Design,Construction And Luminescence-Electricity-Magnetism Functionalization Of One-dimensional Micro/Nano Structures And Arrays

With the rapid development of nanotechnology,the performance requirements for micro/nano-materials are increasing.Single function and large size functional materials gradually cannot meet the development requirements of multi-functional small devices.Therefore,realizing multiple properties in one material has been widely concerned by researchers.Multifunctional materials with fluorescence,conductivity and magnetism have become one of the research hotspots in the field of materials science because of their important application prospects in biomedical and electromagnetic shielding fields.Microstructure plays a crucial role for the performance and application of multifunctional materials.Due to the adverse mutual interference among different functional substances such as fluorescent,conductive and magnetic functional substances,in order to realize the mutual independence and high integration of various functional substances,it is necessary to carry out reasonable microstructure design to obtain multifunctional materials with good fluorescence,conductivity and magnetism properties.The development of fluorescent-conductive-magnetic（denoted as FCM）multifunctional micro-/nano-materials with novel structure and excellent performance is one of the important topics to promote the development of nanotechnology.Based on the above background,the main research contents of this thesis are as follows:1.A specially designed three-layer coaxial spinneret is designed and assembled,and the corresponding spinning device is constructed.It is an innovative way to prepare the core layer by directly connecting with the air instead of spinning solution.[Co Fe₂O₄/polyaniline（PANI）/polymethylmethacrylate（PMMA）]@[Tb（acac）₃bpy/PMMA]bi-layered coaxial hollow microbelts and array are fabricated by one-step three-layer coaxial electrospinning technique.It overcomes the technical problem that the traditional electrospinning technology needs multi-steps to build the hollow structure.The outer wall layer of each bi-layered coaxial hollow microbelt is green fluorescent insulating functional layer,and the inner wall layer is magnetic-conducting functional layer.This special microstructure has two functional partitions and a hollow partition in the middle.While retaining the unique structural advantages of the hollow structure,the rare earth fluorescent substances are separated from the dark-colored conductive PANI and magnetic Co Fe₂O₄which have a great influence on the fluorescence intensity,the influence of conductive and magnetic substances on the fluorescent performance is obviously reduced and the continuity of the conductive PANI is ensured,so that good FCM tri-functions are realized in a single microbelt.The multifunctional adjustability of the array membranes can be achieved by changing the content of functional substances.2.The self-assembled three-layer coaxial spinneret is further improved.A tri-coaxial microbelt with Co Fe₂O₄/PMMA as the core layer,PANI/PMMA as the intermediate layer and Tb（acac）₃bpy/PMMA as the shell layer and its array are designed and fabricated via one-step electrospinning technology.Microscopically,the tri-coaxial structure realizes the division of three independent regions,which effectively reduces the adverse effects among fluorescent,conductive and magnetic substances.The fluorescence enhancement mechanism of the tri-coaxial microbelt is elucidated.In addition,by regulating the composition,content and arrangement of different functional substances,the macro-multifunctional characteristics of array membranes can be adjusted.This new structure and preparation technology can be applied to construct other multifunctional materials to meet different application requirements.3.The Janus structure and the core-shell structure are innovatively combined,and a novel 1D micromaterial with a special structure is constructed by adopting a self-designed and assembled[parallel needle]@[uniaxial needle]spinneret and the corresponding electrospinning device via one-step electrospinning technology.The[（Co Fe₂O₄/PMMA）//（PANI/PMMA）]@[Tb（acac）₃bpy/PMMA]Janus nanoribbon-in-ribbon embedded structure microbelt and{[Co Fe₂O₄/polyvinylpyrrolidone（PVP）]//[PANI/PVP]}@[Tb（acac）₃bpy/PVP]Janus nanofiber-in-fiber typed microfiber are fabricated by using different substrates,respectively,and they are used as micro-building units to obtain corresponding array membranes.Microscopically,the two 1D structures have three independentpartitions.Inthe[（Co Fe₂O₄/PMMA）//（PANI/PMMA）]@[Tb（acac）₃bpy/PMMA]Janus nanoribbon-in-ribbon embedded structure microbelt,it includes a core layer composed of Janus nanoribbon with conductive-magnetic dual functions and a shell layer composed of microribbon with green fluorescent function.In the[（Co Fe₂O₄/PVP）//（PANI/PVP）]@[Tb（acac）₃bpy/PVP]Janus nanofiber-in-fiber typed microfiber,it includes a core layer composed of Janus nanofibers with conductive-magnetic dual functions and a shell layer composed of microfiber with green fluorescent function.The core layers of these two 1D structures both have two functional partitions.Benefiting from the unique Janus core layer,the core layer of the building unit has anisotropic conductivity.Based on this characteristic,a new concept of"microscopic anisotropic conduction"is proposed.This is the first time to study the anisotropic conductivity of materials at the microscopic level,which is different from the previous studies of macroscopic anisotropic conductive films.The fluorescent,conductive and magnetic substances are limited within their own partitions,which effectively reduces the adverse mutual interference among these functional substances.The adjustable magneticity-microscopic anisotropic conduction-green fluorescence multifunctional properties are obtained by adjusting the content of each functional substances.The formation mechanisms of the special Janus nanoribbon-in-ribbon embedded structure microbelt and the Janus nanofiber-in-fiber typed microfiber are proposed.New technologies for building these special structures and arrays have been established.4.A[coaxial needle]//[coaxial needle]spinneret and the corresponding electrospinning device are designed and constructed.The novel flexible coaxial fiber//coaxial fiber typed Janus microfibers and array are successfully prepared via one-step electrospinning technology.As a case study,{[Co Fe₂O₄/PMMA]@[PANI/PMMA]}//{[Co Fe₂O₄/PMMA]@[Tb（acac）₃bpy/PMMA]}Janus microfibers and array are prepared using PMMA as matrix.Then,in order to prove the universality of this construction technology,[（Anthracene/Rhodamine B/PVP）@（coumarin-6/PVP）]//[（Co Fe₂O₄/PVP）@（PANI/PVP）]Janus microfibers and array membrane are constructed using PVP as matrix.The division of four independent partitions in this coaxial fiber//coaxial fiber typed Janus microfiber is realized on the microscopic level,effectively limiting the conductive,fluorescent and magnetic substances in their own spatial regions,reducing the adverse mutual interference among them,and realizing the high integration and effective separation of various functions.In addition,with the help of this unique structure,the energy transfer among fluorescent substances can be reasonably and effectively suppressed,thus realizing white light emission.By using the coaxial fiber//coaxial fiber typed Janus microfiber as a micro-building unit,the prepared array membrane has strong fluorescence,high conductivity and strong magnetism,the conduction ratio between the conductive direction and the insulating direction can reach 10⁸when the content of PANI is 70%.The formation mechanism of coaxial fiber//coaxial fiber typed Janus microfiber is proposed,and new technologies with universality for constructing coaxial fiber//coaxial fiber typed Janus microfibers and array are established.More importantly,the design idea of this new structure and construction technology provide new ideas for the design and preparation of other multifunctional materials,and lay a certain technical foundation for the development of nanotechnology.