导电高分子优秀课件.ppt

导电高分子第1页，本讲稿共85页Introduction第2页，本讲稿共85页Polymers were thought of as electrial insulators until the discovery that iodine-doped polyacetylene(聚乙炔)exhibited electrical conductivity many orders of magnitude higher than neutral polyacetylene.This discovery was published by Shirakawa,H.,Louis,E.,MacDiarmid,A.,Heeger,A.,(1977).As a result of this pioneering work,they received the 2000 Nobel Prize in Chemistry.Introduction第3页，本讲稿共85页Nobel Prize in Chemistry 2000“For the discovery and development of conductive polymers”G.MacDiarmid H.Shirakawa J.Heeger第4页，本讲稿共85页黑格（黑格（Alan J.Alan J.Heeger,1936Heeger,1936 ）美美国国加利福尼亚大学的加利福尼亚大学的著名物理学家，著名物理学家，20002000年年1010月月1010日，因对导日，因对导电聚合物的发现和发电聚合物的发现和发展而获得诺贝尔化学展而获得诺贝尔化学奖。奖。Introduction第5页，本讲稿共85页麦克迪尔米德麦克迪尔米德（Alan G.Alan G.MacDiarmidMacDiarmid，19371937 ）美国美国宾夕法尼亚大宾夕法尼亚大学的学的著名化学家，著名化学家，20002000年年1010月月1010日，日，因对导电聚合物的因对导电聚合物的发现和发展而获得发现和发展而获得诺贝尔化学奖。诺贝尔化学奖。Introduction第6页，本讲稿共85页白川英树白川英树(Hideki(Hideki ShirakawaShirakawa，19361936 )日本筑波大学的著名日本筑波大学的著名化学家，化学家，20002000年年1010月月1010日，因对导电聚合日，因对导电聚合物的发现和发展而获物的发现和发展而获得诺贝尔化学奖。得诺贝尔化学奖。Introduction第7页，本讲稿共85页ConductivityIntroduction第8页，本讲稿共85页The discovery of conductive polymers is unique in its accomplishment as a possible substitute(替代物替代物)for metallic conductors and semiconductors.Scientists from many disciplines are now combining expertise(专门技术)to study organic solids that exhibit remarkable conducting properties.A large number of organic compounds,which effectively transport charge are roughly divided into three groups i.e.charge transfer complexes/ion radical(基基)salts,organometallic species and conjugated organic polymers.Introduction第9页，本讲稿共85页Electronically conducting polymers differ from all the familiar inorganic crystalline semiconductors in two importantfeatures that polymers are molecular in nature and lack long range order.A key requirement for a polymer to become intrinsically(本征本征)electrically conducting is that there should be an overlap of molecular orbitals to allow the formation of delocalized(离域离域)molecular wave function.Besides this,molecular orbitals must be partially filled so that there is a free movement of electrons throughout the lattice.Introduction第10页，本讲稿共85页Conductingpolymerscontain-electronbackboneresponsiblefor(是的原因)theirunusualelectronicpropertiessuchaselectricalconductivity,lowenergyopticaltransitions,lowionizationpotentialandhighelectronaffinity.Thisextended(延延长长)-conjugatedsystemoftheconductingpolymershavesingleanddoublebondsalternatingalongthepolymerchain.Thehighervaluesoftheelectricalconductivityobtainedinsuchorganicpolymershaveledtothenamesyntheticmetals.Introduction第11页，本讲稿共85页IntroductionThe development of polymers with conductivities equal to semiconductors and metals have been presented in Table 1 and their corresponding structures are shown in Fig.1.第12页，本讲稿共85页Introductionisothianaphthene:异硫茚；异硫茚；azulene:甘菊蓝；甘菊蓝；furan:呋喃呋喃第13页，本讲稿共85页IntroductionPoly-acetylenePoly pyrrolePoly thiophenePoly anilinePoly-p-phenylenePoly-phenylene vinylenePoly-p-phenylene sulphidePoly-iso-thianaphthene第14页，本讲稿共85页Historical background of electronically conducting polymers第15页，本讲稿共85页Historical background of electronically conducting polymersResearch on conducting polymers intensified(增强)soon after the discovery of poly(sulphur nitride)(SN)x in 1975 which becomes superconducting at low temperatures(Greene et al.,1975).Although,conducting polymer complexes in the form of tetracyano(四氰基)and tetraoxalato-platinates(四草酸铂酸盐),the Krogman salts charge transfer complexes had been known earlier,the significance lies in the rediscovery of PA in 1977(initially discovered by Shirakawa et al.,1977 using a Ziegler Natta type polymerization catalyst)by MacDiarmid and Heeger,University of Pennsylvania(宾夕法尼亚).重视第16页，本讲稿共85页TheywereabletoenhancetheelectricalconductivityofPA(109Scm1)byseveralordersi.e.105Scm1bysimpledopingwithoxidizingagentse.g.I2,AsF5,NOPF6(p-doping)orreducingagents(n-doping)e.g.sodiumnapthalide(萘钠).Thishasgeneratedrenewedinterestofthescientificcommunitytowardsthestudyanddiscoveryofnewconductingpolymericsystems.Historical background of electronically conducting polymers第17页，本讲稿共85页Poly-paraphenylene(对苯基)wassynthesizedbyIvoryetal.(1979).Itformshighlyconductingchargetransfercomplexeswithbothnandptypedopants.DopingwithAsF5increasesitsconductivitytoitsvaluesfrom105to500Scm1.TheoreticalmodelsandelectronspinresonancemeasurementsindicatethatthechargetransportinPPPisapolaron(极化子)/bipolaron.PPS(聚苯硫醚)wasthefirstnon-rigid,butnotfullycarbonbackbonelinkedconductingpolymer.Itsdiscoverywasparticularlyexciting,sinceitspropertyofsolutionprocessabilityopenedthedoorforpotentiallyobtainingcommerciallyviableconductingplastics(Raboltetal.,1980).Historical background of electronically conducting polymers第18页，本讲稿共85页Amongstpolyheterocyclines(聚杂环聚杂环),polypyrrole(PPY)hasbeeninvestigatedthemost.TheelectrochemicaloxidationofpyrroleinaqueousH2SO4canbecarriedoutonplatinumelectrode.TheproductisaconductingpolymerknownasPyrroleBlackKanazawaetal.(1979)producedcoherentfilmsofPPYwithaconductivityof100Scm1andexhibitedexcellentairstability.Butthemainhindrance(障碍)ofitsprocessabilityisinitsinsolubilityinanyorganicsolvents.Historical background of electronically conducting polymers第19页，本讲稿共85页PTH(聚噻吩)shows remarkable stability of both oxidized(p-doped)conducting form and its neutral(undoped)insulating form in both air and water.It shows high doping level upto 50%which may be attributed to its partially crystalline nature that has been confirmed by X-ray photoelectron spectroscopy studies.Many other conducting polymers such as polyfuran(聚呋喃聚呋喃),polyindole(聚吲哚聚吲哚),polycarbazole(聚咔唑聚咔唑),polyaniline etc.have also been synthesized.Structures of some typical conducting polymers have been shown in Fig.1.Historical background of electronically conducting polymers第20页，本讲稿共85页Synthesis of conducting polymers第21页，本讲稿共85页There is no singular method for synthesising polymers that can be transformed into conductive polymers,the incorporation of extended(延长延长)-electron conjugation(共轭共轭)is of foremost importance.Conductive polymers except ionomeric(离子交联的)polymers may be synthesised using standard methods of polymerisation including conventional as well as specific routes which include Witting(维狄希),Horner(霍纳)and Grignard(格林尼亚)reactions,polycondensation processes and metal catalysed polymerisation techniques.Oxidative coupling(偶合)with oxidising Lewis acid catalysts generally leads to polymers with aromatic or heterocyclic building blocks(构件构件).Synthesis of conducting polymers第22页，本讲稿共85页Conductive polymers may be synthesised by any one of the following techniques:1.Chemical polymerisation2.Electrochemical polymerisation3.Photochemical polymerisation4.Metathesis(复分解)polymerisation5.Concentrated emulsion(浓乳液浓乳液)polymerisation 6.Inclusion(夹杂)polymerisation7.Solid-state polymerisation8.Plasma(等离子体)polymerisation9.Pyrolysis(高温分解)10.Soluble precursor(前体)polymer preparationSynthesis of conducting polymers第23页，本讲稿共85页Among all the above categories,chemical polymerisation is the most useful method for preparing large amounts of conductive polymers,since it is performed without electrodes.Chemical polymerisation(oxidative coupling)is followed by the oxidation of monomers to a cation(阳离子)radical and their coupling to form dications and the repetition(重复)of this process generates a polymer.All the classes of conjugated polymers may be synthesised by this technique.Synthesis of conducting polymers第24页，本讲稿共85页Electrochemical polymerisation is normally carried out in a single-or dual-compartment(隔间隔间)cell by adopting a standard three-electrode configuration in a supporting electrolyte,both dissolved in an appropriate(适当的适当的)solvent.Electrochemical polymerisation can be carried out potentiometrically by using a suitable power supply(potentiogalvanostat).Synthesis of conducting polymers第25页，本讲稿共85页Generally,potentiostaticconditionsarerecommendedtoobtainthinfilms,whilegalvanostaticconditionsarerecommendedtoobtainthickfilms.Theelectrochemicaltechniquehasreceivedwiderattentionbothbecauseofthesimplicityandtheaddedadvantageofobtainingaconductivepolymerbeingsimultaneouslydoped.Besidesthis,awiderchoiceofcationsandanionsforuseas“dopantions”isavailableintheelectrochemicalpolymerisationprocess.Free-standing(自由选定自由选定)aswellasself-supportingconductivepolymerfilmsofdesiredthicknessorgeometrycanbeobtained.Synthesis of conducting polymers第26页，本讲稿共85页Using this novel technique,a variety of conductive polymers like polypyrrole,polythiophene,polyaniline,polyphenylene oxide pyrrole and polyaniline/polymeric acid composite have been generated.Pyrrole in aqueous acetontrile solvent containing tetraethyl ammonium tetrafluoroborate was electropolymerised in a two-electrode electrochemical cell.Polypyrrole containing the BF4-ion(dopant)was obtained as a film deposited on the platinum electrode surface.Synthesis of conducting polymers第27页，本讲稿共85页This method has also been used to polymeric acetylene(乙炔乙炔).In an electrolytic cell,consisting of Pt as cathode and a Ni strip as anode,acetylene gas is passed over a solution comprising NiBr2 dissolved in CH3CN.On application of voltage varying from 5 to 40 V for about 50 min.polyacetylene films can be easily grown on a Pt electrode.The degree of doping depends on the dopant concentration,voltage applied and the amount of charge passed.Synthesis of conducting polymers第28页，本讲稿共85页Synthesis of conducting polymers第29页，本讲稿共85页Photochemical polymerisation takes place in the presence of sunlight.This technique utilises photons to initiate a polymerisation reaction in the presence of photosensitisers.Recently,pyrrole has been photopolymerised using a ruthenium(II)complex as photosensitiser.Under photoirradiation,Ru(II)is oxidised to Ru(III)and the polymerisation is initiated by a one-electron transfer oxidation process.Polypyrrole(PPy)films may be obtained by photosensitised polymerisation of benzo(C)thiophene(苯并噻吩苯并噻吩)has been carried out in acetonitrile using CCl4 and tetrabutylammoniumbromide.Synthesis of conducting polymers第30页，本讲稿共85页Plasma(等离子体等离子体)polymerisationisatechniqueforpreparingultrathinuniformlayers(500-100)thatstronglyadheretoanappropriatesubstrate.Electricglowdischargeisusedtocreatelow-temperature“cold”plasma.Theadvantageofthistechniqueisthatiteliminatesvariousstepsneededfortheconventionalcoatingprocess.Synthesis of conducting polymers第31页，本讲稿共85页Metathesis(复分解)polymerisation is unique,differing from all other polymerisations in that all the double bonds in the monomer remain in the polymer.It was a natural outgrowth(发展)of Ziegler-Natta polymerisation in that the catalysts used are similar,and often identical(一样的),i.e.a transition metal compound plus usually an organometallic alkylating agent(烷基化剂).Metathesis polymerisation is further divided into three classes:ring-opening metathesis of cyclo-olefins(环状石蜡)(ROMP);metathesis of alkynes(炔烃),acyclic(脂肪族的)or cyclic;and metathesis of diolefins(二烯).By far the greatest amount of work has been done on ROMP.Synthesis of conducting polymers第32页，本讲稿共85页Pyrolysis(高温分解)is probably one of the oldest approach utilised to synthesise conductive polymers by eliminating heteroatoms(杂原子)from the polymer by heating it to form extended aromatic structures.The product of polymer hydrolysis can be a film,powder or a fibre depending on the form and nature of the standing polymer(常规聚合物)including the pyrolysis condition.Synthesis of conducting polymers第33页，本讲稿共85页Nevertheless,conductive polymers have also been synthesised by other techniques such as chain polymerisation,step-growth polymerisation,chemical vapour deposition,solid-state polymerisation,soluble precursor polymer preparation,concentrated emulsion polymerisation etc.However,most of these techniques are time-consuming and involve the use of costly chemicals.Synthesis of conducting polymers第34页，本讲稿共85页Conduction mechanism第35页，本讲稿共85页Conduction mechanismThe mechanism of conduction in such polymers is very complex since such a material exhibits conductivity across a range of about fifteen orders of magnitude and many involve different mechanisms within different regimes(情景情景).Conducting polymers show enhanced electrical conductivity by several orders of magnitude of doping.The concept of solitons(光孤子光孤子),polarons and bipolarons has been used to explain the electronic phenomena in these systems(Heeger,1986).第36页，本讲稿共85页什么是什么是Soliton光孤子是传播时几乎没有能量损失并能保持其形状光孤子是传播时几乎没有能量损失并能保持其形状(即使与即使与其他波相碰撞其他波相碰撞)的的波波，这种现象首先是在水中被观察到的。孤子，这种现象首先是在水中被观察到的。孤子以光脉冲的形式被用于光纤传输系统以提高距离和性能。光孤以光脉冲的形式被用于光纤传输系统以提高距离和性能。光孤子信号按照数字编码方法编码后进入光缆。基于光孤子的设备子信号按照数字编码方法编码后进入光缆。基于光孤子的设备发射通过光缆传播而又不会出现色散的激光短脉冲。发射通过光缆传播而又不会出现色散的激光短脉冲。光弧子是一种特殊的光弧子是一种特殊的ps数量级上的超短光脉冲，由于它在数量级上的超短光脉冲，由于它在光纤的反常色散区，群速度色散和非线性效应相互平衡，因而光纤的反常色散区，群速度色散和非线性效应相互平衡，因而经过光纤长距离传输后，波形和速度都保持不变。光弧子通信经过光纤长距离传输后，波形和速度都保持不变。光弧子通信就是利用光弧子作为载体实现长距离无畸变的通信，在零误码就是利用光弧子作为载体实现长距离无畸变的通信，在零误码的情况下信息传递可达万里之遥。的情况下信息传递可达万里之遥。第37页，本讲稿共85页polaron来作用于来作用于电子电子，改变电子的状态与，改变电子的状态与能量能量，并伴随电子通，并伴随电子通过过点阵点阵运动运动。电子及其周围的。电子及其周围的极化场所极化场所构成的构成的总体总体，称，称为为极化子极化子。极。极化子是化子是离子晶体离子晶体中基本的中基本的载流子载流子。极化子。极化子的尺寸由电子周围的尺寸由电子周围畸畸变变场区域的大小确定。当这个区域场区域的大小确定。当这个区域比比晶格常数晶格常数大很多时，称为大很多时，称为大极化子，这时晶体可作为大极化子，这时晶体可作为连续介质连续介质处理处理;当畸变区等于或小当畸变区等于或小于晶格常数时，称为于晶格常数时，称为小极化子，此时必须考虑小极化子，此时必须考虑晶体结构晶体结构的的原子原子性，用晶格模性，用晶格模型处理。型处理。第38页，本讲稿共85页Conductivity in conducting polymers is influenced by a variety of factors including polaron length,the conjugation length,the overall chain length and by the charge transfer to adjacent molecules(Kroschwitz,1988).These are explained by large number of models based on intersoliton(中间光极子中间光极子)hopping,hopping between localized states assisted by lattice vibrations,intra-chain hopping of bipolarons,variable range hopping in 3-dimensions and charging energy limited tunneling between conducting domains.Conduction mechanism第39页，本讲稿共85页Conductivity improvement techniques第40页，本讲稿共85页The conductivity of a polymer can be increased several-fold by doping it with an oxidative/reductive substituents(取代基)or by donor/acceptor(给体/受体)radicals.Shirakawa and Ikeda discovered that doping of polyacetylene(PA)with metallic regimes(态)increases its conductivity by 9-13 orders of magnitude.Doping is accomplished by chemical methods of direct exposure of the conjugated polymer to a charge transfer agent(dopant)in the gas or solution phase,or by electrochemical oxidation or reduction.Conductivity improvement techniques-doping第41页，本讲稿共85页The doping is usually quantitative and the carrier concentration is directly proportional to the dopant concentration.Doping of conductive polymers involves random dispersion or aggregation of dopants in molar concentrations in the disordered structure of entangled chain and fibrils(原纤).Polymer doping leads to the formation of conjugational defects,viz.solitons,polarons or bipolarons in the polymer chain.An x-ray diffraction study on iodine-doped polyacetylene chain increases with donor doping but decreases on acceptor doping.Conductivity improvement techniques-doping第42页，本讲稿共85页The presence of localised