Mechanochromism of Structural‐Colored Materials

Abstract

In comparison with pigmentary colors, structural colors are with superior chemical stability and are resistant to photobleaching, making them promising candidates for color displays. What is more, the use of toxic dyes can be avoided by utilizing structural-colored materials to display various hues. Structural colors are widespread in nature and observed in opals, [3] beetles, [4] tropical fish, [5] peacock feathers, [6] chameleons, and similar iridescent materials. [7-9] Along with the growing understanding of the morphology and mechanism of natural structural-colored materials, their artificial counterparts have been manufactured with improved performance and functions consequently. Emerging structural-colored materials can be divided into three main categories according to their nanoscale architectures: photonic crystals (PCs), [10] liquid crystals (LCs), [11] and photonic glass. [12] Due to their ability to modulate visible light, the structural-colored materials have been applied in diverse domains such as optical waveguides, [13-16] luminescence enhancement, [17-19] photo electric devices, [20,21] photocatalysts, [22,23] anti-counterfeiting technologies, [24-26] and chemical and biological sensing. [27-29] With ingenious designs of nanostructures, a variety of responsiveness has been obtained on the structural-colored materials, corresponding to varying stimuli such as temperature, [30-32] solvent, [27] gases, [28] magnetic fields, [33] and external forces. [10-12] Among them, the mechanical responsive structural colors are able to visualize invisible stress in the materials, providing effective indicators for mechanical stimuli such as stretching, compression, or bending. Such mechanochromism can be directly achieved by the deformation-induced changes in periodic lattice constants of the structural-colored materials. [34,35] Recently developed mechanochromic structuralcolored materials have extended the responsive functions from conventional mechanical stimuli to complex signals such as electric stimuli. [10] In addition, although the color shift is a predominant method to achieve mechanochromic behavior, [34-36] increasing efforts have been made to develop mechanochromism based on polarization and transparence. [11,37,38] As one of the rapidly developing intelligent materials with multiresponse, [34,39,40] mechanochromic structural-colored materials have become promising in various applications, such as mechanical sensing, [11,41] colorful displays, [10,42] anti-counterfeiting, [26,37] and healthcare materials. [43,44] In this review, we summarize recent advances in mechanochromic structural-colored materials as shown in Figure 1.

Mechanochromism in Structurally Colored Polymeric Materials

“…[63][64][65][66][67] In this review, we examine structurally colored, mechanochromic polymers from the more fundamental standpoint of their mechanosensing capabilities, such as their mechanosensing range and strain sensitivity, complementing a recent review that emphasized the technologically relevant aspects of such materials. [68] We present key design concepts, materials selection criteria, and synthetic strategies employed in the current state-of-the-art, and provide a critical assessment of the mechanosensing and mechanoimaging capabilities of these materials. Biological inspiration will be discussed where it has significantly informed the design of a material.…”

Angle‐Insensitive Fabry–Perot Mechanochromic Sensor for Real‐Time Structural Health Monitoring

“…In particular, mechanochromic sensors, which exhibit color changes in response to mechanical stimuli such as strain and pressure, can potentially be applied in areas ranging from electronic skin, [ 1,2 ] soft robotics, [ 3–5 ] synesthetic device, [ 6 ] and encryption/decryption [ 7–9 ] to displays. [ 10–12 ] Structural health monitoring (SHM) is also an important and promising application area of the mechanochromic sensors. Every year, many engineering structures such as bridges and buildings collapse worldwide, leading to human casualties.…”

Large-strain and full-color change photonic crystal films used as mechanochromic strain sensors

“…The most commonly used method in this field is based on bottom-up approaches to synthesizing mechanochromic photonic crystals (MPCs) [5]. For example, polystyrene microspheres [6][7][8][9][10][11][12][13][14][15], silica nanoparticles [16,17], poly(ethyl acrylate-comethyl methacrylate) colloidal particles [18], gold nanoparticles [19], and aluminum nanowires [20] have been embedded in elastomers as MPCs.…”