Dynamic light scattering from diblock copolymer solutions

Abstract

Polarized (VV) and depolarized (VH) dynamic light scattering was used to investigate the dynamics of an asymmetric diblock copolymer in a non-selective good solvent near the disorder-to-order transition (ODT) as a function of copolymer concentration and temperature. The VV intensity relaxes with three relaxation modes. The fast diffusive mode relates to the cooperative diffusion of copolymer chains. The intermediate extra diffusive relaxation, recently observed in bulk diblocks, is attributed to either the relaxation of the composition field configurations or to the self-diffusion of copolymer chains observable by light scattering through their intrinsic composition polydispersity. The very slow mode is the well investigated cluster relaxation. At low concentrations, the VH scattering intensity is low and the VH correlation function is flat. A q 2-dependent relaxation, with q-dependent amplitude and intensity, appears in the VH correlation function when the solution crosses from the disordered into the ordered state, which is also accompanied by a significant increase in the VH intensity. This is attributed to form birefringence due to the formation of coherently-ordered grains of long cylinders in the ordered state, with coherence length of the O(μm).