Phonon propagation in ordered diblock copolymer solutions

High-resolution inelastic light scattering was employed to measure the dispersion relations for the acoustic excitations in ordered concentrated solutions of poly(styrene)-block-poly(isoprene) copolymers with both symmetric and asymmetric composition and large spacing (220−415 nm). The morphology is manifested in the rich phonon spectrum recorded for different scattering wave vectors q in the range 0.003−0.034 nm-1. The experimental ωs(q) of the sth branch is directly compared with the theoretical dispersion from band structure calculations performed for different directions of q in the reciprocal lattice of lamellar and cylindrical periodic structures. The dispersion relations turn out to be a sensitive index of the microphase morphology and the grain orientation.