Time-Dependent Dynamic Behaviors of a Confined Liquid To Achieve Tailored Adhesion Force with Repeated Contacts...

The adhesion forces between two silica surfaces were measured by using an atomic force microscope with different experimental parameters in air to investigate the dynamic behavior of a confined liquid. Results show that the adhesion force is time-dependent and increases at first sharply and then slightly with dwell time until saturation is reached, with a long equilibrium time. This behavior is well explained by a dynamic meniscus model, in which a liquid bridge grows gradually because of liquid film flow with a large viscosity. Also, the large viscosity was attributed to the formation of orthosilicic acid and subsequent polymerization. With repeated contacts, the liquid bridge changes into two droplets on both surfaces after separation. The liquid in both forms can be controlled to flow into or out of the contact zone by the experimental parameters to achieve tailored adhesion forces. If the liquid of previous contact remains in the contact zone, the adhesion force increases with repeated contacts and then reaches saturation, which can also be explained by the model qualitatively. However, if the liquid droplets vanish before the next contact, the adhesion force usually decreases or remains unchanged. More liquid will be collected with larger contact times. Meanwhile, the droplets remaining on the surfaces get smaller until they vanish without a contact. Moreover, both piezo velocity and scan distance can be used to control the proportion of contact time. In addition, a viscous force should be considered with a large retraction velocity. The changing trend and magnitude of adhesion force depend on the experimental parameters and their coupling effects. The results may facilitate the anti-adhesion design of small-scale silicon-based systems.