Dynamics in adsorbed layers of associative polymers in the limit of strong backbone-surface attractions

Taken together with the shape of the adsorption isotherm, the adsorption and desorption dynamics of hydrophobically end-modified poly(ethylene oxide) (PEO) on silica suggest that adsorbed layers are comprised of two general populations: a tightly adsorbed underlayer and a loosely bound outer layer. The former is driven by a large number of hydrogen bonding interactions between the PEO's ether groups and nondissociated surface silanols, per the classical model of homopolymer adsorption with tails, loops, and trains. The outer layer is held in place by hydrophobic interactions, about 7-8 kT between the chain ends, In the dilute limit, transport-limited adsorption kinetics suggests that chains adsorb individually and that the adsorbed layer contains only the chains tightly bound via backbone-surface interactions. At greater free solution concentrations, still dilute, entire clusters adsorb and the layer contains both tightly bound and hydrophobically associated populations. The, loosely bound outer layer responds to flow: The steadystate adsorbed amount depends on the wall shear rate, decreasing in stronger flows. The loosely bound layer also desorbs at the transport-limited rate in flowing water, facilitating quantification of its, binding strength through the application of a hybrid isotherm model combining features of a Langmuir isotherm with those predicted from mean-field treatments of homopolymer Adsorption.