Abstract
The transport behavior of electromagnetic radiation through a polymeric coating or composite is the basis for the material color, appearance, and overall electromagnetic signature. As multifunctional materials become more advanced and next generation in-service applications become more demanding, a need for predictive design of electromagnetic signature is desired. This paper presents various components developed and used in a computational suite for the study and design of electromagnetic radiation transport properties in polymeric coatings and composites. Focus is given to the treatment of the forward or direct scattering problem on surfaces and in bulk matrices of polymeric materials. The suite consists of surface and bulk light scattering simulation modules that may be coupled together to produce a multiscale model for predicting the electromagnetic signature of various material systems. Geometric optics ray tracing is used to predict surface scattering behavior of realistically rough surfaces, while a coupled ray tracing-finite element approach is used to predict bulk scattering behavior of material matrices consisting of microscale and nanoscale fillers, pigments, fibers, air voids, and other inclusions. Extension of the suite to color change and appearance metamerism is addressed, as well as the differences between discrete versus statistical material modeling.
Highlights
The differentiating traits of novel and high performance materials are increasingly being determined by transport properties
In both of the above cases, when α ≤ 1, the most proper approach to light scattering prediction is the solution of Maxwell’s equations, which govern the coupled transport of electric and magnetic fields interacting with various media, though the effect of the magnetic equations is effectively null for scattering media with magnetic permeability equal to one
Kirchhoff scattering gives the general solution to the scattering of electromagnetic radiation by a rough surface, and serves as the basis for many advanced or evolved surface scattering models [8]
Summary
The differentiating traits of novel and high performance materials are increasingly being determined by transport properties. These are problems where an exact replication in a physical environment would be difficult if not impossible, but where the solutions and modeled behavior are important in making engineering design decisions An example of this in practice would be the simulated single and dependent scattering regime thresholds within a cluster of closely packed specialty pigments embedded in a polymer resin; it may be difficult and cost-inefficient to replicate that material exactly in a laboratory, but the simulated material system will still offer advice regarding optimum pigment geometry and dimensions, ideal pigment volume concentration for a given effect, and predicted formulation thresholds for the onset of undesirable dependent scattering, where pigment scattering cross sections overlap due to proximity. The astute modeler and materials simulator will continue to seek out situations such as this, where the direct computational solution can assist in making quick design decisions, without having to wait for fully-realized direct or inverse solutions to be developed
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