On surfaces well above 100 °C water does not simply boil away. When there is a sufficient heat transfer between the solid and the liquid a continuous vapour layer instantaneous forms under a droplet of water and the drop sits on a cushion of vapour, highly mobile and insulated from the solid surface. This is known as the Leidenfrost effect and the temperature at which this occurs if known as the Leidenfrost transition temperature. In this report, an investigation of discontinuous surfaces, stainless steel meshes, have been tested to determine the effect of the woven material on the Leidenfrost phenomenon. It was found that with increasing the open area of the mesh pushes up the Leidenfrost temperature from 265 °C for an open area of 0.004 mm2 to 315 °C for open area of 0.100 mm2. This allows suppression of the Leidenfrost effect as it can be increase to over 300 °C from 185 °C for a stainless steel surface

Much of the inspiration for the creation of superhydrophobic surfaces has come from nature, from plants such as the sacred lotus (Nelumbo nucifera), where the micro-scale papillae epidermal cells on the surfaces of the leaves are covered with nano-scale epicuticular wax crystalloids. The combination of the surface roughness and the hydrophobic wax coating produces a superhydrophobic wetting state on the leaves, allowing them to self-clean and easily shed water. Here, a simple scaled-up carbon nanoparticle spray coating is presented that mimics the surface of sacred lotus leaves and can be applied to a wide variety of materials, complex structures, and flexible substrates, rendering them superhydrophobic, with contact angles above 160°. The sprayable mixture is produced by combining toluene, polydimethylsiloxane, and inherently hydrophobic rapeseed soot. The ability to spray the superhydrophobic coating allows for the hydrophobisation of complex structures such as metallic meshes, which allows for the production of flexible porous superhydrophobic materials that, when formed into U-shaped channels, can be used to direct flows. The porous meshes, whilst being superhydrophobic, are also oleophilic. Being both superhydrophobic and oleophilic allows oil to pass through the mesh, whilst water remains on the surface. The meshes were tested for their ability to separate mixtures of oil and water in flow conditions. When silicone oil/water mixtures were passed over the meshes, all meshes tested were capable of separating more than 93% of the oil from the mixture.

An energy saving Leidenfrost levitation method is introduced to transport micro-droplets with virtually frictionless contact between the liquid and solid substrate. By micro-engineering the heating units, selective areas of the whole substrate can be electro-thermally activated. A droplet can be levitated as a result of the Leidenfrost effect, and further transported when the substrate is tilted slightly. The selective electro-heating produces a uniform temperature distribution on the heating units within 1 s, in response to a triggering voltage. Alongside these experimental observations, finite element simulations are conducted to understand the temperature profile of the selective heated substrate, and also generate phase diagrams to verify the Leidenfrost regime for different substrate materials. Finally, we demonstrate the possibility of controlling low friction high speed droplet transportation (~ 65 mm/s) when the substrate is tilted (~ 7 °) by structurally designing the substrate. This work establishes the basis for an entirely new approach to droplet microfluidics.

A flexible thin film acoustofluidic device generates hybrid wave modes for microfluidic actuation (Lamb waves) and biosensing (thickness shear waves).