(98f) Microfluidics and Reactors in Porous Materials

Precipitation of a polymer solution on a microstructured mold yields porous replicas in a reliable and reproducible fashion. This process, named phase separation micromolding, is exploited for the fabrication of microfluidic structures [Lab on a Chip 2005, 5, 1240]. As such, the introduction of porosity provides new functionalities in microfluidic and microreactor systems. The porous material can act as a selective barrier layer (a membrane) for specific transport of components through the microchannel or microreactor wall. We have proven this for gas-liquid systems, where the liquid is contained inside the channels and the gas can diffuse through the porous matrix. The porosity is beneficial in this case as it allows rapid transport of gasses through otherwise relative impermeable materials. The fabrication method furthermore results in very thin and flexible fluidic chips, that can be easily stacked in multi-layer constructs. The porosity of the microfluidic layout is well tunable by the adjustment of the phase separation conditions (e.g. polymer concentration, non-solvent, temperature, additives, etc.). A wide variety of morphologies can thus be obtained, ranging from completely porous structures, to porous structures with a dense skin layer, and completely dense structures. An extensive collection of recipes is available from the field of polymeric membrane preparation. This directly implies that membrane materials and morphologies are mimicked in the material in which the fluidic structure is present. Membrane separation processes, as they are know from large scale applications, can then be performed inside microfluidic channels. Although the process stems from the immersion precipitation method to fabricate polymeric membranes, also other non-organic materials can be processed. When ceramic precursor or metallic particles are added to the polymer solution, ceramic or metallic based microfluidics can be obtained. In this approach, the structure needs to be pyrolized and/or sintered after the micromolding process in order to convert the polymer composite into a metallic or ceramic structure. Microfluidics and microreactors obtained by such methods can be used for processes that require harsh conditions, e.g. high temperature or aggressive chemicals. These fluidic structures are of great interest for combining reaction and separation in single devices. They can be fabricated outside the cleanroom in a reproducible and economic fashion.