Flow of a liquid in a nonuniformly hydrophobized capillary

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• 作者：Alexeyev ; Alexander A. ; Vinogradova ; Olga I.
• 关键词：Hydrophobized capillary ; liquid flow
• 刊名：Colloids and Surfaces A: Physicochemical and Engineering Aspects
• 出版年：1996
• 出版时间：March 20, 1996
• 年：1996
• 卷：108
• 期：2-3
• 页码：173-179
• 全文大小：550 K

文摘

We investigate theoretically the flow of a liquid in a plane capillary whose walls are inhomogeneously hydrophobized. The role of hydrophobicity is revealed in the apparent slippage of a liquid over a solid. The origin of the slippage effect is probably linked to a decrease in viscosity in a very thin layer adjacent to the wall. The solution is obtained for a case where the size of the inhomogeneous sectors is much greater than the capillary halfwidth. The formulae derived for a single inhomogeneous slippage region are generalized for several such sectors assuming weak overlapping. It is shown that the contribution to the flow from the inhomogeneously hydrophobized sectors substantially depends on their amplitudes, extents and conditions of the overlapping. It is also demonstrated that the problems in calculating an increase in the flow flom the average (along the capillary axis) and from real variable slip lengths may have different length scales. These observations enable us to explain why an increase in the liquid flow through the hydrophobized capillary has been experimentally found only at a relatively large contact angle, and why such a conventional criterion of surface hydrophobicity as the average advancing contact angle cannot give a reliable prediction of the average value of slip length (and vice versa).