C. M. C., counterion binding and thermodynamics of ethoxylated anionic and cationic surfactants

Abstract

The properties of a series of ionic ethoxylated surfactants of the typeR m (OC2H4) χ SO4Na andR m (OC2H4) χ TAB (m = 10, 12, 14 or 16 andx = 0, 1, 2 or 3) were studied. Surface areas obtained from surface tension measurements increased as the ethoxy group number increased whereas increasing the hydrocarbon chain length had little effect. The c.m.c.'s obtained from conductivity decreased with increase in hydrocarbon chain length and to a smaller extent as the ethoxy group number increased. Values ofΔG° showed the methylene group to be four fold as effective as the ethoxy group in promoting micellisation. As the temperature was varied between 5 and 60 °C all the surfactants exhibited a minimum c.m.c. value close to 25 °C which decreased as the surfactant became more hydrophobic and increased as the surfactant became more hydrophilic. Counterion binding from specific ion electrode measurements increased with increase in hydrocarbon chain length but decreased with increase in ethoxy group number. Counterion binding decreased with increase in temperature.