We study the resistance to sliding of liquid films 1-6 molecules thick. The apparent dynamic viscosity at 1 Hz of nonpolar liquids confined between parallel plates of atomically smooth mica is considerably enhanced over that of the isotropic fluids and shows extreme dependence on pressure. Rapid, reversible switching between liquidlike and noncompliant responses as a function of small changes in normal pressure is also found, suggesting a phase transition to a solidlike structure.

• Received 15 September 1988

DOI:https://doi.org/10.1103/PhysRevLett.61.2570