Role of Surfactants Based on Fatty Acids in the Wetting Behavior of Solid–Oil–Aqueous Solution Systems

Abstract

Surfactants based on fatty acids have attracted extensive attention thanks to their eco-friendly and pH-responsive features. Here, we studied two fatty acid-based surfactants that were paired with the same organic counterion but distinguished by their aliphatic chain lengths (monoethanolamine-oleic acid (MEA-OA) and monoethanolamine-lauric acid (MEA-LA)). Both surfactants exhibited the ability to lower the oil–water interfacial tension but lost their interfacial activity in a low-pH environment. We experimentally investigated their influence on the receding and spreading of oil droplets on solid surfaces. It was found that the interfacial tension reduction could decrease the static contact angle of the aqueous phase and hindered displacement dynamics during the oil droplet receding. Meanwhile, the interfacial activity was more likely to suppress the initiation of the oil droplet spreading due to the more stable thin-film forming prior to the spreading process. Nevertheless, the experimental results also exhibited that MEA-OA was more effective than MEA-LA in suppressing the receding dynamics and the spreading initiation even when they were characterized by similar interfacial tension values. Such an interesting observation could be attributed to the more considerable Marangoni flow in the solution of MEA-OA whose molecules have longer aliphatic chains. The insight from this study is expected to improve the knowledge on the molecular design for more efficient applications of fatty acid-based surfactants.

pH-Responsive Behavior of Pickering Emulsions Stabilized by a Selenium-Containing Surfactant and Alumina Nanoparticles

“…Switchable surfactants have received increasing interest in recent years − since they can reversibly regulate their interfacial activities through environmental stimuli, such as pH, CO 2 , light, redox reactions, , and magnetic fields. , Among the above-mentioned stimuli, pH is an attractive trigger because of its promising applications in pharmaceuticals, enhanced oil recovery, and textile treatment. − Sodium carboxylate-derived surfactants are one type of pH-responsive surfactants, which are commonly recognized as green surfactants and are synthesized from sustainable and biocompatible fatty acids. , However, the carboxylate surfactants with long alkyl chains always suffer from low solubility in water due to their high Krafft point, which hinders their application in many fields as an efficient surfactant.…”

“…10−12 Sodium carboxylate-derived surfactants are one type of pH-responsive surfactants, which are commonly recognized as green surfactants and are synthesized from sustainable and biocompatible fatty acids. 13,14 However, the carboxylate surfactants with long alkyl chains always suffer from low solubility in water due to their high Krafft point, which hinders their application in many fields as an efficient surfactant.…”