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

Abstract

Herein, we describe pH-responsive Pickering emulsions stabilized by a sodium carboxylate-derived selenium surfactant (C 10 -Se-C 10 •(COONa) 2 ) in combination with positively charged alumina nanoparticles. Unlike other bola-type carboxylate surfactants (e.g., disodium eicosanoate), C 10 -Se-C 10 •(COONa) 2 is soluble in water with a low Krafft temperature (36.1 °C). The emulsions are sensitive to pH variations, and efficient demulsification can be achieved by a pH trigger. The carboxylic sodium group in the C 10 -Se-C 10 •(COONa) 2 structure can be reversibly cycled between its anionic and nonionic states (carboxylic acid), resulting in a pH-controlled electrostatic attraction between the surfactant and alumina. The Pickering emulsion can be reversibly switched between "on" (stable) and "off" (unstable) states by pH at least four times. Compared with the emulsions stabilized by specially synthesized stimuli-responsive particles or surfactants, the method reported here is much easier to implement and requires very low concentrations of the surfactant and nanoparticles, with potential applications in the fields of biomedicine, drug delivery, and cosmetics.

pH and Magnetism Dual-Responsive Pickering Emulsion Stabilized by Dynamic Covalent Fe3O4 Nanoparticles

“…Pickering emulsions, which were stabilized by solid particles, have gained much attention thanks to the low toxicity and long-term stability [ 1 , 2 ]. The outstanding stability of Pickering emulsions is required in the field of cosmetic formulations, food storage, and so on [ 3 ].…”

“…Temperature-stimulated systems are energy-demanding [ 31 ]. Among these stimuli, pH is readily implementable and magnetism is non-invasive and reversible [ 2 , 7 , 10 , 32 , 33 ]. Therefore, pH and magnetism dual-responsive Pickering emulsions have promising applications.…”

Performance Evaluation and Mechanism Study of Seawater-Based Circulatory Fracturing Fluid Based on pH-Regulated WormLike Micelles

“…Therefore, it is a critical problem to realize reversible gel breaking with controllable time, complete gel breaking, and low cost for constructing a clean fracturing fluid system. To solve this problem, this article aims to realize the reversible gel breaking of clean fracturing fluid by introducing intelligent control switch, compared with intelligent control switch such as light, oxidation, CO 2 , and temperature; pH switches are time-controlled, thoroughly regulated and cost-effective, with good biocompatibility and high surface activity, so pH-sensitive surfactant is suitable as thickeners for clean fracturing fluids ( Liu et al, 2021a ; Yu et al, 2021 ; Mu et al, 2022 ).…”

Redox- and pH-responsive emulsions based on TiO2 nanoparticles and ferrocene derivates

“…21,22 As we all know, triggers such as pH, CO 2 , redox, ion, magnetic field and light have been widely used for constructing responsive Pickering emulsions. [23][24][25][26][27][28] Yu et al 29 described a pH-responsive behaviour of Pickering emulsions stabilized with alumina nanoparticles and a selenium-containing surfactant, in which the sodium carboxyl group could be reversibly transformed between its anionic and non-ionic states, resulting in the emulsification and demulsification of Pickering emulsions. Besides, Pickering emulsions with multi-responsiveness such as pH-temperature, CO 2 -temperature, light-magnetic field have been also widely studied.…”

“…Meanwhile, the pH responsiveness of emulsions was achieved by utilizing pH-controlled surface charge inversion of TiO 2 nanoparticles, which was different from previous studies that required surfactants to be pH sensitive. 29,31,34 This was expected to potentially further extend the preparation scope of pH-responsive emulsions.…”