A theoretical self-consistent field study of mixed interfacial biopolymer films

The adsorption of a linear polyelectrolyte onto an existing layer of protein at an interface has been investigated. Calculations using a simple model, involving only the short range interactions, show that the polyelectrolyte forms a more extended distinct secondary layer if only ceratin sections of the molecule interact with the protein layer. These results are also confirmed for a more sophisticated model that accounts for the electrostatic interactions between the two biopolymers. It is found that there is a maximum level of adsorption of polyelectrolyte as the number of charged segments of the chains is varied. The peak occurs at higher levels of charging as the background salt concentration is increased. We also consider the effects of pH on the adsorption. The influence of the structure of the mixed layers on colloidal forces, mediated between two surfaces covered by such films, is also discussed