Behavior of Smart Surfactants in Stabilizing pH‐Responsive Emulsions

Abstract

Newly structured pH‐responsive smart surfactants (N+‐(n)‐N, n=14, 16) from alkyl trimethylammonium bromides are reported. In neutral and alkaline media N+‐(n)‐N behaves as a normal cationic surfactant and stabilizes conventional emulsions alone, as well as Pickering emulsions and oil‐in‐dispersion emulsions together with oppositely and similarly charged nanoparticles, respectively. In acidic media N+‐(n)‐N becomes a hydrophilic Bola‐type surfactant, N+‐(n)‐NH+, and is an inferior emulsifier either when used alone or together with charged nanoparticles, resulting in demulsification. N+‐(n)‐NH+ returns to the aqueous phase alone or together with nanoparticles after demulsification without contaminating the oil phase, and the aqueous phase can be recycled when triggered by pH change. This protocol is a green process and leads to preparation of various temporarily stable emulsions which are often used in emulsion polymerization, heterogeneous catalysis, and oil transportation.

A Dual pH‐ and Light‐Responsive Spiropyran‐Based Surfactant: Investigations on Its Switching Behavior and Remote Control over Emulsion Stability

“…[1,4] Other, yet considerable, systems respond on changes of the pH value, since they contain carboxylate [14] and/or amino groups. [14,15,[26][27][28] However, the manipulation of their surfactant properties demands a direct intervention, as an addition of acid or base to the system is necessary. [14,15] A combination of these pH and light responsivities could enable a more differentiated regulation of the properties of a colloidal system.…”

“…[1,4] This feature enables control, e.g. over the formation of vesicles and their manipulation [5][6][7] or surface tension of aqueous solutions, [8][9][10][11] and can, therefore, be exploited to fabricate smart foams [12,13] or emulsions with controllable stability [14,15] among others. Switchable surfactants with a charged head group, beyond that, are suitable functionalizing agents.…”

CO2-responsive Pickering emulsions stabilized by soft protein particles for interfacial biocatalysis

“…1 Indeed, it is a clear advantage if both the formation and demulsification of an emulsion can be controllably accessible. In this sense, environment-responsive emulsifiers, including surfactants, polymers, and solid particles, have recently attracted considerable interest because they not only have the ability to stabilize emulsions but also serve as a tool to engineer the emulsion by responding to environmental changes, such as pH, [5][6][7] temperature, 8 light, 3 chemical agents, [9][10][11] or even a combination of them. The use of stimuliresponsive emulsifiers to carefully control emulsion structure and reversibility could effectively decrease waste generation, surfactant consumption, and process remediation costs, thus promoting the greenness of chemical conversion process.…”

Self-Stabilizing Encapsulation through Fast Interfacial Polymerization of Ethyl α-Cyanoacrylate: From Emulsions to Microcapsule Dispersions

“…Myriads of industrial processes and products are related to emulsions, in which droplets of an organic liquid (oil phase) are dispersed in aqueous solution (water phase) or vice versa . , Still, it is popularly known that droplets of one liquid dispersed in another incompletely miscible one without stabilizers are thermodynamically unstable systems, and therefore, droplets tend to coalesce over time. So far, only three types of stabilizers, also known as interface-active agents, have been discovered for stabilizing the emulsions, including surfactants, amphiphilic polymers, and solid particles. − …”