Order-disorder transition in a poly(styrene-b-isoprene) diblock copolymer at hypersonic frequencies

The order-to-disorder transition (ODT) has been studied in a poly(styrene-b-isoprene) diblock copolymer with a polystyrene (PS) volume fraction f PS of 0.22 at hypersonic frequencies using a tandem Fabry-Perot interferometer. Because of the asymmetric composition we are effectively studying the sound dispersion in a composite material made of hard PS spheres embedded in a soft polyisoprene matrix. All measurements are made in the long-wavelength limit, qD < 1, where q is the scattering wave vector and D is the sphere diameter. The transition temperature ( T ODT ) was identified earlier with rheology and SAXS at 112°C. We have investigated the sound velocity and attenuation at temperatures below and above the transition. We find the signature of T ODT from the broad hypersonic attenuation reflecting the enhanced segmental mobility due to mixing at temperatures near the T ODT .