The polydispersity effect of distributed oxyethylene chains on the cloud points of nonionic surfactants

Abstract

The cloud points of aqueous solutions containing polyoxyethylene surfactant molecules with a distributionof chain lengths were studied for several nonionic surfactants. Experimentally, the cloud pointsincreased as the oxyethylene chain lengths increased with a linear or logarithmic relation of the numberof oxyethylates, as proposed by Schott. An experimental scale, the p Po scale, was previously developedto correspond to the cloud points, where p is the average number of oxyethylene units per molecule andPo is the shortest chain length reference. However, no previous prediction methods of cloud pointaddressed systems containing a range of chain lengths. In this work, we propose a rescaling of therepresentative chain length as s Po, where s is the cloud point-weighted mean ethylene oxide chainbelow p, and approximated as (p Po)/PDI where PDI is the polydispersity index. Using the rescaledlength, the experimental data for C12Es (lauryl alcohol ethoxylate, LAE), NPE-10 (nonyl phenol ethoxylate)and TDE-10 (tridecyl alcohol ethoxylate) were successfully predicted with no additional parameters, suchas {(p Po)/(PDI)}/CP = a + b{(p Po)/(PDI)}, where PDI indicates the Broadness of the chain lengthdistribution.