Abstract:

Objective Photonic crystals (PCs) are composed of different dielectric constant materials in a periodic arrangement possessing a photonic band gap (PBG) that blocks the propagation of electromagnetic waves with certain wavelengths. If the wavelength of the blocked electromagnetic waves is in the visible light range, it forms a structural color. At present, it is difficult to fabricate continuously PCs coated fabrics with structural color in a large area, and it is difficult to balance the structural stability and optical properties of PCs, limiting the practice application of PCs in textile coloring field.

Method A PCs-coated fabric was designed, achieving the rapid and continuous preparation of PCs with high structural stability and high color saturation on the fabric surface. Structural colored fabric was composed of a fabric substrate, a polymer layer and a PC layer. Liquid photonic crystal (LPC) with precrystallized structure was rapidly prepared by the rotary evaporation method, which was used as the working liquid for assembly. The surface of the fabric was coated with special polymer-L slurry with a scraper, and dried at 80 ℃ for 3 min and 120 ℃ for 1 min to form a flat polymer-L film on the surface of the fabric. The LPC was coated on the surface of the fabric pretreated by polymer-L with 20 μm filament rods, and then assembled at 60 ℃ for 5 min to obtain the PCs-coated fabric. Based on the assembly process and method of PCs, a pilot equipment for continuous fabrication of structural colored fabric is designed accordingly.

Results LPCs were prepared by means of physical distillation and concentration to increase the volume fraction of nanospheres in colloidal system. By introducing dispersant-3B into the polystyrene (PS) nanospheres system, the problem of microspheres condensation during the process of spin evaporation was effectively solved. With the increase of dispersant-3B, the structural color brightness of LPC increased. When the dosage of dispersant was 1.5%, the structure color of the dispersion solution was not obvious (Fig.3). In addition, the results showed that the prepared LPC with excellent dynamic recovery exhibited bright structural color, and its optical properties were regulated by the volume fraction and particle size of the nanospheres (Fig.4). When subjected to external disturbance, the LPC was disassembled, and the structural color disappeared. After the external force was released, the LPC with precrystallized structure was rapidly reconstructed and restored, and the structural color was reproduced (completed within 10 s) (Fig.5). LPC was applied to the fabric surface with polymer coating by shear induction of external force, and the LPC was reconstructed and colored quickly (within 1 min) (Fig.8). After proper heating post-treatment (60 ℃, 5 min), as the water in the LPC continued to evaporate, the lattice spacing of the PC was decreased, but the structure color blue-shifts and the brightness of LPC showed significant increased. With the complete evaporation of water, the solid PC was formed. The interfacial molecules of the polymer layer migrate to the interior of PC, stabilizing the structure of color layer of the PC on fabric surface (Fig.9 and Fig.10). Using LPC as the assembly intermediate and self-developed pilot equipment, the rapid and continuous preparation of structurally colored fabrics was achieved (Fig.12).

Conclusion The proposed preparation method of the PC-coated fabric demonstrated the advantages of simple operation and obvious effect. LPC with pre-crystallized structure and excellent dynamic recovery can be prepared rapidly and macroscopically by spinning evaporation. The special dispersant-3B introduced in the process of spin evaporation plays a synergistic role with SDS anionic surfactant in the system, significantly improves the steric hindrance and charge effect between the nanospheres, illustrating the resistance to the condensation of the microspheres. By pretreating the surface of textile substrate with special polymer, the PC layer is stabilized by utilizing the relaxation, activation, diffusion and recuring properties of interfacial polymer molecule, and the consistency of high structure stability and high color saturation of PCs-coated fabric can be achieved. Using LPC as the assembly working liquid, combined with the external force induced self-assembly method and the corresponding continuous processing equipment, the rapid large-scale continuous preparation of the PC-coated fabric with a fascinating iridescent effect can be achieved.

Key words: liquid photonic crystal, structural colored fabric, stability, textile substrate, whirling process