Issue 42, 2009

Formation and stability of nanoemulsions with mixed ionic–nonionic surfactants

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

Supplementary files

Article information

Article type
Paper
Submitted
24 Jun 2009
Accepted
31 Jul 2009
First published
27 Aug 2009

Phys. Chem. Chem. Phys., 2009,11, 9772-9778

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

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements