"Critical" channel diameters were found (below which space confinement takes effect, leading to more uniform and ordered mesopore structures) in the study of evaporation-induced co-assembly of triblock-copolymer (P123) and silica molecular precursors (TEOS, tetraethyl orthosilicate) by employing channels in anodized aluminum oxide (AAO, 13-200 nm channel diameter) and in track-etched polycarbonate (EPC, 10-80 nm channel diameter) and for the first time we have observed a new mesopore structure (i.e., packed hollow spheres) in silica nanowires formed in AAO channels with diameters from 30 to 80 nm.