Fabrication Of Multiscale Functional Structures

Recently,microstructures and nanostructures have promoted to the research of traditional materials in physics,chemistry,and biology.New properties of these functional structures arise from not only the size effects of the small scales but also the composite effects of multiple scales from micrometer to nanometer,the geometric shapes of the structures,periodic arrays of uniform structures,and the responsive changes of shapes to external stimulis.Thus,multiscale functional structures show positive effects on scientific research and practical applications.Both these top-down and bottom-up fabrication methods have been widely applied into specific structures in micrometer,submicron,and nanometer scales.However,it is still difficult to integrate multiple structures with different scales into one device with these existing methods.Thus,we focus on the intergration of multiscale structures from micrometer to nanometer scale.Self-assembly of colloidal crystals,electrohydrodynamic jet(E-jet)printing with colloidal inks,and two-photon polymerization(TPP)are investigated to achieve ordered photonic crystal(PC)structures in submicron scales,structural color patterns in micrometer scales,and 3D devices with multiscale structures.The detail works are as follow:(1)Ordered structures with submicron scales can be achieved by self-assembly of colloidal particles.A colloidal crystal hydrogel film was realized with the polymerization of photosensitive hydrogels and the embedded non-close-packed silica particles.The hydrogel network was used to lock the periodic ordered structures,leading to a photonic band gap(PBG).And the PBG can be tuned by the thickness of the hydrogel film and the interplanar distance of the neighbouring diffracting planes.Based on the linear relationship between the thickness of the hydrogel film and its PBG,continuously varying PBGs in time and space could be achievd by the apllied stress,which have been used in tunable fiber Bragg gratings and diffraction gratings,respectively.The chapter demonstrated the photonic band gaps of ordered submicron structures could be achieved by monodisperse colloidal particles with one size.(2)Structural color patterns with micrometer scales and periodic ordered structures with submicron scales were fabricated by utilizing E-jet printing and self-assembly of colloidal crystals.The self-assembly of colloidal crystals resulted in the PC structure and structural color in each unit and the E-jet printing provided discrete droplets and continuous fibers to achieve dots,rings,and lines.The final size and shape of each PC unit were controlled by the nozzle,the applied voltage signal and wettability of the substrate.The embedded colloidal particles self-aeembled into close-packed periodic ordered structures and amouphous PC structures depending on the solvent and the assemblying process.This work solved the issue of non-templated self-assembly of colloidal particles in controllable micrometer areas.(3)3D structures with micrometer,submicron,and nanometer scales can be directly printed by TPP.Based on the calculation of the distribution of the exposure dose around the fabrication path,the effects on the laser power,the fabrication speed and the scanning path on the polymerization voxels were used to guide the design of complex geographic structures.For solid-state pores,the dimater of the scanning path was used to generate narrow opennings in nanometer and submicron scales.The generated pore structures were stacked to form a channel with desired complex shapes.Moreover,TPP offered the possibility of integrating these structures into deveices with micrometer scales.This chapter demonstrated the direct printing capacity of TPP for arbitrary 3D structures.