(326g) Role of Surface Roughness on Wetting Behavior in Liquid/Liquid Systems

Understanding the wetting behavior of rough solid surfaces is important for a wide range of applications involving, for instance, liquid mixtures in microfluidic devices, many industrial coatings, or oil recovery. Wetting studies have traditionally focused on vapor/liquid/solid systems, the most common scenario being the wetting of solids by water in air, but the competitive wetting of solid surfaces by two immiscible liquids also is important, as the example of oil recovery shows. The theories used to describe this type of wetting are mostly based on experimental data for vapor/liquid/solid systems and do not usually account for possible variations in the relative polarity of the two fluids or the order in which these fluids wet the surface. The objective of this study is to better understand the effect of nanoscale roughness on wetting in water/oil systems using well characterized substrates. In particular, we study the wetting of polymer surfaces with tunable roughness and identical surface chemistry, while varying the reference fluids and the wetting order. We examine equilibrium and dynamic wetting behavior via contact angle measurements and optical high speed video microscopy of droplet spreading respectively. Our experiments show that the extent of surface roughness effects in wetting phenomena is indeed strongly influenced by the relative fluid polarity and the order of wetting.