IRREVERSIBLE ADSORPTION OF MACROMOLECULES AT A LIQUID-SOLID INTERFACE - THEORETICAL-STUDIES OF THE EFFECTS OF CONFORMATIONAL CHANGE

The effects of particle conformational changes on the kinetics and saturation coverage of irreversible macromolecular adsorption at liquid-solid interfaces are investigated by computer simulation of a modified random sequential adsorption model. In this model, macromolecules (modeled as disks of diameter sigma(alpha)) adsorb onto a surface at a rate k(a). Once adsorbed, the particles spread symmetrically and discretely to a larger diameter sigma(beta) at a rate k(s). Adsorption or spreading events which result in the overlap of particles on the surface are not allowed. We investigate the effects of changes in spreading magnitude Sigma (=sigma(beta)/sigma(alpha)) and relative spreading rate K-s (k(s)/k(a)). We observe that the saturation coverage of spread particles decreases while that of unspread particles increases with spreading magnitude. This dependence is most pronounced for small spreading: the derivative of the surface coverage of both spread and unspread particles with respect to Sigma diverges logarithmically when Sigma-->1. An increase in the rate of spreading increases the saturation coverage of spread particles while decreasing that of unspread particles. The dependence of the coverage on spreading rate is weaker than its dependence on spreading magnitude: a four order of magnitude change in K-s results in a factor of 2 change in the partial coverages. The coverage of unspread particles may become nonmonotonic in time for certain values of Sigma and K-s. The total density of particles on the surface decreases and the average particle size increases with K-s, in accordance with recent protein adsorption experiments.