has been calculated. For ortho-terphenyl it is found that this ''low-viscosity'' fragility index is pressure invariant within experimental error. Salol exhibits a more complicated behavior. (C) 1998 American Institute of Physics.