Enhanced adhesion and compliance of film-terminated fibrillar surfaces

Abstract

We present studies of a bio-inspired film-terminated fibrillar surface that has significantly enhanced adhesion and contact compliance compared with a flat control. We show that adhesion hysteresis arises from the architecture of the interfacial region. Measured in cyclic indentation experiments, it can be nearly five times the absolute work of adhesion for a flat control. Using a two-dimensional model, we propose that hysteresis develops as a result of crack trapping by fibril edges. The crack propagation mode is consistent with this model, as is the observation that with increasing hysteresis crack opening adhesion energy increases whereas crack closing adhesion energy decreases compared with a flat control. Contact compliance of the fibrillar structure is up to seven times more than that of a flat control. We present a model for the contact compliance of such structures which is in good agreement with measurements.