Analyzing refractive index profiles of confined fluids by interferometry

Area of Science:

• Surface science
• Interferometry
• Thin film analysis

Background:

• Accurate characterization of thin films and near-surface fluid properties is crucial in various scientific fields.
• Conventional methods may require direct contact or confinement, limiting their applicability.
• Interferometry offers a non-contact approach but requires robust data analysis techniques.

Purpose of the Study:

• To develop and validate a novel interferometry data analysis method for determining optical thickness and refractive index variations.
• To apply this method to surface force apparatus (SFA) data for characterizing films and near-surface fluid phenomena.
• To investigate the impact of errors on data analysis through simulations.

Main Methods:

• Analysis of interferometry data collected at multiple intersurface separation distances (up to 300 nm).
• Application to surface force apparatus (SFA) measurements of adsorbed films and fluid interfaces.
• Simulations to assess the effects of random and systematic errors in SFA data analysis.

Main Results:

• The developed method quantitatively determines film properties, including optical thickness and refractive index gradients.
• Demonstrated successful application to aqueous polyethylenimine (PEI) adsorbed on mica substrates.
• PEI layer thickness measurements were consistent with conventional SFA techniques, validating the new method.

Conclusions:

• The proposed interferometry analysis method provides a reliable, non-contact approach for characterizing thin films and near-surface fluid properties.
• This technique enhances the capabilities of surface force apparatus (SFA) for detailed material and fluid analysis.
• The study offers insights into error analysis, improving the accuracy and reliability of SFA data interpretation.