Ultrathin films of simple nonpolar molecular fluids (3–8 segmental dimensions thick) show a strikingly long relaxation time in response to oscillatory shear when confined between mica plates at 27 °C. When the shear rate exceeds this inverse time, the effective viscosity decays as an apparent power law in the shear rate, implying considerable distortion of the dynamic structure. The relaxation time is orders of magnitude longer than the Brownian relaxation time in the bulk state and may reflect collective motions induced by confinement.

• Received 1 March 1991

DOI:https://doi.org/10.1103/PhysRevLett.66.2758