Adsorption of cellulose derivatives on inorganic oxides

Adsorption of hydroxyethyl cellulose (HEC) and quaternary ammonium substitu ted HEC (QNHEC) oil silica and titanium dioxide has been investigated as a function of pH and electrolyte (NaCl) concentration. Adsorbed amounts have been determined by means of reflectometry. Adsorption of HEC on SiO2 is con stant up to pH=5. At higher pH the adsorption decreases, which is most pron ounced at high (0.5 mol l(-1)) electrolyte concentration. The thickness of the adsorbed layer, determined by dynamic light scattering, is substantial. This indicates an adsorbed layer with extended conformation having loops a nd (few) long tails protruding into the solution. Adsorption on TiO2 in 0.0 1 mol l(-1) NaCl decreases monotonically with increasing pH. Tn 0.5 mol l(- 1) NaCl the adsorption is constant up to pH = 10, beyond which it decreases rapidly. Mechanisms of binding to both surfaces leading to the observed ad sorption behaviour are proposed. Electrostatics dominate the adsorption of QNHEC in 0.01 mol l(-1) NaCl on both surfaces. The adsorbed amount increase s linearly with pH up to pH=10. A decrease is observed for pH>11. The linea rity is interpreted in terms of a molecular condenser which is composed of the surface layer and the polyelectrolyte in the first layer near the surfa ce. In 0.5 mol l(-1) NaCl adsorption on SiO2 is constant up to pH=5. At max imum is observed at pH=10. On TiO2 the adsorption is low. (C) 1998 Elsevier Science B.V. All rights reserved.