Spreading of Liquid Drops over Dry Porous Layers Complete Wetting Case

2 SPREADING OF LIQUID DROPS OVER DRY POROUS LAYERS COMPLETE WETTING CASE 

It has been shown in Section 4.1 that the presence of roughness or a porous sublayer changes the spreading conditions. In the same section, the spreading of small liquid drops over thin porous layers saturated with the same liquid has been investigated. Instead of the slippage conditions, Brinkman s equations have been used in Section 4.1 for the description of the liquid flow inside the porous substrate. 

In the present section, we take up the same problan, as is the case when a drop spreads over a dry porous layer. The problan is treated in the following text 

The kinetics of Uquid motion both in the drop above the porous layer and inside the porous layer itself are taken into account here. The thickness of the porous layer, A, is assumed to be much smaller than the drop height, that is, A h, where h is the scale of the drop height. The drop profile is assumed to have a low slope hJLt 1, where is the scale of the drop base) and the influence of the gravity is neglected (small drops. Bond number pgl ly 1, where p, g, and y are the liquid density, gravity acceleration, and the liquid-air interfacial tension, respectively). That is, only capillary forces are taken into account. 

As in Section 4.2, the profile of axisymmetric drops spreading over the porous substrate (whether dry or saturated with the same liquid) is governed by the following equation  

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Starov, V.M., Kosvintsev, S.R., Sobolev, V.D., Velarde, M.G., and Zhdanov, S.A., Spreading of liquid drops over dry porous layers complete wetting case, J. Colloid... 

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