Contact mechanics based studies of adhesion

Adhesion plays an important role in a legion of technologies ranging from aerospace to biomedical applications to microelectronics. When two materials are brought in contact, the necessary or adequate adhesion between them is of great importance. So it is desirable to find ways to attain the needed adhesive strength between different materials. In order to do so, the mechanisms of adhesion must be understood for a specific system. Many researchers of adhesion deal with polymeric materials because they are widely used in industry.; Contact mechanics based adhesion measurements are important in studying the adhesion phenomenon. To do such measurements, a suitable experimental apparatus is necessary. So a micro-indentation system for soft materials was built in our laboratory. Load and displacement data during loading and unloading are recorded by a computer. From these data, information of adhesive energy can be obtained based on some models.; Using the above experimental apparatus, several experiments were done. One is the contact between poly(butylacrylate) (PBA) and sapphire and another is the self-contact of poly(dimethylsiloxane) (PDMS). The experimental results using spherical indenters show that the widely used JKR theory may not be applicable because of the contact hysteresis between loading and unloading. The experimental results using the cylindrical indenters do not have hysteresis. They are used to show that a diffusion process is involved in the formation of primary bonds for the self-contact of PDMS. The activation energy for diffusion can be obtained from the increase of adhesion energy with time at different temperatures. The results show that the activation energy of diffusion is larger than that of viscous flow for PDMS. The latter is obtained from impression creep tests. Comparing the results using spherical indenters to the results using cylindrical indenters, we think that the work of adhesion from the loading curve during spherical indentation is more reasonable for initial contact than that from the unloading curve.; For situations where analytical solutions are not available, a finite element analysis (FEA) is used in the adhesive contact between an indenter and a thin film deposited on a substrate. The details about such calculations and the application to experiments are shown.; The analysis of adhesive contact between a rigid flat end cylindrical punch and a thin film is also presented in this thesis. The results show that the pull-off force increases when the film thickness decreases.; Finally, a method of measuring the interfacial energy of bi-layer material by bending due to temperature changes is also presented.