LAPLACE PRESSURE-DRIVEN DROP SPREADING

This work concerns the spreading of viscous droplets on a smooth rigid horizontal surface, under the condition of complete wetting (spreadin g parameter S > 0) with the Laplace pressure as the dominant force. Ow ing to the self-similar character foreseeable for this flow, a self-si milar solution is built up by numerical integration from the center of symmetry to the front position to be determined, defined as the point where the free-surface slope becomes zero. Mass and energy conservati on are invoked as the only further conditions to determine the flow. T he resulting fluid thickness at the front is a small but finite (almos t-equal-to 10(-7)) fraction of the height at the center. By comparison with experimental results the regime is determined in which the sprea ding can be described by this solution with good accuracy. Moreover, e ven within this regime, small but systematic deviations from the predi ctions of the theory were observed, showing the need to add terms modi fying the Laplace pressure force.