Reversible Thermochromic Properties Research Articles

Novel high-temperature thermochromic polydiacetylene material and its application as thermal indicator

The design and synthesis of organic high-temperature reversible thermochromic materials is one of the difficult issues in the field of organic chromic materials. In this paper, four diacetylene monomers named DBA-PCDA, TBA-PCDA, DBE-PCDA and TBE-PCDA, each containing multiple diacetylene units, were synthesized from 10,12-pentacosadiynoic acid (PCDA) through the amidation or esterification reactions, using 4,4′-diaminobiphenyl, 1,3,5-tris(4-aminophenyl)benzene, 4,4′-dihydroxybiphenyl, and 1,3,5-tris(4-hydroxyphenyl)benzene as bridging units. The effects of functional groups that can form hydrogen bond and π-π interactions on the solid-state polymerization properties of monomers and the thermochromic properties of the corresponding PDAs were investigated. The results show that only DBA-PCDA and TBA-PCDA, which contain functional groups that can form hydrogen bonding interactions, can be polymerized under 254-nm UV irradiation. The corresponding poly(DBA-PCDA) exhibits reversible thermochromic property even heated up to 200 oC, showing a potential application in the field of high-temperature thermal indicator above 100 °C. This work provides a new perspective to the development of PDA with high-temperature reversible thermochromic property.

Thermally Induced Lattice-Defective Oxygen Breathing in Perovskite-Structure Stannates with High-Contrast Reversible Thermochromism.

Inorganic thermochromic materials exhibit a tunable color gamut and a wide chromatic temperature range, indicating their potential for intelligent adaptive applications in thermal warning, temperature indication, thermal regulation, and interactive light-to-thermal energy conversion. However, most metal-oxide-based thermochromic materials show weak chromaticity adaption with the change of temperature, which needs further understanding of the microscopic principle to clarify the potential route to improve the contrast and identifiability for fabricating better thermochromic materials. Using perovskite-structure (AMO3) alkaline earth metal stannate (Ba1-xSrxSnO3, 0.0 ≤ x ≤ 1.0) as a model system, this paper reports for the first time the mechanism of the properties of thermally induced defect-enhanced charge transfer-type (CTT) thermochromic materials and the strategy for regulating their thermochromic properties by A-site cations. BaSnO3 exhibits continuously reversible thermochromic properties with high contrast from weak light yellow (b* = 11) to strong bright yellow (b* = 58) between room temperature and 550 °C. In-situ high-temperature X-ray diffraction (in-situ XRD), in-situ UV-vis absorption spectroscopy (in-situ UV-vis), thermogravimetric (TG), and electron paramagnetic resonance (EPR) spectra indicate that this excellent thermochromic phenomenon is attributed to the weakening of Sn-O bond hybridization at high temperatures, as well as the formation of a large number of oxygen vacancies at the top of the valence band, and the enhanced charge transfer resulting from the generation of impurity levels in the Sn2+ 5s2 intermediate. Replacing Ba2+ by Sr2+ in Ba1-xSrxSnO3 successfully tuned the thermochromic properties, which is attributed to the Sr2+ doping level-directed oxygen defect concentration and deoxygenation rate. The demonstrated defect-enhanced charge transfer behavior promotes a feasible route for lattice oxygen-mediated thermochromic materials and provides a fundamental relationship between thermally induced defects and colorimetry.

The fabrication of aminoquinoline-functionalized polydiacetylene-based hybrid vesicles with partially reversible thermochromic property

The fabrication of aminoquinoline-functionalized polydiacetylene-based hybrid vesicles with partially reversible thermochromic property

Reversible thermochromic properties of bisphenol A aromatic phenolic resin's composite natural rubber film

Based on open system and solution copolycondensation method, 2,6-monosubstituted bisphenol A aromatic phenolic resin with M‾n of 1.133 × 103 g·mol−1 and PDI of 1.005, was prepared by microwave, using bisphenol A (BPA), terephthalaldehyde (TPD) and isophthalaldehyde (IPD) as monomers. The number of BPA and phthalaldehyde (TPD or IPD) monomers participating in alternating copolymerization were 3 and 3, respectively. TPD and IPD had similar and low activities, therefore their competitive polymerization reactivity ratio was consistent with raw materials' practical molar ratio. The resin's structure was confirmed by 1H NMR, 13C NMR and FTIR. Reversible thermochromic composite natural rubber film was prepared by resin as chromogenic agent. When mass ratio of crystal violet lactone, resin, mixed alcohols (cetyl alcohol and octadecanol) and natural rubber is 1:3.0:30:20, i.e. 0.0075:0.023:0.23 (0.14:0.09):0.15 (g), the composite film was obtained by salivation method. The composite film's total color difference (ΔE) is about 85, and its absorption-scattering color depth difference (ΔKS) values are averagely 15 and 40 at visible light zone of 480–600 nm and 600–660 nm at 20–35 °C respectively. Composite film has good thermal stability and recyclability stability.

Three Anderson and octamolybdate based compounds modified by an asymmetric viologen: Photo-/thermo-chromic and luminescence properties

In this work, POM anions and a viologen ligand were combined to construct appealing electron transfer chromotropic materials. Three kinds of POM-viologen hybrids were obtained in hydrothermal environment, namely [Cu2(1,4-Mbby)2(H2O)6(TeMo6O24)]·H2O (1), [Co2(1,4-Mbby)2(H2O)6(TeMo6O24)]·H2O (2), [Cu2(1,4-Mbby)4(H2O)2(β-Mo8O26)2] (3, 1,4-Mbby·Cl = (1-(4-Methyl-benzyl)-[4,4′]bipyridinyl-1-ium)chloridate). Among them, compounds 1 and 2 are isostructural, showing an infinite inorganic chain with Anderson anions linked by Cu/Co atoms. The 1,4-Mbby suspend on both sides of this chain. Compound 3 exhibits a Mo8 dimer with four 1,4-Mbby as “arms”. POM anions and viologen ligands form a classical donor-acceptor structure, which can promote electron transfer. Therefore, under thermal stimulation, compounds 1–3 show reversible thermochromic properties. Under light stimulation, 1 and 3 have good reversible photochromic properties. Moreover, compound 1 can detect aniline, and 3 can detect ammonia and ethylenediamine through discoloration. Interestingly, compounds 1–3 show luminescence characteristics. Especially, the bright blue fluorescence of 1 can be observed under the irradiation of a 365 nm ultraviolet lamp. Meanwhile, compounds 1–3 have good fluorescence quenching effect under illumination or heating conditions. In other words, these compounds can quickly sense light or heat with color change. This work broadens the applications of POM/viologen compounds in the fields of discoloration and luminescence.

Reversible Thermochromic Microcapsules and Their Applications in Anticounterfeiting.

The common, commercial reversible thermochromic (RT) melamine-formaldehyde resin microcapsules containing formaldehyde are very harmful to human health. To address this issue, we successfully prepared a novel formaldehyde-free microcapsule via interfacial polymerization using RT compositions as the core and poly(urethane-urea) (PUU) as the shell. The core material consisted of a color former (crystal violet lactone), a developer (bisphenol AF), and a solvent (methyl stearate). To optimize the synthesis of the microcapsules, an L9 (34) orthogonal design and single-factor experiments were employed to analyze the effects of four factors (N3300-to-L75 shell material mass ratio, core-to-shell material mass ratio, emulsifier concentration, and shear rate during emulsification) on the encapsulation efficiency. The results showed that the optimal parameter values were as follows: a shear rate of 2500 rpm, N3300-to-L75 shell material mass ratio of 1:4, core-to-shell material mass ratio of 11:5, and emulsifier concentration of 3.5%. The influence of the shear rate on the particle size and distribution, surface morphology, dispersibility, and reversible thermochromic properties of the microcapsules was investigated. Furthermore, analyses on the phase-change characteristics, thermal stability, ultraviolet aging, and solvent and acid-base resistances of the microcapsules were conducted systematically. Finally, a reversible thermochromic mark containing the RTPUU microcapsules was designed and fabricated, which could be used against falsification. Moreover, these RTPUU microcapsules can be potentially used for anticounterfeiting applications.

Pyrochlore structure β-Bi2Sn2O7 as reversible thermochromic pigments

Pyrochlore structure of β-Bi2Sn2O7 shows continuously reversible thermochromic property from pale-yellow (25 °C) to reddish-brown (550 °C) in either heating or cooling process. Calcination for longer time (24 h versus 10 h) for the β-Bi2Sn2O7 pigments synthesized via solid state method relieves the distribution of defects and soften the Bi-O bonds in the orthorhombic Aba2 (No.41) lattice, facilitating lower bandgap and higher chromatic aberration, which indicate a crucial role of oxygen defect control for Bi-O-based thermochromic materials. This new finding is important for the design and fabrication of other charge-transfer type reversible thermochromic materials, which would definitely benefit for the next generations of smart inorganic pigments.

Flame-Retardant and Form-Stable Delignified Wood-Based Phase Change Composites with Superior Energy Storage Density and Reversible Thermochromic Properties for Visual Thermoregulation

The development of form-stable phase change materials (PCMs) with flame retardancy and the visual thermal storage process is crucial for their application in building energy conservation. Herein, an active phosphorus/ammonium-containing non-formaldehyde flame retardant (APA) was synthesized based on the natural compound phytic acid. Then, wood-based form-stable PCM composites (PTPCMs) with high energy storage density, excellent flame retardancy, and real-time and visual reversible thermochromic properties were successfully fabricated by impregnating the thermochromic compound into the APA-grafted delignified wood. The delignified wood well supports the solid–liquid PCMs and avoids their liquid leakage during phase transition due to the high surface tension and strong capillary effect. The differential scanning calorimetry (DSC) results showed that the PTPCMs possessed high thermal energy storage density (165.3–198.6 J/g) and reliable thermal stability. With the concentration of the flame-retardant APA increased, the peak heat release rate (pHRR) and total heat release (THR) of PTPCMs reduced noticeably, demonstrating the enhanced flame retardancy of PTPCMs. Moreover, PTPCM composites had good thermoregulation properties and the visualization of the phase transition process was made possible by the reversible thermochromic properties. In summary, the novel PTPCMs show tremendous application potential for efficient building energy conservation.

Dynamic absorption of bulk phase-change materials for photothermal solar energy storage based on reversible thermochromic

<p indent="0mm">Phase change materials (PCMs) are expected to solve the problems in thermal energy storage and thermal management. However, the energy density and power density of the transient melting front decrease as it moves away from the heat source. In the process of direct solar thermal utilization, the completion of the traditional heating totally depends on the thermal diffusion process of the PCM, and the low thermal conductivity limits the heating rate of the PCM. In this study, a dynamic phase-change material (Dyn PCM) based on reversible thermochromic properties is proposed that can automatically control the displacement of the light-thermal interface to follow the melting frontier. The thermal conductivity of the material would not limit the heating rate of the phase transition material during photothermal conversion. Dyn PCM is composed of two parts: a thermochromic agent and the main PCM. The thermochromic agent uses 2-phenylamino-3-methyl-6-dibutylaminofluoran as the electron donor, 2,2-bis(4-hydroxyphenyl)propane as the electron acceptor, and 4-benzyloxy Phenyl Ethyl Decanoate as a solvent to successfully achieve the transformation from transparent to black. The main PCM takes paraffin as an example. The latent heat of Dyn PCM_5, which contains 83.3 wt.% paraffin, is <sc>154.38 kJ/kg,</sc> which is only 6.6% lower than that of paraffin, and its transparent state shows transmittance of 91.2%, which is close to paraffin. The comparison shows that the charging rate of the Dyn PCM₅ is 260% faster than that of paraffin. The Dyn PCM groups remained unchanged after 80 cycles. The Dyn PCM did not change. Dyn PCM still has good reversible discoloration ability, maintains excellent thermal charge and discharge performance, and has stable light transmittance. As a result, the thermochromic composite Dyn PCM₅ developed in this study is a potential solar heat storage material that may also be used for direct solar energy absorption.

Liquid Crystal Coated Yarns for Thermo-Responsive Textile Structures

We have developed a prototype of breathable thermochromic textile ideal for sensor applications, e.g., medical thermography. The textile was woven/knitted from polyester filaments pre-coated with thermochromic liquid crystal (TLC) ink, in lieu of coating the TLC ink on the woven/knitted textile. This process brings us closer to achieving breathable thermochromic textiles while enhancing the versatility of the textile. A combination of precoated yarns can be preselected according to the desired thermochromic properties of the textile. Swatches from both knitted and handwoven fabrics showed excellent reversible thermochromic property showing color from red to blue as the temperature is raised from 26 to 32 °C, consistent with the unincorporated TLC ink.

Fluorescein-Functionalized Conjugated Polydiacetylenes with Excellent Reversible Thermochromic Properties under Thermal and 980 nm Near-Infrared Light Stimuli

Fluorescein-Functionalized Conjugated Polydiacetylenes with Excellent Reversible Thermochromic Properties under Thermal and 980 nm Near-Infrared Light Stimuli

A Robust Superhydrophobic Smart Coating with Reversible Thermochromic and Photochromic Property

Both thermochromic and photochromic coating have attracted many attentions due to their widely applications, but the low stability is a big obstacle. Inspired by the lotus leaf, to endow the chromic coating with superhydrophobicity is a possible solution. In this research, a dual response coating was prepared by adding photochromic and thermochromic particles simultaneously. The prepared sample demonstrated at least four-state color switching, which can be successfully used in tactile imaging, multi-color fabric, erasable record, and security labels. The superhydrophobicity was achieved by introducing vinyl-terminated polydimethylsiloxane, which not only offers low surface energy but also can cross-link with the particles to increase the adhesion. Thus, the prepared sample maintained superhydrophobicity after various kinds of destruction (such as sandpaper abrasion, corrosive liquid attack, ultrasonic treatment, UV irradiation, and high-speed drops/turbulent jets impact). Even though the superhydrophobicity can be destroyed by plasma etching, it can be recovered after 12 h at room temperature.

High-Sensitivity Organic–Inorganic Hybrid Materials with Reversible Thermochromic Property and Dielectric Switching

Among the stimuli-responsive materials, thermochromic materials have received tremendous scientific attention. However, traditional organic or inorganic thermochromic materials need a complex preparation process and possess a single performance. Herein, we report a new 1D organic–inorganic hybrid material, lead iodide hybrid, [PbI4·4-MAPY] (CP-1) (4-MAPY = pyridin-4-ylmethanamine), with line-sharing PbI6 octahedral chains and excellent reversible thermochromic properties (transition between lemon yellow and carmine red). In addition, the results of experimental and theoretical calculations illustrate that [PbI4·4-MAPY] is an indirect band gap semiconductor, and the band structures are contributed by inorganic chains. Overall, this work might afford a strategy for the detection of new dielectric and thermochromic switchable materials.

Supramolecular polyurea hydrogels with anti-swelling capacity, reversible thermochromic properties, and tunable water content and mechanical performance

Supramolecular polyurea (PU) hydrogels with combined anti-swelling capacity, thermochromic properties, and tunable water content and mechanical performance were obtained by immersing phase separated PU films with hydrophilic soft segments in water till swelling equilibrium. The multiple H-bonds within hard-segment domains are critical to the swelling and mechanical properties, which were rationally designed by using simultaneously two aliphatic diisocyanates with different symmetry and varying molar ratio. Consequently, the hydrogels exhibit a wide range of equilibrium water content (57–80%), elastic modulus (22–476 kPa), breaking strength (33–1720 kPa), and elongation at break (160–1460%). The hydrogels also exhibit fast recovery during cyclic loading-unloading. The incorporation of strong quadruple H-bonds into hard-segment domains endowed the hydrogels with stable anti-swelling capacity. Additionally, the hydrogels changed from transparent to opaque reversibly upon heating and cooling, originating from the phase transition of soft segments. The developed supramolecular PU hydrogels show promising potentials in many fields like smart windows.

A series of multi-responsive viologen-based alkaline-earth metal coordination complexes: Thermochromism, photochromism, and vapochromism

Due to their external stimuli responsive properties, chromic materials have attracted considerable interest in various fields. In this work, a series of alkaline-earth metal based coordination complexes constructed from viologen derivative, [Mg(H2O)6·(bdpbpy)·H2O] (1), [Ca(bdpbpy)(H2O)4] (2), [Sr(bdpbpy)(H2O)4] (3), [Ba(bdpbpy)(H2O)4] (4), (H4bdpbpy·2Cl = 1,1-bis(3,5-dicarboxyphenyl)-4,4-bipyridinium chloride) have been synthesized and characterized by elemental analyses, FT-IR spectroscopy, single-crystal X-ray diffraction, and thermogravimetric analysis. Because of electron transfer between the oxygen atom of carboxylate and bipyridinium moieties, compounds 1–4 exhibit reversible thermochromic and photochromic properties upon thermo treatment or Uv-vis irradiation. Due to presence of electron-deficient bipyridinium moieties (Lewis acidic sites), these compounds can be used as potential colorimetric sensor for ethanediamine vapor detection. The multi-responsive performances of compounds 1–4 can widen their applications in some particular systems that call for color changing properties of external stimuli.

Solar-driven thermochromic fabric based on photothermal conversion for light intensity monitoring

Solar-driven thermochromic fabric with light intensity monitoring functionality based on exceptional photothermal conversion performance and sensitive reversible thermochromic properties was fabricated using screen printing for skin protection.

Mechanical and Optical Properties of Thermochromic Reversible Waterborne Primer Film on Tilia europaea with 1,2-Benzo-6-diethylaminofluorane Based Microcapsules.

A waterborne thermochromic primer film containing thermochromic reversible microcapsules on the surface of Tilia europaea was prepared. The influences of different microcapsule concentrations on the reversible thermochromic, optical, mechanical and liquid resistance properties of the primer films were investigated. Not only were the morphology and structure of microcapsules and films observed, but also the chemical compositions of the microcapsules and films were analyzed. The results showed that for the primer film with microcapsules, the microcapsule concentration had a more significant influence on color difference. The primer film with microcapsules can achieve thermochromic reversibility. The temperature of color change was 32 °C and it had a good color recovery. The film gloss was negatively correlated with the microcapsule concentration, and the film with 5.0%–15.0% concentration had the best gloss. Adding an appropriate concentration of microcapsules can effectively improve the mechanical properties of the film. The film with 0–15.0% microcapsules had better liquid resistance to detergent, i.e., grade 1. The bonding form between the primer film added with microcapsules and Tilia europaea was physical bonding. This study provides a technical reference for the development of modern intelligent discoloration wood products.

Realization of reversible thermochromic polydiacetylene through silica nanoparticle surface modification

AbstractThe novel functionalized poly(silanization alcoholamine diacetylene)/silica nanoparticles (poly(SiDGADA)/SiO2 nanoparticles) have been achieved for reversible thermochromism. The silanized alcoholamine diacetylenic monomer (SiDGADA) is condensed with the hydroxyl group of SiO2 nanoparticle via hydrolysis of the SiDGADA siloxy group, followed by fixation after being polymerized upon UV light stimulation. The maximum thermal decomposition rate of the SiDGADA/SiO2 nanoparticles is 0.65%/°C at 460°C, while the maximum thermal decomposition rate of the SiDGADA is 1.92%/°C at 400°C. Poly(SiDGADA)/SiO2 nanoparticles appears a blue phase after photo polymerization and exhibits a distinctive red phase at the discoloration temperature of 65°C, which is 5°C higher than that of the pure poly(SiDGADA). It shows excellent reversible thermochromic properties, undergoing stable reciprocal blue‐to‐red conversion from 25 to 65°C, and returning to bluish violet after cooling. The extension of the SiDGADA alkyl chain length with formation of the covalent bond, to promote the interaction between the alkyl chains of polydiacetylene (PDA). This work provides a strategy to effectively improve the reversibility of thermochromic PDA.

Study of structural and optical properties of the thermochromic silver and copper tetraiodomercurates (Ag2, Cu2) HgI4 ceramics

Powders of silver (Ag2HgI4) and copper (Cu2HgI4) tetraiodomercurates were synthesized by a simple co-precipitation method. Their phase transition behavior was investigated by differential scanning calorimetry, X-ray diffraction (XRD), as well as diffuse reflectance to determine its reversibility and stability during heating–cooling cycles. Calorimetry showed a sharp transition at 51 °C when heating, and at 40 °C when cooling for Ag2HgI4 samples. For Cu2HgI4 samples in the first cycle, one peak was observed when heating at 69.6 and 49.7 °C when cooling. However, in these samples, the first peak splits into two peaks when heating during the second and third cycles (67.5 and 57.8 °C), indicating a probable loss of crystallinity. XRD and diffuse reflectance showed that the transition starts almost since the beginning of the warming-up process and is more evident around 40 °C for Ag2HgI4 and around 60 °C for Cu2HgI4. The energy bandgap indicates that Ag2HgI4 and Cu2HgI4 behave differently during the transition. Copper tetraiodomercurate follows almost the same path for heating than for cooling. Its reversible thermochromic and superionic properties are promising for several applications and open the possibility of using them as inclusions in smart composite systems.

Durable and tunable temperature responsive silk fabricated with reactive thermochromic pigments

A durable and tunable multiple-color thermochromic natural silk is prepared with vinyl modified thermochromic pigments (VTPs) by thio-ene reaction. The VTPs is obtained by the hydrolysis-polycondensation between the siloxane groups of trietoxyvinylsilane (VTEO) and the hydroxy groups of thermochromic pigments (TP). The reversible thermochromic properties of VTPs perform well in the heating-cooling cycle. The color of VTPs gradually fades during heating, and returns to its origin color when cooled. Its thermal decomposition temperature is up to 272 ℃. The vinyl of VTPs can react with sulfhydryl of 3,3′,3′'-phosphinetriyltripropanoic acid hydrochloride (TCEP) treated silk fabrics and form covalent bonding between vinyl groups and sulfhydryl groups via thio-ene reaction. The color of fabricated thermochromic silk fabrics changes reversibly during heating and cooling cycles, which is consistent with the color change behaviors of VTPs. The sulfhydryl-vinyl covalent bonds formed between silk fibers and VTPs provide good washing fastness (3−4 grade) and rubbing fastness (3 grade). By combining thermochromic pigments with different color and transition temperatures, thermochromic silk fabrics with the features of multiple-color change, various responsive temperatures and continuous color change are fabricated, making it highly promising for smart textile application.