Adsorption of a homopolymer chain onto a heterogeneous stripe-patterned surface studied using a directed walk model of the polymer

Abstract

Adsorption of a homopolymer chain onto a heterogeneous stripe-patterned surface is studied in the framework of the three-dimensional partially directed walk model of the polymer by using the generating function approach. Both annealed random and quenched regular (periodic) stripe-patterned surfaces are considered. For random surfaces the adsorption–desorption transition temperature is analyzed. Comparison of the transition points for random and the ‘equivalent’ regular surfaces (having the same average stripe width) shows that the transition temperature is higher for the random surface. For regular stripe-patterned surfaces, the phase diagram is derived and the temperature dependences of the main conformational and thermodynamic characteristics of the adsorbed chain are obtained. It is demonstrated that adsorption is accompanied by the orientation of the polymer along the stripes. At low temperature (in the strong adsorption regime), the polymer chain is localized onto a single adsorbing stripe. When the surface consists of narrow adsorbing stripes separated by wide nonadsorbing stripes, an additional second peak on the heat capacity temperature dependence emerges, which indicates that adsorption occurs as a two-stage process where chain localization on a single adsorbing stripe is completed prior to its full adsorption on this stripe. This effect is enhanced with increasing distance between adsorbing stripes.