Wetting gradient induced separation of emulsions: A combined experimental and lattice Boltzmann computer simulation study

Abstract

Guided motion of emulsions is studied via combined experimental and theoretical investigations.The focus of the work is on basic issues related to driving forces generated via a step-wise (abrupt) change in wetting properties of the substrate along a given spatial direction. Experiments on binary emulsions unambiguously show that selective wettability of the one of the fluid components (water in our experiments) with respect to the two different parts of the substrate is sufficient in order to drive the separation process. These studies are accompanied by approximate analytic arguments as well as lattice Boltzmann computer simulations, focusing on effects of a wetting gradient on internal droplet dynamics as well as its relative strength compared to volumetric forces driving the fluid flow. These theoretical investigations show qualitatively different dependence of wetting gradient induced forces on contact angle and liquid volume in the case of an open substrate as opposed to a planar channel. In particular, for the parameter range of our experiments, slit geometry is found to give rise to considerably higher separation forces as compared to open substrate.

Polymer Brushes for Surface Tuning

“…It was found that the surface energy hysteresis is the key phenomenon to understand the different droplet coalescence dynamics on open surfaces and inside the gap. [25] Polymer Brushes with Immobilized NPs for Sensing Applications…”

Directional motion of impacting drops on dual-textured surfaces

“…Owing to the recent technological progress in the design and fabrication of micro-and nanotextured surfaces, physicaltexture-based solid surfaces have often been used as a tool to manipulate drops on the surfaces. A familiar example is the use of wettability-gradient surfaces [1][2][3], solid surfaces exhibiting a directional variation in surface wettability, in the transport of liquid drops on solid surfaces and separation of the components in an emulsion [4]. A drop placed gently on these surfaces gets propelled towards the higher-wettability region if it overcomes the resistive forces due to contact angle hysteresis and viscosity.…”

Continuous Hydrolysis and Liquid–Liquid Phase Separation of an Active Pharmaceutical Ingredient Intermediate Using a Miniscale Hydrophobic Membrane Separator

“…Subsequent separation of the immiscible phases may be performed by flow focusing, 26 manipulation of surface wetting characteristics, 16,17,24,27,28 or using capillary forces through a microporous hydrophobic membrane. 1,3,4 Another recent trend is to use hydrophobic ducts 29 through which an organic phase may be separated (somewhat similar to a hydrophobic membrane, but with larger pores and in fewer number), or to stabilize the interface of two contacting phases with the use of micropillars.…”