3-DIMENSIONAL AND 2-DIMENSIONAL EFFECTS IN WETTING KINETICS

Wetting at equilibrium is reviewed in brief, and it is then suggested that a wider class of nonequilibrium problems can exist where an equil ibrium-like behaviour is reached simply because the mechanisms for spr eading are suppressed. The mechanisms of spreading are reviewed to sug gest that experiments of wetting kinetics of liquids with varying vola tilities on mica would lead to interesting results. Such experiments w ere conducted and the results are supportive of the models. It was als o observed that when volatility and surface roughness, two important m echanisms of spreading, are removed, the drop motion presumed to be co ntrolled by surface diffusion at the contact line virtually ceases, al though scanning electron microscopy results show that they are indeed moving. The role of films of ultra-low thicknesses are examined. It is seen that the dynamics of molecular scale droplets are understandable , and can be modelled in many ways, and the features these moving mole cular scale drops exhibit can in some cases affect the movement of mic roscale drops as well. We are able to identify and define two- and thr ee-dimensional volatilities and mobilities that help one to classify t he spreading phenomena, as far as the liquids are concerned. The surfa ces can be smooth or rough, a difference that has a strong effect.