The change in structure of surfactant aggregates during adsorption/desorption processes and its effect on the stability of alumina suspension

The adsorption/desorption behavior of the cationic surfactant tetradecyl trimethyl ammonium chloride (TTAC) at the alumina-water interface and the change in the structure of surfactant aggregates at the interface were studied using the fluorescence spectroscopic technique along with electrophoresis. As expected, the cationic TTAC adsorbed significantly on the negatively charged alumina particles. It was observed that adsorption was reversible in the high concentration range, but in the low concentration range some hysteresis was observed. This can be attributed to the different operative mechanisms for hemimicelle formation and breakup. An energy barrier is proposed for the formation of the TTAC aggregates at the solid-liquid interface with the result that the hemimicelle concentration for the adsorption process is higher than that for the desorption process. This conclusion was further confirmed by the fluorescence spectroscopic test. This adsorption hysteresis affected dispersion properties of alumina suspension with the maximum settling rate shifting to the lower concentrations.