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Separation and transportation of small particles are important processes in various applications such as the food and pharmaceutical industries. Although mechanical, chemical or electrical methods can provide possible solutions, operational or environmental constraints may require alternative methods. Spreading and levitation of clusters (aggregates) of fumed silica nanoparticles placed under atmospheric pressure on a hot plate is reported. In a closed chamber, the particles started to spread horizontally at the threshold temperature of $T_c^*=403 \pm 1$K. The powder spreading in the chamber continued until the temperature-dependent saturation value $r_{sat} (T)$, which grew linearly with the temperature. Open space experiments clearly demonstrated levitation of the powder clouds. The onset of levitation in the open space corresponded to the minimal threshold temperature of $T_o^*=373 \pm 1$K. Qualitative physical analysis of the observed phenomena is suggested. The effect of levitation is explained by the lifting thermo-phoretic force emerging in the Knudsen layer of air on the heater surface. The levitation of the powder under atmospheric pressure becomes possible due to the combination of low adhesion of the fluorinated fumed silica clusters built of nanoparticles to the substrate, relatively low density of the particles and clusters, and their high specific surface area. Ordering of the aggregates of nanoparticles within the levitating powder cloud was quantified with Voronoi diagrams.

Copper oxide nanostructures with spherical (0D), needle (1D) and hierarchical cauliflower (3D) morphologies are used to demonstrate superhydrophobic, superoleophobic and slippery behavior. These nanostructures are synthesized on galvanized steel substrates using a simple chemical bath deposition method by tuning precursor concentration. Subsequent coating of low surface energy polymer, polydimethylsiloxane, results in superhydrophobicity with water contact angle ~160(2){\deg} and critical sliding angle ~2{\deg}. When functionalized with low-surface energy perfluoroalkyl silane, these surfaces display high repellency for low surface tension oils and hydrocarbons. Among them, the hierarchical cauliflower morphology exhibits better re-entrant structure thus show the best superoleophobicity with 149{\deg} contact angle for dodecane having surface tension 25.3 mNm-1. If these nanostructured substrates are infused with lubricant Silicone oil, they show excellent slippery behavior for water drops. Due to the lubricating nature of Silicone oil, the Silicone oil infused slippery surfaces (SOIS) show low contact angle hysteresis (~2{\deg}) and critical tilt angle (~2{\deg}). The hierarchical cauliflower nanostrcuture exhibit better slippery characteristics and stability compared to the other nanostructured surfaces., Comment: 21 pages, 8 figures

We demonstrate a novel technique to fabricate mechanically tunable slippery surfaces using one dimensional (anisotropic) elastic wrinkles. Such wrinkles show tunable topography (amplitude) on the application of mechanical strain. Following Nepenthes pitcher plants, lubricating fluid infused solid surfaces show excellent slippery behavior for test liquid drops. Therefore combining the above two i.e. infusing suitable lubricating fluid on elastic wrinkles would enable us to fabricate mechanically tunable slippery surfaces. Completely stretched (flat) wrinkles have uniform coating of lubricating fluid whereas completely relaxed (full amplitude) wrinkles have most of the lubricating oil in the wrinkle grooves. Therefore water drops on completely stretched surface show excellent slippery behavior whereas on completely relaxed surface they show very poor slippery behavior. Therefore continuous variation of wrinkle stretching provide reversibly tunable slippery behavior on such system. Since the winkles are one dimensional, they show anisotropic tunability of slippery behavior depending upon whether test liquid drops slip parallel or perpendicular to the wrinkles., Comment: 18 pages, 5 figures

In the recent years many research groups have studied slippery properties on lubricating fluid infused rough surfaces using hydrophobic substrates. These surfaces show excellent slippery behaviour for water and other liquids. Here we demonstrate a simple method to fabricate stable slippery surfaces based on silicone oil coated hydrophilic samples. At room temperature, as prepared samples exhibit non-slippery behaviour due to sinking of water drops inside silicone oil layer because of inherently hydrophilic silicon substrate. Subsequent annealing at higher temperatures provides covalent bonding of silicone molecules at silicon surface making the surface hydrophobic which was confirmed by lubricant wash tests. So the silicone oil coated annealed samples show excellent water repellency, very low contact angle hysteresis and very good slippery behavior. But these surfaces show poor oil stability against drops flow due to cloaking of the oil around water drops which can be prevented by using drops of larger volume or continuous flow of water., Comment: 14 pages, 5 figures