|M.Sc Student||Tamir Erez|
|Subject||Wetting and Adhesion in Substrate-Polymer Coating System|
|Department||Department of Polymer Engineering||Supervisor||Professor Emeritus Abraham Marmur|
|Full Thesis text - in Hebrew|
The aim of this research is investigating the relationship between wetting and adhesion in substrate - polymer coating systems. In this study substrates of different materials, characterized by different surface tensions, are used: HMX crystals, Aluminum, PET, Ultem, FR4, and Teflon. Various polymers used for coating the substrates.
Theoretical characterization of wetting can be done by calculating the surface tensions of the substrates used and the thermodynamic work of adhesion of each system. Correlating between interfacial tension of a wetting system and the corresponding surface tensions of the system components wad done using the general correlation developed by Marmur & Valal was used. Using average water contact angles (measured by goniometer) and the general correlation of Marmur & Valal, the surface tensions of each substrate, and also the interfacial tension of each system, were calculated.
The theoretical predictions were investigated experimentally by measuring the strength and the experimental work of adhesion of the various substrate-polymer systems by Pull-off tests.
For HMX-polymer systems the relation between the coating conditions and the degree of adhesion was examined. The results show that the presence of a water film on the surface before coating lowers the degree of adhesion. Adhesion tests with HMX-polymer systems also showed that the surface quality and flatness degree affect the pull-off test.
The experimental work of adhesion was examined as a function of the surface tensions of the substrates (in wetting systems with constant polymer coating), and also as a function of the surface tensions of the polymers (in wetting systems with constant substrate). Clear dependence between the experimental work of adhesion and the thermodynamic work of adhesion was not obtained. Also, the predicted relation between degree of wetting and degree of adhesion was not observed. For wetting systems that comprised constant substrate and various polymer coatings, a trend of decrease in the experimental work of adhesion, with an increase in the polymer surface tensions was observed. An attempt was made to improve the specimen in order to minimize strains and viscoelastic energy dissipation. The dependence between maximum pull-off strength and surface tension was in certain accordance to the theoretical trend, however no dependence between the experimental work of adhesion and the thermodynamic work of adhesion was observed. For future studies using the pull-off test it seems necessary to perform test at a higher tensile rate. Another comparative test such as the shear test may be also considered in order to measure the experimental work of adhesion.