Properties of surfactant films in water-in-CO2 microemulsions obtained by small-angle neutron scattering

Ci Yan, Masanobu Sagisaka, Craig James, Sarah E Rogers, Shirin Alexander, Julian Eastoe*

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

7 Citations (Scopus)
219 Downloads (Pure)

Abstract

Hypothesis

The formation, stability and structural properties of normal liquid phase microemulsions, stabilized by hydrocarbon surfactants, comprising water and hydrocarbon oils can be interpreted in terms of the film bending rigidity (energy) model. Here, this model is tested for unusual water-in-CO2 (w/c) microemulsions, formed at high pressure with supercritical CO2 (sc-CO2) as a solvent and fluorinated surfactants as stabilizers. Hence, it is possible to explore the generality of this model for other types of microemulsions.

Experiments

High Pressure Small-Angle Neutron Scattering (HP-SANS) has been used to study w/c microemulsions, using contrast variation to highlight scattering from the stabilizing fluorinated surfactant films: these data show clear evidence for spherical core–shell structures for the microemulsion droplets.

Findings

The results extend understanding of w/c microemulsions since previous SANS studies are based only on scattering from water core droplets. Here, detailed structural parameters for the surfactant films, such as thickness and film bending energy, have been extracted from the core–shell SANS profiles revealed by controlled contrast variation. Furthermore, at reduced CO2 densities (∼0.7 g cm−3), elongated cylindrical droplet structures have been observed, which are uncommon for CO2 microemulsions/emulsions. The implications of the presence of cylindrical micelles and droplets for applications of CO2, and viscosity enhancements are discussed.

Original languageEnglish
Pages (from-to)112-118
Number of pages7
JournalJournal of Colloid and Interface Science
Volume435
Early online date1 Sep 2014
DOIs
Publication statusPublished - 1 Dec 2014

Keywords

  • Film bending rigidity
  • Fluorinated surfactants
  • Microemulsions
  • Small-angle neutron scattering
  • Supercritical CO

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