Adhesion of thermally reversible gels to solid surfaces

We have developed methods for quantifying very weak adhesive interactions between two bodies in contact. Our approach is based on the use of a low-modulus material in conjunction with a linear elastic fracture mechanics analysis based on the treatment of Johnson, Kendall, and Roberts (JKR.) The JKR theory can be used to describe the effects of adhesive interactions between a soft, elastomeric lens and a solid, rigid surface, under the assumption that the contact area is small relative to the size of the lens. When the ratio of the contact radius to the height of the lens becomes large, it is necessary to account for finite size corrections to the compliance and displacement of the lens. This situation has been addressed by using results from finite element analyses to modify the JKR equations so that an appropriate expression for G, the energy release rate, can be obtained. Adhesion experiments have been performed on low-modulus lenses formed by diluting a triblock copolymer, consisting of poly(methyl methacrylate) end blocks and a poly(n-butyl acrylate) midblock, with 2 ethylhexanol. Rheological studies on this swollen copolymer indicate that the material is completely elastic at room temperature and undergoes a rapid, thermally reversible gelation, thus making it an excellent model system. For this low-modulus material, the applied loads are too low to measure directly. Instead, we obtain expressions for G/E, the energy release rate normalized by Young's modulus. Comparisons to rheological data show that this analysis provides an accurate yet simple method for obtaining this information. Our approach has great potential for quantifying the adhesion of a variety of materials without the need to directly measure the applied load.