Preparation And Modifications Of Structural Color Films Based On Polydopamine

Brilliant colors universally exist in the nature.Apart from the dyes and pigments that we are familiar with,there is also another kind of beautiful colors around us,which is called structural color.For example,the vivid colors showing on the wing of butterflies or plumage of birds usually belong to structural colors.Being different from the coloring mechanism of pigmentary colors,which is ascribed to the specific absorption and reflection of light by molecules,structural colors are derived from the interaction between the micro-/nanostructures of materials and light in the visible range.Currently,the main strategies to artificially fabricate structural color materials focus on the self-assembly of highly monodispersed colloidal microspheres,such as polystyrene(PS)and silica microspheres,which can act as building blocks assembling to structural color films with brilliant color in a self-driven manner.However,previous studies found that structural color films fabricated by colloid microspheres commonly demonstrate low color contrast,and their structural colors can only be observed under specific conditions,such as exposure to strong light or viewing with special angle.Moreover,structural color films fabricated by colloid microspheres are prone to crack after drying,because of the tensile stress produced in the assembly process of colloids.And the fracture performance of structural color films might prevent them from practical application in the area of color display.Further,it has been found that structural color films usually possess poor water-repellent ability,and they will lose their bright structural colors after being wetted by water.In order to address these problems,this work explores the methods to improve the color visibility,prohibit the generation of cracks and enhance the hydrophobicity of structural color films prepared by PS microspheres.(1)Introducing polydopamine(PDA),which acts as black light-absorbing matter,into the system of PS structural color films to substantially improve the contrast of structural colors and fabricate angle-independent structural color films.In the experiments,monodispersed PS microspheres with controlled sizes are first synthesized by an emulsifier-free emulsion polymerization method,followed by a surface modification process of dopamine to fabricate PS@PDA core-shell microspheres.Subsequently,PS@PDA structural color films are prepared by a thermal-assisted self-assembly method.The characterizations of scanning electron microscope(SEM),reflection spectra and optical images indicate that as-prepared PS@PDA structural color films have amorphous photonic structures and show highly enhanced color contrast and angle-independence.The trial results suggest that the PS@PDA structural color films present high color visibility and high reflectance when the mass ratio of added dopamine hydrochloride to PS microspheres lies in the range of 10 % to 30 %.(2)One kind of silane coupling agent – 3-aminopropyltriethoxysilane has been adopted as an additive to co-assemble with PS@PDA microspheres and fabricate crack-free structural color films.The characterizations of SEM,reflection spectra and optical images reveal that asprepared structural color films exhibit devoid of cracks,high color contrast and angleindependence.By varying the amount of dopamine hydrochloride and APTES during experiment,it indicates that as-prepared structural color films can show the optimal performance when the mass ratio of dopamine hydrochloride to PS microspheres is 50 % and the mass ratio of APTES to PS@PDA microspheres is 1 : 5.(3)Hydrophobicity enhanced structural color films have been fabricated by employing polydimethylsiloxane(PDMS)as modifier,which possess low surface energy,to improve the water-repellent ability of PS@PDA/APTES film.The characterizations of SEM and atomic force microscope(AFM)show that as-prepared structural color films apparently present hierarchical micro-/nanostructures,which means the surface of films have good roughness.In addition,the contact and slide angle measuring and the phenomenon of water droplet bouncing demonstrate that the PDMS-modified PS@PDA/APTES structural color films show excellent hydrophobic property,where the contact angle is 151°.It has been found that the hydrophobicity and color contrast of structural color films can arrive at an optimum condition when the mass concentration of PDMS-hexane solution is 1.5 %,under which the water contact angle of structural color films can reach 151° and the slide angle is 3.7°.