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

Abstract

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 108 mPas could be determined. From these data the pressure dependence of the fragility index, corresponding to a reference viscosity of about 108 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.