Nanoindentation of polymer-bound silica agglomerate layers

Abstract

Experimental data are described for the indentation of highly porous particulate coatings on the submicron length scale using a Berkovich probe; they were composed of colloidal silica (20-24 nm in diameter) with a solvent-deposited isotactic poly(methyl methacrylate) as a binder. A wide variation in the data was observed at different surface locations for any single coating owing to their heterogeneous nature; an approximate methodology is described to characterize these variations. The procedure is based on a power-law fitting of apparent hardness data and has been employed to provide closed-form expressions for the depth dependence of the mechanical response. The analyses show that the mechanical properties depend on the binder solvent used in the preparation of a coating and also indicate that the surfaces of the coatings may be harder than the bulk. This would be expected to arise from capillary-induced flow of the binder solution during the coating solidification process.