Microfluidic EDGE emulsification: the importance of interface interactions on droplet formation and pressure stability.

The fact that interactions of components with interfaces can influence processes is well-known; e.g. deposit accumulation on heat exchangers and membrane fouling lead to additional resistances against heat and mass transfer, respectively.

Directional liquid spreading over chemically defined radial wettability gradients.

We investigate the motion of liquid droplets on chemically defined radial wettability gradients. The patterns consist of hydrophobic fluorinated self-assembled monolayers (SAMs) on oxidized silicon substrates. The design comprises a central hydrophobic circle of unpatterned SAMs surrounded by annular regions of radially oriented stripes of alternating wettability, i.

Simulating anisotropic droplet shapes on chemically striped patterned surfaces.

The equilibrium shape of droplets on surfaces, functionalized with stripes of alternating wettability, have been investigated using simulations employing a finite element method. Experiments show that a droplet deposited on a surface with relatively narrow hydrophobic stripes compared to the hydrophilic stripes adopts a strongly elongated shape. The aspect ratio, the length of the droplet divided by the width, decreases toward unity when a droplet is deposited on a surface with relatively narrow hydrophilic stripes.

Metastable droplets on shallow-grooved hydrophobic surfaces.

The equilibrium shapes of water droplets on shallow-grooved hydrophobic surfaces are studied experimentally. The dependence of the two final states, notably metastable Cassie-Baxter and Wenzel, on the underlying geometric pattern is analyzed and discussed. Surprisingly, in contrast to theoretical expectations, a significant portion of the droplets are in the Cassie-Baxter state.

Dynamic dewetting through micropancake growth.

We experimentally investigate the dynamics of nanometer-high, micrometer-wide gassy layers at the interface between a hydrophobic solid and bulk water. These micropancakes grow laterally in time, on the timescale of an hour, leading to partial dewetting of the solid. The growth is directional, mediated by chemical roughness on the substrate, and transient, occurring within the first hour after liquid deposition.

Initial spreading kinetics of high-viscosity droplets on anisotropic surfaces.

Liquid droplets on chemically patterned surfaces consisting of alternating hydrophilic and hydrophobic stripes exhibit an elongated shape. To assess the dynamics during droplet formation, we present experimental results on the spreading of glycerol droplets on such surfaces using a high-speed camera. Two spreading regimes are observed.