The switching behavior of CO2/N2 responsive emulsion systems formed by an amine functionalized quaternary ammonium surfactant

Stimulus-responsive surfactants (N + –C n -N,n = 14 or 16) can stabilize conventional emulsions, Pickering emulsions and oil-in-dispersion emulsions in the presence of oppositely and similarly charged nanoparticles. Rapid demulsification can be successfully achieved by bubbling CO 2 . In the presence of CO 2 , N + –C n -N becomes a hydrophilic Bola-type surfactant, N + –C n -NH + , and is an inferior emulsifier either when used alone or together with charged nanoparticles, resulting in demulsification. In addition, nearly all N + –C n -NH + molecules are present in the aqueous phase after demulsification without contaminating the oil phase. The aqueous phase can be recycled and used again for further emulsification of oils. Compared with the pH responsive systems, there is no accumulation of salt after the gas cycles, and more cycles can be performed. This protocol is a green process and leads to preparation of various temporarily stable emulsions used in oil emulsion transportation, emulsion polymerization, industrial catalysis, nanomaterial synthesis and other fields.