Title: A pinned contact line encodes a detailed memory of its motion.

Author (Talk): Ashbell Abraham,

Abstract:

The contact line around a drop of liquid generally has an irregular shape, revealing the disorder of the solid substrate beneath. In this talk we show that the shape of a contact line also encodes a memory of the magnitude of its past motion. We “train” the system by cyclically injecting and withdrawing a constant volume of liquid. The contact line reaches a steady state and is not changed by further cycles. Once encoded, the memory of this volume can be retrieved by additional cycles of driving, beginning with small amplitudes and increasing. When the training amplitude is reached, the shape of the contact line is recovered. However, when the amplitude iteration exceeds that of the training amplitude, the memory is erased and the steady state is lost. This behavior is reminiscent of return-point memory, a phenomenon best known in ferromagnets. Return-point memory, and the process of reaching a steady state, can provide insight on pinning sites, energy barriers, and dynamics of the contact line, and offers a new framework for manipulating its shape.