Study On The Stability And Rapid Large-scale Assembly Of Photonic Crystals With Structural Color On Flexible Textile Substrates

Textile coloration is traditionally achieved by means of using chemical colorants such as dyes and pigments.In contrast,photonic crystals(PCs)rely on their periodic microstructures to confine and control the propagation of electromagnetic waves in specific wavelength ranges to produce structural colors,then realizing the brilliant structural coloration of textiles.Using monodisperse nanospheres as the building blocks to construct PCs on fabric substrates by colloidal self-assembly is an effective approach for the eco-friendly coloration of textiles.However,the structural stability of the assembled PCs is usually poor due to the weak connection forces,such as hydrogen bonds and van der Waals forces,existed between the adjacent nanospheres.A direct filling or encapsulating with a flexible polymer matrix can effectively improve the stability of the PCs,but it usually results in a decrease in the saturation of the structural color,making a conflict situation between structural stability and color saturation.On the other hand,the self-assembly process of colloidal nanospheres is usually complicated and time-consuming,making it difficult to realize the large-scale assembly.The above issues have greatly limited the practical applications of PCs with structural color in the fields of eco-friendly coloration of textiles.To address the above-mentioned problems in the structural stability and assembly efficiency of PCs,this study focused on the following four areas of research work:(1)The stable SiO₂/P(MMA-BA)composite PCs were constructed by the co-deposition self-assembly of rigid nanospheres(SiO₂)and soft nanoparticles(P(MMA-BA)).The co-deposition self-assembly process and mechanisms were intensively studied.The effects of the volume fraction and the size ratios of the two components on the structural stability and the optical properties were investigated.Besides,this strategy was also extended to the SiO₂ amorphous PC system and the polystyrene(PS)nanospheres PC system.(2)A particular H-SiO₂/PUA inverse opal PCs with H-SiO₂nanospheres as the building blocks and flexible polymer PUA as the skeleton was designed and prepared.Moreover,the regulation mechanisms of the optical properties of the inverse opal PCs and the relationships between the structural elements and the high color saturation were intensively researched.(3)Per-crystallized PS liquid photonic crystals(LCCs)were prepared by concentrating the PS colloidal into a high volume fraction.Also,the optical properties and structural characteristics of LCCs at different volume fractions were analyzed,and the crystallization mechanisms of nanospheres in colloids at high volume fractions were explained by theoretical calculation.(4)A shear-induced assembly technique based on LCCs was developed,and its assembly process,assembly mechanism and assembly conditions were studied.In addition,the effective method for ultrafast and large-scale assembly of PCs on textile substrates was established.Meanwhile,we proposed an effective strategy for patterning the photonic crystal structural colors based on the wettability difference of substrates and explored the patterning effects and mechanisms.The main research results are as follows:1.Monodisperse SiO₂ nanospheres with particle sizes in the range of 170?350 nm were prepared by the St?ber method,while soft P(MMA-BA)latex nanoparticles with particle sizes in the range of 40?140 nm were synthesized by emulsion polymerization.During the co-deposition assembly process of rigid SiO₂ nanospheres and soft P(MMA-BA)nanoparticles,the P(MMA-BA)spheres are confined in the interstices of the crystallizing SiO₂ nanospheres and eventually fused to form a"point-point"physical bonding between the fibers and SiO₂ nanospheres and among the SiO₂ nanospheres,which effectively improved the structural stability of the assembled SiO₂/P(MMA-BA)composite PCs.The structural stability of the PCs increases as the volume ratio of P(MMA-BA)in the system increases,while the saturation of the structural color then decreases.Meanwhile,the smaller the particle sizes of P(MMA-BA)in the system,the smaller the perturbation for the assembly of SiO₂ nanospheres,which is more conducive to forming regular and ordered PCs.The optimized volume ratio and P(MMA-BA)size were 100:1 and 45 nm,respectively.This structural stability strategy was also applicable to the SiO₂ amorphous PC system and the PS nanospheres PC system,showing good generalizability.When this strategy was applied to the photonic structures constructed by SiO₂ nanospheres with low energy surfaces,both mechanical stability and immersion stability can be realized.2.The hollow silica/polyurethane acrylate(H-SiO₂/PUA)inverse opal photonic crystal structure(IOPCs)was prepared by encapsulating H-SiO₂ PCs with a flexible polymer PUA matrix.The periodic air array inside the H-SiO₂/PUA IOPCs forms a high refractive index contrast between the air core and the SiO₂/PUA composite skeleton,making the structure with strong band gap intensity,ensuring the achievement of high color saturation.Meanwhile,the continuous flexible structure formed by PUA polymer encapsulation,ensuring the resultant SiO₂/PUA IOPCs with good flexibility and tough mechanical strength.Finally,high structural stability and high color saturation of the structural color PCs were compatibilities achieved on textile substrates.Besides,the IOPCs can also be patterned by selective local curing using polymerizable PUA precursors as inks for direct writing.3.The macro preparation of PS nanospheres was achieved by an optimized emulsion polymerization method.The concentration of the produced PS colloids allowed the spontaneous crystallization of PS nanospheres at high volume fractions to form pre-crystallized liquid photonic crystal structures(LCCs).With the increase of the volume fraction of nanospheres in the colloid,the colloid system transforms from an amorphous state to a crystalline state,and the crystallization region then gradually increases,and the structural color brightness increases.Simultaneously,the spacing between nanospheres in the crystalline decreases and the structural color gradually shifts blue.Theoretical calculations show that the colloidal nanospheres have a higher potential energy barrier at high volume fractions to overcome the interference of solvent thermal motion,and the Brownian motion is gradually restricted,thus forming a stable and ordered arrangement structure.Meanwhile,the LCCs have excellent recovery ability,enabling them to easily disassemble upon disturbance and then reassemble into crystals when the disturbance is removed.4.During the shear-induced assembly process,bulked LCCs were reconstructed to form an LCCs film on the surface of the substrate under the action of shear force.Then,with the evaporation of the solvent in the lattice,the structure undergoes two-stage blue-shift processes and finally transformed from the non-close packed arrangement into a highly ordered close-packed solid PCs.The assembly process of the well-ordered PCs can be rapidly completed within 2 min,and large scale PCs can be fabricated using conventional dyeing and finishing equipment and coating methods,regardless of the size limitation.Moreover,by programming the wettability of the fabric substrate with a hydrophilic-hydrophobic pattern,the PCs can be restrict assembled in the hydrophilic region,thus enabling the fabrication of multiple brilliant structural color patterns.