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Lyotropic phases reinforced by hydrogen bonding.
Stephen M Martin1, Michael D Ward
1Department of Chemical Engineering and Materials Science, University of Minnesota, 421 Washington Avenue SE, Minneapolis, Minnesota 55455, USA.
Langmuir : the ACS Journal of Surfaces and Colloids
|June 1, 2005
Summary
Amphiphilic guanidinium alkylbenzenesulfonates form gels in organic solvents via hydrogen-bonded lamellar phases. These compounds also exhibit complex lyotropic behavior in water, expanding known liquid crystal properties.
Area of Science:
- Materials Science
- Supramolecular Chemistry
- Soft Matter Physics
Background:
- Amphiphilic molecules self-assemble into various structures in solution.
- Guanidinium salts are known for their ability to form strong hydrogen bonds.
- Understanding the self-assembly of amphiphiles is crucial for designing new materials.
Purpose of the Study:
- To investigate the lyotropic behavior of amphiphilic guanidinium alkylbenzenesulfonates (GCnBS).
- To elucidate the role of hydrogen bonding in the gelation of GCnBS in organic solvents.
- To explore the liquid crystalline phase behavior of GCnBS in both organic and aqueous media.
Main Methods:
- Synthesis and characterization of guanidinium alkylbenzenesulfonates (GCnBS).
- Lyotropic phase behavior studies in various organic solvents and water.
- Infrared spectroscopy to confirm hydrogen bonding interactions.
- Small-angle X-ray scattering (SAXS) to determine lamellar phase structures.
- Rheological measurements to assess gel-like properties.
Main Results:
- GCnBS compounds formed gel-like phases in cyclic organic solvents, attributed to swollen interdigitated lamellar phases stabilized by hydrogen bonding.
- Hydrogen bonding between guanidinium and sulfonate groups was essential for gel formation, unlike homologous sodium salts.
- SAXS revealed lamellar structures with temperature-dependent interlayer spacings, suggesting solvent absorption.
- In water, GCnBS formed complex lyotropic phases, including structures resembling entangled worm-like micelles.
- Observed phases expanded the known liquid crystal behavior of guanidinium sulfonate compounds.
Conclusions:
- Guanidinium alkylbenzenesulfonates are effective gelators in organic solvents due to specific hydrogen bonding interactions.
- The study demonstrates a broader range of lyotropic liquid crystalline behavior for guanidinium sulfonate compounds.
- These findings contribute to the understanding of self-assembly in amphiphilic systems and the design of novel soft materials.