Microstructure evolution during nano-emulsification by NMR and microscopy

Carmine D'Agostino; Valentina Preziosi; Abdulaziz Khan; Mick Mantle; Einar Fridjonsson; Stefano Guido

doi:10.1016/j.jcis.2019.04.098

Microstructure evolution during nano-emulsification by NMR and microscopy

J Colloid Interface Sci. 2019 Sep 1:551:138-146. doi: 10.1016/j.jcis.2019.04.098. Epub 2019 May 2.

Authors

Carmine D'Agostino¹, Valentina Preziosi², Abdulaziz Khan³, Mick Mantle³, Einar Fridjonsson⁴, Stefano Guido⁵

Affiliations

¹ School of Chemical Engineering and Analytical Science, The University of Manchester, The Mill, Sackville Street, Manchester M13 9PL, UK. Electronic address: carmine.dagostino@manchester.ac.uk.
² Dipartimento di Ingegneria Chimica, dei Materiali e della Produzione Industriale, Università di Napoli Federico II, UdR INSTM, P.le Tecchio, 80, 80125 Napoli, Italy. Electronic address: valentina.preziosi@unina.it.
³ Department of Chemical Engineering and Biotechnology, University of Cambridge, Philippa Fawcett Drive, West Cambridge Site, Cambridge CB3 0AS, UK.
⁴ Department of Chemical Engineering, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia.
⁵ Dipartimento di Ingegneria Chimica, dei Materiali e della Produzione Industriale, Università di Napoli Federico II, UdR INSTM, P.le Tecchio, 80, 80125 Napoli, Italy.

PMID: 31075628
DOI: 10.1016/j.jcis.2019.04.098

Abstract

Hypothesis: Microstructure evolution in emulsions as a function of composition is of great interest but fundamentals have not yet been fully elucidated. Here, pulsed-field gradient (PFG) NMR diffusion measurements have been combined with confocal laser scanning microscopy (CLSM) to assess evolution of dynamics and microstructure during nano-emulsification.

Experiments: Diffusion coefficients of emulsions made of water, mineral oil and surfactants (Span 20 and Tween 80) were measured as a function of water composition and compared with the morphological features of the emulsions obtained by CLSM.

Findings: In the absence of water, two phases are visible from CLSM, and two diffusion components are observed with PFG NMR, a major fast component attributed to a continuous oil phase containing the more hydrophobic surfactant Span 20 with traces of Tween 80, and a minor slow component attributed to a dispersed phase of the more hydrophilic surfactant Tween 80 with traces of mineral oil and Span 20. At the inversion point (25 wt% water) the two-component diffusion behavior of the oil-rich phase is drastically reversed in terms of populations, with the slow diffusion process becoming dominant. This suggests a significant structuring of the oil-rich phase in the presence of surfactants enhanced by water, which can be explained by the formation of aggregates in the oil phase as reverse micelles or of a lamellar structure, and ties in well with the rheological measurements.

Keywords: CLSM; Diffusion; Nano-emulsions; PFG NMR; Phase inversion emulsification.