Concentration dependent refractive index of a binary mixture at high pressure

Area of Science:

• Physical Chemistry
• Fluid Dynamics
• Optical Physics

Background:

• Understanding the behavior of hydrocarbon mixtures under pressure is crucial for various industrial applications.
• The concentration contrast factor (CF) is a key parameter influencing optical properties of mixtures.
• Previous studies have not fully explored the pressure dependence of CF in miscible hydrocarbon systems.

Purpose of the Study:

• To investigate the pressure dependence of the concentration contrast factor (CF) in binary mixtures of 1,2,3,4-tetrahydronaphthalene (THN) and n-dodecane (C12).
• To compare experimental results with theoretical predictions from Lorentz-Lorenz and Looyenga models.
• To validate experimental methods using pure fluids.

Main Methods:

• Binary mixtures of THN and C12 at varying concentrations were subjected to pressures up to 50 MPa.
• Refractive index measurements were performed using a Mach-Zehnder interferometer.
• Experimental setup and procedure were validated with pure fluids.

Main Results:

• The refractive index of THN-C12 mixtures varies with both pressure and concentration.
• The concentration contrast factor (CF) was observed to decrease exponentially with increasing pressure.
• Experimental refractive indices showed excellent agreement with Looyenga's predictions.
• Measured CF values deviated by approximately 6% from Looyenga's predictions and more than double from Lorentz-Lorenz predictions.

Conclusions:

• The study provides valuable experimental data on the pressure-dependent optical properties of hydrocarbon mixtures.
• Looyenga's model offers a more accurate prediction for refractive indices compared to the Lorentz-Lorenz formula for this system.
• The significant deviations in CF highlight the need for refined theoretical models for high-pressure fluid mixtures.