ADSORPTION OF A FLEXIBLE POLYMER ONTO A RIGID-ROD - A MODEL STUDY

The adsorption of a flexible polymer from a good solvent onto a rigid cylindrical rod has been investigated by model calculations using hete rogeneous lattice theory. The excess adsorbed amount per unit surface area (Gamma(ex)), the. concentration of the adsorbed polymer at the ro d surface (phi(1)), and the excess surface free energy (A(d)egrees) ha ve been studied, for various choices of rod radius (R = 0.5-10 lattice layers), polymer length (r(p) = 10-500 segments), and excess polymer- surface interaction (Delta(chi) drop (chi polymer,surface) - (chi solv ent,surface)). For R exceeding a few lattice layers, all effects of su rface curvature are weak, and the adsorption characteristics are close to those found for a flat surface. For very thin rods, phi(1) decreas es significantly with decreasing R, especially for moderately attracti ve Delta(chi). This effect is attributed to the decrease in adsorption energy (at constant Delta(chi)) for decreasing R. In contrast, Gamma( ex) may either increase or decrease with decreasing R, depending on De lta(chi) and r(p). For weakly anchored polymers (weak attraction or sh ort polymers), the effect of the decreased adsorption energy for small radii dominates, leading to a decrease in Gamma(ex) for decreasing R. For strongly anchored polymers (strong attraction or long polymers), however, Gamma(ex) is larger for smaller R, owing to the larger access ible volume per surface area for nonadsorbed polymer segments. The imp lications of the results for the mixed association of flexible and rod like polymers, as observed experimentally in certain gelling polysacch aride mixtures, are discussed.