Photochromic Microcapsules Research Articles

Modulation of an Si-O-Si structure in uniformly photochromic microcapsules for solar heat and daylight management

Photochromic microcapsules adjust to sunlight adaptively and using them to fill windows is an attractive option for constructing smart windows that can manage solar heat and daylight. However, fabricating high-durability polymer-composite photochromic microcapsules for use in outdoor glass windows remains challenging, requiring high contrast ratio, high transparency, and low haze. Herein, we synthesized a novel poly(urea-siloxane) shell monomer containing Si-O-Si bonds and successfully prepared a photochromic microcapsule by modulating the mass ratios of shell monomers and emulsifiers. The photochromic poly(urea-siloxane)-based microcapsule-coated glass (PCPUS MCG) showed high luminance transmittance (83.66 %) and low haze (20.31 %). The as-prepared PCPUS MCG exhibited self-adaptive sunlight control without additional energy input, with strong solar modulation ability (Δτsol of 38.30 %). Furthermore, the response indoor air temperature was reduced by approximately 3.7 °C in a field test using a model house equipped with PCPUS MCG windows, showing promising energy-saving potential compared with conventional windows. Therefore, uniform photochromic-microcapsule modification using Si-O-Si bonds warrants attention in future energy-saving window designs.

Multifunctional finishes on photochromic microcapsule-printed cotton fabrics using titanium oxide nanoparticles

Purpose This paper aims to study the combination of photochromic microcapsules, which use the ultraviolet (UV) rays for colour changing phenomena, and titanium oxide (TiO2) nanoparticles (NPs), which block the UV rays by their photocatalytic activity in the sunlight on the cotton fabric. Design/methodology/approach The TiO2 NPs mixed with photochromic printing paste are used for coating on cotton fabric and further curing is performed in a one-step process. The photochromic pigment printed fabric impregnated in a liquid solution is processed in a two-step process with two variables such as 1% TiO2 and 2% TiO2. The characterization of samples was done with a UV transmittance analyser, surface contact angle, antimicrobial test and fabric physical properties. Findings The UV protection of TiO2-treated photochromic printed fabric was high and gives the ultraviolet protection factor rating of 2,000 which denotes almost maximum blocking of UV rays. The antibacterial activity of the one-step samples shows the highest 36 mm zone of inhibition (ZOI) against S. aureus (gram-positive) and 32 mm ZOI against E. coli (gram-negative) bacteria. The one-step sample shows the highest static water contact angle of 118.6° representing more hydrophobicity, whereas the untreated fabric is fully wetted (0.4°). In two-step processes, as the concentration of TiO2 increased, the antibacterial activity, UV blocking and hydrophobicity became better. Originality/value This work achieves the multifunctional finishes by using photochromic microcapsules and NPs in a single process as a first attempt. The results inferred that one-step sample has achieved higher values in most of the tests conducted when compared to all other sample.

Photochromic performance optimization of polyurethane microcapsules by interfacial polymerization method

AbstractSpiropyran photochromic materials have been widely studied in military camouflage, optical data storage, information encryption, and fashion ornaments. The non‐photochromism and low endurance of solid spiropyran make the challenges of their application. Photochromic microcapsules with a butyl acetate solution of spiropyran as core and polyurethane as shell are synthesized via interfacial polymerization. The optimized polyurethane photochromic microcapsules are prepared with a Tween 20 concentration of 4 wt%, core–shell ratio of 16:5, and spiropyran concentration of 0.40 wt%. Polyurethane photochromic microcapsules with a mean particle diameter of 0.33 μm are obtained. The morphology shows smooth spheres, and the core–shell structure is observed. Butyl acetate in the microcapsule core does not evaporate at a temperature lower than 218.01°C as the microcapsule shell insulates heat. The polyurethane photochromic microcapsules are mixed with adhesive, thickener, and water into a paste and screen‐printed on cotton fabric. The printed fabric shows the ΔE of 17.56, 11.93, and 6.96 after 80s irradiation with the xenon lamp intensity of 102, 68, and 34 mW cm−2. The light stability of the photochromic fabric is excellent as ΔE decreases about 8.28% after 20 cycles of UV‐Vis irradiation.

Structural modification of photochromic microcapsule shell to enhance acid resistance

Enhancement of weather fastness and acid resistance of photochromic (PC) materials when exposed to outdoor actual weather conditions is crucial for practical application. In this paper, by introducing amine and ether bonding groups, we have developed a typical composite structure shell with strong acid resistance, high sealing capacity and good fatigue resistance, then further self-assembled and embedded photo-transformation powder. The acid resistance, photochromic response, fatigue resistance and thermal stability of fabricated photochromic microcapsule were investigated systematically. Not only the obtained end products exhibited excellent photochromic ability, also the retention of absorption reached 95.97% under 100 times cycles of visible light irradiation (λ>420 nm) and ultraviolet light irradiation (λ<400 nm), uninterruptedly. Here, we prepare stabilized photochromic microcapsules utilizing polyetheramine (PEA) modified melamine formaldehyde (MF) as shell material for further application in the field of UV indication in extreme environments such as viscose fiber spinning.

Preparation of Photochromic Microcapsules of Poly(methyl methacrylate)/Inorganic Metal Oxide Composite Shells with UV‐Resistant Properties and Application to Printing on Cotton Fabrics

AbstractTo further enhance the fatigue resistance of spiropyran‐based photochromic materials and to explore the functionality of organic–inorganic metal oxide microcapsule shell materials, cross‐linked (P(MMA‐PETA)) and homopolymer (PMMA) shells have been developed by cross‐linking TiO2 and hybridizing ZnO on a PMMA matrix. PMMA/TiO2 photochromic microcapsules and PMMA/ZnO photochromic microcapsules with ultraviolet (UV)‐absorbing function are prepared by successfully encapsulating spiropyran photochromic compounds using these two composite shells. The results show that both microcapsules exhibit a complete spherical core–shell structure with good UV resistance and thermal stability. The TG test underlines a 50% coating rate of PMMA/ZnO microcapsules on spiropyran photochromic material, with an optimal ZnO addition of 10% and particle size range from 2 to 8 µm, effectively blocking UV‐A and part UV‐B radiation. Further, a 75% maximal coating rate is observed for PMMA/TiO2 microcapsules on spiropyran with optimal TiO2 addition at 2–4%, a particle size of around 5 µm, diffusely reflecting 48% of UV rays. The photochromic fabrics prepared with PMMA/TiO2 microcapsules have better UV resistance, with a UV protection factor value of 59.48, and excellent fatigue resistance after at least 30 cycles of UV–visible light irradiation.

Effect of Composite Addition of Antibacterial/Photochromic/Self-Repairing Microcapsules on the Performance of Coatings for Medium-Density Fiberboard

In order to expand the research on a combination of functional microcapsules and water-based coatings, antibacterial microcapsules using 3.0% sodium dodecyl benzene sulfonate as an emulsifier, self-repairing microcapsules, and photochromic microcapsules were added to water-based coatings separately or in combination and coated on medium-density fiberboard to analyze the various properties of the coating. From the perspective of the antibacterial effect, the photochromic microcapsules have little negative impact on antibacterial properties and can be used in combination with antibacterial microcapsules. When the photochromic microcapsules and antibacterial microcapsules were combined, their antibacterial rates against Staphylococcus aureus and Escherichia coli were 51.9% and 55.6%, respectively. The self-repairing microcapsules in combination with antibacterial microcapsules lead to a significant decrease in the antibacterial rate and are not suitable for use in combination with antibacterial microcapsules. From the perspective of the photochromic effect, the addition of self-repairing microcapsules can accelerate the photochromic speed of the coating, improving the photochromic effect. The addition of antibacterial microcapsules made the photochromic rate slower. Both the antibacterial microcapsules and photochromic microcapsules have weakened the self-repairing ability of self-repairing microcapsules. The width change rate in coating scratches has decreased from 21.9% to 14.7% and 17.6%, respectively. However, compared with the coating without microcapsules, the self-repairing ability still improved. The results have broad prospects in the application of antibacterial microcapsules, self-repairing microcapsules, and photochromic microcapsules for coatings on medium-density fiberboards.

An All‐Stretchable, Ultraviolet Protective, and Electromagnetic‐Interference‐Free E‐Textile

AbstractFlexible and skin‐mountable electronics have drawn tremendous research attention with the booming of smart medical systems and wearing technologies, however, their environmental adaptability to electromagnetic and solar radiation has long been neglected. Herein, a novel health monitoring e‐textile with robust ultraviolet (UV) protecting and strong electromagnetic interference (EMI) shielding performance is rationally developed on an ultraelastic and bilayered nonwoven textile. Via the respective incorporation of silver flake‐modified liquid metal (AgLM) and silver nanoparticles (AgNPs) on each side of a permeable substrate, a Janus sensing layer with electrophysiological monitoring function, Joule heating ability, and excellent EMI shielding capability (up to 38.5 dB in X band) is first fabricated. Elastic microfibers embedded with sensitive photochromic microcapsules are then in situ assembled on the bioelectric‐sensing layer, achieving a bilayered e‐textile with a reversible UV‐chromic property and an extraordinary UV protection factor (UPF) of 335.56. The developed all‐stretchable and UV‐EMI proof e‐textile is utilized as a safe and comfortable on‐skin electronic to provide point‐of‐care health regulation under complex UV/EMI radiative environments. Specifically, stable Joule heating performance and accurate monitoring of electrocardiogram (ECG) and surface electromyography (sEMG) are simultaneously obtained, demonstrating promising applications in multifunctional and robust wearing electronics.

Preparation of poly(methyl methacrylate) photochromic microcapsules containing spiro-pyran by solvent volatilization

Preparation of poly(methyl methacrylate) photochromic microcapsules containing spiro-pyran by solvent volatilization

Smart photochromic materials based on polylactic acid

The smart photochromic materials based on polylactic acid (PLA) were prepared by melt-blending and hot-pressing, in which photochromic microcapsules (PM) were used as a functional additive, and poly(vinyl acetate) (PVAc) was introduced into the photochromic PLA blends for the first time to improve their properties. The crystallization and melting behavior, morphology, and photochromic performance of PLA/PVAc/PM blends were characterized by differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and spectrophotometer, respectively. The results showed that PVAc significantly improved the photochromic properties of PLA/PM blends. Under 30 s UV irradiation, the blends reached a value of ΔE that could be recognized in 3 s by human eyes. This discriminative ΔE value could be maintained for at least 3 min after removal from UV irradiation. Meanwhile, the blend had outstanding photochromic durability and recyclability. Compared to ΔE for 0.5 h of continuous light irradiation, ΔE for 8 h of continuous light irradiation decreased by only about 1, to 14.1. In 25 cycles of 3 s UV irradiation, the values of ΔE for the first and 25th irradiation were 11.4 and 11.6, respectively. The blend showed different photochromic responses to different light intensities. The ΔE values of 8.6, 14.6, 14.6, and 18.4 for irradiation at 600, 800, 1000, and 1200 W/m2 of solar intensity, respectively.

Influence of Photochromic Microcapsules on Properties of Waterborne Coating on Wood and Metal Substrates

With the development of the economy and science and technology, consumers have put forward higher requirements for the functionality of surface coatings on wood products and metal products, which requires us to endow traditional coatings with new functions. Innovative research of coatings has been a research hotspot in recent years, and the combination of microencapsulation technology with coatings is a research direction attracting much attention. In this paper, a kind of spirooxazine color-changing microcapsules containing photochromic purple dye was selected to explore the effect of different loadings of the photochromic microcapsules on the properties of the coatings. The photochromic microcapsules were added to the waterborne coating with loadings of 5.0%, 10.0%, 15.0%, 20.0% and 25.0%. The coatings were coated on Tilia europaea boards and aluminum alloy plates to explore the optical properties, mechanical properties, cold liquid resistance and aging resistance of the coatings. The results showed that the coating had good photochromic property on wood substrate and metal substrate. When the loading was 15.0% and 10.0%, the comprehensive performance of the coating was good. The color difference of the coating before and after photochromism was 51.0 and 62.0, the glossiness was 7.1% and 15.9%, the hardness was 3H, the adhesion grade was 1, the impact resistance was 4 kg·cm, the roughness was 1.2 μm and 0.9 μm and the liquid resistance grade was 1. The research results show that the photochromic microcapsule can endow the paint with a reversible color change function and improve some mechanical properties of the coating, which indicates that the composite prepared in this study can be used in the surface finishing of wood and metal and has certain research value and application potential.

Effect of Thermochromic and Photochromic Microcapsules on the Surface Coating Properties for Metal Substrates

A coating with thermochromic and photochromic microcapsules can enhance a product’s attractiveness. Different coating processes may affect the performance of coatings. Therefore, the micromorphology, chemical composition, chromatic difference, gloss, hardness, adhesion, impact resistance, roughness, cold liquid resistance, and ultraviolet photooxidation resistance of the surface coating on the metal substrate were assessed by choosing three coating processes. The thermochromic color difference of the coating with photochromic microcapsules in the primer and thermochromic microcapsules in the topcoat changes greatly. When the temperature reached 80 °C, the maximum color difference of the coating was found to be 23.0. The color difference of the coating with the thermochromic microcapsules in the primer and photochromic microcapsules in the topcoat was the most obvious, with a color difference of 71.7. The gloss of the coating mixed with thermochromic microcapsules and photochromic microcapsules was the highest, which was found to be 81.7 GU. The coating gloss of thermochromic microcapsules in the primer and photochromic microcapsules in the topcoat was found to be 15.6. The mechanical property of the coating mixed with thermochromic microcapsules and photochromic microcapsules was the best—the hardness was found to be 2H, the adhesion was found to be level 1, and the impact resistance was found to be 12.5 kg·cm. The mechanical property of the coating prepared by the other two coating sequences was poor. The coating prepared by the three finishing processes on the metal substrate had sufficient cold liquid resistance, and the gloss of the coating before and after the cold liquid resistance changed slightly. By studying the coating process of thermochromic coating and photochromic coating, a technical reference is provided for creating dual-function intelligent coatings.

Effect of Coating Process of Photochromic and Thermochromic Composite Microcapsules on Coating Properties for Basswood

In this paper, photochromic and thermochromic microcapsules were selected. There are three different coating processes: “the primer with the photochromic microcapsules, the topcoat with the thermochromic microcapsules”, “the primer with the thermochromic microcapsules, the topcoat with the photochromic microcapsules”, and “the photochromic and thermochromic microcapsules added into the primer and topcoats” to explore the color-changing effect of the coating on the surface of basswood (Tilia) and the comprehensive properties of the paint film. The optical properties, mechanical properties, cold liquid resistance, and aging resistance of the coating were mainly analyzed. It was concluded that the comprehensive performance of the coating was the best when thermochromic and photochromic microcapsules were mixed on the surface of basswood (Tilia). At a temperature of 80 °C, the color difference reached a maximum of 20.2, and the coating was completely discolored. The color difference of the coating after discoloration under visible light illumination was 56.9. The gloss under the angle of incidence at 60° was 37.4, hardness was 3H, adhesion grade was 1, impact resistance was 10.0 kg·cm, and cold liquid resistance grade was 1. The method of mixing the two microcapsules had better aging resistance. In this paper, the photochromic and thermochromic properties of the coating were studied, and the optimal discoloration of the surface coating of the basswood substrate was solved by different coating processes. This study provided a method for a coating to achieve both photochromic and thermochromic discoloration, broadening the application of discoloration coatings.

Cotton fabric containing photochromic microcapsules combined thermal energy storage features

Reversible photochromic microencapsulated phase change materials (RP-PCMs) not only possess color-changing performance under sunshine/UV, but also can adsorb, store or release amount of latent heat under certain temperature. A novel RP-PCMs were incorporated into cotton fabric by adopting the water-soluble polyurethane (WPU) as a medium. The combination of cotton fiber and RP-PCMs enabled cotton fiber with photochromic & thermo-regulated properties. Natural nontoxic biomaterial chitosan was selected as the raw material of RP-PCMs shell, providing favorable conditions for its further application in cotton fabric. Comprehensive analysis has shown that RP-PCMs was successfully integrated into cotton fabric. The thermal performance, thermal stability and thermo-regulated property of cotton fabric/WPU/RP-PCMs were systematically researched. Photochromic features were also investigated. The thermo-regulated property of cotton fabric/WPU/RP-PCMs was demonstrated through infrared camera indicating that the cotton fabric/WPU/RP-PCMs presented promising application in the flexible photochromic clothing field.

Rewritable Polymer Materials for Ultraviolet Laser Based on Photochromic Microcapsules

Rewritable Polymer Materials for Ultraviolet Laser Based on Photochromic Microcapsules

Photochromic Microcapsules for Textile Materials by Spray Drying—Part 3: Application of Photochromic Microcapsules on Cotton Fabrics

Photochromic textiles, a class of functional textiles, have a color build up feature under ultraviolet light irradiation. However, photochromic dye application onto textile materials by conventional finishing techniques has difficulties due to their low water solubility and low affinity to the textile materials. Encapsulation technology could be used to overcome these problems in the production of photochromic textile materials. This article, which is the third in a three-part series, deals with the application of photochromic dye microcapsules produced by a spray drying method onto cotton fabrics. The photochromic dye microcapsules were applied onto cotton fabrics by a pad–dry–cure process. Color build up and ultraviolet transmittance of the resultant photochromic fabrics were evaluated after the application and consecutive washing. Moreover, the fatigue resistance of the photochromic fabrics was studied and the effects of the incorporation of hindered amine light stabilizers into microcapsules were investigated. Ultraviolet protection factor values of the samples were found to be 50+ even after 20 washing cycles. It was shown that the photochromic fabrics have a loss of 10% in ultraviolet protection factor values and 20% in color values after 20 ultraviolet irradiation cycles and the fatigue resistance of the photochromic dye capsules improved with the use of hindered amine light stabilizer compounds during microcapsule production.

Photochromic Microcapsules for Textile Materials by Spray Drying: Part 2—Exergy Analysis of Spray Drying Process

In this study, the second part of a three-part series, exergy analysis of microencapsulation of photochromic dyes by the spray drying method was investigated. Since the spray dryers are thermal systems, energetic examination of the system components is an important issue for sustainable production with high efficiency. Exergy analysis is an important tool used in recent years for the analysis, design, and performance evaluation of thermal systems. The spray drying process was investigated considering two subsystems: the heater and the dryer sections. An exergy model for the process of encapsulation of spirooxazine-based photochromic dye with ethyl cellulose by the spray drying method was proposed. The highest exergy efficiency was achieved at a drying temperature of 120 °C and using an aqueous system as the solvent.

Photochromic Microcapsules for Textile Materials by Spray Drying—Part 1: Production and Characterization of Photochromic Microcapsules

This study, which is the first in a three-part series, deals with the encapsulation of photochromic dyes by spray drying. An aqueous ethyl cellulose dispersion and a spirooxazine-based photochromic dye were used as a shell and core material, respectively. The effects of main encapsulation parameters, such as solvent type, inlet temperature, feed rate, solid content, and aspirator rate were investigated. The encapsulation results were evaluated by scanning electron microscopy (SEM) images, particle size measurements, thermogravimetric analysis (TGA) and X-ray diffraction (XRD). The microcapsules obtained from a water-ethanol mixture exhibited photochromic properties. For microcapsule production, the optimum feed rate, total solid content, and aspirator rate were determined. Capsule formation improved with increased inlet air temperature. Spray drying to produce photochromic microcapsules could be a practical method for production of photochromic smart textiles.

Microencapsulation of Photochromic Solution with Polyurea by Interfacial Polymerization.

Photochromic materials are interesting materials because of their color-changing property under UV light and visible light irradiation. However, they are vulnerable to many factors, such as pH oxygen, ion, solvent, etc. because of the unsaturated bonds existing on the photochromic molecular. Microencapsulation of the photochromic materials can separate them from the surroundings. Here, photochromic microcapsules using 3,3-Diphenyl-3H-naphtho[2,1-b] pyran (NP)/solution as core and polyurea as shell via interfacial polymerization were prepared, and bis(2,2,6,6-tetramethyl-4-piperidinyl)sebacate (HALS 770) was used as photostabilizer. Fourier transform infrared spectroscopy (FTIR), a laser particle size analyzer, a scanning electron microscope (SEM), a thermogravimetric analyzer and an ultraviolet-visible spectrophotometer were used for characterization. The results showed that the microcapsules had a uniform particle size of about 0.56 μm when the percentage of the oil phase (core) in the emulsion was less than 15%, the addition amount of the emulsifier was 0.4%, and the stirring rate was 1800 r/min. The microcapsules showed better performance in thermal stability when the core/shell ratio was 1:1. The photostabilizer had little impact on the color-changing property of the microcapsule, but it could protect the microcapsules from UV light radiation aging.

Reversible photochromic energy storage polyurea microcapsules via in-situ polymerization

In this study, reversible photochromic polyurea (PU) microcapsules had been innovatively designed and prepared by in-situ polymerization successfully, which exhibited good latent heat storage and release properties. For the microcapsules, butyl stearate containing photochromic dye (spirooxazine) was used as the core material and PU as the shell material. The surface morphology, melt crystallization, thermal cycling durability, thermal stability and mechanical properties of PU microcapsules were systematically investigated with field emission scanning electron microscope (FE-SEM), different scanning calorimetry (DSC), thermogravimetric (TG) and dynamic mechanical analysis (DMA). And the light-to-thermal conversion performance was studied under sun simulation system. The results showed that the microcapsules synthesized with F2850, a new lipophilic amine, had better morphologies and uniform particle size distribution. When the mass ratio of isophorone diisocyanate (IPDI) to F2850 was 1:2, the surface of the microcapsules was smooth and compact thus resulting in the microcapsules with the highest mechanical strength. In addition, the PU microcapsules exhibited high energy storage efficiency, excellent thermal stability and thermal cyclic durability. Finally, the reversible photochromic microcapsules also presented prominent light-to-thermal conversion properties. What’s more, the temperature of the reversible photochromic microcapsules was nearly 4.9 °C higher than that of microcapsules at the same irradiation time.

Photochromic microcapsules anchored on cotton fabric by layer-by-layer self-assembly method with erasable property

Photochromic materials have great potential applications in many fields due to their reversible color change under light irradiation. Herein, a novel photochromic cotton fabric with high fatigue resistance was creatively fabricated via a facile electrostatic layer-by-layer self-assembly technology of photochromic microcapsules and sodium alginate. Chitosan was used to encapsulate photochromic dyes to form microcapsules to improve fatigue resistance, meanwhile, as the wall material of microcapsules in weak acid environment can provide the positive charge needed for electrostatic layer-by-layer self-assembly process. After the anionic modification of cotton fabric to achieve negative charge, electrostatic layer-by-layer self-assembly was taken place between -NH3+ on the wall material of microcapsules and -COO− in sodium alginate under the condition of pH = 5. For clear characterization of the regular charge changes of fabric surface during the assembly process, the methylene blue (a kind of cationic dye) dyeing of cotton fabrics was carried out, the K/S and Lab value of the dyed fabric showed a regular “odd-even” oscillation. The assembled five-layer microcapsules fabric can change from colorless to purple rapidly within 12 s under UV light, and reversibly return to the original state under the irradiation of green light quickly in 90 s. It can maintain excellent reusability photochromic performance (94.65%) after more than 20 reversible color-changing cycles, implying the good reusability in erasable optical data storage. Furthermore, since the photochromic dyes can absorb UV light, the as-prepared photochromic cotton fabric has excellent UV protection properties.