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Hydrogen-bonded monolayers and interdigitated multilayers at the air-water interface.
Stephen M Martin1, Kristian Kjaer, Markus J Weygand
1Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455, USA.
The Journal of Physical Chemistry. B
|July 21, 2006
Summary
Stable crystalline monolayers of octadecylsulfonate amphiphiles (C18S) with guanidinium (G) spacers formed via hydrogen bonding. These structures exhibit significant alkyl chain tilt, enabling close packing and unique compression-induced transformations.
Area of Science:
- Materials Science
- Surface Chemistry
- Supramolecular Chemistry
Background:
- Amphiphilic molecules self-assemble at interfaces, forming ordered structures.
- Hydrogen bonding plays a crucial role in stabilizing molecular assemblies.
- Understanding interfacial behavior is key for designing advanced materials.
Purpose of the Study:
- To investigate the formation and properties of crystalline monolayers of octadecylsulfonate (C18S) with guanidinium (G) spacers.
- To explore the structural transformations of these monolayers under compression.
- To compare the behavior of (G)C18S monolayers with previously studied systems.
Main Methods:
- Formation of monolayers at the air-water interface.
- Surface pressure-area isotherm measurements.
- In-situ grazing incidence X-ray diffraction (GIXD) analysis.
Main Results:
- Stable crystalline monolayers of (G)C18S were formed, stabilized by hydrogen bonding.
- Alkyl chains exhibited substantial tilt (49°) relative to the surface normal.
- Compression led to transformation into a self-interdigitated crystalline multilayer, dependent on compression rate.
Conclusions:
- Hydrogen bonding effectively stabilizes tilted crystalline monolayers of (G)C18S.
- Compression induces a kinetic-limited transformation to a multilayer structure.
- The tilt and hydrogen bonding are critical for the observed monolayer stability and transformation behavior.