Abstract
The adsorption and desorption rate of dodecyl sulfate (DS) ions to and from polystyrene latex (PS) particles was investigated by the stopped-flow technique with electric conductivity detection at 25 °C and pH 5.9 below the critical micell concentration. The apparatus in this work was modified in order to study adsorption kinetics of surfactant ions at the solid/liquid interface. The modification was the sample mixing chamber making dead time shorter than the chamber used previously. The particle suspensions were rapidly mixed with sodium dodecyl sulfate (SDS) in the case of measuring adsorption rate by the sample mixing chamber. On the other hand, in the desorption the particle suspensions containing SDS were quickly diluted with ion exchanged distilled water by the equipment. In adsorption process the electric conductivity decreased with time, while in desorption it increased with time. These changes were monitored by a data store scope and a personal computer. The adsorption and desorption rate constants (ka, kd) of DS ions to and from polystyrene latex surface were determined to be 4.29 x 105 mol-1dm3 s-1 and 8.71 s-1, respectively. The usefulness of the apparatus in this reserch was ascertained with comparison between the adsorption/desorption rate constants (ka, kd) in the literature and the experimental ones (ka, kd) of DS ions to and from nylon 12 particles, which were obtained by measurement with this apparatus. The validity of the experimental adsorption rate constant (ka) was also confirmed by estimating the adsorption rate constant (ka') from the experimental desorption rate constant (kd)and equilibrium constant (K).
