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Complex layering observed in high internal phase emulsions at a silicon surface by neutron reflectometry
Philip A Reynolds1, Mark J Henderson, Johann Zank
1Research School of Chemistry, Australian National University, Canberra, ACT 0200, Australia. phil@rsc.anu.edu.au
Journal of Colloid and Interface Science
|September 20, 2011
Summary
Neutron reflectivity reveals ordered layers at the silicon-emulsion interface. Increasing surfactant hydrophilicity enhances this ordering, forming lamellar or sponge phases in high internal phase emulsions.
Area of Science:
- Materials Science
- Colloid and Surface Chemistry
- Soft Matter Physics
Background:
- High internal phase emulsions (HIPEs) are complex colloidal systems with potential applications in various fields.
- Understanding the interfacial structure of HIPEs is crucial for controlling their properties and stability.
- Surfactant hydrophilicity plays a key role in the self-assembly and phase behavior of emulsions.
Purpose of the Study:
- To investigate the interfacial structure between silicon and HIPEs with varying surfactant hydrophilicity using neutron reflectivity.
- To elucidate the role of surfactant hydrophilicity in the formation of ordered layers at the interface.
- To correlate interfacial structures with the bulk phase behavior of the emulsions.
Main Methods:
- Neutron reflectivity measurements were performed at the silicon-emulsion interface for HIPEs with systematically varied surfactant hydrophilicity.
- Two isotopic contrasts were employed for each surfactant to enhance structural sensitivity.
- Layered models were used to analyze the reflectivity profiles and determine interfacial structures.
Main Results:
- The oxidized silicon surface is consistently covered by a surfactant monolayer.
- A distinct oil layer forms between the surfactant monolayer and the bulk emulsion due to droplet reorganization.
- Increasing surfactant hydrophilicity leads to the formation of alternating aqueous and oil+surfactant layers, resembling lamellar phases.
- The bulk emulsions exhibit increasing lamellar or sponge phase behavior with enhanced surfactant hydrophilicity.
Conclusions:
- The interfacial structure of HIPEs is highly sensitive to surfactant hydrophilicity, leading to ordered layered structures.
- The observed interfacial ordering correlates with the bulk phase behavior, suggesting a unified self-assembly mechanism.
- Neutron reflectivity is a powerful tool for characterizing complex emulsion interfaces and understanding structure-property relationships.
