Surface free energies of electroless Ni-P based composite coatings

Surface free energy of a solid surface gives a direct measure of intermolecular interactions at interfaces and has a strong influence on adsorption and adhesion behaviour. However few data are available for the surface free energies of electroless Ni-P based composition coatings. In this paper, the electroless Ni-P, Ni-P-surfactant, Ni-Cu-P, Ni-P-PTFE and Ni-Cu-P-PTFE composite coatings were prepared under various coating conditions. The chemical compositions, surface morphology and thickness of the coatings were measured using an energy dispersive X-ray microanalysis (EDX), a scanning electron microscope (SEM) and a digital micrometer respectively. The contact angles of water, diiodomethane and ethylene glycol on the coatings were measured automatically using dataphysics OCA-20 contact angle analyser. The surface free energy of the coatings and their components (e.g. dispersion, polar or acid/base portions) were calculated using various methods. The experimental results showed that the incorporation of surfactant or PTFE particles into Ni-P matrixes has a significant influence on the surface free energy of the coatings, while the incorporation of copper into Ni-P matrixes has no significant influence on the surface free energy of the coatings.