Adsorption of Ethyl(hydroxyethyl)cellulose onto Silica Particles: The Role of Surface Chemistry and Temperature

The adsorption characteristics of an ethyl(hydroxyethyl)cellulose (EHEC) polymer onto colloidal silica particles from aqueous solution have been investigated. The influence of solution temperature and the silica surface chemistry on EHEC adsorption isotherms and adsorbed layer thicknesses have been determined in an attempt to elucidate the mechanisms of adsorption. As the hydrophobicity of the silica particles are increased by physical and chemical treatment, the plateau EHEC adsorbed amount increased, while the corresponding adsorbed layer thickness decreased. The estimated free energy of adsorption (ΔGoads) was shown to be dependent on the silica surface chemistry, but did not correlate directly with silica's advancing water contact angle and suggests that EHEC adsorption is not directly controlled by hydrophobicity alone. As the solution temperature increased from 18 to 37°C, the plateau coverage of EHEC increased while the layer thickness generally decreased, this concurred with a reduction in the solvency. For hydrophilic and dehydrated silica particles, ΔGoads decreased in magnitude with increasing temperature, whereas for chemically treated silica, ΔGoads increased with temperature. These findings are discussed with respect to the specific interactions between EHEC segments and surface sites, which control the adsorption mechanisms of cellulose polymers.