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Issue 42, 2009
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Formation and stability of nanoemulsions with mixed ionic–nonionic surfactants

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Abstract

A simple, low-energy two-step dilution process has been applied with binary mixtures of ionic–nonionic surfactants to prepare nanoemulsions. The systems consist of water/DDAB-C12E5/decane. Nanoemulsions were obtained by dilution of concentrates located in bicontinuous microemulsion or lamellar liquid crystal phase regions. The nanoemulsions generated were investigated both by contrast-variation small-angle neutron scattering (SANS) and dynamic light scattering (DLS). The SANS profiles show that C12E5 nanodroplets suffer essentially no structural change on incorporation of the cationic DDAB surfactant, except for increased electrostatic repulsive interactions. Interestingly, SANS indicated that the preferred droplet sizes were hardly affected by the surfactant mixture composition (up to a DDAB molar ratio (mDDAB/(mDDAB + mC12E5) of 0.40) and droplet volume fraction, ϕ, between 0.006 and 0.120. No notable changes in the structure or radius of nanoemulsion droplets were observed by SANS over the test period of 1 d, although the droplet number intensity decreased significantly in systems stabilized by C12E5 only. However, the DLS sizing shows a marked increase with time, with higher droplet volume fractions giving rise to the largest changes. The discrepancy between apparent nanoemulsion droplet size determined by DLS and SANS data can be attributed to long-range droplet interactions occurring outside of the SANS sensitivity range. The combined SANS and DLS results suggest flocculation is the main mechanism of instability for these nanoemulsions. The flocculation rate is shown to be significantly retarded by addition of the charged DDAB, which may be due to enhanced electrostatic repulsive forces between droplets, leading to improved stability of the nanoemulsions.

Graphical abstract: Formation and stability of nanoemulsions with mixed ionic–nonionic surfactants

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Supplementary files

Article information


Submitted
24 Jun 2009
Accepted
31 Jul 2009
First published
27 Aug 2009

Phys. Chem. Chem. Phys., 2009,11, 9772-9778
Article type
Paper

Formation and stability of nanoemulsions with mixed ionic–nonionic surfactants

L. Wang, R. Tabor, J. Eastoe, X. Li, R. K. Heenan and J. Dong, Phys. Chem. Chem. Phys., 2009, 11, 9772
DOI: 10.1039/B912460H

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