Novel Oil‐in‐Water Emulsions Stabilised by Ionic Surfactant and Similarly Charged Nanoparticles at Very Low Concentrations

• Published in: Angewandte Chemie International Edition Vol. 57; no. 26; pp. 7738 - 7742
• Main Authors: Xu, Maodong, Jiang, Jianzhong, Pei, Xiaomei, Song, Binglei, Cui, Zhenggang, Binks, Bernard P.
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 25.06.2018
• Edition: International ed. in English
• Subjects: Alkanes; alumina; Aluminum oxide; Aromatic hydrocarbons; cetyltrimethyl ammonium bromide (CTAB); Charged particles; Charging; Coalescence; Coalescing; Droplets; electrical repulsion; Emulsions; Flocculation; Hydrocarbons; Ion pairs; Ionic surface active agents; Ions; Lamellae; Low concentrations; Molecular chains; Mud-water interfaces; Nanoparticles; Oil; Oils & fats; Surface tension; Surfactants; Thick films; Triglycerides; alumina; nanoparticles; electrical repulsion; cetyltrimethyl ammonium bromide (CTAB); emulsions
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201802266

Novel oil‐in‐water (O/W) emulsions are prepared which are stabilised by a cationic surfactant in combination with similarly charged alumina nanoparticles at concentrations as low as 10−5 m and 10−4 wt %, respectively. The surfactant molecules adsorb at the oil‐water interface to reduce the interfacial tension and endow droplets with charge ensuring electrical repulsion between them, whereas the charged particles are dispersed in the aqueous films between droplets retaining thick lamellae, reducing water drainage and hindering flocculation and coalescence of droplets. This stabilization mechanism is universal as it occurs with different oils (alkanes, aromatic hydrocarbons and triglycerides) and in mixtures of anionic surfactant and negatively charged nanoparticles. Further, such emulsions can be switched between stable and unstable by addition of an equimolar amount of oppositely charged surfactant which forms ion pairs with the original surfactant destroying the repulsion between droplets. Getting Al emulsional: Oil‐in‐water emulsions are prepared which are stabilised by a cationic surfactant in combination with similarly charged alumina nanoparticles at very low concentrations. The stabilisation mechanism is applicable to different oils and is universal for positively charged particles with cationic surfactant and negatively charged particles with anionic surfactant.