Dynamics in Adsorbed Layers of Associative Polymers in the Limit of Strong Backbone−Surface Attractions

Abstract

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.

Adsorption of copolymers aggregates: From kinetics to adsorbed layer structure

“…Indeed, high molecular weight PEO adsorbs to silica through hydrogen bonding and can be extremely difficult to rinse away or displace through the exchange of like polymer [53,54]. Also, associative polymers with modest molecular weight PEO and smaller hydrophobes show elevated coverages on silica compared with that of pure PEO [55]. Such interfacial associations and micelles have been seen for other PEG-siloxane surfactants on hydrophilic mica [31].…”

Adsorption of organic molecules on silica surface

“…Huang and Santore [181] investigated the adsorption of hydrophobically modified PEO, focusing on the model system comprised of a 35,000 narrow molecular weight backbone, endcapped with C 16 hydrophobes. Adsorption of hexadecyl urethane (NH 2 COOC 16 H 33 ) onto planar silica, which serves as a model for many different substrates exhibiting attractions between the surface and the main polymer backbone was studied, which indicates that hydrophobe adsorption to the surface is not the main driving force for adsorption, though the hydrophobes may indeed adsorb at some coverage levels.…”

Adsorption of poly(ethylene glycol)‐modified ribonuclease A to a poly(lactide‐co‐glycolide) surface

“…PEG is surface active on a variety of materials, including hydrophobic (Baker and Berg, 1988;Charron and Tilton, 1996;Cowell and Vincent, 1983;Kelly and Santore, 1995;Pagac et al, 1997) as well as acidic surfaces (Huang and Santore, 2002;Mathur and Moudgil, 1998;van der Beek et al, 1991), so it should not be assumed that PEGylation will always tend to decrease protein adsorption. Depending on the lactide/glycolide ratio, PLG can be hydrophobic on initial exposure to water, only to become hydrophilic and increasingly negatively charged as it ages.…”