Structural studies of amphiphiles adsorbed at liquid-liquid interfaces using neutron reflectometry

Area of Science:

• Surface and Interfacial Science
• Materials Science
• Physical Chemistry

Background:

• Understanding liquid-liquid interfaces is crucial for various applications.
• Neutron reflectometry is a powerful technique for probing interfacial structures.
• A refined method enables detailed structural studies at liquid-liquid interfaces.

Purpose of the Study:

• To apply and refine a neutron reflectometry method for liquid-liquid interface structural analysis.
• To investigate the interfacial structure of hexadecane with Pluronic L64 copolymer.
• To examine the interfacial structure of hexadecane with tetradecyltrimethylammonium bromide (C14TAB) surfactant.

Main Methods:

• Developed a technique involving entrapment of a thin oil layer (hexadecane) between a silicon substrate and an aqueous subphase.
• Prepared thin oil films via spin-coating onto an oleophilically treated silicon substrate.
• Utilized neutron reflectometry, varying the angle of incidence and measuring neutron reflectivity to determine oil-layer thickness and interfacial structure.

Main Results:

• For the C14TAB system, reflectivity data confirmed a highly concentrated C14TAB region on the oil side of the interface.
• For the Pluronic L64 system, data indicated polymer adsorption at the interface, spanning both oil and water phases.
• Model scattering length density profiles were generated to represent the observed interfacial structures.

Conclusions:

• The refined neutron reflectometry method effectively characterizes liquid-liquid interfacial structures.
• Specific interfacial behaviors of Pluronic L64 and C14TAB at the hexadecane-water interface were elucidated.
• The study provides detailed structural insights into surfactant and polymer adsorption at interfaces.