离散型织构表面液滴的铺展及其接触线的力学特性分析

针对离散型织构表面上液滴的铺展过程,采用数值模拟和润湿性实验相结合的方法,引入织构润湿因子θ*,得到了不同类型的离散型织构对固体表面润湿性的影响,在此基础之上分析了液滴铺展过程中接触线的力学特性,以期从微观界面力学的角度解释微织构对液滴铺展过程的促进作用.研究表明:离散型织构增大了液滴铺展过程中的固-液接触面积,位于铺展前沿的液体分子部分浸润织构内部,导致液面曲率和液滴内部的拉普拉斯压力增大,相邻离散型织构间的液体获得了额外的驱动力和能量,铺展速度加快,平衡接触角减小;槽状离散型织构对表面润湿性的影响程度最大,液滴在其上铺展过程具有各向异性特性.另外数值仿真分析表明,接触线的钉扎效应与固体表面粗糙度的大小和微织构类型密切相关,表面粗糙度越大,钉扎效应越明显,其中槽状织构对接触线的钉扎作用还具有方向性. 

MECHANICAL ANALYSIS OF A DROPLET SPREADING ON THE DISCRETE TEXTURED SURFACES

The spreading of a droplet on a solid surface is of obvious importance in a number of practical situations, such as lubrication and coating.In this paper, droplet spreading behaviors on the surfaces with four discrete textures were studied through numerical simulations and wetting experiments.Mechanical analysis on the movement of triple contact line was conducted from interface mechanics in micro-scale.We also introduce a new parameter, texture wetting factor θ^*, to characterize the influence of texture type on wettability.Results show that the discrete textures on the substrates provide excess contact area between liquid and solid, and the spreading fringe partly penetrates into the space among the textures, which leads to the increase of curvature, and the increase of Laplace pressure in the droplet provides excess driving force and accelerates the liquid as it approaches.Droplet on the grooved surface shows spreading anisotropy.In addition, simulation analysis indicates that the pinning effect of contact line has a close relationship with surface roughness and texture type, the greater the surface roughness, the greater the pinning effect, and the pinning effect on the grooved surface also shows directivity.