Dynamics of spreading of liquid on solid surface

Based on assuming that there is the precursor film in the front of the apparent contact line (ACL), a model was proposed to understand the dynamic wetting process and associated dynamic contact angle. The present model indicated that a new dimensionless characteristic parameter, lambda, affects the dynamic wetting process and associated dynamic contact angle as well. However, the previous model suggested that the dynamic contact angle is dependent on the capillary number and static contact angle only. An experimental investigation was conducted to measure the dynamic wetting behavior of silicon oil moving over glass, aluminum and stainless steel surfaces. It concluded that when the value of lambda was selected as 0.07, 0.16 and 0.35 for glass, aluminum and stainless steel, respectively, the experimental results were in good accordance with the prediction of the model. Furthermore, the comparison of the model with Strom's experimental data showed that lambda is independent on the species of liquids. Apparently, lambda should be interpreted as the effect of the solid surface properties on the dynamic wetting process. Meanwhile, it is found in the present experiment that the Hoffman-Voinov-Tanner law, which is valid at very low capillary number (Ca << 1 or theta(D) <10 degrees) recommend by Cazabat, still holds for higher contact angles, even up to 70 degrees-80 degrees. This is explained by the present model very well.