Journal
NANOMATERIALS
Volume 11, Issue 2, Pages -Publisher
MDPI
DOI: 10.3390/nano11020331
Keywords
emulsion; sugar-based surfactant; pseudo-phase diagram; electron paramagnetic resonance
Categories
Funding
- European Union (FSE, POC Ricerca e Innovazione 2014-2020, Azione I.1 Dottorati Innovativi con caratterizzazione Industriale)
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The study found that the microstructure of surfactants in emulsions is closely related to the emulsion stability, playing a crucial role in prolonging the stability of emulsions.
Identification of strategies to prolong emulsion kinetic stability is a fundamental challenge for many scientists and technologists. We investigated the relationship between the emulsion stability and the surfactant supramolecular organization at the oil-water interface. The pseudo-phase diagrams of emulsions formed by water and, alternatively, a linear or a branched oil, stabilized by mixtures of two sugar-based surfactants, Span80 and Tween80, are presented. The surfactant ordering and dynamics were analyzed by electron paramagnetic resonance (EPR) spectroscopy. In Oil-in-Water (O/W) emulsions, which are stable for more than four days, disordered surfactant tails formed a compact and viscous layer. In Water-in-Oil (W/O) emulsions, whose stability is much lower, surfactants formed an ordered layer of extended tails pointing toward the continuous apolar medium. If linear oil was used, a narrow range of surfactant mixture composition existed, in which emulsions did not demix in the whole range of water/oil ratio, thus making it possible to study the phase inversion from O/W to W/O structures. While conductometry showed an abrupt inversion occurring at a well-defined water/oil ratio, the surfactant layer microstructure changed gradually between the two limiting situations. Overall, our results demonstrate the interconnection between the emulsion stability and the surfactant layer microstructuring, thus indicating directions for their rational design.
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