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

The cloud points of aqueous solutions containing polyoxyethylene surfactant molecules with a distribution of chain lengths were studied for several nonionic surfactants. Experimentally, the cloud points increased as the oxyethylene chain lengths increased with a linear or logarithmic relation of the number of oxyethylates, as proposed by Schott. An experimental scale, the p − Po scale, was previously developed to correspond to the cloud points, where p is the average number of oxyethylene units per molecule and Po is the shortest chain length reference. However, no previous prediction methods of cloud point addressed systems containing a range of chain lengths. In this work, we propose a rescaling of the representative chain length as s − Po, where s is the cloud point-weighted mean ethylene oxide chain below p, and approximated as (p − Po)/PDI where PDI is the polydispersity index. Using the rescaled length, 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, such as {(p − Po)/(PDI)}/CP = a + b{(p − Po)/(PDI)}, where PDI indicates the Broadness of the chain length distribution.

The cloud points of nonionic surfactants vary with the distribution of polyoxyethylene head group size. An extended Schott’s equation can be used to predict the cloud points of various mixtures of distributed nonionic surfactants, which has relevance in a range of industrial fields.Figure optionsDownload high-quality image (93 K)Download as PowerPoint slideResearch highlights
► The cloud point (CP) of nonionic surfactant varied with the polyoxyethylene distribution.
► The short ethylene oxide chains led to the reductions of CPs.
► The extended Schott’s equation rescaled with PDI successfully predicts the CPs.
► The extended Schott’s equation is as {(p − Po)/(PDI)}/CP = a + b{(p − Po)/(PDI)}.