Electrophoretic Mobility and Size Determination of Aerosol OT Inverse Micelle in Decane Using Phase Analysis Light Scattering (PALS) and Dynamic Light Scattering (DLS) Respectively

Aerosol OT is a well known surfactant used as negative charging agent. When dissolved in a solvent an Aerosol OT molecule is ionized to become negatively charged head group (RSO-3) and a positively charged sodium ion (Na+). The head groups are supposed to adsorb onto the surface of dispersed particles leaving positively charged counter-ions in the solution. However, silica particles are positively charged when suspended in the dispersion of Aerosol OT in decane. Only at concentrations below approximately 0.5mM the data showed that silica particles are negatively charged.In searching for strong evidences supporting the above fact, inverse micelles of Aerosol OT in decane were observed in term of their charge and size growth using Phase Analysis Light Scattering (PALS) and Dynamic Light Scattering (DLS) respectively. The results showed that inverse micelles of Aerosol OT in decane were negatively charged. This evidence strongly support that the positive ions adsorb onto the particle to impart positive charge. Further measurement on electrophoretic mobility of silica particles in the system show that at Aerosol OT concentrations 100mM-1000mM silica particles are positively charged. The negativity of Aerosol OT inverse micelle in decane is growing along with the growth of the size of micelles and the growth of Aerosol OT inverse micelles was aboserved at Aerosol OT concentration 100-1000mM