Chen Longquan, Bonaccurso Elmar
Center of Smart Interfaces, Technische Universität Darmstadt, Alarich-Weiss-Strasse 10, 64287 Darmstadt, Germany.
Phys Rev E Stat Nonlin Soft Matter Phys. 2014 Aug;90(2):022401. doi: 10.1103/PhysRevE.90.022401. Epub 2014 Aug 4.
In this paper, we experimentally investigated the dynamic spreading of liquid drops on solid surfaces. Drop of glycerol water mixtures and pure water that have comparable surface tensions (62.3-72.8 mN/m) but different viscosities (1.0-60.1 cP) were used. The size of the drops was 0.5-1.2 mm. Solid surfaces with different lyophilic and lyophobic coatings (equilibrium contact angle θ(eq) of 0°-112°) were used to study the effect of surface wettability. We show that surface wettability and liquid viscosity influence wetting dynamics and affect either the coefficient or the exponent of the power law that describes the growth of the wetting radius. In the early inertial wetting regime, the coefficient of the wetting power law increases with surface wettability but decreases with liquid viscosity. In contrast, the exponent of the power law does only depend on surface wettability as also reported in literature. It was further found that surface wettability does not affect the duration of inertial wetting, whereas the viscosity of the liquid does. For low viscosity liquids, the duration of inertial wetting corresponds to the time of capillary wave propagation, which can be determined by Lamb's drop oscillation model for inviscid liquids. For relatively high viscosity liquids, the inertial wetting time increases with liquid viscosity, which may due to the viscous damping of the surface capillary waves. Furthermore, we observed a viscous wetting regime only on surfaces with an equilibrium contact angle θ(eq) smaller than a critical angle θ(c) depending on viscosity. A scaling analysis based on Navier-Stokes equations is presented at the end, and the predicted θ(c) matches with experimental observations without any additional fitting parameters.
在本文中，我们通过实验研究了液滴在固体表面上的动态铺展。使用了表面张力相当（62.3 - 72.8 mN/m）但粘度不同（1.0 - 60.1 cP）的甘油水混合物和纯水液滴。液滴尺寸为0.5 - 1.2 mm。使用具有不同亲液和疏液涂层（平衡接触角θ(eq)为0° - 112°）的固体表面来研究表面润湿性的影响。我们表明，表面润湿性和液体粘度会影响润湿动力学，并影响描述润湿半径增长的幂律的系数或指数。在早期惯性润湿阶段，润湿幂律的系数随表面润湿性增加而增加，但随液体粘度降低。相比之下，幂律的指数仅如文献中所报道的那样取决于表面润湿性。还进一步发现，表面润湿性不影响惯性润湿的持续时间，而液体粘度会影响。对于低粘度液体，惯性润湿的持续时间对应于毛细波传播的时间，这可以由无粘液体的兰姆液滴振荡模型确定。对于相对高粘度的液体，惯性润湿时间随液体粘度增加，这可能是由于表面毛细波的粘性阻尼。此外，我们仅在平衡接触角θ(eq)小于取决于粘度的临界角θ(c)的表面上观察到粘性润湿阶段。最后给出了基于纳维 - 斯托克斯方程的标度分析，预测的θ(c)与实验观察结果相符，无需任何额外的拟合参数。
