Mesoporous silica films with cylindrical or spherical pores up to 40 nm in diameter were fabricated by replicating the morphologies of polystyrene-b-poly(tert-butyl acrylate), PS-b-PtBA, copolymers using CO2-assisted infusion and phase selective condensation of tetraethylorthosilicate within the polymer template. The template structures, including domain packing, orientation and spacing were controlled by adjusting the molecular weight, volume fraction and polydispersities of the block copolymers and by solvent annealing. Cylinder alignment was achieved in polymer templates through directed self-assembly (DSA). The structural details imparted to the template prior to precursor infusion were retained in the mesoporous films. In one example, aligned PS-b-PtBA templates were replicated to yield massively parallel arrays of cylindrical pores with pore diameters up to similar to 20 nm. The ability to tune pore sizes in this range within aligned nanochannels is attractive for applications involving biomolecules.