Preparation of CO2-responsive emulsions with switchable hydrophobic tertiary amine

Abstract We prepared a CO 2 responsive emulsion by using switchable hydrophobic tertiary amine, N , N -dimethylcyclohexylamine (DMCHA). DMCHA exhibits little miscibility with water in the absence of CO 2 , but shows a complete miscibility with water in the presence of CO 2 . DMCHA converts to water-soluble bicarbonate salts upon treatment with CO 2 , which could induce the ionic strength increase of aqueous phase. Together with paraffin oil, DMCHA was used to prepare CO 2 responsive O/W emulsions with a conventional surfactant, sodium dodecyl benzene sulfonate (SDBS), as the emulsifier. Emulsions containing DMCHA in paraffin oil were more stable than those without DMCHA, as a result of electrostatic interactions between a small fraction of protonated DMCHA and SDBS, confirmed by surface tension and 1 H NMR measurements. However, when exposed to CO 2 most of the paraffin oil and water separate from the emulsion with formation of a middle phase microemulsion. More significantly, DMCHA could be separated from the lower water phase upon removal of CO 2 and recycled.