Many fluids appear white because refractive index differences lead to multiple scattering. In this paper, we use safe, low-cost commercial index matching fluids to quantitatively study light transmission as a function of index mismatch, reduce multiple scattering to allow single scattering probes, and to precisely determine the index of refraction of suspended material. The transmission profile is compared with Rayleigh-Gans and Mie theory predictions. The procedure is accessible as a student laboratory project, while providing advantages over other standard methods of measuring the refractive index of an unknown nanoparticle, making it valuable to researchers.
PMMA particles provided by Andrew Schofield, School of Physics and Astronomy, University of Edinburgh.
Micropipettes may not be common in many physics laboratories. They can be purchased at most chemical supply companies as well from Amazon.com. Users new to using a micropipette should be trained as accurate volume transfer is critical to the success of this method.
Curve fits were implemented in Excel using “Goal Seek” to minimize the sum of squares of the residuals. Goal Seek does not provide an estimate of uncertainty in the fitting parameters.
A Mie calculation algorithm could be placed inside a non-linear least squares fitting routine so as to yield the best fit refractive index of the particle and particle diameter.