The three-dimensional periodicity of porous membrane structures shows enormous potential in the fields of photonics, chemical sensing, catalysis, biological scaffolding and separations technology. Many of the currently implemented membrane fabrication methods utilize soft lithography methods.¹ Unlike lithography, often limited to two-dimensional and layered structures, self-assembling colloids offer superior flexibility for complex periodic shapes in membrane templating. Our work is concerned with processes of colloidal template formation (opal structure) in microcapillaries and the fabrication of porous membranes (inverse opal structure) via dissolution of colloidal templates after infiltration with a polymer matrix.

     We have convectively assembled 0.5, 2.4, and 9.6 µm sized sulfate-polystyrene (PS) particles in 12 µm and 50 µm inner-diameter polymethylmethacrylate (PMMA) capillaries. Cylindrical colloidal crystals with closed-packed hexagonal packing are formed. Fabrication of a porous membrane from this template is achieved by infiltrating a UV curable prepolymer into the interstitial spaces of the colloidal crystal. The prepolymer is subsequently cured under long-wave UV light (365 nm). The cured particle-polymer assembly is treated with a sequence of organic solvents to remove both the PMMA capillary and the PS particles and form cylindrical porous membranes. We have investigated the structure of the colloidal assemblies and the porous membranes using scanning electron microscopy and will present our findings. Further, knowledge of properties and characteristics of these membranes are critical in practical applications. UV, IR, and tensile strength analysis of the porous membranes are underway to determine the areas of applicability.

1 S.M. Yang, S.G. Jang, D.G. Choi, S. Kim, H.K. Yu, Small. 2006, 2, 458.