Poly(ethylene glycol) Grafted to Quartz: Analysis In Terms Of A Site-Dissociation Model of Electroosmotic Fluid Flow

Poly(ethylene glycol) coatings are known to control a variety of surface phenomena including nonspecific protein adsorption, wetting, and electrokinetic effects. These and other properties make such coatings useful for biocompatible materials and in improving the efficiency of analytical and preparative separations where analyte-surface interactions play a role. In the present study terminally activated poly(ethylene glycol) derivatives were grafted onto quartz functionally activated with (3-aminopropyl)triethoxysilane, (3-mercaptopropyl)trimethoxysilane, or poly(ethylenimine). Grafts and activated surfaces were electro-kinetically characterized by measuring the pH dependence of induced electroosmotic fluid flow. A site-dissociation model of electroosmotic fluid flow based on the Smoluchowski equation, the Gouy-Chapman theory of the electrical double layer, and exact solutions to the Poisson-Boltzmann equation is presented in order to relate electroosmosis to the chemistry of the surface. Results include indications of relative coating stability and estimates of grafting density as well as effective coating thickness.