WETTING KINETICS OF A DROP ON A HORIZONTAL SOLID-SURFACE UNDER A VISCOUS AMBIENT LIQUID

The wetting kinetics of a drop on a horizontal solid surface covered b y a viscous liquid has been investigated. Theory indicates the rates o f movement behave similarly for cases when the ratio of the ambient fl uid viscosity to the drop viscosity chi is very high to very low. The case where the above viscosity ratio is low is well-known, since sprea ding rates are usually measured in air. The experimental data for chi similar to 1 are provided here. The extent of spreading is proportiona l to time raised to a power which is closer to 1/7 than the expected v alue of 1/10. Contact line instability was also observed in that the c ontact lines were seen to be wavy. It is suggested here that the devia tion seen in the power is related to the contact line instability.