SEQUENCE FLUCTUATION-DEPENDENT ADSORPTION-DEPLETION TRANSITION FOR RANDOM HETEROPOLYMERS

We develop a model for the adsorption of random heteropolymers onto so lid surfaces from solutions that have a finite concentration of polyme r. Previous studies that properly average over the quenched sequence d istribution have been concerned with isolated chains near surfaces. Ou r self-consistent-field theory predicts a transition from situations w here the surface segment density is enhanced compared with bulk soluti on concentration to one wherein the surface segment density is deplete d. For a specific chemical identity of the random heteropolymer segmen ts and the surface, this adsorption-depletion transition occurs above a threshold value of the strength of the sequence fluctuations. This i ntriguing finding can be tested directly via neutron scattering experi ments (in the reflection mode), and offers opportunities for manipulat ing interfacial properties. The variation of the excess surface densit y of segments with polymer concentration in solution near the adsorpti on-depletion transition is also elucidated. (C) 1996 American Institut e of Physics.