ELLIPSOMETRY STUDIES OF THE ADSORPTION OF CELLULOSE ETHERS

The adsorption properties of a nonionic polymer, ethyl(hydroxyethyl)cellulose (EHEC), at hydrophobic and hydrophilic silica surfaces were studied by means of in situ ellipsometry. Special emphasis is put on the relation between the adsorption properties and the phase behavior of the polymer-water system, e.g., by studying the effects of adding different cosolutes (salts and alcohols) and of changing the temperature. It is observed that as the solvency increases (decreases) both the adsorbed amount and the average apparent Him concentration decrease (increase). The effects of temperature cycles were studied to provide some information on the time scale for the adsorption, as well as on its reversibility. In these experiments, it was found that conformational changes take place even after the adsorbed amount has reached its limiting value. The complete adsorption process thus extends over an extremely long time scale, indicating entanglement effects. Completely reversible changes take place at shorter incubation times. Furthermore, we have studied the effects of surface hydrophobicity on the adsorption of EHEC. It was found that both the absolute value and the temperature dependence of the adsorbed amount are much larger at a hydrophobic surface than at a hydrophilic one. These experiments indicate that the EHEC molecules become more hydrophobic at higher temperatures. © 1990, American Chemical Society. All rights reserved.