DEPOLARIZED DYNAMIC LIGHT-SCATTERING FROM DIBLOCK COPOLYMER SOLUTIONSNEAR THE ORDER-DISORDER TRANSITION

Dynamic light scattering in the depolarized geometry has been used to investigate the behavior of solutions of an asymmetric diblock copolym er in a nonselective good solvent near the order-disorder transition ( ODT), as a function of concentration, temperature, and scattering vect or, q. A new q2-dependent relaxation with q-dependent amplitude and de polarized intensity appears in the correlation function when the solut ion crosses from the disordered into the ordered state, which is accom panied by a significant increase in the depolarized intensity. This is attributed to the formation of grains of coherently-ordered long cyli nders in the ordered state, with estimated coherence length of O (mum) , that gives rise to a large form anisotropy in the microstructured so lution. The coupled translational/rotational motion of these orientati onally uncorrelated grains explains the observed diffusive relaxationa l dynamics.