Sequential droplet deposition on geometrically and chemically patterned substrates

Abstract eng:
We experimentally investigate the use of topographical features and spatially varying wettability (with moderate receding contact angle) to fill and confine a linearly deposited sequence of overlapping micro-droplets (30 pm in diameter) into a stadium-shaped well region (Figure 1). Our experiments determine the parameter regimes for which droplet lines are contained within shallow wells (~l um depth) and, moreover, reveal that the presence of topography results in the formation of contact line cusps during fluid redistribution .On surfaces with wettability variations, controlled wetting resulting in accurate fluid positioning is achieved without any extreme deformation of the contact line. We extend a previously developed quasi-static lubrication model that predicts the post-impact, drop by drop evolution of a liquid line on a flat substrate [1] to include topographical and wettability patterns. The model is shown to reproduce the overall experimental features accurately.

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