Design and fabrication of porous polymer wick structures

Wicks are often an integral part of fluid capacitance and transport in many systems, including heat pipes, fuel cells, and lateral flow chemical assays on cellulose paper. In this paper, we explore porous polymer monoliths as a new wick material potentially applicable to these and other applications. Polymer monolith chemistries, long used for high surface-to-volume ratio separation and filtering media in analytical chemistry, offer tremendous flexibility in resulting monolith pore structure, chemical composition, and surface chemistry (including wettability). We leverage this flexibility to design, fabricate, and characterize hydrophilic porous monoliths, with the aim of achieving high permeability wick materials. We show that variations in monomer concentration and porogen composition can affect mode pore diameters ranging from 6.3 to 10.1 μm and permeabilities ranging from 0.73 × 10−12 to 1.9 × 10−12 m2. In addition, we identify a rough dependence of monolith permeability on porosity times the square of mode pore diameter and discuss key figures of merit characterizing capillary transport. As an example application, we then detail a custom injection molding procedure, where we in situ polymerize ∼150 μm thick wicks conformally onto the surface of metal channels of a polymer electrolyte fuel cell cathode.