Memory effects in the attachment of thin films to liquid surfaces

We study the dynamics of depositing or peeling off a thin polymer film at an air-water surface. In our experiment, we control the velocity of the film withdrawal or attachment while measuring the force required to do so. The observed dynamics is hysteretic, wherein the force depends on the direction of motion even at the lowest attainable velocities, but the magnitude of the hysteresis loop appears to be independent of the velocity. When the motion of the film is halted, the relaxation to equilibrium configuration is extremely slow, and appears to be logarithmic in time. Quite remarkably, the relaxation dynamics retains the memory of velocity history. This behavior, involving hysteresis, slow relaxation and memory effects are hallmarks of glassy systems which have access to a large number of relaxation modes with a broad distribution of relaxation times. It is surprising that our simple system exhibits some of these features.