Using Selective Withdrawal to Coat Microparticles

Abstract

We report a method that uses the process of selective withdrawal of one fluid through a second immiscible fluid to coat small particles with polymer films. Fluid is withdrawn through a tube with its orifice slightly above a water-oil interface. Upon increasing the flow rate, there is a transition from a state where only oil is withdrawn to a state where the water, containing the particles to be coated and appropriate prepolymer reagents, is entrained in a thin spout along with the oil. The entrained particles eventually cause the spout interface to break, producing a thin coat of controllable thickness around each particle, which can be subsequently polymerized using chemical reagents, light, or heat. This method allows flexibility in the chemical composition and thickness of the conformal coatings.

Porous polymer particles—A comprehensive guide to synthesis, characterization, functionalization and applications

“…Another technique waiting to be used for porous particle production is called selective withdrawal [251][252][253][254][255]. Reported initially by Nagel et al [251], the bottom liquid, which is going to be the dispersed phase, is withdrawn just from the interface by a tube where the continuous phase liquid is on top (Fig.…”

“…Reported initially by Nagel et al [251], the bottom liquid, which is going to be the dispersed phase, is withdrawn just from the interface by a tube where the continuous phase liquid is on top (Fig. 23).…”

Free surface electrospinning from a wire electrode

“…However, related geometries have been studied. Spherical particles can be coated by a viscous, dense liquid as they rise under the action of the buoyancy force through the interface with a second, less viscous and less dense liquid [21,22]. Buoyancy forces have been used to coat particles when particles of a lesser density travel from one liquid to another liquid [23].…”

Emulsification in a microfluidic flow-focusing device: effect of the viscosities of the liquids

“…Recently, several research groups have reported synthesis of polymer particles in microfluidic reactors (Cohen et al 2001;Dendukuri et al 2005;Jeong et al 2005;Lewis et al 2005;Loscertales et al 2002;Nie et al 2005Nie et al , 2006Nisisako et al 2004;Seo et al 2005aSeo et al , 2005bTakeuchi et al 2005;Utada et al 2005;Xu et al 2005;Zhang et al 2006). The syntheses included a two-step process: (1) microfluidic emulsification of monomer or polymeric fluids, and (2) subsequent in-situ (on chip) solidification of the droplets by means of polymerization, gelation, or solvent evaporation.…”