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Regensburg 2004 – scientific programme

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DY: Dynamik und Statistische Physik

DY 51: Polymers and Colloids

DY 51.5: Talk

Friday, March 12, 2004, 11:45–12:00, H3

Phase diagram of random copolymers — •Christian Wald1, Annette Zippelius1 und Ben Vollmayr-Lee21Institut für Theoretische Physik, Universität Göttingen — 2Department of Physics, Bucknell University, Lewisburg, PA 17837, USA

The phase diagram of random copolymers is still controversial: Whereas Flory-Huggins theory predicts a sequence of separations into many homogeneous phases [1], Landau theory favors microphase separation into self-organized microstructures [2]. Simulations disagree with both models [3].

We show that the Flory-Huggins free energy can be obtained by coarse-graining the same microscopic model which also yields the Ginzburg-Landau expansion for a second order transition. The phase diagram is discussed for both pictures. Within Landau theory we find a sequence of transitions from a disordered phase to two macroscopic phases and finally to microphases. In contrast to the literature [1] we also find that the microphase transition is always of first order and characterized by a finite length scale. Consequently, a coexistence of three phases should be observable. The treatment of both theories is extended to include the effects of compressibility.

[1] A. Nesarikar et al., J. Chem. Phys. 98(9), 7385 (1993)

[2] G. H. Fredrickson et al., Macromol. 25(23), 6341 (1992)

[3] J. Houdayer and M. Müller, Europhys. Lett. 58(5), 660 (2002)

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