Shielding effect of hydrophobic graphene on contact time dependence of adhesion force and instability with repeated contacts at silica/silica interface.

Contact time dependence of adhesion force demands clarification. Under a humid condition, with some tipless silica cantilevers, adhesion forces on silica and silica-based graphene were measured with an atomic force microscope (AFM) to investigate the dependence and the role of surface hydrophilicity in the dependence. The results show that hydrophobic graphene can shield the contact time dependence and instability with repeated contacts at a silica/silica interface. Depending on surface hydrophilicity, there are three different adhesion force behaviors with dwell time for the silica/silica contact: (1) three stages with stable-increasing-stable trends; (2) logarithmic increase; (3) independence. Furthermore, the adhesion force at the silica/silica interface is greatly influenced by repeated contacts with an unstable behavior. These behaviors are mainly attributed to the evolution process of a liquid bridge. However, adhesion forces on graphene do not depend on dwell time, and the factor of repeated contacts has little effect on the results. These behaviors at the silica/graphene interface are attributed to the hydrophobic property and chemical inertness of the graphene. The outcomes presented here can help to reveal the adhesion mechanism and promote the anti-adhesion design for silicon-based structures and devices in the microscale and nanoscale. [ABSTRACT FROM AUTHOR]