J. Phys. II France
Volume 7, Numéro 8, August 1997
Page(s) 1111 - 1121
DOI: 10.1051/jp2:1997175
J. Phys. II France 7 (1997) 1111-1121

Forces between Surfaces with Weakly End-Adsorbed Polymers

J.I. Martin1, Z.-G. Wang1, D. Zuckerman2, R. Bruinsma3 and P. Pincus4

1  Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA
2  Institute for Physical Science and Technology, University of Maryland, College Park, MD 20742, USA
3  Department of Physics, University of California, Los Angeles, CA 90024, USA
4  Departments of Physics and Materials, University of California, Santa Barbara, CA 93106 USA

(Received 9 October 1996, revised 10 April 1997, accepted 22 April 1997)

We study the interaction forces between two plates in a semi-dilute solution of polymers each having one weakly adsorbing end-group. We show that this system exhibits both repulsive and attractive interactions of comparable magnitude and well-separated length scales: when the plate separation is within a range of order the end-to-end distance of the end-adsorbed polymer, repulsion arises with a magnitude of $\epsilon\frac{\Phi}{Na^3}$ where $\epsilon$ is the end-adsorption energy, N is the degree of polymerization, a is the Kuhn length and $\Phi$ the volume fraction of the polymer. This repulsion is due to desorption of the end-adsorbed chains. At plate separations of order the correlation length of the solution, a depletion attraction sets in with a magnitude that scales with the bulk osmotic pressure.

© Les Editions de Physique 1997