Time-Dependent Pinning of Nanoblisters Confined by Two-Dimensional Sheets. Part 2: Contact Line Pinning

Pinning of droplets on solids is an omnipresent wetting phenomenon that attracts intense research interest. Unlike in classical wetting, pinning effects in a novel wetting problem where droplets are confined onto the substrates by elastic films have hardly been investigated. Here, following our study in an accompanying paper (part 1) on the static mechanics of nanoscale blisters confined between a two-dimensional elastic sheet and its substrate, we investigate in this part the pinning behaviors of such blisters by using atomic force microscopy. The blisters' lateral retention forces are shown to scale almost linearly with their contact lines and to increase until saturation upon increasing their resting times. Our analysis reveals a mechanism of microdeformation of the substrate at the contact line. The creep of the microdeformation is found to cause the time-dependent pinning, which is evidenced by residual fine ridge structures left by blisters after their spread after long resting times.