Superlattice formation in a binary mixture of block copolymer micelles

A binary solution mixture of distinct block copolymer micelles is found to adopt a superlattice. The larger micelles, formed from polystyrene-polyisoprene diblocks, have a nominal radius of 29 nm; the smaller micelles, formed from polystyrene-polydimethylsiloxane diblocks, have a nominal radius of 16 nm. The superlattice unit cell dimension is 156 nm and is assigned to space group Fm3c; it corresponds to the AB13 structure. As these diblocks are uncharged, the driving force for superlattice formation is primarily free volume entropy, as in sterically stabilized colloidal hard spheres.