Evidence for capillarity contributions to gecko adhesion from single spatula nanomechanical measurements
Huber, G., Mantz, H., Spolenak, R., Mecke, K., Jacobs, K., Gorb, S., Arzt, E., Proc. Natl Acad. Sci. USA 102, 16293–16296 (2005).
capillarity, adhesion, monolayer, spatula, contact angle
This paper shows that humidity affects gecko adhesion on the spatular level, i.e., the smallest level of the hierarchial gecko foot structure. This finding disagrees with previous studies which rejected the contribution of capillarity and which suggested that van der Waals forces dominate the high adhesion.
Because of the small size of the spatulae (<math>\approx</math> 200 nm wide and long), atomic force microscopy (AFM) was used to determine the pull-off force of a single spatula. Two types of Si wafers were used as surfaces: type N, with a thin Si oxide layer; and type T, with an Si oxide layer <math>\sim</math> 100 times thicker.