Wetting of planar solid surfaces by bicontinuous sugar surfactant-based microemulsions

Abstract

Optimal wetting of solid substrates is an essential prerequisite for extractive mass transport out of the surface into a microemulsion. In contrast to its importance for practical applications, the wetting properties of microemulsions still are partly unknown. Here, we use contact angle goniometry and Wilhelmy-type force measurements to characterize the wetting of bicontinuous microemulsions at hydrophilic and hydrophobic solid substrates. Microemulsions of different oil-to-water ratios from the bicontinuous region of two quaternary systems, built up by oil (a nonpolar (tetradecane) and a polar oil (methyl oleate)) in combination with water, sugar surfactant, and alcohol (pentanol) have been used. For all microemulsions, a partial wetting regime was found at planar model surfaces. The wetting of hydrophobic surfaces shows differences related to the wetting behavior of the oil component and its adhesion to the substrate. The contact angle hysteresis indicates the formation of adsorption layers between surface and microemulsion bulk.