Maximizing the grain growth rate during the disorder-to-order transition in block copolymer melts

The factors controlling grain growth during the disorder-to-order transition in a polystyrene-block-polyisoprene copolymer melt were studied with time-resolved depolarized light scattering. The ordered phase consisted of hexagonally packed polyisoprene cylinders, and the order-disorder-transition temperature of the block copolymer (T_ODT) was 132 ± 1°C. Our objective was to identify the temperature at which the grain growth rate was maximized (T_max) and compare it with theoretical predictions. We conducted seeded grain growth experiments, which comprised two steps. In the first step, which lasted for 43 min, the sample was cooled from the disordered state to 124°C. This resulted in the formation of a small number of ordered grains or seeds. This was followed by a second step in which the sample was heated to temperatures between 124 and 132°C and the seeds grew with time. Our objective was to study grain growth at different temperatures starting from the same initial condition. The value of T_max obtained experimentally was 128°C. The theoretically predicted value of T_max, based entirely on the rheological properties of the disordered sample and T_ODT, was also 128°C.