| Abstract
| - Taken together with the shape of the adsorption isotherm, the adsorption and desorption dynamics ofhydrophobically end-modified poly(ethylene oxide) (PEO) on silica suggest that adsorbed layers are comprisedof two general populations: a tightly adsorbed underlayer and a loosely bound outer layer. The formeris driven by a large number of hydrogen bonding interactions between the PEO's ether groups andnondissociated surface silanols, per the classical model of homopolymer adsorption with tails, loops, andtrains. 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 thatthe adsorbed layer contains only the chains tightly bound via backbone−surface interactions. At greaterfree solution concentrations, still dilute, entire clusters adsorb and the layer contains both tightly boundand hydrophobically associated populations. The loosely bound outer layer responds to flow: The steady-state adsorbed amount depends on the wall shear rate, decreasing in stronger flows. The loosely boundlayer also desorbs at the transport-limited rate in flowing water, facilitating quantification of its bindingstrength through the application of a hybrid isotherm model combining features of a Langmuir isothermwith those predicted from mean-field treatments of homopolymer adsorption.
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