Optical Reflectance of Composites with Aligned Engineered Microplatelets

The reflection of light from distributed microplatelets is an effective approach to creating color and controlling the optical properties in paints, security features, and optical filters. However, predictive tools for the design and manufacturing of such composite materials are limited due to the complex light–matter interactions that determine their optical response. Here, the optical reflectance of individual reflective microplatelets and of polymer‐based composites containing these engineered platelets as an aligned, dispersed phase are experimentally studied and analytically calculated. Transfer‐matrix calculations are used to interpret the effect of the platelet architecture, the number of platelets, and their size distribution on the experimentally measured reflectance of composites prepared using a previously established magnetic alignment technique. It is demonstrated that the reflectance of the composites can be understood as the averaged response of an array of Fabry–Pérot resonators, in which the microplatelets act as semi‐transparent flat reflectors and the polymer as cavity medium. By using an analytical model and computer simulations to describe the interaction of light with platelets embedded in a polymer matrix, this work provides useful tools for the design and fabrication of composites with tailored optical reflectance. The optical properties of microplatelet‐laden composites are governed by complex light–matter interactions that are often described by numerical simulations with limited physical insights. Here, an analytical physical model is proposed and compared with experiments to shed light on the effect of microplatelet geometry, composition, and orientation on the optical properties of composites containing magnetically aligned microplatelets.