Study On The Preparation And Fluorescence Properties Of Quantum Dot/Polyarylene Ether Nitrile Composite Microspheres

Semiconductor quantum dot(QD)is one kind of low-dimensional nanomaterial with excellent fluorescence properties,thus it has been widely applied in optoelectronic devices,chemical detection and biomedicine.However,high-quality semiconductor quantum dots usually contain heavy metal elements(such as cadmium,lead)and are generally oil-soluble,which lead to high biotoxicity and limitation of their application in aqueous system.Therefore,a range of surface modification methods of quantum dots have been proposed to improve the above-mentioned defects.Among these methods,using a polymer matrix to encapsulate the quantum dots to form quantum dots/polymer composite microspheres can not only prepare composite microspheres with high fluorescence intensity and water dispersibility,but also can obtain biofunctional microspheres with adjustable size.In this dissertation,to realize the water dispersibility and long-term stability of oil-soluble fluorescent quantum dots,polyarylene ether nitrile(PEN)with intrinsic fluorescence emission and rigid-flexible main chain is employed as the polymer matrix to encapsulate QD.First,the method called three-dimensional confined emulsion self-assembly is adopted to study the assembly properties of PEN homopolymers,random copolymers and block copolymers.Next,the PEN with outstanding properties to form microspheres were selected to encapsulate QD and a series of QD/PEN composite microspheres with stable fluorescence properties were acquired.The assembly principles were further studied and finally explored the application fields of the obtained composite microspheres.The main research contents of this dissertation are as follows:1.Different structured PEN homopolymers,random copolymers and block copolymers were synthesized via molecular design,and the chemical structure,molecular weight and molecular weight distribution,thermal properties,solubility,fluorescence properties and contact angle of the obtained PEN were characterized.The results indicated that intrinsic blue emitting PEN with different hydrophilic properties can be obtained by adjusting the monomer and mole ratio of hydrophilic side groups,and the synthesized PEN block copolymers are multi-block polymers.Meanwhile,all of the obtained PEN have excellent solubility except the biphenyl-typed(with partially crystallinity)homopolymer.Furthermore,the glass transition temperature and the thermal decomposition temperature at 5 wt.%of the synthesized PEN are higher than 150°C and300°C,respectively,thus PEN could be the potential polymer matrix to encapsulate oil-soluble quantum dots stably.2.The assembly properties and particle size control methods of the different structured PEN homopolymers and random copolymers in three-dimensional confined emulsion droplets were studied,and the structure can be assembled into microspheres was selected to encapsulate quantum dots and the properties of the composite microspheres were explored.The results demonstrated that under the same emulsion conditions,the bisphenol A-typed PEN homopolymer(homo-BPA)can be assembled into microspheres by the bending and folding of the segments in the selective solvent thus have with the best microspheres-forming performance.At the same time,the cyano group of the microspheres prepared by homo-BPA can be partially hydrolyzed into carboxyl groups under alkaline conditions and further coupled with protein to achieve biofunctionalization,but the immune separation ability is worse than that of commercial beads.Besides,quantum dots can be co-assembled with homo-BPA to obtain composite microspheres with fluorescence stability and adjustable particle size,which were further used for microbeads size screening of macrophages phagocytosis and the result indicated that the composite microspheres in size of 280 nm?400 nm can be easily phagocytosed by macrophages.However,the distribution of quantum dots in the microspheres is nonuniform,so the PEN matrix for encapsulating quantum dots should be further optimized.3.The abilities to form microspheres and the size control methodologys of the amphiphilic PEN block copolymers(am PEN)with different structures were studied via three-dimensional confined emulsion assembly.And a methodology of in-situ growth of silver nanoparticles based on the coordination between Ag⁺and active groups of PEN is developed to explore the assembling mechanism of PEN.The results indicated that all of the synthesized am PEN can be drived to form microspheres via the microphase separation at the hydrophilic and hydrophobic interface of the oil-in-water droplets stabilized by surfactants.And the synergistic effect of dispersed phase,continuous phase and external conditions on the assembly process can effectively control the particle size of PEN microspheres.Besides,the am PEN microspheres with carboxyl groups can be directly activated and coupled with protein to achieve comparable immune separation effect with commercial beads.Furthermore,the co-assembling performance of am PEN and quantum dots was studied.We found that quantum dots are uniformly encapsulated in the am PEN microspheres via the hydrophobic interaction between QD and am PEN,and the size and fluorescence properties of the composite microspheres can be effectively controlled by emulsion conditions.Meanwhile,the macrophage labeling ability of QD/am PEN is better than the composite microspheres prepare by QD and PEN homopolymer.Furthermore,QD/am PEN composite microspheres showed the superior encapsulating stability than that of commercial QD/polystyrene microspheres,which was performed that QD/am PEN have excellent acid and alkali resistance,salt resistance and resistance high temperature and high pressure properties.4.Thanks to the intrinsic fluorescence emission of am PEN,quantum dots with different emission characteristics were employed to fabricate QD/am PEN composite microspheres probes with three-band fluorescence emission.And the composite microspheres were used as fluorescent probes for heavy metal ions(Ag⁺,Cu²⁺,Hg²⁺and Fe³⁺)detection according to their different fluorescence response behaviors to the fluorescent probes.The study shows that the detection result would not be affected whether the three different metal ions are added in order or after being mixed within the detection capability range of fluorescent probes.Based on this,a mathematical model was established for simultaneous detection of multiple metal ions by composite microspheres.5.Fluorescent films based on the QD/am PEN composite microspheres can be constructed by introducing Ca²⁺into the continuous phase of the three-dimensional comfined emulsion assembly.The study found that the introduced Ca²⁺can simultaneously interact with the carboxyl group of am PEN and the surfactant(sodium dodecyl sulfonate,SDS),and the nanosheets formed by the interaction between Ca²⁺and SDS can be used as phase change materials to be co-encapsulated with quantum dots into am PEN.After heat treatment,the coordinated composite microspheres exhibited the characteristics of fluorescent color change under laser irradiation and were expected to be further applied in optical anti-counterfeiting.In this dissertation,the intrinsic fluorescence emitted PEN with rigid-flexible main chains was used as polymer matrix,and their emulsion assembly performance,encapsulation performance as well as the co-assembly mechanism with QD were studied.After which,the water dispersive and biocompatible QD/PEN composite microspheres with stable fluorescence properties were synthesized,and the application potential was further explored both the composite microspheres in liquid phase and solid state.This research provides a theoretical basis for the study on the assembly(especially in 3D confined emulsion droplet)behavior of polymers with rigid-flexible main chains and provides a practical basis for the preparation of novel polymer composite microspheres,and finally provides a new idea for further construction of novel polymer-based functional materials and devices.