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Kinetics of phase transition from lamellar to hexagonally packed cylinders for a triblock copolymer in a selective solvent
We examined the kinetics of the transformation from the lamellar (LAM) to the
hexagonally packed cylinder (HEX) phase for the triblock copolymer,
polystyrene-b-poly (ethylene-co-butylene)-b-polystyrene (SEBS) in dibutyl
phthalate (DBP), a selective solvent for polystyrene (PS), using time-resolved
small angle x-ray scattering (SAXS). We observe the HEX phase with the EB block
in the cores at a lower temperature than the LAM phase due to the solvent
selectivity of DBP for the PS block. Analysis of the SAXS data for a deep
temperature quench well below the LAM-HEX transition shows that the
transformation occurs in a one-step process. We calculate the scattering using
a geometric model of rippled layers with adjacent layers totally out of phase
during the transformation. The agreement of the calculations with the data
further supports the continuous transformation mechanism from the LAM to HEX
for a deep quench. In contrast, for a shallow quench close to the OOT we find
agreement with a two-step nucleation and growth mechanism
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