Development of structural-coloured textile materials via self-assembly of photonic crystals

Abstract

Structural colour derived from physical interactions of photons upon periodically arranged nanostructures with the specific chromatic mechanisms that is not achievable with those traditional dyes and pigments, has attracted great scientific interests in recent years by virtue of its superior fadeless, dye-free, colour tunable characteristics. Patterning of colloidal phonic crystals or colloidal amorphous arrays based on self-assembly of colloidal inorganic or polymer nanoparticles has been intensively investigated in recent years, and it has been widely accepted that those colloidal nanoparticles and its functionalised derivatives are good candidates to be utilised to form the building blocks for generating structural colours. However, the facile construction of periodic colloidal arrays that exhibiting brilliant structural colours with good mechanical robustness still need to be further studied. In this study, silica (SiO2) and poly(styrene-methyl methacrylate-acrylic acid) (Poly(St-MMA-AA) nanoparticles were synthesised with controllable sizes and were utilised as the building blocks to construct both photonic crystals and colloidal amorphous arrays with the enhancement of structural colours on glasses, fabrics or nonwoven substrates to further investigate the potential practical applications in smart displays, paintings and related optical fields. To investigate the enhancement of structural colours, the scattered light absorbers like graphene oxide (GO) was employed as the dopants into colloidal nanoparticle suspensions to establish photonic crystal films (PCFs) with colour-strengthened property by drop-coating method. SiO2 NPs has been successfully synthesised based on the Stöber method with a range of particle sizes by adjusting the amounts of variates including ammonia water (NH3·H2O), denionised water (H2O), tetraethyl orthosilicate (TEOS) and ethanol (EtOH) during the synthesis process. From SEM observation, SiO2 PCFs with spherical shapes of SiO2 NPs as well as the face-centred cubic (fcc) nanostructures were confirmed, and the optical reflectance result shows that 0.05% of GO tends to be the optimum weight percent with lowest reflectance intensity and achieves broadening of reflectance wavelength peak. Since the non-iridescent structural colours arising from amorphous photonic nanostructures possessing short-range ordered arrangement based on the incoherent light scattering have drawn great considerable attention, we presented novel structural­coloured photonic SiO2 spray paints (PSPs) on Kraft paper substrates with nonwoven structures by spray coating method that endows PSPs coated patterns with nearly angle-independent properties and non-iridescent structural colours. The experimental results showed that the angle-independent property of SiO2 PSPs coated patterns with four spraying layers with PolyU logos has been proved under different viewing angles of 30°, 45°, 60° and 90°. It is also noticeable that broader photonic band gap based on coherent reflection was yielded from photonic amorphous structures in short-range order of PSPs coated patterns by spray coating, substantially differing from the narrow one in photonic crystalline arrays of SiO2 PCFs. Since the structural stability of SiO2 photonic crystal or amorphous film is poor because of the high glass transition temperature (Tg) of SiO2 along with weak van der Waal's attraction among the SiO2 NPs, poly(methyl methacrylate-butyl acrylate) (PMB) as an additive was synthesised and embedded to fabricate robust PSPs coated patterns with abrasion resistance. It is worth nothing that the amorphous photonic structures possessing a strong incoherent light scattering in the visible light region result in whitish structural colours, in order to resolve this issue, black novel carbon-based materials GO and reduced graphene oxide (RGO) in nanometres with certain amounts have been added into SiO2 PSPs to suppress incoherent multiple scattering and improve the colour visibility. It has been also proved that pure SiO2 PSPs coated film was vulnerable to crack on a large scale, while the crack-free surface and continuity of amorphous structures about SiO2/PMB PSPs, SiO2/PMB/GO, SiO2/PMB/RGO PSPs coated films was convinced. In sandpaper abrasion test, the four-leaf clover patterns with the addition of PMB exhibited better abrasion repellence. PSPs coated structurally coloured materials with GO and RGO enhanced colours with excellent structural stability are expected to be desirable in broader applications in the fields of paintings, optical relative areas. Except for the addition of adhesive (PMB) to improve the structural stability of structural colours, introducing soft polymers into polymerisation process to synthesise core-shell nanoparticles with hard core and soft shell is another feasible and effective way. In our study, we proposed a structural-coloured Poly(St-MMA-AA) deposited carbon fabrics (Poly(St-MMA-AA)/PCFs) with good mechanical properties, electrical conductivity, thermal resistance and chemical stability that can be potentially used in traffic warning displays by thermal-assisted gravity sedimentation approach. Particle sizes of Poly(St-MMA-AA) copolymers with core/shell structures was controlled by the change of sodium dodecyl sulfate (SDS) emulsifier amount during emulsion polymerisation, subsequently resulting in the corresponding tunable structural colours. SEM results proved the core-shell structures with spherical shapes of Poly(St-MMA-AA) nanoparticles, the deformation shapes of Poly(St-MMA-AA) appeared when the peripheries of nanoparticles were conjoined with the adjacent particles under inter-particle interactions. The presence of the intrinsic chemical information with different characteristic peaks of Poly(St-MMA-AA) copolymer has been confirmed by Fourier Transform Infrared (FT-IR) and Raman spectrum observation. Colour difference of structurally coloured Poly(St-MMA-AA)/PCFs before and after dipping treatment were also observed under optical microscopy. The differential electrical property in electric resistivity between Poly(St-MMA-AA)/PCFs before and after dipping treatment provides Poly(St-MMA-AA)/PCFs more promising potentials to be applied in smart displays especially for traffic warning signals.