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From regular solutions to microemulsions

Tseng, Shih Yu ; Strey, Reinhard ; Olsson, Ulf LU orcid and Sottmann, Thomas (2025) In Soft Matter 21(19). p.3839-3849
Abstract

We address the structure of homogeneous mixtures of equal volumes of water and oil rendered miscible by the addition of amphiphilic molecules. Specifically, we study the pathway from regular ternary solutions to structured microemulsions with increasing amphiphilic chain length, i.e., increasing i and j for alkyl polyglycol ether surfactants (CiEj) from C3E0 (i.e., propanol) to C5E2, using contrast variation small angle neutron scattering (SANS). The bulk-contrast SANS pattern of the symmetric system water-cyclohexane-(2-propanol/1-propanol) with nearly horizontal tie-lines matches Ornstein-Zernike behavior with characteristic q−2 decay, implying critical... (More)

We address the structure of homogeneous mixtures of equal volumes of water and oil rendered miscible by the addition of amphiphilic molecules. Specifically, we study the pathway from regular ternary solutions to structured microemulsions with increasing amphiphilic chain length, i.e., increasing i and j for alkyl polyglycol ether surfactants (CiEj) from C3E0 (i.e., propanol) to C5E2, using contrast variation small angle neutron scattering (SANS). The bulk-contrast SANS pattern of the symmetric system water-cyclohexane-(2-propanol/1-propanol) with nearly horizontal tie-lines matches Ornstein-Zernike behavior with characteristic q−2 decay, implying critical composition fluctuations occurring predominantly in the water-oil ratio. Weak scattering signals were detected in film-contrast SANS possibly due to the existence of the nearby tricritical point (TCP). After passing the TCP, the increasing amphiphilic strength leads to the gradual build-up of well-defined amphiphilic interfaces stabilizing water- and oil-rich domains of colloidal dimensions, as evidenced by the well-known q−4 behavior observed in bulk-contrast SANS pattern at large q. The amphiphilicity factor fa ranging from +1.15 to −0.60 reveals the crossing of the disorder line, the Lifshitz line, and the wetting to non-wetting transition. Precursors of structuring in those mixtures with compositions, where the lamellar phase appears for even longer-chain amphiphiles, are also borne out by the experiments.

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author
; ; and
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Soft Matter
volume
21
issue
19
pages
11 pages
publisher
Royal Society of Chemistry
external identifiers
  • pmid:40261023
  • scopus:105003500617
ISSN
1744-683X
DOI
10.1039/d4sm01258e
language
English
LU publication?
yes
additional info
Publisher Copyright: © 2025 The Royal Society of Chemistry.
id
5e989208-0196-423d-b301-c0e99d3313f6
date added to LUP
2025-08-06 10:00:35
date last changed
2025-08-06 10:08:47
@article{5e989208-0196-423d-b301-c0e99d3313f6,
  abstract     = {{<p>We address the structure of homogeneous mixtures of equal volumes of water and oil rendered miscible by the addition of amphiphilic molecules. Specifically, we study the pathway from regular ternary solutions to structured microemulsions with increasing amphiphilic chain length, i.e., increasing i and j for alkyl polyglycol ether surfactants (C<sub>i</sub>E<sub>j</sub>) from C<sub>3</sub>E<sub>0</sub> (i.e., propanol) to C<sub>5</sub>E<sub>2</sub>, using contrast variation small angle neutron scattering (SANS). The bulk-contrast SANS pattern of the symmetric system water-cyclohexane-(2-propanol/1-propanol) with nearly horizontal tie-lines matches Ornstein-Zernike behavior with characteristic q<sup>−2</sup> decay, implying critical composition fluctuations occurring predominantly in the water-oil ratio. Weak scattering signals were detected in film-contrast SANS possibly due to the existence of the nearby tricritical point (TCP). After passing the TCP, the increasing amphiphilic strength leads to the gradual build-up of well-defined amphiphilic interfaces stabilizing water- and oil-rich domains of colloidal dimensions, as evidenced by the well-known q<sup>−4</sup> behavior observed in bulk-contrast SANS pattern at large q. The amphiphilicity factor f<sub>a</sub> ranging from +1.15 to −0.60 reveals the crossing of the disorder line, the Lifshitz line, and the wetting to non-wetting transition. Precursors of structuring in those mixtures with compositions, where the lamellar phase appears for even longer-chain amphiphiles, are also borne out by the experiments.</p>}},
  author       = {{Tseng, Shih Yu and Strey, Reinhard and Olsson, Ulf and Sottmann, Thomas}},
  issn         = {{1744-683X}},
  language     = {{eng}},
  month        = {{04}},
  number       = {{19}},
  pages        = {{3839--3849}},
  publisher    = {{Royal Society of Chemistry}},
  series       = {{Soft Matter}},
  title        = {{From regular solutions to microemulsions}},
  url          = {{http://dx.doi.org/10.1039/d4sm01258e}},
  doi          = {{10.1039/d4sm01258e}},
  volume       = {{21}},
  year         = {{2025}},
}