SEMIFLEXIBLE POLYMERS AT A LIQUID-LIQUID INTERFACE - SELF-CONSISTENT-FIELD CALCULATIONS

The adsorption of semi-flexible polymers at a liquid-liquid interface largely differs from that at a solid surface. The width of the interfa ce is an additional length scale in the problem, making the system beh avior particularly rich. We consider two phase-separating monomeric li quids, C and D, and a polymer A(N) which dissolves equally well in bot h liquids. We study this system in a self-consistent held 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 xi, the persistence length q, and the chain length N are relevan t parameters in the adsorption behavior. A key observation is that, wh ile keeping N-1/2/xi constant, the adsorbed amount goes through a mini mum with increasing q/xi. An initial increase of q/xi (q/xi less than or similar to 1) effectively leads to a larger coil size, leading to a decrease of the adsorbed amount. However, when q/xi much greater than 1, alignment of parts of the polymer within the interfacial region oc curs due to the lack of entropic penalties. This alignment process ind uces an increase of the adsorbed amount. These observations also have implications for the ongoing discussion, which species shows preferent ial adsorption in a mixture of flexible and stiff polymers. In this di scussion one should consider the effects of the finite size of the int erfacial region. (C) 1998 American Institute of Physics.