分离压力
接触角
拉普拉斯压力
润湿
表面张力
化学
曲率
楔形(几何)
毛细管作用
润湿转变
拉普拉斯方程
凝聚态物理
物理
光学
热力学
几何学
量子力学
数学
微分方程
作者
Margarita Díaz,Javier Calvo Fuentes,Ramón L. Cerro,M. Savage
标识
DOI:10.1016/j.jcis.2010.04.030
摘要
A model is formulated for a static puddle on a horizontal substrate taking account of capillarity, gravity and disjoining pressure arising from molecular interactions. There are three regions of interest--the molecular, transition and capillary regions with characteristic film thickness, hm, ht and hc. An analytical solution is presented for the shape of the vapour-liquid interface outside the molecular region where interfacial tension can be assumed constant. This solution is used to shed new light on the static contact angle and, specifically, it is shown that. (i) There is no point in the vapour-liquid interface where the angle of inclination, theta, is identically equal to the static contact angle, theta(o), but the angle at the point of null curvature is the closest with the difference of O(epsilon2) where epsilon2 = ht/hc is a small parameter. (ii) The liquid film is to O(epsilon) a wedge of angle theta(o) extending from a few nanometers to a few micrometers of the contact line. A second analytical solution for the shape of interface within the molecular region reveals that cos theta has a logarithmic variation with film thickness, cos theta=cos theta-ln[1-h2(m)/2h2]. The case, hm = 0, is of special significance since it refers to a unique configuration in which the effect of molecular interactions vanishes, disjoining pressure is everywhere zero and the vapour-liquid interface is now described exactly by the Young-Laplace equation and includes a wedge of angle, theta(o), extending down to the solid substrate.
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