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![Cholesteric (chiral nematic) liquid crystal structure; direction of molecular orientation gradually changes between layers [36].](publication/287946048/figure/fig11/AS:438516061609989@1481561784180/Cholesteric-chiral-nematic-liquid-crystal-structure-direction-of-molecular-orientation.png)
Cholesteric (chiral nematic) liquid crystal structure; direction of molecular orientation gradually changes between layers [36].
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![FIGURE 1. Behavior of commercially important photochromic colorants [5].](publication/287946048/figure/fig1/AS:438516057415680@1481561783647/Behavior-of-commercially-important-photochromic-colorants-5_Q320.jpg)
![FIGURE 4. Photochromism of spirooxazines [7].](publication/287946048/figure/fig3/AS:438516057415684@1481561783848/Photochromism-of-spirooxazines-7_Q320.jpg)
Commercial photochromic and thermochromic colorants that change rapidly and reversibly from colorless to colored state when activated by stimuli like ultraviolet irradiation, temperature or pH are well established class of colorants for manufacturing of niche products. Use of photochromic and thermochromic systems in applications like medical therm...
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... The use of thermochromic materials in food packaging has notably enhanced food safety and consumer interaction. Chowdhury et al. [81] explored photochromic and thermochromic colourants in packaging, enhancing quality control and consumer interaction. Similarly, Liu et al. [206] introduced non-toxic microcapsules housing thermochromic materials in ink and film, broadening their potential in food packaging. ...
... Thermochromic materials play a pivotal role in industrial se ings, enabling effective temperature monitoring and process optimization. Techniques like infrared and thermal imaging are key for characterising these materials, offering visual insights into temperature gradients, and identifying equipment hotspots [81,105]. However, ensuring the durability and stability of these materials under demanding industrial conditions is crucial. ...
... The optimisation of the coating process has potential applications in furniture engineering Offers control over coating quality and creating intelligent wood coatings [81,210] Electrical Equipment Development of temperature-responsive microcapsules to enable insulating materials from excessive external temperature Colour changes in response to temperature variations and localization of hotspots. ...
Reversible thermochromic polymers have emerged as compelling candidates in recent years, captivating attention for their application in heat detection systems. This comprehensive review navigates through the multifaceted landscape, intricately exploring both the virtues and hurdles inherent in their integration within these systems. Their innate capacity to change colour in response to temperature fluctuations renders reversible thermochromic nanocomposites promising assets for heat detection technologies. However, despite their inherent potential, certain barriers hinder their widespread adoption. Factors such as a restricted colour spectrum, reliance on external triggers, and cost considerations have restrained their pervasive use. For instance, these polymer-based materials exhibit utility in the domain of building insulation, where their colour-changing ability serves as a beacon, flagging areas of heat loss or inadequate insulation, thus alerting building managers and homeowners to potential energy inefficiencies. Nevertheless, the limited range of discernible colours may impede precise temperature differentiation. Additionally, dependency on external stimuli, such as electricity or UV light, can complicate implementation and inflate costs. Realising the full potential of these polymer-based materials in heat detection systems necessitates addressing these challenges head-on. Continuous research endeavours aimed at augmenting colour diversity and diminishing reliance on external stimuli offer promising avenues to enhance their efficacy. Hence, this review aims to delve into the intricate nuances surrounding reversible thermochromic nanocomposites, highlighting their transformative potential in heat detection and sensing. By exploring their mechanisms, properties, and current applications, this manuscript endeavours to shed light on their significance, providing insights crucial for further research and potential applications.
... Thermochromism occurs due to various mechanisms based on the compound's molecular structure. The thermochromic mechanism can be categorized into three main groups: change in crystal structure, stereoisomerism, and molecular rearrangement [13]. To be used in textiles to detect body temperature, the component must (1) have a reversible and solid (or encapsulated) system that is appropriate for dyeing and printing, (2) display a distinct colour change within a narrow temperature range, usually from low ambient temperatures to body temperature, and (3) be cost-effective [14,15]. ...
... To be used in textiles to detect body temperature, the component must (1) have a reversible and solid (or encapsulated) system that is appropriate for dyeing and printing, (2) display a distinct colour change within a narrow temperature range, usually from low ambient temperatures to body temperature, and (3) be cost-effective [14,15]. These criteria make the molecular rearrangement mechanism, where temperature changes lead to a molecular rearrangement in a compound, causing an increase in conjugation within the molecule and the creation of a new chromophore, resulting in a colour change, the most achievable option [13]. However, thermochromic materials cannot dye the fibre directly due to their lack of affinity with it, necessitating microencapsulation [16]. ...
... When recording colour differences, Potuck et al. [17] assessed the variation in colour perception by observing visual discrepancies. Other researchers examined colour variations by analysing the spectrum of reflected light [13,24]. This study examined both visual differences and spectrum changes for performance comparison. ...
The existing literature emphasizes the significance of and needs for developing body temperature monitoring devices that can consistently and discreetly assess the temperatures of young children. Such products could offer a method to check children’s body temperature and alleviate parents’ concerns over fever. However, research gaps and challenges exist in preserving material flexibility, conducting tests in a controlled setting that mimics body temperature, and investigating consumer perceptions of this type of functional textile product. Therefore, this research aimed to investigate functional textiles using thermochromic yarns for young children’s body temperature detection, particularly focusing on testing prototypes in a controlled environment and empirically investigating target consumers’ perceptions of such products. Experimental prototype testing and a consumer survey were conducted in this study. The findings validate the practicality and market potential of such products. We also proposed alternative mediums for implementing the functional yarn and recommendations for developing these products based on target consumers’ concerns and suggestions. This research helped identify potential economic development possibilities for functional textiles.
... properties. [13][14][15] Polydiacetylenes (PDAs) exhibit unique optical and chemical properties due to conjugated ene-yne bonds of overlapping pi orbitals. [16][17][18][19][20][21] PDAs also undergo topochemical polymerization to form highly ordered crystalline polymer. ...
... Hz, 3H).13 C NMR (101 MHz, DMSO-d6) δ: 159.02, 143.46, 107.42, 74.42, 68.88, 60.57, ...
Thermochromic materials are of great interest because of their color transition characteristic as a function of temperature, and this property may find potential applications as a temperature indicator. Irreversible thermochromic materials that display color change at low temperatures can be utilized as a temperature indicator to ensure the safety and quality of deep-frozen products during storage and transportation. In this work, we have successfully prepared a novel colorimetric sensor based on a functionalized polydiacetylene dye. In order to achieve thermochromic transition of different temperature ranges, pentacosadiynoic acid (PC) was functionalized with ethylene glycol monomethylether (EGME), diethylene glycol monomethyl ether (DGME) and triethylene glycol monomethyl ether (TGME), resulting the formation of ester head groups. Photopolymerization of the synthesized diacetylene dyes was carried out to convert the monomers of the dyes into polymers. The Fourier transform infrared spectroscopy (FTIR), Nuclear magnetic resonance (NMR), and Raman spectroscopy were used to characterize the synthesized product. The absorption spectroscopy and optical images study revealed that the functionalized dyes underwent irreversible thermochromic transition when exposed to freezing temperatures. This property of irreversible color transition can make them a reliable indicator of temperature change. The functional dye was incorporated into a polymer film to apply directly on deep freeze products as a polymer strip and when the temperature increases upon freezing level, the color of the thermochromic strip changes which can provide a visual warning to the consumers and manufacturers.
... Photochromic materials are classified as smart materials and are found in optoelectronic devices and optical storage systems [18][19][20][21][22]; UV markings and sensors; security documents [18]; smart textiles [2,10,[23][24][25]; and elsewhere. They are widely used for their colour-changing properties and have been exploited for attractive designs and for different functional applications. ...
Photochromism refers to a reversible colour change induced by the irradiation of pho-tochromic materials with ultraviolet (UV) or visible light that reverts to the original colour after the light source is removed. This effect arises from chemical transformations between two isomers with different absorption spectra, involving processes like proton transfer, chemical-bond formation, and isomerisation. These photochromic inks, appearing as crystalline powders with micro-sized particles, require dissolution in a suitable matrix to achieve the colour change. Photochromic inks are used in security, as functional coatings for paper and packaging, in the fabric industry, and in other ways. This study examines the influence of varying concentrations of micro-sized photochromic pigments and different ink-coating thicknesses on the photochromic effect on sustainable paperboard substrates. Artificial ageing was performed to assess the photochromic response and lightfastness in relation to pigment concentration, ink-coating thickness, and the influence of the paperboard substrates. The results of this research could contribute to enhancing knowledge on employing photochromic inks for diverse packaging applications.
... Herein, we fabricated simple low-cost multifunctional transition and temperature-sensitive contact lenses based on photochromic and thermochromic powders. Although these dyes were discovered decades ago, their utilization in applications like textiles, optics, smart wearables, and sustainable buildings is very recent [30][31][32][33] . Photochromic micro-powders are generally made of a core photochromic material like spirooxazine or spiropyran, which upon exposure to UV radiation isomerizes reversibly and forms a merocyanine structure (Fig. 1a) 34 . ...
Smart contact lenses have recently gained traction due to their functionalization as noninvasive diagnostic and therapeutic wearables that can address several ocular diseases. Herein, multifunctional contact lenses exhibiting UV-transition and temperature-responsive capabilities were developed utilizing chromogenic materials that were integrated simultaneously into poly(2-hydroxyethyl methacrylate) (pHEMA) contact lenses. The functionalities of the contact lenses were optically evaluated in both their activated and non-activated states. Transition contact lenses offered excellent UV and blue light blocking capabilities (~45%) at their inactive states. When activated via UV exposure, the transparent lenses darkened instantaneously and absorbed portions of the visible light spectrum. The absorption intensity and transient discoloration of the transition lenses relied primarily on the utilized photochromic material. Likewise, the temperature-responsive contact lenses exhibited distinct colorimetric variations in response to temperature changes within the physiological range (33–38 °C). The maximum sensitivity of the thermochromic lens was 8% transmitted light per Celsius degree shift. Physiochemical and morphological analysis indicated the adequacy of the contact lenses. Hence, the multifunctional contact lenses can be deployed as smart wearables to manage ophthalmic deficiencies that are deterred by UV radiations and variations in ocular surface temperature.
... Since the 1970s, the designing and synthesis of thermochromic materials have been an important interdisciplinary research field because of their excellent efficiency in changing their characteristics concerning temperature [1,2]. Several applications of thermochromic materials have been reported, such as in cosmetics [3], as food quality indicators, forehead thermometers [4,5], thermal mapping, refrigeration thermometers, thermochromic sensors [6,7], memory devices and cholesteric liquid crystals (which are used in biomedical therapy) [8] etc. ...
Switchable nonlinear optical (NLO) materials have widespread applications in electronics and optoelectronics. Thermo-switches generate many times higher NLO responses as compared to photo-switches. Herein, we have investigated the geometric, electronic, and nonlinear optical properties of spiropyranes thermochromes via DFT methods. The stabilities of close and open isomers of selected spiropyranes are investigated through relative energies. Electronic properties are studied through frontier molecular orbitals (FMOs) analysis. The lower HOMO-LUMO energy gap and lower excitation energy are observed for open isomers of spiropyranes, which imparts the large first hyperpolarizability value. The delocalization of π-electrons, asymmetric distribution and elongated conjugation system are dominant factors for high hyperpolarizability values of open isomers. For deep understanding, we also analyzed the frequency-dependent hyperpolarizability and refractive index of considered thermochromes. The NLO response increased significantly with increasing frequency. Among all those compounds, the highest refractive index value is observed for the open isomer of the spiropyran 1 (1.99 × 10−17 cm2/W). Molecular absorption analysis confirmed the electronic excitation in the open isomers compared to closed isomers. The results show that reversible thermochromic compounds act as excellent NLO molecular switches and can be used to design advanced electronics.
... The following example, Fig. 2, shows an intelligent smart bandage, which changes color when it detects an infection. British researchers from the University of Bath in the United Kingdom have developed this product in particular for monitoring severe burn wounds and which alerts the patient when he detects the formation of a bacterial bio-film [21][22][23]. ...
Smart textiles in healthcare are able to react on their own by adapting to their environment. They allow integrating functions and expand the design options. The development of these textiles will lead to create more comfortable products. The textiles of the future will improve our daily lives and offer new perspectives for industry, health services and the environment. To reach those objectives, smart products incorporate more and more innovative functional materials and fibers such as X-chrome materials with color-changing properties under pressure, temperature, light, etc. In this survey we will present the state of arts of the x-chromic materials, and mainly x-chromic textile materials. An overview of the main textile applications of chromic materials will be discussed through ongoing research towards technical and smart textile applications. Applications as reactive indicators adapted to the user need with focus on newborns needs will be detailed.
... Thermochromic properties materials used in food, textile, paint, cosmetic, pharmaceutical industry, medicine, etc. For example, in the production of indicator films for foodstuff, safety markers for banknotes, documents, sensors temperature to ensure safety and product quality control, biosensing systems [7][8][9][10][11][12][13][14]. ...
In the current study a number of 4-hydroxystyryl dyes (4-HSD), 4-[-2-(4-hydroxy-3-methoxyphenyl)vinyl]-1-octylpyridinium bromide (4OP-MS) and 2-[2-(3,5-dimethyl-4-hydroxystyryl)]-1-methylquinoline iodide (2MQ-DMS), were synthesized and characterized using NMR, IR and Raman spectroscopy methods. The solvatochromic and thermochromic properties of their merocyanine form in solutions (water, ethanol, propanol-2, butanol-1) were observed and studied via UV–Vis spectrophotometry and tristimulus colorimetry methods. The sensitivity of the studied representatives to temperature changes in the range of 20.0–70.0 °C showed opposite thermochromic effects in solutions. Thus, the 4OP-MS shows a bathochromic shift of the spectrum (up to 17 nm) with increasing temperature and a significant increase in intensity in alcohol media (up to 3.5%—without taking into account the thermal expansion of the solvent). Under similar conditions, the 2MQ-DMS shows a significant decrease in intensity, which reaches 44% in the case of butanol, with practically no shifts in the light absorption maximum with temperature. When passing from aqueous to propanol-2 solutions, the thermosolvatochromic effect in the case of 4OP-MS increases slightly from 108 to 113 nm with an increase in temperature by 50.0 °C, and for 2MQ-DMS, on the contrary, it decreases from 64 to 48 nm. These effects indicate, on the one hand, the possibility of using such dyes to create liquid thermochromic systems, and on the other hand, the need to take them into account when creating and using molecular optical sensors.
... The literature refers to these dyestuffs as intelligent dyestuffs, which have the potential to be used to manufacture smart textile materials, due to their ability to generate new innovative designs that can dynamically adjust looks of the garments to suit people's moods, styles, and so on, despite their poor resistance to visible light, heat, and other environmental stimuli, as well as their high price. Photochromism and thermochromism, both, have substantial commercial uses in ophthalmic purposes, including the familiar spectacles that turn into sunglasses when exposed to sunlight, dye lasers, information recording materials, security printing, and camouflage [113]. ...
... The absorption spectra of these two types are distinct from one another. Depending on the nature of reversal mechanism, photochromic textiles can further be classified as Ttype (thermally driven) and P-type (photochemically driven) [113]. Moreover, the open ring structures of P-type photochromic molecules are colourless, while closed ring structures are coloured, and vice versa for T-type molecules [114,115]. ...
... A typical end use has been towelling and beachwear in the textile sector, UV-light sensitive curtain, and knapsacks. Other potential applications include chromic sensors that provide a self-contained response (without using any additional electrical circuitry) to a change in environment by a visible colour change, and responsive camouflage fabrics for military applications [113,[120][121][122][123]. ...
“Smart textiles”, also known as functional fabrics or e-textiles, are changing the way of thinking about fabrics. The term “functional textiles” refers to textiles with integrated functions that control or adjust according to the application. Nowadays, electronics
and photonics have greatly influenced the evolution of technical textiles. Smart textiles are functional fabrics integrated with a sensor array or functional nanomaterial/polymer or an optical fibre. Various fibres (conductive and high-performance), chemicals/additives (finishing and coating chemicals, smart polymers, nanomaterials, etc.) and technologies (spinning, weaving, knitting, nonwoven, braiding, finishing, coating,
lamination, etc.) are combined to create smart fabrics, depending on their use.
This chapter covers all the main areas of applications of smart and functional textiles, including textiles with various functionalities (antimicrobial, UV-resistant, fireretardant, oil/water-repellent, stain-repellent, wrinkle-resistant, anti-order, antistatic,
superabsorbent, etc.), coated/laminated high-performance textiles, conductive textiles, textile-based sensors, energy-harvesting textiles, medical textiles, protective textiles, textiles
for military and defence, automotive textiles, and so on. This chapter also discusses the potential of emerging 3D printing technologies for making smart and functional textiles.
Finally, the current challenges as well as future perspectives of functional and smart textiles have also been summarized.
... They are also used as sensors (if the temperature accuracy is not so crucial), warning messages, security elements for tickets, smart cards, erasable pens, and documents, or as temperature indicators for products such as beverages, ice-cream, and others [1,10,11]. The most common thermochromic dyes of spirolactone type are fluorans, crystal violet lactone, spiropyrans and fulgides (Fig. 1), and are the color formers in a multi-component system [12]. ...
