Phase equilibria in random multiblock copolymers |
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Authors: | AV Subbotin AN Semenov |
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Institution: | (1) Institute of Petrochemical Synthesis, Russian Academy of Sciences, Moscow 117912, Russia, RU;(2) Department of Applied Mathematics, University of Leeds, Leeds LS2 9JT, UK, GB |
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Abstract: | A mean-field theory for domain structures in random multiblock copolymer melts is developed. We focus on the finite molecular
weight effects resulting in a competition between macroscopic phase separation and microdomain formation in the system. We
identify an essential parameter N
ε controlling the phase behavior of the system, where N is the number of blocks per chain and ε is the composition asymmetry parameter (= the difference between the mean copolymer
composition and its critical value). The phase diagram involving N
ε and the reduced temperature as variables is obtained. The regions of coexistence of two or more phases are identified. We
show that a superstructure formation on cooling is always pre-empted by a macroscopic phase separation of the macroscopically
homogeneous (disordered) system yielding two homogeneous phases: H
0↦H
1 + H
2. The third (lamellar) phase separates on further cooling. Then hexagonal and body-centred-cubic phases take over if N
ε
1. As the Flory interaction parameter χ increases further, the standard transitions BCC↦HEX↦LAM take place.
Received 13 July 2001 |
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Keywords: | PACS 36 20 -r Macromolecules and polymer molecules – 61 25 Hq Macromolecular and polymer solutions polymer melts swelling – 61 41 +e Polymers elastomers and plastics – 36 20 Ey Conformation (statistics and dynamics) |
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