Preparation of CO2-responsive emulsions with switchable hydrophobic tertiary amine

•First, we introduce a novel method of breaking emulsions by using CO2 switchable solvent N,N-dimethylcyclohexylamine (DMCHA).•Second, nowadays, studies on preparation of CO2-responsive emulsions were mainly focused on using switchable surfactants.•Here, we used a conventional surfactant sodium dodecyl benzene sulfonate (SDBS) to prepare CO2-responsive emulsions.•Finally, DMCHA could be separated from the lower water phase upon removal of CO2 and recycled.Figure optionsDownload full-size imageDownload as PowerPoint slideProposed emulsification and phase separation process.

We prepared a CO2 responsive emulsion by using switchable hydrophobic tertiary amine, N,N-dimethylcyclohexylamine (DMCHA). DMCHA exhibits little miscibility with water in the absence of CO2, but shows a complete miscibility with water in the presence of CO2. DMCHA converts to water-soluble bicarbonate salts upon treatment with CO2, which could induce the ionic strength increase of aqueous phase. Together with paraffin oil, DMCHA was used to prepare CO2 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 1H NMR measurements. However, when exposed to CO2 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 CO2 and recycled.

Graphical abstractSchematic illustration of the phase separation process.Figure optionsDownload full-size imageDownload as PowerPoint slide