SANS Investigation of PS−PB Block Copolymer Micelles in a Short Chain PB Homopolymer Matrix

Abstract

A micelle forming polystyrene (PS)−polybutadiene (PB) block copolymer was mixed with a short (relative to the PB block of the copolymer) PB homopolymer to investigate the structural properties of the micelles by small-angle neutron scattering. Samples with varying block copolymer concentration were measured at 90 °C in both core and shell contrast. The obtained intensities were analyzed using a core/shell model with a constant core density and a variable density profile for the corona. A reasonable analysis of the data was only possible by assuming that in the measured concentration range the unimer concentration is not constant but increases with increasing polymer concentration, while the aggregation number of the micelles stays constant. The data analysis further revealed that the corona of micelles shows almost constant density which stays in contrast to micelles of block copolymers with comparable block length ratio in low molecular solvents. These could be interpreted in terms of the starlike model of Halperin, where the outer shell has a fast decaying density profile.