Europhys. Lett.
Volume 61, Number 2, January 2003
Page(s) 214 - 220
Section Condensed matter: structure, mechanical and thermal properties
Published online 01 January 2003
DOI: 10.1209/epl/i2003-00215-y
Europhys. Lett., 61 (2) , pp. 214-220 (2003)

Anomalous scaling of the critical temperature of unmixing with chain length for two-dimensional polymer blends

A. Cavallo1, 2, M. Müller1 and K. Binder1

1  Institut für Physik, WA331, Johannes Gutenberg-Universität D-55099 Mainz, Staudinger Weg 7, Germany
2  Dipartimento di Fisica "E. R. Caianiello", Università degli Studi di Salerno Via S. Allende, I-84081 Baronissi (SA), Italy

(Received 23 August 2002; accepted in final form 28 October 2002)

The thermodynamics, structure and the chain configurations of symmetrical polymer mixtures confined into ultrathin films are studied by Monte Carlo simulations of the bond fluctuation model. It is shown that the Flory-Huggins-type scaling of the critical temperature ( $T_\ab{c} \sim N$) with chain length N in the bulk is replaced by a weaker increase, $T_\ab{c} \sim N^{1/2}$, in an ultrathin film, and this is interpreted in terms of geometric arguments. The pair-correlation function g(r) of monomers from different chains exhibits a pronounced correlation hole, and the density of intermolecular contacts $z_\ab{c}$ decreases with N as $z_\ab{c} \sim N^{-1/2}$.

61.41.+e - Polymers, elastomers, and plastics.
64.75.+g - Solubility, segregation, and mixing; phase separation.
68.60.-p - Physical properties of thin films, nonelectronic.

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