This paper presents an investigation of the morphology of blends containing 5 wt% styrene butadiene diblock copolymer in a high-molecular-weight polystyrene matrix. Different samples of these blends were prepared by melt compounding in an extruder and by solvent casting. Transmission electron microscopy was used to determine their morphology. The extruded blend contained well dispersed, disc-shaped micelles of the diblock. The morphology of the solvent-cast blend was strikingly different, with onion-skinned structures of diblock copolymer that spanned up to several micrometres. However, upon annealing at 200'C, the morphology of the extruded blend and of the solvent-cast blend evolved towards the same relaxed state. The micelles became more spherical, grew in size and slowly agglomerated into cluster formations. The kinetics of this evolfition were observed for the extruded blend. Micelle growth and clustering rates at 200°C and also at 180°C were determined by characterizing their size, shape and spatial distribution. The micelles became more spherical quickly and formed clusters over a longer time period. The changes in micelle shape became apparent in blends annealed at 180°C for as little as 5 min. The micelle clustering, however, was only evident in the blends annealed at 200°C. The rate of clustering was quantified by plots of nearest-neighbour distributions at different times. Analysis of these plots indicates a diffusion mechanism for the clustering. The results seem to support theoretical assertions of Semenov on dynamics of block-copolymer micelles in a high-molecular-weight polymer matrix.
Посилання на статтю:
Micelle growth and clustering in blends of polystyrene and styrene-butadiene diblock copolymer / R. Polance, K. L. Nichols* and K. Jayaramanf // Polymer. – 1994. – Vol 35. – P. 5051-5056.