Painting by Numbers: Nanoparticle‐Based Colorants in the Post‐Empirical Age

Abstract

The visual appearance of the artificial world is largely governed by films or composites containing particles with at least one dimension smaller than a micron. Over the past century and a half, the optical properties of such materials have been scrutinized and a broad range of colorant products, based mostly on empirical microstructural improvements, developed. With the advent of advanced synthetic approaches capable of tailoring particle shape, size and composition on the nanoscale, the question of what is the optimum particle for a certain optical property can no longer be answered solely by experimentation. Instead, new and improved computational approaches are required to invert the structure-function relationship. This progress report reviews the development in our understanding of this relationship and indicates recent examples of how theoretical design is taking an ever increasingly important role in the search for enhanced or multifunctional colorants.

Applicability of Effective Medium Approximations to Modelling of Mesocrystal Optical Properties

“…The output of the method is a set of the field expansion coefficients (which are too complex and bulky to be presented here) allowing to compute electromagnetic fields at any point in space. The field expansion coefficients are usually used to compute extinction cross section of the simulated objects, which can ¼ be directly compared to light transmission measurements of diluted particle suspensions [3,8]. The ½ extinction cross section spectrum obtained with the superposition T-matrix method for the ZnO The superposition T-matrix approach requires significant investments in equipment and also takes a certain amount of computation time.…”

“…This approach was applied in [12][13][14][15] to study the accuracy of the effective medium description of spherical objects composed of random particulate media. Simulations presented in this paper are closely related to one of the prospective applications of mesocrystals-the functional pigments [3], where the optical response of the pigment particles can be tuned by controlling the mesocrystal's density and shape, and the reported results can be used to optimize the properties of such systems.…”

“…Mesocrystals composed of optical materials can significantly extend the range of material properties available for optical devises and applications. Optical properties of mesocrystals can be fine tuned by changing the size of nanocrystallites, the mesocrystal's constitutive parts, their density and internal arrangement [3].…”

Color from hierarchy: Diverse optical properties of micron-sized spherical colloidal assemblies

“…At the micron scale, regular structural features act as diffraction gratings that produce vivid, rainbow coloration (7) and are used to control scattering (8) and to direct the emission of light by mirror-like reflections (9). At the molecular level, broadband absorption, for example by melanin, can be used to reduce unwanted scattering due to structural imperfections, which, if not eliminated, can lead to a whitish appearance (10).Several advantages of structural coloration compared with pigmentation hues have led to a strong interest in mimicking nature's photonic design principles in technology (11,12). These advantages include increased color longevity by the absence of photobleaching; the ability to use benign and nontoxic materials; broad variation in colors arising from simple changes in geometry of the same material; and the presence of vivid optical effects such as sparkle, luster, and iridescence, not achievable by conventional pigments.…”

“…Several advantages of structural coloration compared with pigmentation hues have led to a strong interest in mimicking nature's photonic design principles in technology (11,12). These advantages include increased color longevity by the absence of photobleaching; the ability to use benign and nontoxic materials; broad variation in colors arising from simple changes in geometry of the same material; and the presence of vivid optical effects such as sparkle, luster, and iridescence, not achievable by conventional pigments.…”