Fabrication And Hydrophobic Modification Of PS@PDA/CS Functional Structural Color Coatings

In traditional color materials,the aging and depigmentation of the chemical dyes and pigments have always been an issue for traditional color displaying.For example,murals fade and fall off after prolonged exposure.Inspired by nature,researchers found that colors of some nature creatures were generated from their own micro/nanostructures which could maintain the beautiful colors unchanged for years.The color,which is attributed to the specific absorption and reflection of light by micro/nanostructures,is named as structural color.Owing to their unique performances on anti-fade,structural colors exhibit enormous potential applications in many fields especially in color-related fields.The non-iridescent structural colors are usually constructed by long-range disordered and/or short-range ordered amorphous photonic structures featuring angle-independent characteristic.However,the amorphous structures have vital incoherent scattering impact on light,which leading to the structural color is whitish and at low color saturation.Besides,the structural colors are very fragile and feeble mechanically stable due to the weak interaction between the colloidal particles in traditional threedimensional photonic crystals structures.It hinders the practical applications of structural color materials.In addition,structural color will fade when it is wetted by water,which limits the application of structural color.In order to solve these problems of structural color materials,this paper explores the method of improve the color saturation,mechanical stability and hydrophobicity of structural color coatings.(1)At first,monodispersed PS nanoparticles with controlled sizes are made by an emulsifier-free emulsion polymerization method and the size of PS nanoparticles are 158 nm,201 nm and 247 nm.And then monodispersed PS@PDA nanoparticles with the size of 179 nm,223 nm and 260 nm are prepared by PS colloidal nanoparticles coated polydopamine(PS@PDA),which polydopamine(PDA)acts as black light-absorbing matter.PS@PDA nanoparticles are prepared as self-assembled structural units for structural color coatings.(2)The chitosan(CS)co-assembles with PS@PDA nanoparticles and fabricates the robust functional structural color coatings.The introduction of CS into the PS@PDA nanoparticles assembly system not only exhibits angle-independent structural color but also greatly restrains the generation of cracks and enhances the mechanical stability of the structural color coatings.That are proved by the characterizations of scanning electron microscope(SEM),reflection spectra and optical images,etc.By investigating the effect of the mass ratio between CS and PS@PDA nanoparticles on the performance of structural color coatings,the optimal mass ratio of CS to PS@PDA nanoparticles is 1.0:10.And the as-prepared functional photonic coatings exhibit crack-free gorgeous structural colors with a good mechanical stability,which can be resisted 300 times finger wiping test and 90 min ultrasonic treatment.On the one hand,the PS@PDA/CS functional coatings can apply on smooth hard substrates.The adhesion stress of structural color coatings is of 2.42 MPa on the glass,0.74 MPa on the PVC,3.63 MPa on the stainless-steel plate and 4.13 MPa on the tile.On the other hand,the functional structural color coatings can be coated on flexible cotton fabrics.The non-iridescent structural color coatings on cotton fabrics show strong mechanical stability and good color saturation after 2 times folding,15 times rubbing and 15 min simulated washing tests(3)In order to enhance the water-repellent ability of PS@PDA/CS functional coatings,the hydrophobic non-iridescent structural color coatings are fabricated by employing monohydroxyl-terminated poly-(dimethylsiloxane)(PDMS)and hexamethylene diisocyanate trimer(HDIT).The characterizations of SEM and atom force microscope(AFM)indicate that the surface of the functional coatings have good roughness,which is 447 nm.The effect of different concentrations of PDMS on the performance of functional structural color coatings has been investigated.When the concentration of PDMS is 2 wt%,the hydrophobicity of functional structural color coatings is the best and the contact angle is 142°.At the same time,the functional coatings still keep a good color visibility.It is proved by the characterizations of contact angle measuring,SEM,reflection spectra and optical images,etc.