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| - Direct Measurements of Interactions betweenHydrophobically Anchored Strongly ChargedPolyelectrolyte Brushes
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| - We investigated the nature and the range of interactions between negatively charged polyelectrolyte-coated surfaces as a function of salt concentration using the surface forces apparatus. The measured forceprofiles (interaction forces versus separation distance) are purely repulsive and show long-range electrostaticand short-range steric interactions. The measured range of interaction in salt-free as well as in low ionicstrengths extends well beyond the contour length of the polyelectrolyte chain. It is shown that the interactionrange between the ionic brush layers and the grafting density depend on the ionic strength of the solution.In salt-free solution, the counterions associated with polyelectrolyte cause the chains to stretch and giverise to long-range double-layer electrostatic repulsions between the opposing chains. When salt is addedto the system, the electrostatic interactions are partially screened and the polymer chain regains itsflexibility and therefore the range of interactions is reduced. The measured total range of interactionexhibits relatively weaker dependence on the salt concentration. We find that our force−distance profileswith added salt in a compressed regime can be very well described by the Pincus scaling model.
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