Adhesive and Elastic Properties of Thin Gel Layers

We employ linear elastic fracture mechanics to describe the adhesive and frictional properties of thin, elastic gel layers against a glass, hemispherical indenter. A triblock copolymer with poly (methyl methacrylate) endblocks and a poly (n-butyl acrylate) midblock is diluted with a selective solvent for the center block in order to form a low modulus, thermally reversible gel that behaves as an elastic solid at room temperature. Through simultaneous measurements of the circular contact area, normal displacement, and applied load, we show that the fracture mechanics expressions provide an accurate means to describe the adhesive behavior of the highly compliant polymer gels. By modifying the surface properties of the indenter, we show that the relationship between load and displacement is sensitive to the response of shear forces at the gel/indenter interface, whereas the relationship between the contact area and displacement is unaffected by this response. In addition, we demonstrate the utility of our methodology for quantifying adhesion in situations where the applied load cannot be measured directly.