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Phase behavior of polyelectrolyte-surfactant complexes at planar surfaces Adi Shafir* and David Andelman

Summary: Phase behavior of polyelectrolyte-surfactant complexes at planar surfaces
Adi Shafir* and David Andelman
School of Physics and Astronomy Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Ramat Aviv, Tel Aviv
69978, Israel
Received 17 May 2006; published 16 August 2006
We investigate theoretically the phase diagram of an insoluble charged surfactant monolayer in contact with
a semidilute polyelectrolyte solution of opposite charge . The polyelectrolytes are assumed to have long-range
and attractive electrostatic interaction with the surfactant molecules. In addition, we introduce a short-range
chemical interaction which is either attractive or repulsive. The surfactant monolayer can have a lateral phase
separation between dilute and condensed phases. Three different regimes of the coupled system are investi-
gated depending on system parameters. A regime where the polyelectrolyte is depleted due to short range
repulsion from the surface, and two adsorption regimes, one being dominated by electrostatics, whereas the
other by short range chemical attraction similar to neutral polymers . When the polyelectrolyte is more
attracted or at least less repelled by the surfactant molecules as compared with the bare water-air interface, it
will shift upwards the surfactant critical temperature. For repulsive short-range interactions the effect is oppo-
site. Finally, the addition of salt to the solution is found to increase the critical temperature for attractive
surfaces, but does not show any significant effect for repulsive surfaces.
DOI: 10.1103/PhysRevE.74.021803 PACS number s : 82.35.Gh, 82.35.Rs, 61.41. e
Complexation between surfactants and macromolecules


Source: Andelman, David - School of Physics and Astronomy, Tel Aviv University


Collections: Materials Science; Physics