Experimental Investigation of Dynamic Contact Angles on Horizontal and Inclined Surfaces Part I: Flat Silicon Oxide Surfaces

Abstract

Abstract In the last decades, many attempts have been made to investigate influence quantities on the formation of contact angles and their interpretation. The effect of gravitation on the measured contact angles is a controversially discussed mater. In 1876 J. W. Gibbs already formulated conditions for equilibrium and therefore even for the equilibrium contact angle θ e which describe the acting gravitational field on a fluid component. Nevertheless, these relations often are not considered. The presented study illustrates differences between the apparent contact angles of sessile drops which are obtained by dynamical measurements with the inclined-plate and the needle-in method. This fact demonstrates that the force distibution at the triple line additionally differs in dependence on the used measuring method. The force distribution at the triple line depends on the relative position in the gravitational field (e.g. inclined or horizontal sample position) and on the curvature of the liquid-vapour interface (interfacial tension). Hence, theses effects on the apparent contact angles have to be considered for a reasonable interpretation of the measurement data. For this purpose, an approach to describe the effect of forces related to gravity effects on contact angles will be presented.