Structural Color Mixing in Microcapsules through Exclusive Crystallization of Binary and Ternary Colloids

Abstract

Colloidal crystals are designed as photonic microparticles for various applications. However, conventional microparticles generally have only one stopband from a single lattice constant, which restricts the range of colors and optical codes available. Here, photonic microcapsules are created that contain two or three distinct crystalline grains, resulting in dual or triple stopbands that offer a wider range of colors through structural color mixing. To produce distinct colloidal crystallites from binary or ternary colloidal mixtures, the interparticle interaction is manipulated using depletion forces in double‐emulsion droplets. Aqueous dispersions of binary or ternary colloidal mixtures in the innermost droplet are gently concentrated in the presence of a depletant and salt by imposing hypertonic conditions. Different‐sized particles crystallize into their own crystals rather than forming random glassy alloys to minimize free energy. The average size of the crystalline grains can be adjusted with osmotic pressure, and the relative ratio of distinct grains can be controlled with the mixing ratio of particles. The resulting microcapsules with small grains and high surface coverage are almost optically isotropic and exhibit highly‐saturated mixed structural colors and multiple reflectance peaks. The mixed color and reflectance spectrum are controllable with the selection of particle sizes and mixing ratios.

Advances in the construction of photonic structures with dual stopbands and beyond

“…143–145 Exhibiting complex optical effects like selective wavelength reflection, the microcapsules are ideal for their applications in anti-counterfeiting, sensors, and information coding. 146–149 Their responsiveness to environmental stimuli and flexibility in fabrication, allowing precise size and shape control, make them highly promising for high-tech applications, including smart materials and biomedicine. 150,151…”

“…In the study of triple stopband photonic structures, Yang et al used depletion interaction within double-emulsion droplets to manipulate colloidal building block interactions, successfully fabricating PC microcapsules with three stopbands. 149 As shown in Fig. 6j, a mixture of binary or ternary PS colloidal particles was encapsulated in the core part of the droplet microcapsule, and dissipative agents and salts were added to enhance the depletion attraction between the colloidal particles.…”

Tailoring the Hole Transport Layer and Understanding the Impact of Sn Oxidation for Different Mixed Halide Perovskite Active Layers: On a Quest for the Perfect Match

“…The perovskite structure ABX 3 [A = methylammonium (MA) + /formamidinium (FA) + , or they are mixed; B = Pb/Sn/mixed; and X = halogen anion I, Br, or Cl] offered multiple advantages over Si solar cells. − The PCE of PSCs has increased significantly from 3% in 2006 to over 25% today, as reported by the United States Department of Energy Solar Energy Technologies Office (SETO) . Perovskites show high performance and excellent results because of their unique optoelectronic properties, such as high absorption coefficient, dielectric constant, and charge-carrier mobilities, generating superior efficiencies. − An ideal solar cell has a direct bandgap of 1.4 eV to absorb the most photons from the sun’s energy, and perovskites have an energy gap close to the calculated value of the ideal bandgap .…”

Structural Color Inks Containing Photonic Microbeads for Direct Writing

“…Colloidal arrays have been produced in a microbead format using emulsion droplets, offering structural colorants in photonic inks, which are potentially useful for structural color printing. − For example, colloidal particles self-assemble within the droplets through enrichment by evaporation or osmotic extraction. − Although these photonic microspheres, composed of close-packed arrays, exhibit structural colors, the colloidal assembly requires a long time for crystallization, and the microspheres have low mechanical stability due to the absence of particle binders, thereby restricting their applications. To overcome these limitations, photonic microspheres with non-close-packed arrays in a solid matrix have been developed. ,,− Silica particles dispersed in polymerizable resins spontaneously form non-close-packed arrays by interparticle repulsion, which are captured in the polymeric matrix by in situ polymerization, reducing production time and securing high mechanical stability.…”