Mesoporous silica films with well ordered nanochannels (approximately 7 nm in diameter) oriented parallel to the substrate were synthesized using supercritical carbon dioxide mediated silica deposition within templates comprised of triblock copolymers blended with strongly associating homopolymers. The films were patterned at the device level by conventional lithography and etched to yield periodic circular features approximately 20 µm in diameter. The nanoscale channels remained accessible to penetrant diffusion as shown by dye uptake experiments. The nanochannel arrays were used as miniature size exclusion columns to mediate nanoparticle diffusion.