Lamellar phases and microemulsions in model ternary blends containing amphiphilic block copolymers

The order-disorder transition (ODT), microdomain structures and the phase diagram for ternary blends of low molecular weight PS, PI and PS-PI have been determined by a combination of X-ray scattering and transmission electron microscopy. The distribution of the homopolymer within the layers of a related PS/PB/PS-PB system has also been determined by a combination of X-ray and neutron reflectivity. A series of nearly symmetric, ternary blends of polystyrene (PS), polyisoprene (PI) and polystyrene-block-polyisoprene (PS-PI) have been studied by small angle X-ray scattering, static light scattering and transmission electron microscopy. The molecular weight of the homopolymers and block copolymer were in the ratio N-H/N-BCP = 0.19, which gave a block copolymer ODT and a homopolymer blend T-C that were similar (T-C/T-ODT approximate to 1.1). The block copolymer and its blends showed a weakly first-order transition from a lamellar phase to a fluctuating disordered phase in the volume fraction range Phi (H) less than or equal to0.77. A bicontinuous microemulsion was found between Phi (H) = 0.79 and Phi (H) = 0.93, and for Phi (H) greater than or equal to 0.93 macrophase separation was observed. In a similar PS, polybutadiene (PB) and polystyrene-block-polybutadiene (PS-PB) system the distribution of the homopolymer diluent was studied by X-ray and neutron reflectivity with deuterium labelled PS. The initial microstructure formed on spin coating had a dry-brush structure with the homopolymer concentrated in the centre of the domains and on subsequent annealing a wet-brush morphology was observed with the homopolymers uniformly distributed.