Time-resolved synchrotron X-ray scattering of the crystallization of a soft hexagonal columnar crystal

We have recently shown (Langmuir 2000, 16, 5846) that a soft surfactant hexagonal phase exhibits, above a critical shear rate, a shear-melting transition, where a two-dimensional polycrystalline texture is converted into a liquid of rods aligned along the flow. Moreover, after abrupt cessation of high shear, a monocrystal-like structure is obtained. In this paper, we investigate the kinetics of crystallization from the shear-melted phase by means of time-resolved synchrotron X-ray scattering experiments. After a latency time, the sample is found to continuously evolve from a liquid of rods to a monocrystal of rods. We show that the crystallization results from a coupling between bulk crystallization and interfacial crystallization, due to a specific anchoring of the liquid crystal at the walls of the shear cell. A detailed analysis of the experimental data allows the evaluation of the propagation of the interfacial front and the time evolution of the size of the crystallites. We find that the size scales as t(v) with v approximately equal to 0.3, in fair agreement with recent theories and simulations on grain rotation-induced grain growth of columnar polycrystalline structures.