Conductance of dialkyl sodium sulfosuccinate surface-active agents

Abstract

The conductance of solutions of very carefully purified di- n-octyl, di- n-hexyl, di- n-amyl, di- n-butyl, and di(2-ethylhexyl) sodium sulfosuccinate was measured at 29.92°C. Plots of equivalent conductance against the square root of the concentration showed that only di- n-hexyl and di(2-ethylhexyl) had the sharp break in equivalent conductance that was considered characteristic of surface-active agents. The equivalent conductance of di- n-octyl sodium sulfosuccinate had a flat maximum at concentrations just above the critical micelle concentration. Plots of the equivalent conductance of di- n-amyl and di- n-butyl sodium sulfosuccinate were smooth curves. Critical micelle concentrations were estimated from plots of specific conductance against concentration and, where possible, from plots of equivalent conductance against the square root of concentration. Except for di(2-ethylhexyl), values of the critical micelle concentrations obtained from conductance agreed nicely with critical micelle concentrations from surface tension. The reason for the difference between the values for the critical micelle concentration of di(2-ethylhexyl) sodium sulfosuccinate when measured by conductance and by surface tension has been considered.