Interfacial Properties of Extended‐Surfactant‐Based Microemulsions and Related Macroemulsions

Abstract

Extended surfactants containing an intermediatepolarity spacer, such as polypropylene oxide, in between the hydrophilic head and the hydrocarbon tail are known to result in superior solubilization and low interfacial tension, though they exhibit slow kinetics. The present work seeks to evaluate both equilibrium and kinetic aspects of extendedsurfactant-based micro-and macroemulsions. The interfacial morphology of the extended surfactant membrane, i.e., characteristic length (n) and interfacial rigidity (E r ) at optimum middle-phase microemulsion conditions, was characterized using the net-average curvature model. The results showed that extended surfactants resulted in a relatively rigid interfacial membrane compared with conventional surfactants having similar hydrocarbon chain length. In addition, both n and E r parameters increased with the length of the polypropylene oxide spacer. Increasing E r values correlated to the slow coalescence rates of extended surfactant emulsified systems. Two alternative approaches (the addition of combined linkers and co-surfactant) are shown to overcome the slow kinetics of coalescence while maintaining desirable high solubilization and low interfacial tension.

Phase Behavior of Microemulsions Formulated with Sodium Alkyl Polypropylene Oxide Sulfate and a Cationic Hydrotrope

“…This was shown by estimating the characteristic length (n) and the interfacial rigidity (E r ). [8] Both parameters increased with increasing the length of the polypropylene oxide region. The addition of linkers or co-surfactants was found to produce a reduction in the n value, indicating a decrease in solubilization, and a decrease in E r value, that means a less rigid surfactant membrane, leading to a faster coalescence rate and a shorter equilibrium time.…”

Palm Oil Removal from Fabric Using Microemulsion‐Based Formulations

“…As the salinity and surfactant concentration change as the wash cycle transitions to the rinse cycles, the contact angle is hypothesized to change, enhancing detachment of the residual oil left after snap-off. Elucidation of the exact effect and mechanism requires further study since it is not known whether a change in concentration with such extended surfactant mixtures results in species partitioning and formulation shifts as with conventional surfactants [40]; this is likely the case since extended surfactants have been recently shown to behave as the synthetic or natural ones [20,21,23,[41][42][43][44], with the exception of the temperature effect [45]. …”

Influence of the Mixed Propoxy/Ethoxy Spacer Arrangement Order and of the Ionic Head Group Nature on the Adsorption and Aggregation of Extended Surfactants

“…Only a few experimental species of the alkyl polypropylene oxide sulfate type have been made available by surfactant manufacturers and have been tested in applications such as detergency or solubilization of polar oils [11][12][13][14][15][16]. Extended surfactants behave in some aspect as conventional ones and may be mixed with other surfactants with fairly linear mixing rules [17,18].…”