A Simplified Methodology to Measure the Characteristic Curvature (Cc) of Alkyl Ethoxylate Nonionic Surfactants

Abstract

This work introduces a simplified methodology for measuring the characteristic curvature (Cc) of commercial alkyl ethoxylate nonionic surfactants using carefully selected reference surfactants and oils that produce rapid and well defined separations in salinity scans. The Cc of the commercial reference surfactants was calculated using optimal salinities (S*) obtained from solubilization parameter curves, from interfacial tensions (for a selected system), and from emulsion stability tests. The latter provided a fast detection of S*, in a matter of minutes. The calibrated Cc of the reference surfactants was subsequently used to measure the Cc of various commercial alkyl ethoxylate surfactants. The combination of mixtures of test and reference surfactants and emulsion stability tests produced reproducible Cc values that could be obtained with simple bottle tests and in a timely manner. The values obtained using this methodology were cross‐checked, and proved to be consistent, when using different combinations of reference surfactants and oils, and when conducted by different individuals. The standard deviation of Cc from these measurements was typically ±0.2 Cc units, but it could be as large as 25 % of the Cc value for highly hydrophilic surfactants. After comparing the values of Cc obtained experimentally with values calculated from nominal structures (via a group contribution model) it became clear that there are differences between these values, likely because of the polydispersity of alkyl ethoxylate surfactants.

Prediction of Cloud Point Curves of Alkyl Ethoxylates with the Hydrophilic–Lipophilic‐Difference and Net‐Average‐Curvature (HLD‐NAC) Framework

“…Offsets in the prediction of cloud point should be expected with the HLD because of the uncertainties in the experimental values of its parameters, particularly the value of C c . Zarate et al suggested that the minimum uncertainty on the value of C c is in the order of 0.2 HLD units (Zarate‐Muñoz et al, ). Considering the HLD equation, and the term c T being typically 0.06 HLD units °C −1 , then ±0.2 HLD units would be an equivalent of at least 3.3 °C uncertainty in cloud point predictions.…”

Microemulsion Microstructure(s): A Tutorial Review

“…Accordingly, the term accounting for the surfactant hydrophobicity was called the surfactant characteristic curvature Cc . A wide database of Cc and EACN values are listed in many works by Salager, Acosta, Aubry, and Harwell [ 79 , 82 , 84 , 85 , 86 , 87 , 88 ] allowing the prediction of the HLD ( H 0 ) of several μEs.…”

Correlation between Detergency of Different Oily and Solid Non‐Particulate Soils and Hydrophilic–Lipophilic Deviation

“…All vials containing the mixtures were mixed well by hand once a day for 3 days and placed in a temperature-controlled water bath at 25 C. The S* was visually observed and determined after simultaneously shaking all the vials in the phase scan. The surfactant formulation with shortest coalescence time for each set of phase scan was defined as the S* (Budhathoki et al, 2016;Zarate-Munoz et al, 2016).…”

“…The HLD equation was first proposed by Salager et al (1979) to describe the microemulsion phase behavior. The HLD value indicates the deviation of the surfactant formulation from the optimum condition (S*) (Acosta et al, 2008;Budhathoki et al, 2016;Zarate-Munoz et al, 2016) where an equal amount of water and oil are solubilized in the middle phase, the coalescence rate is fastest, the IFT is minimum (denoted as IFT*), and the solubilization capacity (SP) is highest (SP*). Negative, zero, and positive values of HLD correspond to Winsor Type I, III, and II microemulsions, respectively.…”