Thin films of dispersions of light absorbing solid particles or emulsions containing a light absorbing solute all have a non-uniform distribution of light absorbing species throughout the sample volume. This results in non-uniform light absorption over the illuminated area which causes the optical absorbance, as measured using a conventional specular UV-vis spectrophotometer, to deviate from the Beer-Lambert relationship. We have developed a theoretical model to account for the absorbance properties of such films which are shown to depend on the size and volume fraction of the light absorbing particles plus other sample variables. We have compared model predictions with measured spectra for samples consisting of emulsions containing a dissolved light absorbing solute. Using no adjustable parameters, the model successfully predicts the behaviour of non-uniform, light absorbing emulsion films with varying values of droplet size, volume fraction and other parameters.
Binks, B. P., Fletcher, P. D., Johnson, A. J., Marinopoulos, I., Crowther, J. M., & Thompson, M. A. (2017). Spectrophotometry of thin films of light absorbing particles. Langmuir : the ACS journal of surfaces and colloids, 33(15), 3720-3730. https://doi.org/10.1021/acs.langmuir.6b04443