Conformational evolution under steady shear flow: a comparison between cyclic and linear block copolymers |
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Authors: | Quan Chen |
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Institution: | (1) Institute for Chemical Research, Kyoto University, Uji Kyoto, 611-0011, Japan |
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Abstract: | Cyclic block copolymer is a special type of block copolymer having no free ends. Comparison of the dynamic behavior between
cyclic and linear block copolymers enables an understanding of the role of chain ends in dynamics of the latter. In relation
to this point, analysis was made on the conformational dynamics for a cyclic bead-spring type diblock copolymer chain, AoB,
under the steady shear flow. Further comparison was made on the conformational behavior of the AoB chain and that of two symmetric
linear triblock copolymer chains, A–B–A and B–A–B. For these chains, the mobility was set to be higher for the A segments
than the B segments. Thus, for the AoB chain under the steady shear flow, the segments of the A block exhibit less orientational
anisotropy than those of the B block. This orientational contrast is enhanced for the A–B–A chain partly because the constraint
for the motion of the segments is less near the chain ends than near the chain center. Nevertheless, for the B–A–B chain,
the segmental orientation over the A block becomes more anisotropic than that over the B block. Detailed analysis shows that
this result is attributable to a high orientational correlation for the segments of two end B blocks, in particularly for
those near the block junctions. The correlated B segments exert a tensile force on the A block thereby significantly enhancing
the orientational anisotropy of the A segments. |
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