Use of a Nonionic Surfactant to Inhibit precipitation of Anionic Surfactants by Calcium

摘要

Precipitation of anionic surfactants by calcium ions has always been a major concern in formulations using anionic surfactants in hard water. In our previous work, it was found that the precipitation reaction was delayed when a mixture of anionic surfactants (sodium dodecyl sulfate and sodium octylbenzene sulfonate) was used at a certain mole ratio that would give the minimum in the difference in the supersaturation ratios between the two precipitating surfactants. In this work, the addition of nonylphenol ethoxylate (NP(EO)_(10)) as a nonionic surfactant is shown to delay the onset of precipitation for a longer time. The zeta potential of precipitates reveals that the NP(EO)_(10) is able to slow down the precipitate growth by adsorbing onto the precipitate crystals and this results in larger mean particle size.