Non‐linearchanges in phase inversion temperature for oil and water emulsions of nonionic surfactant mixtures

Abstract

Hydrophilic–lipophilic deviation (HLD) is a semiempirical framework for surfactant‐oil–water (SOW) formulation that has effectively assimilated SOW properties such as phase inversion temperature (PIT) and Winsor Type I ↔ II ↔ III ↔ IV microemulsion behavior. The HLD system's reliance on surfactant and oil parameters necessitates their experimental determination when relevant and accurate values are not available. In this study, experiments have been of the type commonly used to generate test surfactant HLD parameters based on perturbation of a well‐defined SOW reference system and assumption of linear mixing behavior for PIT versus component mole fractions. The reference SOW compositions comprised n‐octane, 0.01 M aqueous NaCl, and pure n‐decyl tetraethylene glycol ether (C10E4) reference surfactant. Test surfactants were primary alcohol ethoxylates and nonylphenol ethoxylates comprising disperse PEG (polyethylene glycol) chain lengths that are inherent to commercial production of nonionic ethoxylate surfactants. We observe non‐linear behavior of PIT versus test surfactant mole fraction, even when accounting for surfactant concentration effects, so the desired linear correlation that could otherwise be used to assign an HLD parameter has not been obtained. Since an objective of this study has been to improve the predictive utility of the HLD framework for commercial nonionic surfactants, relevant terms in the HLD equation have been assessed in terms of their potential contributions to non‐linear behavior. One current working‐explanation relates substantial non‐linear PIT contribution to oil‐like surfactant components in disperse commercial ethoxylates.

Dynamic salinity‐induced phase‐inversion conductivity measurements used to characterize alcohol ethoxylate based surfactant/oil/water systems

“…The data presented in Figure 6 demonstrates a relationship between the amount of nonionic surfactant to the f(S*)−αΔT (as determined by the Dy‐SPI conductivity measurements). This relationship between the amount of surfactant and the phase‐inversion properties is in general agreement with the findings from Dado's PIT experiments (Dado et al, 2021). Additionally, Acosta et al (2022) found a similar linear relationship between a nonionic surfactant's concentration and the sigma value (also referred to as the characteristic curvature, CC).…”

“…It is interesting to note that the concentration of the surfactant in the SOW system plays a role in the Dy‐SPI conductivity measurements. Dado et al (2021) demonstrated that by varying the amount of tridecyl alcohol ethoxylate (POE = 6), the PIT of the SOW decreased as the surfactant concentration increased up to 14% in the SOW. The data presented in Figure 6 demonstrates a relationship between the amount of nonionic surfactant to the f(S*)−αΔT (as determined by the Dy‐SPI conductivity measurements).…”

“…Onset and termination information gathered from the dynamic salinity-induced phase-inversion (Dy-SPI) conductivity measurements of bC 13 -POE 6 (40 g/100 ml decanes) performed at different surfactant/oil/water solution with low salinity (SOW LOW ) addition rates.Addition rate (Q) f(S σ = 5% )ÀαΔT f(S*)ÀαΔT f(S σ = 95% )ÀαΔT Conductivity measurements for the dynamic salinity phase inversion of (a) lC 12-14 -POE 7 (20 g/ml oil) in decanes at 40 C and (b) bC 13 -POE 9 (40 g/ml oil) in decanes at 40 C. for both plots (a & b), the grayed area correlates to the salinity ranges that exist between 5% and 95% of the normalized conductivity. conductivity measurements Dado et al (2021). demonstrated that by varying the amount of tridecyl alcohol ethoxylate (POE = 6), the PIT of the SOW decreased as the surfactant concentration increased up to 14% in the SOW.…”

Fragranced consumer products: Formulation practices, related models, and recommendations to enable wider hydrophilic–lipophilic difference (HLD) application

“…Challenges remain for Cc/k characterization for polydisperse ethoxylate surfactants. Zarate‐Muñoz et al (2016) and Dado et al (2022) discuss complex PIT behavior, likely related to hydrophobic portions of the surfactant mixture.…”

Surfactant mixtures: A short review

“…This partitioning is most often noted in alcohol ethoxylates, since a commercial alcohol ethoxylate contains species that are more oil soluble and those that are more water soluble. Manifestation of this effect is seen in very complicated phase‐inversion temperature behavior that depends on water–oil ratio (Marfisi et al, 2005), differences in the surfactant parameter in the Hydrophilic–Lipophilic Difference model (Acosta et al, 2023) when different concentrations of surfactants are used (Acosta & Natali, 2022; Dado et al, 2022), and differences in solubilization of oils (Butler & Hayes, 1998). Only recently was the concept of interfacial tension synergism (e.g., a lower interfacial tension than either single species) explored in a well‐defined experiment where one surfactant is soluble in water and the other in oil (Hsieh et al, 2021), although of course such synergism is undoubtedly occurring in the alcohol ethoxylate system and very possibly could contribute to the reason that alcohol ethoxylates are often used to break emulsions.…”