Conformational properties of a polymer confined between two adsorbing surfaces

Abstract

We have studied the conformation of an ideal polymer confined between two planar adsorbing surfaces. “Confined” means that one segment is permanently adsorbed to one of the surfaces. “Ideal” means that the distance between segments is governed by an angle-independent (freely rotating) probability density function with characteristic length a. The segment/surface interaction is determined by an adsorption parameter W. Segment/segment interactions are neglected. We show that for identical surfaces separated by a distance l, (i) if W/a < 1, the pressure is positive and the average segment density distribution has a maximum midway between the plates, (ii) if W/a > 1, the pressure is negative and most of the beads are strongly adsorbed. No turning points were found for the pressure regardless of the value of W/a. A summary of the results for the pressure, fraction of segments adsorbed and the density of segments between the plates for different values of the adsorption strength, W/a, is tabulated. For different surfaces, one with adsorption parameter W₀, the other with zero adsorption parameter, the pressure is always positive regardless of the value of W₀.