| As an electrochromic material,the liquid crystal(LC)has the advantages of full-spectrum tunable,reversible,and repeatable color-changing,low driving voltage,fast response rate,and precise controllability.Therefore,the preparation of the new generation of smart textiles through LC materials has broad development potential in application scenarios such as anti-counterfeiting detection,security monitoring,and clothing decoration.However,traditional liquid crystal displays(LCDs)are mostly rigid devices with conductive glass as the auxiliary base electrode,which cannot meet the requirements of smart textiles.In addition,there is no affinity between LC and fabric fibers.Besides,due to its fluidity,it is easy to bend and leak when combined with textiles,which greatly limits the further application of LC in textiles.Therefore,the sandwich structure of the LCDs is constructed through a specific packaging technology,the discoloration mechanism of LC packaging was also been studied,and the electrochromic response sensitivity and display contrast of the packaged LC are improved,which promoted the development and application of the consumable flexible electrochromic LC textile devices.This paper firstly prepared a monochromatic electrochromic LC microcapsule-coated fabric by microencapsulating dye-doped liquid crystal(DDLC)and adjusting its morphological structure and optoelectronic properties;Then,multi-colorful color-changing electrochromic DDLC microcapsules was synthesized by seed emulsion polymerization;Further,multiband electro-optically modulated LC microcapsules are synthesized,and multi-spectral tunable non-woven fabrics were also prepared by electrospinning technology;In addition,the phase change materials(PCMs)was used to improve the confinement anchoring effect,and DDLC-microcapsules/calcium-alginate-based fibers with bistable electrochromic properties were also prepared;Finally,composite two-dimensional nanosheets and cholesteric liquid crystal(CLC)microcapsules to prepare multi-stimuli-responsive color-changing LC fabrics,which provided a theoretical and practical basis for the continuous production of large-area LC fabrics.The main work is as follows:(1)DDLC microcapsules were prepared by emulsion polymerization,and the morphology and structure of the DDLC microcapsules were effectively controlled.The results show that DDLC microcapsules have a regular spherical and core-shell structure.The microcapsules show bright red under natural light and have a birefringence effect under polarized light.The loading of the core material is about 70%,and the clearing point of the core material is about 59.8 ~oC;the microencapsulation is beneficial to delay the phase separation behavior of DDLC,thereby improving its service life(>96h);The driving voltage of DDLC microcapsules increases with the particle size of the microcapsules and the thickness of the shell layer increased.The optimized DDLC microcapsules were coated on conductive fabrics,and the optical appearance of the device can be reversibly transformed between red and colorless under the stimulation of DC power.When DDLC microcapsules are 30μm,the driving voltage is about 4.5 V,which can be used for flexible LCDs.(2)Based on the cloud point effect of the non-ionic surfactant Brij-35,the temperature of the reaction system was adjusted to change the hydrophilic-lipophilic properties of the surface of the seed microcapsules,and the outer DDLC layer was induced to adsorb on the surface of the inner seed microcapsules.Then the multicolor electrochromic DDLC microcapsules were prepared by seed emulsion polymerization.The prepared microcapsules with yolk-shell structure and 12μm particle size and has good monodispersity;as the electric field increases from 0 V to 4.8 V,the microcapsules show blue,blue-purple,red,light red,colorless multicolor electrochromic process,the driving voltage is about 4.8 V.The multicolor electrochromic LC fibers were prepared by compounding the microcapsule with calcium alginate via wet spinning technology.Besides,the maximum driving voltage(9.0 V)of fiber is lower than the human safety voltage with good cycle stability(>50 times),which shows its potential application value in wearable electrochromic textiles.(3)Electro-responsive multispectral controllable LC microcapsules were prepared by seed emulsion polymerization by introducing magnetic seeds with excellent electromagnetic wave absorption properties.The prepared LC microcapsules with a yolk-shell structure have a 2.377μm particle size and 51.69%core DDLC loading.The introduction of magnetic seeds weakens the light scattering phenomenon of DDLC and endure the color enhancement effect.In addition,the microcapsules exhibited reversible electrochromic ability from dark red to dark gray,and the driving voltage,response time,and relaxation time were 9.3 V,62 s,and 32 s,respectively.The electro-responsive multispectral controllable non-woven fabric was also prepared by encapsulating LC microcapsules in the polyvinylpyrrolidone nanofiber via electrospinning technology.The reflectivity in the near-infrared spectral region(wavelength 1300-1500 nm and1800-2100 nm)of fabric can be modulated.In addition,it also exhibits good electromagnetic wave absorption ability(waveband 2～18GHz).(4)A novel polymer microcapsule-filled DDLC and PCMs system inspired by biological was first proposed,which were further encapsulated into the calcium-alginate substrate by wet spinning for making an electrochromic fiber with both bistable electric-optical capability and knitting characteristics.Results show that the optical appearance of the optimized microcapsules and fiber can be reversibly changed between colored and colorless states according to the electric field by switching the DDLCs between isotropic(I)and anisotropic(A)states.Moreover,both I and A states can be stable for more than one week after removing the electric field,due to the synergy of the greatly increased spatial hindrance of PCMs with core loading of 22.58%and the confinement effect from the polymer microcapsules shell material.Aside from the long-term optical stability,the high content of the densely packed DDLCs also endows the electrochromic fiber with a satisfactory driving voltage of 9.7 V which is below the human safe voltage,showing great potential applications in a wide range of uses,such as flexible displays,energy-saving smart windows,and wearable advance textiles.(5)Using polydopamine-modified cotton fabric as the substrate,a two-dimensional titanium carbide nanosheet(MXene)layer as the multi-stimulus-conversion-thermal layer,and CLC microcapsules as the thermochromic layer,thereby an integrated multi-stimuli-responsive chromism liquid crystal functionalized(MCLCF)fabrics were prepared.The results show that the MCLCF fabric retains the excellent flexibility of ordinary fabrics.The introduction of the MXene layer and microcapsule technology also endows it with color enhancement effect and angle-independent properties.Thus the MCLCF fabric show multi-stimuli-responsive color-changing properties to temperature(26.5-29.5 ~oC,50%of the CIE1931 color gamut),electric field(which can quickly change color when the driving voltage is 4 V with the 1.3s response time;and the steady color rendering within the driving voltage range of 2.0 V to 3.3 V with>60s steady time),near-infrared(light intensity 100W,illumination distance 30 cm,and response time 0.9s),and simulated sunlight(irradiation intensity 1000 W/cm~2,response time 3.5s),which is available broad application prospects in the field of wearable flexible display and wearable sensing.In conclusion,a variety of electro-responsive LC textile materials were designed and fabricated in this paper.From single color change to multicolor color change to multi-spectral tunable,from monostable color change to bi-stable display,from traditional rigid sandwich structure to flexible fabric structure without external electrodes,and from one-dimensional small-sized fibers to two-dimensional large-area fabrics,to construct a multi-level electrical-responsive textile with bright colors,low driving voltage and high response sensitivity,which provides opinions for the development of LC applications in the textile field,and presents its industrial application prospects. |
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