Highly organized mesoporous silica monoliths were reproducibly prepared by nanocasting mixtures of fluorinated nonionic surfactants and micelles of two hydrocarbon block copolymers. It is the special feature of this fluorocarbon/hydrocarbon template mixture that they form not mixed micelles but individual micelles instead. By careful analysis of the pore architectures by gas sorption measurements and transmission electron microscopy in dependence on the relative template concentration, two different situations could be identified: (a) mesoscopically demixed samples and (b) mixed micellar phases where the two different micelles are packed in some type of organized alloy phase. Besides identification of such mixed phases for the first time for fluorocarbon/hydrocarbon mixtures, the resulting porous systems with controlled bimodal pore size distribution might be interesting from a materials perspective.