Influence of physical and interfacial characteristics on the wetting and spreading of fluids on powders

The wetting and spreading of liquid on compacts of carbon black and silica powders has been studied with the aim of investigating the degree to which the physical properties and chemical nature of the fluid govern the phenomena. Wetting experiments were performed with six fluids (glycerin, ethylene-propylene copolymer, squalene, poly(dimethylsiloxane), l-butanol, and water) selected to provide a range of interfacial chemistries. The viscosity of these fluids spanned a range of three orders of magnitude. Capillary rise experiments gave insight into the wetting phenomena that occur between powders and large quantities of fluid. The observed infiltration kinetics was found to exhibit a different sensitivity to the fluid viscosity than what is explicitly predicted by the conventional Washburn analysis. This deviation is attributed to variation in the degree of saturation of the powder compacts arising from differences in viscosity of the infiltrating liquid. The wetting of compacts by small amounts of fluid was studied by contacting single drops of fluid onto carbon black compacts. Observed spreading and infiltration rates indicate that the wetting phenomena cannot be predicted on the basis of a simple balance between capillary and viscous forces. Cracking and microstructural rearrangement within powder compacts driven by the infiltrating liquid were also observed. The nature of this rearrangement was found to be strongly correlated with the kinetics of the wetting process. (C) 1999 Elsevier Science S.A. All rights reserved.