Assembly And Construction Of Stable Amorphous Colloid Arrays By Microfiltration Method And Its Performance Study

Amorphous colloid arrays(ACAs)exhibit angle-independent color structures due to their short-range ordered arrangement.Compared with traditional dyes and pigments,ACAs can show a broad application prospect in the field of color display because of their low toxicity and fading resistance.The process of infiltration-driven colloidal assembly is simple and flexible,which is very suitable for the design and preparation of amorphous colloid array patterns on paper materials.However,due to the weak interaction force between colloidal microspheres and between microspheres and paper materials,the mechanical stability of ACAs is poor.As a result,the ACAs are easy to be damaged by external forces,thereby losing the structure color.In this paper,a series of monodisperse polystyrene(PS)microspheres were prepared,and ACAs with different structural colors were assembled on paper by infiltration-driven colloidal assembly method.At the same time,the mechanical stability of the ACAs was improved by surface coating,co-assembly of microspheres and nanoparticles with small size,and design of core-shell microspheres.(1)Anionic and cationic monodisperse PS microspheres were prepared by soap-free emulsion polymerization.By adjusting the content of anionic emulsifier or cationic monomer,the size of the microspheres was well controlled,and a series of PS monodisperse microspheres with different sizes were then prepared.After the PS microspheres were assembled on the paper via infiltration-driven colloidal assembly method,the microspheres were arranged in a short range order.Accordingly,a series of ACAs with red,green or blue angle-independent structural color were obtained.On this basis,the ACAs were coated with polyacrylate(PA)emulsion and a continuous film was formed on the surface ACAs.The changes of structural color and mechanical stability before and after coating PA film were further studied.Results showed that the mechanical stability of ACAs was improved significantly after surface coating.Although the ACAs showed good tolerance to friction and ultrasonic washing,the structural color quality was declined markedly after surface coating.(2)Three kinds of cationic monodisperse PS microspheres of different sizes were selected and mixed with PA nanoparticles with small size,and then used to fabricate ACAs with blue,green or red structural colors via an infiltration-driven colloidal assembly process on paper.The effects of PA particle content(PA/PS=0/100,1/20,1/10,1/5,1/3 and 1/1)on the microstructure and structural color of the colloid array were systematically studied.As the content of PA nanoparticles increased,the adhesion phenomenon between microspheres became significantly,and hence the colloid array stability was enhanced;meanwhile,the reflection spectrum of colloid array exhibited a red shift,and the structural color quality was gradually declined.When PA/PS ratio was equal to 1/10 or 1/5,the array could still maintain good structural color;however,although the blue colloid array showed good friction tolerance,the green and red arrays could be destroyed after repeated friction.This might be attributed to the uneven distribution of PA nanoparticles,and the stratification of PA particles became significant with the increase of PS microsphere size.(3)Cationic monodisperse PS microspheres with different sizes were used as the core and butyl acrylate(BA)and methyl methacrylate(MMA)were used as the shell monomers.A series of core core-shell microspheres with soft shell and hard were prepared by seed emulsion polymerization.Effect of shell glass transition temperature(T_g)on the microstructure and structural color of the ACAs prepared by infiltration-driven colloidal assembly method was investigated in detail.When the T_gof shell was relatively low(<37 ~oC),the core-shell microspheres preferred to adhere with each other to form a continuous film during the assembly process.As a result,the refractive index contrast between the microsphere and the medium decreased,resulting in poor structural color quality.When the shell T_gwas relatively high(45-55 ~oC),the adhesion between microsphere shell was not obvious;accordingly,the structural color quality was good,but the mechanical stability was poor.However,when the microsphere shell was moderately merged via proper heating,the mechanical stability of the colloid array could be significantly enhanced;meanwhile,the structural color could also be well maintained.The colloid array patterns showed good tolerance to friction and ultrasonic.