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 transitio n in a polystyrene-block-polyisoprene copolymer melt were studied with time -resolved depolarized light scattering. The ordered phase consisted of hexa gonally packed polyisoprene cylinders, and the order-disorder-transition te mperature of the block copolymer (T-ODT) was 132 +/- 1 degreesC. Our object ive was to identify the temperature at which the grain growth rate was maxi mized (T-max) and compare it with theoretical predictions. We conducted see ded grain growth experiments, which comprised two steps. In the first step, which lasted for 43 min, the sample was cooled from the disordered state t o 124 degreesC. 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 wa s heated to temperatures between 124 and 132 degreesC and the seeds grew wi th time. Our objective was to study grain growth at different temperatures starting from the same initial condition. The value of T-max, obtained expe rimentally was 128 degreesC. The theoretically predicted value of T-max, ba sed entirely on the rheological properties of the disordered sample and T-O DT, was also 128 degreesC. (C) 2001 John Wiley & Sons, Inc.