Fabrication Of Functional Polymer Micro-and Nano-Assemblies

Polymer performs the strong mechanical,high thermal and chemical stability,superior processability,and rich phase behavior as well as self-assembly characteristics.Besides,aggregates of polymer show good stability compared to that of small molecules.Therefore,self-assembly of polymers and fabrication of micro-and nano-structures have attracted more and more attention.The basic theory and technique in colloid and interface chemistry facilitates the fabrication of the micro-and nano-materials and understanding of polymer self-assembly,vice versa,the research field of micro-and nano-material fabrication can enrich the discipline construction of colloid and interface chemistry as well.Our group has fabricated various polymer/metal ion composite thin films via adsorption and self-assembly of polymers at liquid/liquid and air/liquid interface.In this thesis,on the basis of our group's previous work,a facile and versatile approach to fabricate composite thin film at the air/liquid interface was reported.Furthermore,influences of various experimental parameters were investigated here.The study of micro-and nanostructure fabrication is not only out of academic interest,but also useful for the pratical application.The outlines and content are as follows:1.A novle way to fabricate polymer micro-and nano-structures at the air/liquid interfacePolystyrene-b-poly(2-vinylpyridine)was dissolved in mixed DMF/CHCl3 solution.After Ag+ aqueous solution was added and covered the organic solution,a planar liquid/liquid interface was formed between the aqueous phase and organic solution.We had anticipated that hierarchical micro-and nanostructures of PS-b-P2VP would be fabricated using this emulsion-directed assembly and adsorption method.However,to our surprise,a thin free-standing film apperared quickly at air/liquid interface rather than at the liquid/liquid interface.Hence,the morphology and structure of the films were investigated,and the formation mechanism was explored and illuminated.After the formation of liquid/liquid interface,because of the miscibility of DMF with CHCl3 and water,DMF carrying PS-b-P2VP and a small amount of CHCl3 migrated into the aqueous phase,and water carrying Ag+simultaneously migrated into the organic phase.Due to ouzo effect,emulsion formed at aqueous and organic solution.The DMF in the drops diffused into the water due to the miscibility between water and DMF,leading to the formation of polymer aggregates,including cylindrical micelles,spherical micelles,and vesicles.Eventually,these aggregates,together with the polymer molecules adsorbed at the air/liquid interface,formed thin films with the morphology of nanowires,nanospheres,hollow spheres,or foam,among which the nanowires with parallel alignment were up to hundreds of micrometer.This approach has been utilized to tune the morophology of the film by varying emperimental parameters such as the concentration of Ag+ or polymer,the volume ratio of DMF and CHCl3 and so on.During this process,some Ag+ ions were reduced by DMF to form Ag nanoparticles in the composite thin film,which exhibited efficient catalytic properties.2.The influences of block copolymer structure and inorganic species on the morphology of thin filmTo test the versatility of this approach,it was utilized to other polymers such as PS-b-P2VP with different length of P2VP block.We found that the different molecular structures of polymers exerted different influences on the self-assembly of polymers and the morphology of the composite thin film.For example,when varying the length of P2VP,apart from nanowires,foam appeared on the film as well.Furthermore,in PS-b-P2VP system,the different inorganic species(AuCl4-and AuCl2-)exerted different influences on the morphology and formation of composite thin film,which was illuminated by theoretical computation.Nanowires and planar aggregates appeared on composite thin film of PS-b-P2VP/AuCl4-,however,only foam formed on the composite thin film of PS-b-P2VP/AuCl2-at the air/liquid interface.Combined with our previous system of PS-b-P2VP,the influences of different substituent position of N atom in P2VP and P4VP on the morphology of films were investigated.When using PS-b-P4VP,different substituent position of N atom in P4VP compared to in P2VP,the diameter of nanowires varied with the variation of concentration of inorganic species,by contrast,the diameter of the nanowires formed with PS-b-P2VP and inorganic species kept unchanged.Finally,the potential applications of the composite thin films were investigated in the thesis.The composite thin film with metal nanoparticles exhibited efficient catalytic properties.Additionally,these hybrid films doped with silver nanoparticles provided potential application in surface enhanced Raman scattering(SERS)for small molecule probing as well.3.Fabrication of two-dimensional arrays of diameter-tunable PS-b-P2VP nanowiresComposite thin film with the morphology of two-dimensional arrays of nanowires with the diameter of 43 nm can be fabricated at air/liquid interface via self-assembly of PS-b-P2VP.It was shown that these homo-PS molecules were incorporated into the core of the nanowires,leading to variation of the nanowire diameters from 45 to 247 nm by encapsulating PS in the core of the nanowires.A series of h-PSs with varying molecular weights of less than,almost equeal to,and more than the molecular weight of PS block in PS-b-P2VP were used to study their influences on nanowire structures.When the molecular weight of PS was smaller than that of PS block in PS-b-P2VP,the diameter of nanowires increased linearly with the increasing amount of PS;when the molecular weight of PS was amlost equal to that of PS block in PS-b-P2VP,the diameter increased at first then reached a saturated value;when the molecular weight of PS was more than that of PS block in PS-b-P2VP,the diameter of nanowires was slightly larger than that of pure PS-b-P2VP nanowires,however almost kept unchanged with the increasing amount of PS.The variation of the diameter of nanowires in all the cases was related to the different existing state of PS in the core of the nanowires.4.Tuning ? phases in PFO nanoparticles and their photocatalytic efficiencyWe demonstrated that exceptionally high beta-phase fractions(up to?50%)could be achieved via a synergy between i)polymer-polymer blending,?)nano-confinement and iii)suppressed solvent evaporation.We analyzed the resulting blend nanoparticles using steady state UV-vis absorption and fluorescence spectroscopy in thin film and dispersion and compare the results with those obtained on blend films prepared by spin-coating directly from organic solvents.We observed a dependence of the final beta-phase content not only on molecular weight of the blended PS,but also on blend ratio and even particle size.The NPs with the formation of ?-phase PFO were investigated as photocatalyst to degrade RhB,which showed that the NPs of blended PFO and PS with higher ?-phase content possessed much higher photocatalyst efficiency,providing new insights for the design of efficient and visible light driven photocatalytic nanoparticles.