Controlled Synthesis Of Silver Nanoparticles And Their Influence On The Crystallization Of Optically Modified Polyester

Silver nanostructures have attracted increasing research interests both in academic and industrial fields,mainly due to their outstanding physicochemical and biological properties.For instance,silver nanostructures with different morphology can be employed as the building blocks of advanced nano-antennas to manipulate the light-mater interaction in the nanoscale thanks to their inherent near-field optical properties(i.e.localized surface plasmon resonance).Thus,they have been widely involved in various surface enhanced spectroscopy techniques including surface enhanced Raman spectroscopy(SERS),metal enhanced fluorescence(MEF),etc.Besides,silver nanostructures were widely used as the good catalyst in various chemical reactions as well as effective anti-bacterial agent in biochemical and microbiological fields.Generally,the morphology control of silver nanostructures is one of the most important factors to determine their efficiency of the above mentioned applications.Polyethylene terephthalate(PET)is a kind of well-developed polyester and thanks for its low production cost and easy processability,PET has been widely applied in packaging industry,precision device packaging,electronics,building decoration,car accessories,and many other fields.However,on the one hand,the further development and application of PET are severely limited by its bad toughness and low crystallization rate,on the other hand,with the development of material science and industrial technology,PET with single structure is more and more difficult to meet the needs of some special field,thus requires us to develop some modified PET with excellent performance and diversified functions.As a result,modified polyester with high toughness,high crystallization rate,and optical properties would be a good research direction.This paper did a series of research mainly focus on the controllable synthesis of silver nanoparticles,the optical modification of polyester,and the crystallization behavior effect of silver nanoparticles on the optical modified PET.The research content mainly includes the following parts:Firstly,a series of research have been done on the theme of controlled synthesis of silver nanoparticles.In this part,as a kind of special polymeric material,Poly aryl ether nitrile(PEN)has been used to synthesis silver nanoparticles rely on its combine ability between N,O atoms and silver irons.First of all,by controlling the ratio of reactants,reaction temperature and reaction time on reaction conditions,we successfully obtained silver nanoparticles with different structures including microspheres and nanorods etc.Besides,as the further test characterization of these products continues,we found that different shapes of silver nanoparticles revealed distinct optical properties.The silver nanoparticles with larger size correspond with localized surface plasmon resonance,while smaller silver nanoparticles shown fluorescence property.Then,by using different structure of poly(aryl ether nitrile as surface agent,we further studied the fluorescence properties of ultra-small silver nanoparticles,and prepared the nanoparticles with different fluorescence emission wavelength by controlling its size.These features above make silver nanoparticles have potential application value on optical sensor,which means the result of our research improved the synthesis measure of silver nanoparticles and its application in a certain degree.The second part is mainly about the optical modification of polyester(PET).First of all,from the perspective of molecular design,PET-PEG with good toughness,high transparency,and fluorescent property was synthesized by the copolymerization of terephthalic acid(PTA),ethylene glycol(EG)and polyethylene glycol(PEG).In the process of the copolymerization,PTA and EG is the monomer of traditional polyester PET,while PGE as flexible chain segment,can be used to enhance the toughness of the modified polyester.In addition,when heated at a high temperature,PEG will partly decompose into carbon quantum dots with fluorescence emission,further leads to fluorescent property of PET-PEG co-polyester.Then,in order to solve the problem of PET-PEG becoming opaque via crystallization when the storage time prolongs,1,4-cyclohexanedimethanol(CHDM)was introduced into the backbone of PET to prepare the semicrystalline polyester PETG-PEG.CHDM as an additional monomer,can hinder the thermal motion of molecular chain,thus suppressing the crystallization of polyester.The PETG-PEG co-polyester has a good stretchability and can be recovered from a certain degree of stretch,furthermore,PETG-PEG co-polyester will not appear whitish phenomenon during the process of tensile stress,and will not arise crystallization after a long time storage.More importantly,the fluorescence intensity of modified polyester will change with the different stretch degree the tensile strength,which gives the prospect of its application in optical stress sensor.Finally,in the third part,we mainly studied the effect of silver nanoparticles with different sizes on the crystallization behavior of polyester.As we all know,in some industrial applications,it is necessary for the polyester to have a good crystallization performance,the crystallization rate of polyester will directly affect the hot casting molding process and other aspect of PET.However,as the existence of flexible segment: PEG,the PET-PEG flexible polyester that we synthesized before have a very slow crystallization speed,and it will become totally amorphous after process of rapid cooling.But through adding the previously synthesized silver nanoparticles with different sizes(reaction time were 0.5 h,1 h and 3 h)into the polymerization process of polyester,we found that the crystallization rate of polyester was promoted by silver nanoparticles,and silver nanoparticles with reaction time of 1 h has the most evident promoting effect.The reason can be concluded as: in the process of polymerization,silver nanoparticles can play the role of nucleating agent and provide the crystal nucleus,making the crystallization rate faster,along with smaller crystal size and larger crystallization density.In addition,the addition of silver nanoparticles did not affect the toughness and the fluorescent properties of polyester obviously,thus the silver nanoparticles can be used as a nucleating agent of PET-PEG polyester,which can broaden the path for the application of the modified polyester.