Influences of Relative Humidity and Dwell Time on Silica/Graphene Adhesion Force of a Cone–Plane Contact

Graphene has exceptional electronic, mechanical, and thermal properties, and it is expected to have important applications in integrated circuits and other microelectronic fields. Its performances are greatly affected by surface adhesion force when it is used in a humid environment. In this paper, based on the law of variable water contact angle changing in the process of water vapor condensation, we established a cone-plane contact model, which is related to relative humidity and dwell time, to reveal the internal mechanism of the influence of relative humidity and dwell time on silica/graphene adhesion force. First, the silica/graphene adhesion force dependence of dwell time was measured by atomic force microscopy (AFM) at 45-85% RH. Then, the changing process of the meniscus between the AFM tip and the graphene surface was discussed, and the function of adhesion force with variables of dwell time and contact angle was established. Furthermore, the theoretical and experimental results were compared and analyzed. The results show that with the increase of relative humidity and dwell time, the capillary condensation increases, but the water contact angle of the cone material decreases. This causes the adhesion force to increase first and then decrease after it reaches a threshold value. Furthermore, the variable water contact angle of the graphene surface increases, but the adhesion force decreases gradually with the increase of surface water film. The theoretical results are in good agreement with the experimental results.