Preparation And Properties Of Thermochromic Capsules Based On Electronic Delocalization Effect

Smart materials with thermal response mainly include thermochromic materials,thermofluorescent materials and thermoresponsive polymer materials.Thermochromic materials have vivid colors,and can indicate the change of surface temperature as well as temperature distribution by color change.When thermochromic materials are applied to fabric,fabric will display thermochromic performances,realizing the real-time monitoring of the temperature,integrating functionality and aesthetics.It is also a great advance in wearable functional textiles.Thermochromic materials are sensitive to environmental stimuli,which need to be encapsulated to avoid the environmental stimuli such as pH,solvent,light and so on,ensuring the good thermochromism and last application.At present,the thermochromic textiles are mainly obtained by coating capsules onto the fabric,due to the lack of reactive group between the capsules and fabric.The thermochromic textiles usually have problems such as aldehyde content,poor hand feel and reduced sensitivity.The energy storage function of thermochromic capsule in the process of discoloration has been reported a lot,but it can not work in coordination with thermochromic performance.In addition,the discoloration response of the thermochromic capsule in a single visible light band not only reduces the brightness of the discoloration,but also limits the function of thermochromism.Therefore,the development of reactable multi-band thermochromic capsules and design capsules with synergistic thermochromism and energy storage functions have become urgent issues.The thermochromic capsule modified by epoxy group was prepared by hydrolysis polycondensation reaction between siloxane group of silane coupling agent and hydroxyl group on the surface of thermochromic capsule.The epoxy group on the surface of the thermochromic capsule can react with the hydroxyl group on the cotton fabric and form a covalent bond,which gave the cotton fabric durable color and thermochromic property.The temperature-responsive discoloration performance of thermochromic capsules,the mechanism of coloring cotton fabrics,and the discoloration performance of thermochromic cotton fabrics were discussed.The chemical structure,morphology and thermal stability of the capsules and thermochromic cotton fabric were analyzed.Both of the modified thermochromic capsule and the thermochromic cotton fabric had good reversible thermochromic properties.When the temperature was higher than 45?,the capsules changed from blue to white,and when the temperature was lower than 45?,they would turn back to white.The color difference value was as high as 78 during heating-cooling progress.The reversible thermochromic effect reached 300?.The color fastness of the thermochromic cotton fabric was improved obviously.Among which,the washing fastness was up to 3-4,and the rubbing fastness was up to 4.Therefore,the preparation of reactive thermochromic capsules is an effective and simple method to obtain durable thermochromic textiles.Thermochromic capsule based on silica shell was prepared by sol-gel method using tetraethyl orthosilicate as shell material,crystal violet lactone,bisphenol A and hexadecanol as core materials.The thermochromic capsules had a particle size of 20-40 nm.The thermochromic mechanism of the capsule was studied by density functional theory,and its morphology,thermal stability and chemical structure were characterized.The thermal responsive color of the thermochromic capsule changed obviously,and the color change was sensitive and reversible.The color of the capsule changed to light blue?45??from dark blue?25??and finally became colorless?80??.When the temperature decreased,the color returned to dark blue.The color difference before and after the color change was as high as 30,which had better thermochromic effect.The thermal stability of the capsule was higher than130?.The thermochromic capsule was used to treat polyester fabric via high temperature and high pressure dyeing method.Compared with the morphology of the blank polyester fabric,the prepared thermochromic polyester fabric was dark blue,and there were a lot of capsules on the surface and gap of the fabric,meanwhile,the inner of dyed polyester fiber was also blue,indicating the thermochromic capsules had good coloring performance.The thermochromic polyester fabric not only had the same thermochromic property as the thermochromic capsule,but also had higher color fastness.Among them,both of the rubbing fastness and washing fastness were more than 4 grades.The results showed that the preparation of thermochromic capsules via sol-gel method broadened the way to prepare thermochromic fibers.Paraffin based phase change capsules were prepared by emulsion polymerization using glycidyl methacrylate,acrylic acid and styrene as reaction monomers and paraffin as phase change materials.By adjusting the mass ratio of core-shell materials,phase change capsules with an average particle size of about 400 nm,loading capacity of 90.7%,enthalpy of 118.7J/g and thermal stability of higher than 180?were obtained.The thermochromic silica nanoparticles with reactive amino groups were prepared through sol-gel method with 3-glycidyl ether propyl trimethoxysilane and tetraethyl orthosilicate as raw materials.Thermochromic silica nanoparticles were grafted on the surface of phase change capsules by the addition reaction between amino groups and epoxy groups to obtain temperature regulative thermochromic capsules,which had an average particle size of 450 nm.The morphology,thermal stability,thermal conductivity,color properties before and after heating and the changes of light absorption/reflection of temperature regulative thermochromic capsules were analyzed.By adjusting the load of thermochromic capsules,the synchronous response between the phase change temperature and thermochromic temperature of temperature regulative thermochromic capsules was realized.Temperature regulative thermochromic capsules have the ability to adjust temperature through color change.When the temperature was lower than the phase change temperature?46??,the color would be dark,which was conducive to improving solar energy absorption.When the temperature was higher than the phase change temperature?46??,the color would change from dark to white,which would increase the reflection of sunlight and reduce energy absorption,so as to prevent the temperature increase and maintain the temperature near the phase change point.Compared with the control sample,the thermochromic capsules showed a temperature adjustment of7?in the application of temperature regulation,showing excellent thermal regulation performance.The results showed that the thermochromic capsule was a kind of material which can adjust the heat energy intelligently and effectively,meanwhile,it was another function display of the thermochromic material except color indication.Rhodamine B was modified to obtain UV/visible dual band thermochromic material via the amidation reaction.UV/visible dual band thermochromic capsule was prepared by sol-gel method with silica as shell material,with an average particle size of about 35 nm.The fluorescent thermochromism of UV/visible dual band thermochromic materials in solution?liquid system?and long chain alcohol?solid system?were investigated.In solution,the fluorescence intensity rised with the increase of temperature.There was a reasonable linear relationship between temperature and fluorescence intensity in the temperature range of 37?to 45??R₂=0.9934?.At the same time,due to the electron transition to a higher level under the thermal excitation,the fluorescence intensity of the solution rised with the increase of temperature,showing the UV/visible dual band temperature response color change.In the solid system,when the temperature exceeded the melting point of long-chain alcohol,the thermochromic material changed from rose red to light yellow,the phosphor disappeared,and the average thermochromic response speed was 0.05 s^-1.The UV/visible dual band thermochromic capsule prepared with solid-state thermochromic system had good thermal stability,and its thermochromic performance was not affected by the encapsulation progress.With the increase of temperature,it changed from pink?25??to light yellow?higher than45??,and the fluorescence intensity decreased gradually.It showed that the thermochromic capsule had stable UV/visible dual band temperature response color change performance,which can indicate and monitor the temperature change in more special fields.A kind of thermochromic material with fluorescence enhanced function was designed and developed by the combination of bioindocyanoquinoxadione?IQA?organic dye molecules and long chain aliphatic alcohol.The enhanced fluorescent thermochromic material was microencapsulated by condensation polymerization of tetraethyl orthosilicate to obtain the purple powder thermochromic fluorescence enhanced UV/visible dual band response capsule.The size of the capsule was between 10 nm and 30 nm,and its thermal stability was over 140?.After heating,the capsule changed from dark purple?30??to orange red?higher than 45??under visible light.Under ultraviolet light?365 nm?,the capsule changed from non-fluorescence state?30??to strong golden fluorescence?higher than 45??.The thermochromic finishing of polyester fabric was executed through high temperature and high pressure dyeing.The thermochromic property of the capsule was retained after dyeing.The mechanism of thermochromism and fluorescence enhancement of the capsule were studied,meanwhile,the temperature-color change and reversibility were monitored.Both capsules and dyed fabrics showed clear reversible color change,rare fluorescence state change with high contrast in a real-time response to the change of external environment temperature.After heating,it changed from dark purple?30??to orange red?higher than 45??under visible light,and changed from non-fluorescent state?30??to strong golden yellow fluorescence?higher than 45??under ultraviolet light?365 nm?.The transition temperature of the dye system also can be controlled by choosing different melting point fatty alcohol solvent.