EPL

Issue		Europhys. Lett. Volume 55, Number 2, July 2001
Page(s)		221 - 227
Section		Interdisciplinary physics and related areas of science and technology
DOI		10.1209/epl/i2001-00403-3

DOI: 10.1209/epl/i2001-00403-3

Europhys. Lett., 55 (2) , pp. 221-227 (2001)

Wetting of a short chain liquid on a brush: First-order and critical wetting transitions

M. Müller and L. G. MacDowell

Institut für Physik, WA 331, Johannes Gutenberg Universität D-55099 Mainz, Germany

(Received 2 October 2000; accepted in final form 3 May 2001)

Abstract
We investigate the wetting behaviour of short chains on a surface covered with a brush of end-grafted chains of the same architecture by a combination of self-consistent field calculations and liquid-state theory. The surface interacts with the monomers via (non-retarded) van der Waals interactions of strength A. At low grafting densities, we find first-order wetting transitions. The value of the effective Hamaker constant $A_{\rm wet}> 0$ , at which the transition occurs, decreases and the strength of the first-order transition becomes weaker as we increase the grafting density. In an intermediate range of grafting densities, we encounter second-order wetting transitions at a vanishing Hamaker constant $A_{\rm wet}=0$ . The second-order transition is preceded by a first-order transition between a thin and a thick liquid layer ("frustrated" complete wet state) at negative values of A. This line of first-order transition terminates in a critical point. Upon increasing the grafting density further, we encounter a tricritical point, beyond which the wetting transition is again of first order and occurs at $A_{\rm wet}> 0$ . At these high grafting densities, the brush expels the free chains (autophobicity).

PACS
68.08.Bc - Wetting.
61.25.Hq - Macromolecular and polymer solutions; polymer melts; swelling.
05.70.Np - Interface and surface thermodynamics.

© EDP Sciences 2001

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