Understanding the particle size/shape ambiguity and its impact on optical responses of particulate composites, 2010 TAPPI Advanced Coating Fundamentals Symposium

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The aspect ratio of component pigments is one of the desired design parameters for optical coatings. This paper will examine how the aspect ratio can be measured in polydisperse pigment systems and its relevance to formulating optical coatings. We will show that aspect ratio can indeed be exactly determined for individual particles by using polarimetric scattering approaches, but it cannot be measured in practically relevant situations involving distributions of particle sizes and shapes. Moreover, we will show in the final properties of the composite material the asymmetry parameters are folded together with many other factors. If distributions of sizes and shapes cannot be avoided then the relevance of controlling the aspect ratio of constituents is diminished.