Oil-in-Water emulsions stabilized by alumina nanoparticles with organic electrolytes: Fate of particles

Raojun Zheng; Jingjing Tian; Bernard P Binks; Zhenggang Cui; Wenshui Xia; Jianzhong Jiang

doi:10.1016/j.jcis.2022.07.085

Oil-in-Water emulsions stabilized by alumina nanoparticles with organic electrolytes: Fate of particles

J Colloid Interface Sci. 2022 Dec:627:749-760. doi: 10.1016/j.jcis.2022.07.085. Epub 2022 Jul 16.

Authors

Raojun Zheng¹, Jingjing Tian¹, Bernard P Binks², Zhenggang Cui¹, Wenshui Xia³, Jianzhong Jiang⁴

Affiliations

¹ The Key Laboratory of Synthetic and Biological Colloids, Ministry of Education, School of Chemical & Material Engineering, Jiangnan University, 1800 Lihu Road, Wuxi, Jiangsu 214122, China.
² Department of Chemistry, University of Hull, Hull HU6 7RX. UK.
³ State Key Laboratory of Food Science and Technology, School of Food Science and Technology, Jiangnan University, 1800 Lihu Road, Wuxi, Jiangsu 214122, China.
⁴ The Key Laboratory of Synthetic and Biological Colloids, Ministry of Education, School of Chemical & Material Engineering, Jiangnan University, 1800 Lihu Road, Wuxi, Jiangsu 214122, China. Electronic address: jzjiang@jiangnan.edu.cn.

PMID: 35878465
DOI: 10.1016/j.jcis.2022.07.085

Abstract

Hypothesis: Oil-in-dispersion emulsions can be stabilized by like charged particles and surfactant. Surfactant adsorbs at the oil-water interface to reduce the interfacial tension and endow the interface with charge, while particles remain dispersed in the aqueous phase to provide electrostatic repulsion between droplets and particles. Can weakly surface-active organic electrolytes adsorb at the oil-water interface and behave like surfactants in stabilizing oil-in-dispersion emulsions with like charged particles?

Experiments: Symmetrical organic electrolytes, tetraalkylammonium bromides (R₄NBr), with either no or very low interfacial activity endowing oil droplets with charge were combined with alumina nanoparticles to stabilize emulsions. The effect of R chain length (varying from methyl to butyl) on the type and stability of emulsions was investigated.

Findings: Mixtures of high concentrations of short chain R₄NBr salts (R = methyl or ethyl) and alumina particles stabilise oil-in-water Pickering emulsions, whereas longer chain (R = propyl or butyl) analogues stabilize oil-in-dispersion emulsions assisted by alumina particles. Tetrapropylammonium and tetrabutylammonium cations adsorb at the oil-water interface reducing the interfacial tension and endowing the interface with charge. The stability of the oil-in-dispersion emulsions is dominated by the electrostatic repulsion between the droplets and between droplets and particles in the continuous aqueous phase.

Keywords: Electrostatic repulsion; Oil-in-dispersion emulsions; Pickering emulsions; Tetraalkylammonium salts.