The sub-wavelength structures in moth eyes exhibit fascinating antireflective properties over the broadband wavelength region and at large incident angle by generating an air-mixed heterogeneous optical interface. In this work, antireflective behavior of transparent glass is observed with the elaborate controls of the nanopillar morphology. The reflectance spectrum shows a red shift and a notable light scattering with increase of the height of the nanopillars. The nanopillar arrays with a pointed cone shape have better optical performance in visible range than the rounded cone shape which is typical antireflective nanostructures in nature. Based on the observed antireflective behaviors, the flat and low value reflectance spectrum in the visible wavelength range is demonstrated by moth eye mimicking nanostructures on both sides of a glass surface. It is a unique strategy to realize a flat and broadband spectrum in the visible range showing 99% transparency via the appropriate matching of nanopillar height on the front and back sides of glass. The controlled reflection based color tuning on the antireflective and transparent glass is also obtained by adjusting the height of the nanopillar arrays on both sides. The visibility and self-cleaning ability of moth eye mimicking glass are examined for practical applications such as antireflection and self-cleaning.

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Optical methods for microfluidic flow manipulation offer a flexible, noncontact technique for both fluid actuation and valving. At present, however, such techniques are limited by their high laser power requirements, low achieved flow rates, or poor valve switching times. Here we demonstrate a microfluidic valving technique based on optothermorheological manipulation using a low-power 40 mW laser with switching times on the order of 1 s at high flow rates of 1 mm/s. In our approach a laser beam incident on an absorbing substrate is used to locally heat a thermorheological fluid flowing in a microfluidic channel. The resulting gelation in the heated region creates a reversible fluid valve.

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Pinning and depinning of droplets on heterogeneous substrates are widely seen in nature and need to be carefully controlled in industrial processes such as substrate cleaning and spray coating. In this work, a two-dimensional droplet sliding on an inclined substrate with a topographical defect is studied with a thin-film evolution equation. Using results from time-dependent finite-difference calculations, we focus our discussion on the dynamic interactions between the sliding droplet and the topographical defect. For a Gaussian defect shape, we find that droplet pinning is primarily determined by the advancing contact line pinning at the defect surface where the topography slope is minimum. We demonstrate that with certain combinations of defect heights and widths, residual droplets can form on the defect as a result of geometric constraints involving the receding droplet meniscus and the defect shape. We show that the delay in sliding caused by the defect is mainly due to the pinning and depinning of the receding contact line, and less affected by the dynamic behavior of the advancing contact line. This topography-induced delay in sliding of an individual droplet may have important implications for controlling the collective sliding behavior of multiple droplets.