Deviation from linear relationship between adhesion strength and surface free energy on a low energy surface

Abstract

The deviation from the linear relationship between the adhesion strength and surface free energy on a low energy surface was observed for the first time. Although the linear relationship between the adhesion strength and surface free energy in the adhesion between epoxy resin and polymer was previously reported, it was only observed for the region of surface free energy greater than 20 mN/m. In particular, no data were previously reported for the region of surface free energy less than 20 mN/m. The aim of this study was to investigate the existence of the linear relationship in the region of surface free energy less than 20 mN/m. The linear relationship was investigated for the case wherein the epoxy resin adhesive was diluted. No data were previously reported due to the difficulty associated with the preparation of the low surface free energy adherend. In this study, the low surface free energy adherend was prepared by coating the adherend with a low surface energy layer such as a polytetrafluoroethylene particle dispersion composite. The lower limit of the linear relationship between the adhesion strength and surface free energy extended from the conventional value of 20 mN/m to 15.3 mN/m. In the region of surface free energy less than 15.3 mN/m to 2.3 mN/m, the adhesion strength was almost constant, which represents a deviation from the linear relationship. The abovementioned phenomena were observed when the epoxy resin was diluted by egg white by up to 40 vol.%.