Colorimetric Detection of Mechanical Deformation in Metals using Thin‐Film Mechanochromic Sensor (Adv. Mater. Technol. 10/2021)

respond to one or more external stimuli (e.g., light, temperature, strain, humidity, pH or electromagnetic fields) by changing their own properties (e.g., shape, size, viscosity, stiffness, color, among others). In this framework, soft optomechanical materials have the capacity to merge the unique optical properties of plasmonic and/or photonic structures, carbon-based nanomaterials (CNMs) or macromolecules with the high tunability and elasticity of soft polymers. Given the high transparency of many soft polymers in the visible and near-infrared (NIR) spectral ranges, together with the possibility to incorporate such optical structures with high compliancy in polymers that can withstand large mechanical deformations, makes this combination of optical and mechanical features ideal for the development of functional optomechanical devices. [1] Soft optomechanical systems can be designed to change their optical properties under mechanical stimuli induced, for example, by strain, temperature, pH and so on, to develop cost-effective and highly sensitive sensors and optical modulators handling large strains, keeping their properties after many deformation cycles and adapting to complex and irregular surfaces. Note that, for example, sensors detecting mechanical deformations (e.g., strain or displacements) are required in structures such as buildings, vehicles, packages or wearable devices, where it is necessary to determine the experienced mechanical stress. Conversely, mechanical sensors can be used as transducers to detect other kind of external stimuli (e.g., chemical, biochemical, optical, to mention a few) that are able to produce mechanical deformations in the material. This category includes, e.g., some biosensors and micro-electromechanical systems (MEMS) that have been widely developed during the last decade. Soft mechanical sensors require a compliant transducer, being the electrical and optical transduction methods the most widely developed. However, optical transduction offers several advantages, particularly, its wireless detection nature, high sensitivity, easy readout, and the capacity to provide 2D strain mapping, even with sub-micron scale spatial resolution. [2][3][4] The high optical tunability of soft optomechanical systems by external mechanical stimuli can also be exploited to build mechanical modulators to modify the color or transparency of surfaces, having great potential in the development of smart windows, [5] rewritable optical displays, encryption, and anticounterfeiting applications, [6] among others. [7]

Section: Soft Optomechanical Systems For Sensing and Modulationmentioning

confidence: 99%

Soft Optomechanical Systems for Sensing, Modulation, and Actuation

Pujol‐Vila

Güell‐Grau

Nogués

et al. 2023

“…Mechanochromism has two main mechanisms, one is pigmentary color change based on chemical conversion of mechanophores, [20][21][22][23][24][25][26] and another is structural color change based on the structural periodicity alteration of photonic crystals (PCs). [27][28][29] However, most of the mechanophores are difficult to synthesize and only effective in highmodulus material systems, especially since they usually have low sensitivity and dull switch-on or switch-off color, which greatly limits their more extensive application. Therefore, low costs and highly efficient self-assembled PCs with tunable selective reflection (SBR) color are considered as promising stimuli-responsive materials for mechanochromism.…”

Section: Introductionmentioning

confidence: 99%

Reversible Information Storage Based on Rhodamine Derivative in Mechanochromic Cholesteric Liquid Crystalline Elastomer

Zhang,

Sun,

Zhang

et al. 2023

With the demand for the diversity and security of information deliveries increasing, advanced security tag for data encryption has attracted great interest from the scientific community. It is promising to achieve composite dynamic information storage by the combination of multisource stimuli‐responsive mechanism. Here, mechano‐ and chemochromism cholesteric liquid crystal elastomers (CLCEs) are prepared by introducing a rhodamine lactam‐based functional trigger by two different strategies, one of which is one‐pot method and another is postfunctionalization method. The performances of the CLCEs from two strategies are investigated, which are demonstrated to be effective methods in endowing material with new function, and suitable for different application scenarios. The composite material combines the force‐induced structural periodicity variation of CLCE and the pigmentary and fluorescent properties changes of the functional trigger caused by the chemical environment. The orthogonal construction of dynamic structural color pattern and reversible pigmentary and fluorescent colors pattern enable the information in the CLCE to display double encryption mode, which exhibits great potential in the information storage and anti‐counterfeiting.

“…Mechanochromic materials, which alter their nanoscale structural color in response to mechanical‐stress‐inducing events, such as stretching, compression, and bending, are drawing considerable attention owing to their applicability in contexts such as strain sensing, [ 1,2 ] structural health monitoring, [ 3,4 ] anticounterfeiting, [ 5 ] and encryption. [ 6,7 ] Mechanochromic materials based on the structural color can be designed to exhibit a range of optical responses, from reversible changes in color or fluorescence to more complex changes in refractive index or light scattering.…”

Section: Introductionmentioning

confidence: 99%

“…The pitch of CLCEs can be externally manipulated, similar to their internal molecular constituents, under various stimuli such as temperature, [ 13 ] electric fields, [ 14 ] light, [ 11 ] chemicals, [ 15–17 ] and mechanical stress, [ 10,18,19 ] resulting in tunable light reflection of a broad wavelength range from ultraviolet to infrared. [ 2 ] The tunable and selective light reflection of CLCEs permits their use in developing sensors, [ 1–3,6 ] lasers, [ 18,20 ] displays, [ 21 ] and camouflage technology. [ 19,22 ]…”

Section: Introductionmentioning

confidence: 99%

Direct‐Ink‐Written Cholesteric Liquid Crystal Elastomer with Programmable Mechanochromic Response

Choi,

Lee

et al. 2023

Cholesteric liquid crystal elastomers (CLCEs) are unique anisotropic rubbers that can change their structural color in response to various stimuli such as heat, chemicals, electric fields, and mechanical stress. Methods such as anisotropic deswelling and surface alignment have been adopted to prepare CLCEs; however, they have limitations in creating spatially controlled CLCE geometries. In this work, a direct ink writing (DIW)‐based 3D‐printable CLCE that can be prepared by extruding viscous CLC ink is developed through a 3D printer nozzle, followed by photopolymerization. Interestingly, the helical axis is inclined to the printing direction by ≈32° due to a combination of the shear‐induced alignment causes during extrusion and the elongational force generated during deposition onto the substrate. This unusual helical axis distortion leads to both blue and red shifts of the reflection color depending on the direction of observation relative to the printing axis. Notably, the printed CLCE exhibits anisotropic mechanochromism upon stretching, because of the stretching‐direction‐dependent variations in the slant angle of the helical axis. This anisotropic mechanochromism can be harnessed to develop a unique CLCE‐based strain sensor displaying intricate color patterns upon stretching, with significant application potential in encryption, anticounterfeiting, and structural health monitoring.