Effects of Thickness and Curvature on the Adhesion Properties of Cylindrical Soft Materials by a Point Contact Method

Abstract

The effects of the sample thickness, h, and the curvature, R, on the adhesion properties between two viscoelastic materials were investigated with the use of a point contact method. Poly (sodium acrylate) (PSA) hydrogels and cross-linked polydimethylsiloxane (PDMS) were used in this study, where h and R were independently changed. The W (normal load)-dependences of the apparent contact area, S 0, and the displacement of the bulk deformation, Δh, were measured simultaneously by a point contact in a crossed-cylinder geometry. With decreasing h/R, the slope of Δh vs. W was found to decrease and to deviate largely from the prediction of the Hertz contact (= 2/3). An equation between S 0 and Δh in the range of 2 < W < 100gf was obtained, by which S 0 can be empirically estimated using the obtained Δh if h and R are given. The effects of h/R on the separation energy, E A, were discussed on the basis of the changes in the density of molecular-to-molecular contacts between polymer chains at the surface and in the degree of deformation of the bulk.