Denk, Patrick and Matthews, Lauren and Prevost, Sylvain and Zemb, Thomas and Kunz, Werner (2024) A dilute nematic gel produced by intramicellar segregation of two polyoxyethylene alkyl ether carboxylic acids. JOURNAL OF COLLOID AND INTERFACE SCIENCE, 659. pp. 833-848. ISSN 0021-9797, 1095-7103
Full text not available from this repository. (Request a copy)Abstract
Motivation: Surfactants like C8E8CH2COOH have such bulky headgroups that they cannot show the common sphere-to-cylinder transition, while surfactants like C18:1E2CH2COOH are mimicking lipids and form only bilayers. Mixing these two types of surfactants allows one to investigate the competition between intramicellar segregation leading to disc-like bicelles and the temperature dependent curvature constraints imposed by the mismatch between heads and tails. Experiments: We establish phase diagrams as a function of temperature, surfactant mole ratio, and active matter content. We locate the isotropic liquid-isotropic liquid phase separation common to all nonionic surfactant systems, as well as nematic and lamellar phases. The stability and rheology of the nematic phase is investigated. Texture determination by polarizing microscopy allows us to distinguish between the different phases. Finally, SANS and SAXS give intermicellar distances as well as micellar sizes and shapes present for different compositions in the phase diagrams. Findings: In a defined mole ratio between the two components, intramicellar segregation wins and a viscoelastic discotic nematic phase is present at low temperature. Partial intramicellar mixing upon heating leads to disc growth and eventually to a pseudo-lamellar phase. Further heating leads to complete random mixing and an isotropic phase, showing the common liquid-liquid miscibility gap. This uncommon phase sequence, bicelles, lamellar phase, micelles, and water-poor packed micelles, is due to temperature induced mixing combined with dehydration of the headgroups. This general molecular mechanism explains also why a metastable water-poor lamellar phase quenched by cooling can be easily and reproducibly transformed into a nematic phase by gentle hand shaking at room temperature, as well as the entrapment of air bubbles of any size without encapsulation by bilayers or polymers.
| Item Type: | Article |
|---|---|
| Uncontrolled Keywords: | LYOTROPIC LIQUID-CRYSTALS; MULTILAMELLAR VESICLES; SURFACTANT SYSTEMS; TEMPERATURE-DEPENDENCE; NONIONIC SURFACTANT; DISK-LIKE; X-RAY; PHASE; BILAYERS; MIXTURES; Nematic gel; Small -angle scattering; Akypo LF2; Akypo RO 20 VG; Polyoxyethylene alkyl ether carboxylic acid; Lyotropic liquid crystal; Molecular segregation; Bicelle; Discotic nematic phase |
| Subjects: | 500 Science > 540 Chemistry & allied sciences |
| Divisions: | Chemistry and Pharmacy > Institut für Physikalische und Theoretische Chemie > Chair of Chemistry VI - Physical Chemistry (Solution Chemistry) > Prof. Dr. Werner Kunz |
| Depositing User: | Dr. Gernot Deinzer |
| Date Deposited: | 14 Jul 2025 15:01 |
| Last Modified: | 14 Jul 2025 15:01 |
| URI: | https://pred.uni-regensburg.de/id/eprint/64301 |
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