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Phase Behavior of Charged Vesicles Under Symmetric and Asymmetric Solution Conditions Monitored with Fluorescence Microscopy
Published on: October 24, 2017
Spontaneous thermoreversible formation of cationic vesicles in a protic ionic liquid
Carlos R López-Barrón1, Dongcui Li, Leo DeRita
1Center for Neutron Science, Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, Delaware 19716, USA.
Journal of the American Chemical Society
|October 4, 2012
Summary
Researchers discovered spontaneous vesicle formation in a pure cationic surfactant (didodecyldimethylammonium bromide) within a protic ionic liquid (ethylammonium nitrate). This finding provides the first evidence of equilibrium vesicles and a sponge phase in such systems.
Area of Science:
- Materials Science
- Physical Chemistry
- Colloid Science
Background:
- Stable vesicular structures are highly sought after for various applications.
- Few surfactant systems spontaneously form vesicles in true thermodynamic equilibrium.
- Understanding self-assembly in novel solvents like ionic liquids is crucial.
Purpose of the Study:
- To investigate the spontaneous formation of vesicles from a pure cationic double-tail surfactant in a protic ionic liquid.
- To characterize the resulting vesicular structures and phases using advanced scattering and microscopy techniques.
- To provide experimental evidence for the existence of equilibrium vesicles in this system.
Main Methods:
- Small and ultra-small angle neutron scattering (SANS/USANS) to determine structural properties.
- Rheology to assess solution viscosity and flow behavior.
- Bright field microscopy for direct visualization of vesicle morphology and size.
Main Results:
- First experimental evidence of spontaneous vesicle formation for didodecyldimethylammonium bromide (DDAB) in ethylammonium nitrate (EAN).
- Identification of two coexisting vesicle-containing phases: a low-density, high-viscosity phase with giant vesicles and a sponge phase, and a dilute, high-density phase with large vesicles.
- Vesicles form spontaneously via different thermodynamic routes, exhibiting consistent size distribution, supporting true thermodynamic equilibrium.
- Facilitation of equilibrium vesicle and L(3) phase formation by ion exchange and solvophobic effects within the protic ionic liquid.
Conclusions:
- The study demonstrates the spontaneous formation of equilibrium vesicles from a pure cationic surfactant in a protic ionic liquid.
- Ion exchange and solvophobic interactions within the ionic liquid are key drivers for the formation of these stable structures.
- This work opens new avenues for designing self-assembled soft materials in ionic liquid environments.
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