CO2/N2-responsive oil-in-water emulsions using a novel switchable surfactant

An Chen; Jingsi Chen; Duo Wang; Jianhong Xu; Hongbo Zeng

doi:10.1016/j.jcis.2020.03.045

CO₂/N₂-responsive oil-in-water emulsions using a novel switchable surfactant

J Colloid Interface Sci. 2020 Jul 1:571:134-141. doi: 10.1016/j.jcis.2020.03.045. Epub 2020 Mar 12.

Authors

An Chen¹, Jingsi Chen², Duo Wang², Jianhong Xu³, Hongbo Zeng⁴

Affiliations

¹ The State Key Lab of Chemical Engineering, Department of Chemical Engineering, Tsinghua University, Beijing 100084, China; Department of Chemical and Materials Engineering, University of Alberta, Edmonton, AB T6G 1H9, Canada.
² Department of Chemical and Materials Engineering, University of Alberta, Edmonton, AB T6G 1H9, Canada.
³ The State Key Lab of Chemical Engineering, Department of Chemical Engineering, Tsinghua University, Beijing 100084, China. Electronic address: xujianhong@tsinghua.edu.cn.
⁴ Department of Chemical and Materials Engineering, University of Alberta, Edmonton, AB T6G 1H9, Canada. Electronic address: hongbo.zeng@ualberta.ca.

PMID: 32199266
DOI: 10.1016/j.jcis.2020.03.045

Abstract

Hypothesis: Recently, switchable or stimuli-responsive emulsions have attracted much research interest in many industrial fields. In this work, a novel CO₂/N₂-responsive surfactant was designed and developed to facilitate the formation of switchable oil-in-water (O/W) emulsions with fast switching characteristics between a stable emulsion and separate phases upon alternatively bubbling CO₂ and N₂.

Experiments: The novel CO₂/N₂-responsive surfactant was facilely prepared by mixing an anionic fatty acid (oleic acid) and a cationic amine (1,3-Bis (aminopropyl) tetramethyldisiloxane) at a 1:1 molecular ratio, which was assembled based on electrostatic interactions. The structure and properties of the novel CO₂/N₂-responsive switchable surfactant were investigated by Fourier-transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (¹H NMR) spectroscopy, and interfacial tensions.

Findings: The developed surfactant shows an excellent interfacial activity at the oil/water interface, which can significantly reduce the dosage of the switchable surfactant compared with previous CO₂/N₂-responsive surfactants. The dynamic interfacial tension of n-decane and aqueous phase decreased from 45 mN m^-1 to 5 mN m^-1 within 100 s with the addition of 0.2 mM surfactant. In this work, a low concentration of the novel switchable surfactant (e.g., 20.0 mM) can realize reversible emulsification and demulsification in an emulsion system as compared with the high dosage (e.g., ~150 mM) in previous reports, which will bring huge economic benefits in industrial applications in the future. Moreover, this work expands the family of ion-pair surfactants to small amino-functionalized molecules beyond Jeffamine D-230, which promotes the development of simple and switchable ion-pair surfactant. It is found that the O/W emulsions stabilized by the switchable surfactant show excellent stability, which can be stored for over 60 days at room temperature without any obvious change. Interestingly, the stable O/W emulsion is completely demulsified upon bubbling CO₂ for 30 s and can be easily re-emulsified to the initial state after purging N₂ at 60 °C within 10 min, which demonstrates a rapid and highly efficient switching behavior. The reversible emulsification and demulsification process is ascribed to the reversible assembly and disassembly of the switchable surfactant, which is induced by the removal and purge of CO₂.

Keywords: CO(2)/N(2) trigger; Emulsification and demulsification; Fatty acid; Rapid stimuli responsive; Switchable surfactant.