Membranes for Microfluidic Applications

Abstract

Abstract This article provides an overview of major membrane microfluidic techniques for the production and modification of liquid‐liquid and gas‐liquid dispersions and the most common membranes used in these processes. The main emphasis is on Shirasu porous glass (SPG) membrane, microengineered membranes, and single‐crystal silicon microchannel (MC) plates. For each membrane type, fabrication process and microfluidic applications are discussed. SPG membrane is an interconnected‐type membrane fabricated by spinodal decomposition, which has been widely used in membrane emulsification (ME) and membrane micromixing/nanoprecipitation processes leading to the generation of emulsions, micro‐ and nanobubbles, and micro‐ and nanoparticles. Typical microengineered membranes used in microfluidic applications are silicon nitride microsieves fabricated by photolithography and reactive ion etching, nickel membranes fabricated by UV‐LIGA process, and stainless steel membranes with laser‐drilled pores. Microengineered membranes are used in stirred cell, cross‐flow, and pulsating cross‐flow ME systems. In order to prevent damage to shear‐sensitive materials in the product stream, a shear stress on the downstream side of the membrane can be provided using oscillating (vibrating) or spinning (rotating) membrane. MC plates are microchips with 3D architecture consisting of an array of horizontal microgrooves or vertical straight‐through channels integrating with other features such as terrace lines, steps, and cross‐flow channels. They are usually fabricated in single‐crystal silicon by photolithography and anisotropic wet etching or deep reactive ion etching.