EDGE PROFILES AND DYNAMIC CONTACT ANGLES OF A SPREADING DROP
EDGE PROFILES AND DYNAMIC CONTACT ANGLES OF A SPREADING DROP
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DOI：
10.1016/0021-9797(92)90129-a
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发表时间：
1992-01-01
影响因子：
9.9
通讯作者：
WADA, N
中科院分区：
文献类型：
--
作者：
CHEN, JD;WADA, N
用激光干涉显微法研究了落边的扩散动力学。根据干涉条纹的影像，测量了干涉条纹在下降边缘处的扩散速度，重建了干涉条纹的边缘轮廓。实验得到的不同速度下的边缘轮廓与Hervet和de Gennes关于一维表面张力恒定且均匀的薄展边理论的预测非常吻合。利用不同毛细数C的标度规律，可以将不同毛细数C的边缘轮廓压缩成一条无量纲曲线。实验与理论的一致表明，在我们的实验中，液滴的表面张力在扩散过程中保持恒定和均匀。动态接触角θ与距离和c的关系也与他们的理论一致。在离三相接触线较远的地方，边缘轮廓几乎是一条直线，随着距离的减小，边缘轮廓向气相方向凹。轮廓随着c的减小而变平。因此，θ随距离的减小和c的减小而减小。在距离三相接触线较大距离处的动态接触角θ1，与另外两个接触角θ0和θ rh在不同ci处的比较，由扩大水滴轮廓的42倍放大照片获得。θ0是实心平面与水滴边缘轮廓切线之间的夹角，θ rhis是假设水滴形状为球形帽的边缘夹角。θ1、θ0和θ rare也与在毛细管中运动的半月板作为c的函数的相关性进行了比较。对于相同的c，θ 1,θ0,θRH，理论和相关性之间有很好的一致性。数据还表明，θ1和θ0是相同的角度。
The spreading dynamics of a drop edge is studied experimentally using a laser light interference microscopy method. From the movie of the interference fringes, the spreading speed at the drop edge is measured and the edge profile is reconstructed. The experimental edge profiles at different speeds agree very well with those predicted by Hervet and de Gennes' theory on a one-dimensional thin spreading edge with a constant and uniform surface tension. The edge profiles at different capillary numbers,C, can be collapsed into one dimensionless curve, using their scaling laws. The agreement between experiments and theory suggests that in our experiments the surface tension of the drop remains constant and uniform during spreading. The dependence of the dynamic contact angle, θ, on distance andCalso agrees with their theory. The edge profile is almost a straight line at a large distance from the three-phase contact line and becomes concave toward the air phase as the distance decreases. The profile becomes flatter asCdecreases. As a result, θ decreases with decreasing distance and decreasingC. The dynamic contact angle at large distance away from the three-phase contact line,θ1, at differentCis compared with two other contact angles,θ0andθRH, obtained from photographs at 42× magnification of the silhouette of a spreading drop.θ0is the angle between the solid plane and the tangent to the silhouette at the drop edge, andθRHis the angle at the edge assuming the drop shape is a spherical cap.θ1,θ0, andθRHare also compared with a correlation for a meniscus moving in a capillary tube as functions ofC. For the sameC, there is a good agreement betweenθ1,θ0,θRH, the theory, and the correlation. Data also suggest thatθ1andθ0are the same angle.