Hysteretic wetting and dewetting of a thin sheet peeling off a liquid interface

We peel a thin polymeric sheet on and off an air-water interface with controlled velocity.

Under near-quasistatic conditions, measuring the force of peeling allows us to obtain contact

angles via force balance at various scales, as we have shown in prior work. This configuration

allows us to determine the local wetting angle at the 3-phase contact line between air, water

and sheet, and characterize the time-dependent wetting dynamics with higher temporal and

force resolution than is possible with imaging. In pulling up or pushing down the sheet, we find

that the contact line does not slip until we reach an angle close to the receding or advancing

contact angles, respectively. This point at which slip occurs is reproducible and independent of

velocity, while the final advancing or receding angle has a weak dependence on the speed of

peeling. Beyond this point, there is a steady state characterized by slipping and fluctuations of

the contact line. On stopping the peeling process, the contact angle relaxes very slowly to

equilibrium, with a time dependence that depends on whether the relaxation is from advancing

or receding conditions, also depending weakly on the speed of peeling. Repeated loops of

wetting and dewetting retain details of microscopic noise structure, which we identify as elastic

events occurring due to forcing at the contact line.