Oil-in-Water Emulsions Probed Using Fluorescence Multivariate-Curve-Resolution Spectroscopy

Area of Science:

• Physical Chemistry
• Surface Science
• Spectroscopy

Background:

• Hydrophobic surfaces and immiscible fluid interfaces are crucial in natural processes.
• Probing these interfaces, especially in nanoemulsions, presents significant challenges.
• Understanding interfacial behavior is key to fields like biochemistry and materials science.

Purpose of the Study:

• To develop and demonstrate a novel fluorescence-based technique for probing oil-water interfaces.
• To investigate interfacial dielectric properties and the impact of surfactants.
• To analyze interfacial processes in hexadecane-in-water nanoemulsions.

Main Methods:

• Utilizing Nile Red fluorescence spectroscopy in hexadecane-in-water nanoemulsions.
• Applying multivariate curve resolution (MCR) to deconvolute spectral components.
• Performing concentration-dependent measurements with anionic (sodium dodecylbenzenesulfonate) and cationic (cetyltrimethylammonium bromide) surfactants.

Main Results:

• Identified three distinct spectral components: bulk hexadecane, bulk water, and an interfacial band around 640 nm.
• Successfully deconvoluted spectra to isolate interface-correlated fluorescence.
• Observed charge-dependent spectral shifts: anionic surfactants caused a red shift (dielectric increase), while cationic surfactants caused a blue shift (dielectric decrease).

Conclusions:

• The developed fluorescence method effectively probes oil-water interfaces and their dielectric properties.
• Surfactant charge significantly influences the interfacial dielectric environment.
• This technique offers a versatile tool for studying alterations at various interfaces beyond oil/water systems.