Abstract
Particle-doped thin films that are translucent and diffusive have applications in cosmetics, coatings, and display technologies, but finding material combinations that produce these effects simultaneously is challenging: formulations tend to be either transparent or opaque. Using a combination of Mie scattering calculations and spectral transmission measurements on monodisperse colloidal suspensions, we demonstrate that the two characteristic optical properties of the films, total transmittance and haze, scale with the effective backscattering and forward scattering cross sections, both of which are properties of single particles. These scalings enable an efficient computational search for combinations of particle sizes, concentrations, and refractive indices that break the trade-off between translucency and diffusion. The optimum particle sizes and concentrations obey power-law dependences on the refractive index difference, a result of the interference condition for resonances in the scattering cross sections. The power laws serve as design equations for formulating particle-doped thin films.
Highlights
Coatings and thin films of small particles suspended in a medium are important for many applications, including personal care products, paints, paper, display technologies, and polymer composites
We take an intermediate approach that combines spectral transmission measurements and Mie scattering calculations. With applications such as light diffuser plates and soft focus cosmetics in mind, we focus on coatings and thin films that maximize both total transmittance and haze
For a given particle size, we find that both total transmittance and haze are monotonic functions of the particle concentration, with T decreasing and H increasing with increasing φ
Summary
Coatings and thin films of small particles suspended in a medium are important for many applications, including personal care products, paints, paper, display technologies, and polymer composites. Light diffuser plates in liquid crystal displays (LCD) [1] and ‘soft focus’ cosmetic products [2] require thin films that are both translucent and diffusive. That is, they must allow light to pass through, but that transmitted light should be scattered so as to appear diffuse. Achieving translucency and diffusion simultaneously is challenging: as one increases the other tends to decrease This trade-off, coupled with the wide variety of available ingredients, makes it difficult to formulate materials with the desired combination of translucency and diffusion by trial and error. Models and design rules able to predict bulk optical properties from single-particle attributes are needed
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