Dual CO2 Responsiveness of an Oil-In-Water Emulsion by Using Sodium Oleate and Water-Soluble Tertiary Amines.

Two kinds of water-soluble tertiary amines (TAs), triethylamine (TEA, monoamine), and tetramethyltrimethylenediamine (TMA, diamine) were introduced into a NaOA stable oil-water (O/W) emulsion, respectively, and their dual reactivity to carbon dioxide was studied. TA was converted into bicarbonate after bubbling of CO2, which induced the increase of ionic strength of the aqueous phase, and formed ion pair with NaOA through electrostatic interaction. NaOA itself can also be protonated into oleic acid, which can be reverently deprotonated by alternating bubbles of CO2 at 25 °C and N2 at 50 °C, thus affecting the stability and demulsification process of the emulsion. In order to demonstrate TA's and NaOA's synergistic effect on CO2 responsiveness, gas chromatography-mass spectrometry, ζ potential, electrical conductivity, pH value, 1H nuclear magnetic resonance, morphological evolution, and interfacial tension were used to study the contributions of the single component and two components of NaOA, TEA, and TMA to emulsion stability and CO2 responsiveness, respectively. Combined with the composition distribution under different pH conditions, it was further proved that TAs had an effect on the stability and CO2 responsiveness of the NaOA emulsion.