Rapid Preparation Of Liquid Photonic Crystals And Their Application In Structural Coloration Of Textiles

Bionic structural coloration is a physical coloration technology,which could produce rich colors without using chemical colorants(dyes/pigments).Self-assembling colloidal nanospheres to form photonic crystals(PCs)on textile substrates is considered to be the simplest and most convenient way to realize the bionic structural color,ensuring controllable assembly process and easy access to long-range ordered structures at the low requirements for equipment.However,the conventional self-assembly process needs to undergo complex crystal nucleation and crystal growth,which usually takes more than several hours and it is difficult to realize the rapid construction of PC structure.Liquid photonic crystals(LPCs)is a kind of pre-crystallized PC with liquid(usually water)as the filling medium.Due to the fluidity and dynamic reversibility,LPCs can be applied onto the textile substrate through the shear-induced self-assembly under an external force and quickly reconstructed,which can realize the rapid preparation of large-area structural color PCs on the textile substrate.However,the preparation process of LPCs themselves is usually time-consuming and difficult to control,which greatly limits the practical application of LPCs in rapid and large-area preparation of structural color textiles.Aiming at the preparation efficiency of the above LPC and the stability of the PC structure,this work mainly studies the following three aspects:(1)The physical rotary evaporation/surfactant method was established to efficient prepare high quality fractional LPCs.The mechanism of action of surfactants in rotary evaporation system and the formation mechanism of LPCs were explored,and then the optical properties and dynamic reversibility of LPCs were studied.(2)LPCs were directly prepared by chemical polymerization.The high quality(40 wt%)PS nanosphere dispersion solution was prepared by direct synthesis method.The internal causes and key influencing factors of system instability in the polymerization process were observed and analyzed,and the effects of p H regulator,polymerization temperature and emulsifier on the polymerization reaction were studied.After dialysis,the LPC with pre-crystallization form was formed.The changes before and after dialysis and purification of nanosphere dispersion solution were studied,and the formation mechanism of LPC was studied.Then the optical properties of LPCs and self-assembled PCs were studied.At last,the direct chemical synthesis method and physical rotary evaporation/surfactant method were compared for the preparation of LPCs.(3)The assembly mechanism and conditions of LPC in the process of self-assembly were studied;The protective layer was prepared on the PC to achieve the unification of its structure stability and color saturation,the PC structural color fabric with both structural stability and color saturation was prepared.The large-area PC structural color fabric was prepared by external shear-induced technology,and the PC structural color fabric with iridescence effect was prepared by spraying method.The main research results are as follows:(1)30 wt%PS nanospheres dispersion solution with particle size ranging from 180nm to 320 nm was synthesized by emulsion polymerization.Then,the dispersion solution of 30 wt%PS nanospheres was concentrated by rotary evaporation.Through the synergistic effect of anionic/nonionic surfactants in the rotary evaporation process,the nanospheres were stably dispersed under the combined action of electrostatic repulsions and steric hindrance,which allowed one to effectively solve the problem of aggregation and sedimentation of the nanospheres with the increase of mass fraction.The low mass fraction monodisperse nanospheres emulsion could be rapidly made into a pre-crystallized LPC system in a short minute,and the mass fraction of nanospheres in the prepared LPC reached 55%.The optical properties of LPCs could be controlled by adjusting the mass fraction and particle size of nanospheres.The prepared LPCs exhibited excellent dynamic reversibility.Under the applied external force,the LPC disassembled and its structural color vanished.After the external force was removed,a pre-crystallized LPC was rapidly(in about 10 s)reconstructed,and its structural color was recovered,demonstrating the fast response performance of the LPC.(2)The key problems and internal reasons of unstable polymerization system in the process of preparing high quality fraction nanospheres dispersion solution by direct synthesis were investigated.The p H regulator was added in the process of emulsion polymerization so as to solve the problem of phase transformation caused by the thermal decomposition of initiator to produce hydrogen ions(H~+).This prevented the emulsifier from reducing emulsification ability at a low p H condition,directly achieving the high mass fraction(up to 40 wt%)of the PS nanospheres in the dispersion solution.The solution was then dialyzed to remove oligomers,small molecular salts and other substances in the system with the aim of purifying the colloidal system and improving the electrostatic repulsion potential between the nanospheres,and the nanocrystals spontaneously arrange and assemble to form the pre-crystallized LPC under the balance of van der Waals force and electrostatic repulsion force,which can meet the needs of transfer and reconstruction on the textile substrate.(3)The LPC is applied to the textile substrate to form the LPC film,which can quickly reconstruct and develop color.Because the LPC has a small amount of solvent,it can be quickly transformed into a solid PC film in 2 min.Using LPC as the assembly intermediate,the rapid and large-area preparation of the PC structural color fabric was realized,and the PC structural color fabric with iridescent effect was prepared by combining with spraying method.The prepared PC structural color film presents different colors with the change of viewing angle,which shows unique iridescent effect.Through the encapsulation of PC layer with polymer encapsulation agent,the PC structure can be improved to withstand external forces(bending,rubbing,washing,etc.),so as to significantly improve the stability of the PC structure,and can retain the refractive index difference inside the PC,present a higher brightness structural color,and achieve the high stability and high saturation consistency of the PC structural color fabrics.