Surface forces induced by ideal equilibrium polymers

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Abstract
The behavior of a dilute solution of ideal equilibrium (or “living”) polymers confined between two surfaces and the effect on the surface forces are investigated theoretically. Exact analytical expressions are obtained for the concentration profile and the average length of chains in the gap, the adsorbed amount, and the disjoining pressure for chains with an arbitrary interaction with the surfaces. If the adsorption energy of the segments increases, the excess amount of segments in the gap and the average chain length increase and diverge continuously at a critical value of the adsorption energy which depends on the average length of the chains in the bulk and on the width of the gap. If the chain ends have no specific interaction with the surfaces, the equilibrium polymers cause an attraction between the surfaces, either via the depletion mechanism in the case of nonadsorbing polymers or via the formation of bridges in the case of adsorbing polymers. If only one of the functional groups adsorbs preferentially on the surface, the interaction becomes repulsive (if the main-chain segments do not adsorb), due to steric repulsion. On the other hand, if both functional groups adsorb preferentially, the interaction is attractive as a result of the formation of bridges with one adsorbed end on either surface.