We experimentally investigate the spreading and receding behavior of small water droplets immersed in viscous oils on grid-patterned surfaces using synchronized bottom and profile views. In particular, the evolution of apparent advancing and receding contact angles of droplets fed at constant flow rate is studied as a function of grid surface coverage and height for a wide range of external phase viscosity. Detailed examination of droplet aspect ratio during inflation process provides an averaging method for characterization of quasi-static advancing angles on heterogeneous surfaces. Droplets spreading in partial Cassie state on planar microfluidic grids are also shown to capture oil patches that further evolve into trapped oil droplets depending on grid aspect ratio. The natural retraction velocity of thin water films is examined based on external phase velocity and regime maps of trapped droplets are delineated based on control parameters.

中文翻译：

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粘性表面的液-液润湿和反润湿

我们使用同步的底部和轮廓视图，通过实验研究了浸入网格图案表面上的粘性油中的小水滴的扩散和后退行为。特别地，研究了在较大的外相粘度范围内，以恒定流速进料的液滴的表观前进和后退接触角的演变与格栅表面覆盖率和高度的关系。在膨胀过程中对液滴纵横比的详细检查提供了一种表征异质表面上准静态前进角的平均方法。还显示了以部分卡西状态散布在平面微流体网格上的液滴捕获了油斑，这些斑块根据网格的纵横比进一步发展为捕获的油滴。