Dual‐Tunable Structural Colors from Liquid‐Infused Aerogels

Abstract

Materials with ordered structures normally present structural colors with viewing angle-dependency that are termed iridescence. [10] Liquid crystals with oriented structures cause light interference, thus showing iridescent colors. [11] Photonic crystals composed of periodically arranged monodisperse structural units induce specific diffraction of light. The highly ordered microstructures with different dielectric constants create photonic bandgaps, in which light of certain frequencies cannot propagate. [8,12] Generally, the iridescent color varying with the angle of observation or the illumination [13] might interfere with the stimuli-responsive color change. With monodisperse particles, non-iridescent structural colors can also be obtained due to the isotropic photonic pseudo-bandgap of the short-range ordered structures. [14] On the other hand, structural colors can originate due to the light scattering by amorphous scatterers whose angleindependency is favored for various applications. [15] This type of structural color has been found from several two-phase systems that can be constructed by either the phase separation of polymer gels [16] or the dispersed microparticles. [17,18] Materials with disordered microstructures can even display super white [19] or super black colors [20] by scattering or absorbing light in all wavelengths. In common, these systems have amorphous structures and the colors are independent of the observation angle. The coloration has been attributed to the specific scattering of light while most of them are accompanied by the Christiansen effect. [18] Certain colors are presented because light with specific wavelengths can selectively pass through while light with other wavelengths is scattered. The colors are tunable by varying the temperature or the composition of the copolymer. There is, however, a common drawback in these previous reports that the liquids were all volatile and encapsulation is indispensable for practical applications.Despite these pioneering efforts, however, to the best of our knowledge, structural color from amorphous structures of aerogels and their derivatives has not been reported. Aerogels are derived from gels where the liquid component was replaced with air using special techniques to avoid pore collapse. [21] Infusing liquids back into mesoporous aerogels is as challenging as drying the gels because the capillary gradient would easily collapse the pores and shred the highly porous materials into pieces.Herein, dual-tunable structural colors generated from liquid-infused, robust silsesquioxane aerogels due to the specific light scattering by the aerogel skeleton in liquids with matching refractive indices, are reported. The colors are tunable by changing the temperature and the composition of the liquid that roots from the coherence between the colors and the refractive index of the infused liquid. The finding provides new insights and tools for constructing structural colors and light management. It also opens applications of stimuli-responsive smart w...

Nanophotonic Structural Colors

“…[194][195][196][197][198][199][200][201] Structural color elements can be designed such that they visually respond to different external stimuli such as temperature, chemicals, and humidity through the use of suitable materials in an optically resonant system. [202][203][204][205][206][207][208][209][210][211][212][213] The benefit of colorimetric sensing is in realizing passive devices that are untethered to an energy source.…”

Solid–Liquid Host–Guest Composites: The Marriage of Porous Solids and Functional Liquids

“…After long‐time diffusion, a fine gradient color is formed due to the liquid migration between the neighboring segments. [ 69 ] Another example is drawn from smart window prototypes prepared by laminating multilayers of light‐responsive solid‐liquid composite films (Figure 13b). The windows became deep‐colored under the irradiation of sunlight while recovering transparent and colorless in the dark.…”

“…[7,28,32,67] In this case, liquid can work as a structural material to create slippery surfaces, liquid gating membranes, or thermal storage devices, relying on molecular smoothness of liquid surface, [45] the capillary force from the porous matrix, [7] and thermal transformation of the infused liquid, [19] respectively. The SLHGC with bi-phase continuity displays unprecedented omniphobic, [6,13] liquid gating, [7] antifouling, [7,23,32] energy-saving, [7,29,36] self-healing, [6] transparent, [46,68,69] and dynamically adaptive properties, [23,28,32] etc. These aspects of liquid properties have been well summarized in relative reviews by Aizenberg et al, [9,45] Jiang et al, [70] and Hou et al [10,11,71,72] For example, when a low-surface-tension liquid is infused in a porous matrix, the perfection and molecularly smoothness of the liquid surface provide a versatile solution for liquid repellency.…”

“…iv,v) Low-emitting insulating glass unit (low-E IGU) coated with the photochromic film under solar irradiation and temperature increase resulting from solar simulator irradiation through glasses coated or without coating with the photochromic film. a) Reproduced with permission [69]. Copyright 2020, Wiley-VCH.…”

“…c) The visualization of fluorescent or colored materials inside a microchannel made of solid-liquid host-guest composite. a) Reproduced with permission [69]. Copyright 2020, Wiley-VCH.…”