EPJ

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EPJ E - Soft Matter and Biological Physics
Soft Matter and Biological Physics


Eur. Phys. J. E 7, 49-64 (2002)
DOI: 10.1140/epje/i200101101

Phase equilibria in random multiblock copolymers

A.V. Subbotin1 and A.N. Semenov2

1  Institute of Petrochemical Synthesis, Russian Academy of Sciences, Moscow 117912, Russia
2  Department of Applied Mathematics, University of Leeds, Leeds LS2 9JT, UK

a.semenov@leeds.ac.uk

(Received 13 July 2001)

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 $N\left\vert\epsilon\right\vert$ controlling the phase behavior of the system, where N is the number of blocks per chain and $\epsilon$ is the composition asymmetry parameter (= the difference between the mean copolymer composition and its critical value). The phase diagram involving $N\left\vert\epsilon\right\vert$ 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: $\rm H_0\to H_1+H_2$. The third (lamellar) phase separates on further cooling. Then hexagonal and body-centred-cubic phases take over if $N\left\vert\epsilon\right\vert\gtrsim 1$. As the Flory interaction parameter $\chi$ increases further, the standard transitions ${\rm BCC}\to {\rm HEX}\to \rm LAM$ take place.

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).


© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2002

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