A FIELD-THEORY OF RANDOM HETEROPOLYMERS NEAR SOLID-SURFACES - ANALYSIS OF INTERFACIAL ORGANIZATION AND ADSORPTION-DESORPTION PHASE-DIAGRAM

Understanding the interfacial organization of heteropolymers near soli d surfaces is an issue of fundamental interest that is relevant for ma ny technological and biological applications. In this paper we address several questions pertaining to the surface-induced ordering and the adsorption-desorption phase behavior of a dilute solution of two-lette r random heteropolymers interacting with a solid surface. Our analysis is based on a statistical field theoretic formulation of the propagat or for the problem of interest. We employ the replica trick to allevia te analytical difficulties which arise when considering averaging over the sequence distribution of the A and the B units. In order to highl ight the effects of the surface, we consider the situation wherein the intersegment interactions are of the excluded volume type while the s egment-surface interactions of the A and B segments are arbitrarily di fferent. Within the replica symmetric solution, we show that proper co arse-graining of the interaction potentials leads to exact analytical expressions for the self-consistent propagator of the heteropolymer at theta conditions and for the case where excluded volume interactions prevail. One of our interesting findings is that heteropolymers underg o an adsorption-desorption transition in the vicinity of a surface tha t interacts with the different types of segments in arbitrarily differ ent ways. This is consistent with our previous numerical findings for much more restricted circumstances. We explicitly analyze the influenc e of the fluctuations in the sequence distribution on the conformation al organization of the adsorbed chains and obtain the scaling behavior of properties of interest in the vicinity of the adsorption-desorptio n threshold with respect to the disorder strength and other polymer in teraction parameters. Specifically, invoking the Ehrenfest theorem we find that the adsorption-desorption transition at theta conditions is a second-order phase transition while in the case where excluded volum e interaction prevails the transition becomes first order. We also obt ain exact analytical expressions for the adsorption-desorption thresho ld. The threshold exhibits quite an unusual dependence on the strength of the disorder. Finally, we compute the point of onset of repulsive forces between plates that confine a random copolymer solution as a fu nction of chain sequence distribution. We suggest specific experiments employing the surface force apparatus that could directly test our pr edictions. (C) 1995 American Institute of Physics.