Growth of AOT Reversed Micelles and the Solvent Effect Investigated by Dielectric and Light-Scattering Measurements

Abstract

Abstract The relative permittivity (εr) and the conductivity (κ) at a frequency (f) of 50 kHz, and the dynamic light-scattering were measured for ternary systems of (AOT + r·H2O) solved in cyclohexane, heptane, octane, decane, and dodecane at a temperature of 298.15 K as a function of the amount ratio (r) of water to AOT (r = [H2O]/[AOT]) up to the onset of percolation. The molality (m) of AOT for those solutions was 0.15 mol kg−1, and increased to 0.30 mol kg−1 for solutions with dodecane. By increasing r, spherical reversed micelles were formed at r ≈ 6 in straight-chain hydrocarbons. The light-scattering measurements indicated that the mean hydrodynamic diameter of the micelles increased with increasing r, showing a sigmoid curve. The growth of micelles was promoted in a longer chain hydrocarbon. The percolation transition occurred as the particles grew to a critical diameter of about 50 nm. On the other hand, the growth of particles in c-hexane was moderate, and percolation did not occur up to r = 90, where the solution turned turbid. The growth of particles found from light-scattering measurements was well correlated to dielectric observations.