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Soft Matter and Biological Physics


Eur. Phys. J. E 5, 337-351

Scaling theory of mixed amphiphilic monolayers

Shigeyuki Komura1, 2 and S.A. Safran2

1  Department of Chemistry, Faculty of Science, Tokyo Metropolitan University, Tokyo 192-0397, Japan
2  Department of Materials and Interfaces, Weizmann Institute of Science, Rehovot 76100, Israel

komura@comp.metro-u.ac.jp
sam.safran@weizmann.ac.il

(Received 29 December 2000 and Received in final form 19 March 2001)

Abstract
We predict the elastic properties of mixed amphiphilic monolayers in the swollen state within the blob model using scaling arguments. First the elastic moduli and the spontaneous curvature of a bimodal brush are determined as a function of the composition and the relative chain length. We obtain simple and useful scaling functions which interpolate between the elastic moduli of a pure short-chain brush and a pure long-chain brush. By using the analogy between block copolymer interfaces and polymeric brushes, the effect of mixing on self-assembled diblock copolymer monolayers is investigated in the swollen state. We calculate various interfacial properties, such as the equilibrium surface coverage, interface curvature, and the mixing free energy as a function of the composition. In general, we find a nonlinear dependence on the composition, which deviates from the simple linear averaging of the properties of pure components. Our results are used to discuss a recent experiment on the effect of amphiphilic block copolymers on the efficiency of microemulsions.

PACS
36.20.-r - Macromolecules and polymer molecules.
68.05.-n - Liquid-liquid interfaces.
82.70.-y - Disperse systems; complex fluids.


© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2001