The Preparation Of The Polymer Template-based Metal Nanoparticles, Characterization And Applications

In recent years,size- and shape-controllable metal nanoparticles or atom clusters,especially copper and silver nanoparticles,have attracted considerable attention due to their unique physical and chemical properties and potential applications in various fields as catalysts,biological sensors, optical,magnetic and electronic devices.Unfortunately,the problem of agglomeration often exists when these metal nanoparticles are used during practical operations.However,metal nanoparticles highly dispersed in a host material are more desired for practical applications.Although copper and silver nanoparticles are considered as nontoxic and environmentally friendly elctroconductive and antibacterial materials,this flaw has restricted their functionality and applications due to their poor binding characteristic with surfaces,Polymer and/or polymer hydrogel networks templates are outstanding approaches for assembling this kind of size-stabile and well-dispered metal nanoparticles inconductivity and antibacterial applications.For these reasons,this article has done a great deal of work by using polyacrylamide or its derivative,poly(N,N-dimethyl acrylamide), grafted poly(vinyl alcohol),((PAAm-g-PVA) or PDMAA-g-PVA) as a template for the assembly of copper and silver nanoparticles and their related applications in the following aspects.This work mainly includes the following two parts.1) A vapor-sensitive electroconductive film was designed and assembled by inserting Cu²⁺ particles into a polyacrylamide grafted poly(vinyl alcohol)(PAAm-g-PVA) in virtue of a complexation between Cu²⁺ and PVA even PAAm,as well as the establishment of inter- and intramolecular attractions between polymer matrices,which were in turn reduced into Cu nanoparticles by sodium hypophosphite as a reducing agent.The PAAm-g-PVA graft copolymer was prepared via a simple free radical polymerization reaction initiated by a redox reaction.The structure and morphologies of the PAAm-g-PVA/Cu were characterized by a Fourier transform infrared spectroscope and a transmission electron microscope.The resistance responsiveness of the film samples to various organic vapor surroundings was investigated.The responsive magnitude,response time and recovery properties depend on the molecular weight of the graft polymer or the PAAm chain length and initial resistances of the film samples or Cu particle contents upon exposed to ether and petroleum ether vapor,etc.The response mechanism of the PAAm-g-PVA/Cu films to solvent vapors was accounted for by a swelling theory and an interaction between solvent vapor molecules and nanocomposites as well as the type and strength of interaction that each solvent vapor exhibits on the material.2) Grafting p(N,N-dimethylacrylamide)-g-poly(vinyl alcohol)(PDMAA-g-PVA) hydrogel networks were designed and prepared via a simple free radical polymerization reaction initiated by a PVA-(NH4)₂Ce(NO₃)₆ redox reaction.Highly-stable and well-distributed silver nanoparticles have been assembled by using these hydrogel networks as templates/nanoreactor via in situ reduction of silver nitrate in the presence of PVA as a reducing agent.Meanwhile the PDMAA or PVA chains can efficiently act as stabilizing agents for the Ag nanoparticles in that Ag⁺ would be complex via oxygen atom and nitrogen atom,and it would form weak bonds,thus astricting Ag⁺. The structure of the PDMAA-g-PVA/Ag was characterized by a Fourier transform infrared spectroscope(FTIR).The morphologies of pure PDMAA-g-PVA hydrogels and PDMAA-g-PVA/Ag nanocomposite hydrogels were examined by a scanning electron microscopy (SEM) and transmission electron microscope(TEM).XRD results show all relevant Bragg's reflection for crystal structure of Ag nanopaticles.TEM micrographs reveal the presence of nearly spherical and well-separated Ag nanoparticles with diameters ranging from 10 to 20 nm, depending on their reduction routes.UV-vis studies apparently show the characteristic surface plasmon band at 410～440 nm for the existence of Ag nanoparticles within the hydrogel matrix. The swelling kinetics demonstrates that the transport mechanism belongs to non-Fickian mode for the PDMAA-g-PVA hydrogels and PDMAA-g-PVA/Ag nanocomposite hydrogels.With increasing the DMAA proportion,the r₀ and S_∞are enhanced for each system.The assembly of Ag nanoparticles and the swelling behavior may be controlled and modulated by means of the compositional ratios of PVA to DMAA.