Study On Preparation And Properties Of Rare-earth Nanocrystals Complex Nanogels

Hydrogel is a three-dimensional polymer network composed of polymer chains and water.As a three-dimensional crosslinked hydrophilic polymer network,hydrogel can swell or disexpand reversibly in water and retain a large number of liquids in the swelling state.Hydrogels can be designed to have controllable responses,shrinking or expanding with changes in external environmental conditions.They can make significant volume changes in response to various physical and chemical stimuli,including temperature,electric or magnetic fields,light,pressure and sound,while chemical stimuli include pH,solvent composition.Two kinds of rare-earth nanocrystals NaYF4 were prepared by hydrothermal method.They were filled into the hydrogel as inorganic materials.The complex hydrogels with multiple responses were prepared.The photonic crystal luminescence characteristics were studied by self-assembly of the nanocrystals.The main contents of this paper include:1.In this work,NaYF₄:Yb³⁺,Er³⁺nanocrystals were prepared by hydrothermal method,then they were decorated by 3-benzylsulfanylthio-carbonylsufanylpropionic acid（BSPA）to obtain functionalized nanocrystals.A vinyl functional Rhodamine 6G（R6GHA monomer）was synthesized through a series of reactions.Then they were used as the donor and acceptor to construct a fluorescence resonance energy transfer（FRET）system respectively.Finally,a novel multi-responsive complex fluorescent nanogel NaYF₄:Yb³⁺,Er³⁺/PNIPAm-R6GHA was prepared by reversible addition-fragmentation chain transfer（RAFT）polymerization and a thiol-ene click reaction.The microstructure of the nanogels was characterized by transmission electron microscopy（TEM）,X-ray diffraction（XRD）,Fourier transform infrared spectroscopy（FTIR）and differential scanning calorimeter（DSC）.The fluorescence response behaviors of the nanogels to different metal ions,pH and ambient temperature were investigated by photoluminescence spectroscopy（PL）in detail and the mechanism was discussed respectively.The results show that ambient temperature play important roles to affect the fluorescence emission of the nanogels,and fluorescence emission of nanogel is influenced little by many metal ions except Hg²⁺.Under 980?nm irradiation,energy can transfer from nanocrystals to R6GHA moieties when the nanogel was placed in acidic solution or in solution containing Hg²⁺.Besides,according to the fluorescence intensity ratio of nanocrystals and R6GHA moieties,the detection of Hg²⁺can be conducted by PL conveniently.2.NaYF₄:Eu³⁺-PNIPAm complex nanogels were prepared by hydrothermal method.NaYF₄:Eu³⁺-PNIPAm complex nanogels were prepared by the modification of butenylamine and the free radical polymerization of potassium persulfate to form PNIPAm.Then,the complex nanogels is self-assembled into a colloidal crystal.The structure and morphology of the complex nanogels were characterized by transmission electron microscopy（TEM）,scanning electron microscope（SEM）,X-ray diffraction（XRD）and fluorescence resonance energy transfer（FTIR）.The temperature-sensitive properties of the products were characterized by scanning calorimeter（DSC）and dynamic light scattering（DLS）.The optical photographs showed the special structural color of the product;ultraviolet–visible spectroscopy（UV-vis）and photoluminescence spectroscopy（PL）were used to study the temperature-sensitive optical properties of self-assembled colloidal crystals with different concentrations of complex nanogels at different ambient temperatures,and the related mechanisms were discussed.The results show that we can change the density of colloidal particles by changing the concentration of the complex nanogels before assembly to change the crystal plane distance,and study the crystal structure from optical changes.And by the thermal response properties of PNIPAm,temperature changes cause the colloidal crystals to crystallize and melt reproducible.By changing the ambient temperature,the colloidal particles in the colloidal crystal are induced to undergo a phase transition to change the crystal spacing,which causes a sharp change in the peak intensity of the fluorescent emission.