Departamento de Ingenieria Quimica y Textil, Universidad de Salamanca, Plaza de los Caidos 1-5, Salamanca, 37008, Spain.
J Colloid Interface Sci. 2010 Mar 15;343(2):574-83. doi: 10.1016/j.jcis.2009.11.055. Epub 2009 Dec 4.
A theory, based on the presence of an adsorbed film in the vicinity of the triple contact line, provides a molecular interpretation of intrinsic hysteresis during the measurement of static contact angles. Static contact angles are measured by placing a sessile drop on top of a flat solid surface. If the solid surface has not been previously in contact with a vapor phase saturated with the molecules of the liquid phase, the solid surface is free of adsorbed liquid molecules. In the absence of an adsorbed film, molecular forces configure an advancing contact angle larger than the static contact angle. After some time, due to an evaporation/adsorption process, the interface of the drop coexists with an adsorbed film of liquid molecules as part of the equilibrium configuration, denoted as the static contact angle. This equilibrium configuration is metastable because the droplet has a larger vapor pressure than the surrounding flat film. As the drop evaporates, the vapor/liquid interface contracts and the apparent contact line moves towards the center of the drop. During this process, the film left behind is thicker than the adsorbed film and molecular attraction results in a receding contact angle, smaller than the equilibrium contact angle.
一种基于在三相接触线附近存在吸附膜的理论，为测量静态接触角时的固有滞后现象提供了分子解释。静态接触角是通过将液滴放置在平坦固体表面上来测量的。如果固体表面以前没有与饱和有液相分子的气相接触，则固体表面没有吸附的液相分子。在不存在吸附膜的情况下，分子力配置了一个大于静态接触角的前进接触角。一段时间后，由于蒸发/吸附过程，液滴的界面与作为平衡配置一部分的液体分子吸附膜共存，称为静态接触角。这种平衡配置是亚稳的，因为液滴的蒸气压大于周围的平膜。随着液滴的蒸发，蒸气/液体界面收缩，表观接触线向液滴的中心移动。在这个过程中，留下的薄膜比吸附膜厚，分子吸引力导致后退接触角小于平衡接触角。
