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Optical surfaces that can repel both water and oil have much potential for applications in a diverse array of technologies including self-cleaning solar panels, anti-icing windows and windshields for automobiles and aircrafts, low-drag surfaces, and antismudge touch screens. By exploiting a hierarchical geometry made of two-tier nanostructures, primary nanopillars of length scale ∼ 100-200 nm superposed with secondary branching nanostructures made of nanoparticles of length scale ∼ 10-30 nm, we have achieved static contact angles of more than 170° and 160° for water and oil, respectively, while the sliding angles were lower than 4°. At the same time, with respect to the initial flat bare glass, the nanotextured surface presented significantly reduced reflection (<0.5%), increased transmission (93.8% average over the 400 to 700 nm wavelength range), and very low scattering values (about 1% haze). To the authors' knowledge, these are the highest optical performances in conjunction with superomniphobicity reported to date in the literature. The primary nanopillars are monolithically integrated in the glass surface using lithography-free metal dewetting followed by reactive ion etching,1 while the smaller and higher surface area branching structure made of secondary nanoparticles are deposited by the NanoSpray2 combustion chemical vapor deposition (CCVD).

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Metal nanoparticles have been used for coloring glass since antiquity. Colors are produced by light scattering and absorption associated with plasmon resonances of the particles. Recently, dewetting at high temperature has been demonstrated as a straightforward high-yield/low-cost technique for nanopatterning thin metal films into planar arrays of spherical nanocaps. Here, we show that by simply tuning the contact angle of the metal dewetted nanocaps one can achieve narrow resonances and large tunability compared with traditional approaches such as changing particle size. A vast range of colors is obtained, covering the whole visible spectrum and readily controlled by the choice of film thickness and materials. The small size of the particles results in a mild dependence on incidence illumination angle, whereas their high anisotropy gives rise to strong dichroism. We also show color tuning through 65 simple, low-cost lithography-free surface nanostructuring, 66 which is ideal for industrially scalable applications.

In the two-phase region of a peritectic system, experimental studies have shown that the primary phase (␣) often forms a large treelike structure that is surrounded by the peritectic phase (␤). The formation of this novel structure has been attributed to the presence of convection in the liquid. Here, specific physical mechanisms of convection-induced treelike structure formation are proposed. A mathematical model based on advection-diffusion of solute, with prototype flows for advection, is presented and solved numerically to show that an oscillating fluid motion can give rise to a complex oscillatory, treelike structure. Three different regimes are established: diffusive, steady convective, and unsteady convective regimes. In the diffusive regime, a banded structure is predicted within a narrow composition range, and the spacing of the bands is dictated by the nucleation undercoolings of the two phases. Under steady convection, the primary phase transforms into the peritectic phase with a curved ␣:␤ interface. Finally, in the presence of oscillating convection, a treelike shape of the primary phase is predicted, as observed experimentally.