Journal
JOURNAL OF COLLOID AND INTERFACE SCIENCE
Volume 608, Issue -, Pages 2025-2038Publisher
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.jcis.2021.10.130
Keywords
Nanodiamond; Pickering emulsion; Membrane emulsification; Saponification
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Funding
- Chinese Scholarship Council [CSC 201906950049]
- Vice-Chancellor's Scholarship Fund
- Aragon Regional Government [E25_20R]
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The study demonstrates that carboxylated nanodiamonds can provide stability to Pickering emulsions, with experiments showing the mechanism of emulsion formation and stability under different conditions.
Hypothesis: Surfactants in emulsions sometimes do not provide adequate stability against coalescence, whereas Pickering emulsions often offer greater stability. In a search for stabilizers offering biocompatibility, we hypothesized that carboxylated nanodiamonds (ND) would impart stability to Pickering emulsions. Experiments: We successfully prepared Pickering emulsions of sunflower oil in water via two different methods: membrane emulsification and probe sonication. The first method was only possible when the pH of the aqueous ND suspension was <= 4. Findings: Pendant-drop tensiometry confirmed that carboxylated ND is adsorbed at the oil/water interface, with a greater decrease in interfacial tension found with increasing ND concentrations in the aqueous phase. The carboxylated ND become more hydrophilic with increasing pH, according to three-phase contact angle analysis, because of deprotonation of the carboxylic acid groups. Membrane emulsification yielded larger (about 30 mu m) oil droplets, probe sonication produced smaller (sub-mu m) oil droplets. The Pickering emulsions show high stability against mechanical vibration and long-term storage for one year. They remain stable against coalescence across a wide range of pH values. Sonicated emulsions show stability against creaming. In this first-ever systematic study of carboxylated ND-stabilized Pickering emulsions, we demonstrate a promising application in the delivery of beta-carotene, as a model active ingredient. (C) 2021 Elsevier Inc. All rights reserved.
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