| Colloidal chemistry is an important subject in studying of physicochemical properties and mesoscopic scale of dispersed systems.As a crucial part of colloidal chemistry,amphiphilic molecules can spontaneously assemble into various ordered aggregates of soft matters,such as micelles,vesicles,liquid crystals,emulsions and gels.How to control the morphology,properties and functional diversification of ordered aggregates,and how to introduce functional materials into ordered aggregates to construct functional soft materials combining of their unique properties and structural characteristics,has become a research hotspot in the interdisciplinary fields of chemistry,materials science and biomedicine.Lanthanide-doped upconversion nanoparticles(UCNPs)capable of converting near-infrared excitation into visible emissions are a kind of new functional fluorescent material,whose luminescence mechanism follows the "anti-Stokes luminescence" and two-photon or multi-photon absorption.Because of their excellent fluorescence and photovoltaic conversion properties,upconversion materials are becoming a very competitive alternative material.During the development of colloidal chemistry,the growing trend of functional soft materials is becoming diversified and multi-functional.Introducing of UCNPs into colloidal soft materials and the exploration of their functional applications are no longer limited to simply mixing them and exploring their respective properties.Instead,it focuses on how to introduce functional upconversion materials into ordered aggregates to construct functional soft materials,and how to combine the unique optical/electrical properties of functional materials with the structural characteristics of ordered aggregates.Accordingly,in this paper,we based on the designability of the surface ligand to take functional UCNPs as the building blocks and introduce them into ordered soft matter by non-covalent interaction and dynamic covalent interaction.On the one hand,through regulating the structure-activity relations,we have constructed the multifunctional gels,emulsions and ordered colloidal clusters.On the other hand,the colloidal soft matters constructed by upconversion materials can not only retain or even improve the optical/electrical properties of the building blocks,but also give full play to the flexibility and adaptability of soft materials,thus achieving breakthroughs in specific functions and optical/electrical applications.In Chapter Ⅰ,introduction.From the concept of colloid chemistry,the formation and types of soft matters from ordered aggregates constructed by amphiphilic molecules are described.Based on the development status of functional colloidal soft matters,upconversion luminescent nanoparticles(UCNPs)were introduced,and their luminescence mechanism,design and synthesis,surface functionalization and photoelectrical applications were summarized.Furthermore,the nanocomposite hydrogel systems,emulsion systems and liquid crystal systems participated with UCNPs were reviewed in detail,mainly including the construction methods,mechanisms,properties and applications.The advantages and functions of the constructed colloidal soft materials based on UCNPs are presented,and the limitations are also pointed out.Finally,we put forward the thesis idea,research content and significance.In Chapter Ⅱ,we designed and synthesized polydopamine-coated upconversion nanoparticles(UCNPs@PDA).Then,based on dynamic covalent Schiff-base linkages,a composite hydrogel was formed in situ by chemically linking cross-linker of carboxymethyl chitosan(CMCS)with UCNPs@PDA and oxidized sodium alginate(OSA).The enhanced mechanical strength and formed imine bonds of this composite hydrogel fully demonstrated that UCNPs@PDA participated in the construction of a hydrogel skeleton.In this work,UCNPs@PDA not only served as the construction units,but also acted as the NIR-excited fluorescent probe due to their excellent fluorescence property,playing the role of "one stone two birds".Therefore,the in vitro enzymatic biodegradation simulation test of the composite hydrogel was conducted by immerging into a lysozyme solution,where the degradation signals were real-time tracking by the decrease in fluorescence intensity.We found that the changes in fluorescence intensity corresponded to the weight changes in composite hydrogels,suggesting the feasibility and accuracy of the UCNPs@PDA in consecutively tracking the in vitro hydrogel degradation.Hopefully,this strategy provides strong evidence in predicting degradation behaviors in vivo.In Chapter Ⅲ,in order to realize multi-mode luminescence,we prepared red-green-blue(RGB)three-primary-color UCNPs by doping with different lanthanide ions and tailoring the molar ratio.Since the surface modification of UCNPs would reduce its fluorescence performance,in order to avoid the problem of fluorescence intensity weakening caused by phase transfer,the emulsion was introduced.So in this chapter,the hydrophobic RGB-UCNPs were encapsulated into an oil-in water nanoemulsion(O/W NE)to retain its excellent fluorescence properties and then to obtain a dual-mode,tunable full-color,long-term stable and environment friendly fluorescence anti-counterfeiting ink.Such an ingenious design combines several advantages:(ⅰ)The dual-mode fluorescent nanoparticles could prevent the production of inferior quality inks resulting from simply mixing inhomogeneous nanoparticles;(ⅱ)The O/W NE selected as the carrier not only can encapsulate the hydrophobic UC NPs and CQDs inside the oil droplets,avoiding removal of ligands and retaining their excellent fluorescence properties,but also endows water-based anti-counterfeiting inks with long-term stability for 8 months due to the dynamic stability of the O/W NE;(ⅲ)The physical and chemical properties of NE inks,e.g.,viscosity,surface tension and density,could match well with the requirements of inkjet printing,achieving multi-mode and diverse patterns.In Chapter Ⅳ,based on a facile emulsion self-assembly method,the 3D ordered icosahedron-like and face-centered cubes(FCC)CSPs were successfully fabricated using UCNPs as building units.Then the shape,size and surface charge of the CSPs can be regulated through altering concentrations and types of surfactants,and polarity of solvents,respectively.One-step emulsion self-assembly approach not only can immediately transform hydrophobic UCNPs into water-dispersible CSPs,but also endow CSPs with ordered morphology that reserves the predominant fluorescence properties.Therefore,when the negative surfactant of SDS is used as the stabilizer,the CSPs are electronegative.After coating CSPs with electropositive PEI by electrostatic interaction,the CSPs can serve as an excellent fluorescence probe to detect Cu2+ without auto-fluorescence and background light interference due to the generation of PEI-Cu2+complexes,which can act as energy receptor of CSPs leading to upconversion fluorescence quenching.This method is really vital towards both transformation of hydrophobic UCNPs into hydrophilic CSPs,and effective replacement of the complex synthesis method.At the same time,the CSPs with the unique morphology reduce the specific surface area of the UCNPs,so that the lattice defects on the surface of the particles can be repaired to a certain extent and thus maintain good fluorescence performance.This method is of great significance for the construction of new colloid clusters with ordered structure and excellent function.In Chapter Ⅴ,in addition to the colloidal clusters,colloidal nanocrystalline superlattices(SPs)with hollow interiors and hierarchical porous structure can also be successfully obtained by an emulsion-based self-assembly process using OA-capped UCNPs.From the aspect of structure,its internal hollow and porous structure can open mass transfer channels;and from the function level,the hollow porous structures and photovoltaic property are integrally retained during the ligand carbonization process,where the close-packed carbon shells derived from the native OA ligands in situ generate an interconnected electron transport network,enhancing the electrochemical activity.Accordingly,we printed these materials onto PET flexible substrates by screen printing to construct asymmetric,flexible,and all-solid-state micro-supercapacitors(MSCs).The MSCs possess high areal capacitance,Cs=21.8 mF/cm2 at 0.36 A/cm2 and E=0.00684 mWh/cm2,superior flexibility,outstanding cycling ability,and sensitive NIR photoelectrical response.These MSCs based on UCNP-SPs are expected to be developed toward multifunctional integration in flexible wearable electronics.In Chapter Ⅵ,we constructed an O/W emulsion which is co-stabilized by ionic liquid and UCNPs with the amphiphilic and wettability,whose stabilization mechanism was different from traditional emulsion,so we named as "novel"emulsions.Then emulsion gels were formed by polymerizing monomers of[VCnIm]Br(n=4 or 12)in the continuous phase under UV initiation after introducing initiators and crosslinking agents.After removing dispersed phase by freeze-drying,the hierarchically porous aerogels were obtained when using monomers[VC12Im]Br.We find that self-supporting flexible gels with high ionic conductivity(8.42 mS/cm),superior mechanical strength,excellent thermal stability and freezing resistance can be prepared while using monomers[VC4Im]Br.Finally,the aerogels were used as electrode material and flexible gel as electrolytes to fabricate the all-solid-state supercapacitor.Various characterizations demonstrated that the prepared supercapacitor device exhibited an excellent electrochemical performance and sensitive NIR photoelectric response.This new one-step synthetic approach provides a distinct and complimentary methodology for developing next-generation energy storage and harvest. |
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