Semi-flexible polymers at a liquid–liquid interface: Self-consistent field calculations

Abstract

The adsorption of semi-flexible polymers at a liquid–liquid interface largely differs from that at a solid surface. The width of the interface is an additional length scale in the problem, making the system behavior particularly rich. We consider two phase-separating monomeric liquids, C and D, and a polymer AN which dissolves equally well in both liquids. We study this system in a self-consistent field model in the dilute regime. The stiffness of the polymer is controlled by the use of a rotational isomeric state approach. We show that the interfacial width ξ, the persistence length q, and the chain length N are relevant parameters in the adsorption behavior. A key observation is that, while keeping N1/2/ξ constant, the adsorbed amount goes through a minimum with increasing q/ξ. An initial increase of q/ξ (q/ξ≲1) effectively leads to a larger coil size, leading to a decrease of the adsorbed amount. However, when q/ξ≫1, alignment of parts of the polymer within the interfacial region occurs due to the lack of entropic penalties. This alignment process induces an increase of the adsorbed amount. These observations also have implications for the ongoing discussion, which species shows preferential adsorption in a mixture of flexible and stiff polymers. In this discussion one should consider the effects of the finite size of the interfacial region.