Electrical interfacial layer at TiO2/poly(4-styrene sulfonate) aqueous interface

The interfacial properties of the system titanium(IV) oxide/poly(4-styrenesulfonate) (PSS) over a broad pH region in the presence of different alkali metal chlorides of different concentrations were investigated by means of electrokinetic, adsorption and surface potential measurements. Adsorption and electrokinetic data were obtained with colloid TiO₂ particles, while surface potential data were obtained using a single crystal rutile electrode with the 001 plane exposed to the liquid medium. The electrokinetic and surface potentials of TiO₂ were measured in the absence and presence of PSS. Since the presence of PSS did not significantly affect surface potentials, it was concluded that negative PSS molecules adsorbed at the surface by forming an outer-sphere surface complex rather than inner-sphere complex. The adsorption decreases significantly with pH, while the electrokinetic potential in the presence of PSS is negative in the whole investigated pH region. Amount of adsorbed PSS molecules is limited by the electrostatic repulsion which suppresses further adsorption, i.e. above critical potential of ?50 millivolts. In the acidic region, where the surface is originally positively charged the amount of adsorbed PSS molecules is high since negative PSS molecules should at first compensate original positive charge and in the second step reverse the charge to reach the critical potential. In the basic region the surface charge is already negative so that small amount of adsorbed PSS molecules creates critical potential that prevents further adsorption.