高介電聚合物基復(fù)合材料的制備與性能

附件2論文中英文摘要格式作者姓名：沈洋論文題目：高介電聚合物基復(fù)合材料的制備與性能作者簡(jiǎn)介：沈洋，男，1980年11月出生，2002年9月師從于清華大學(xué)南策文教授，于2007年1月獲博士學(xué)位。中文摘要電子設(shè)備日益小型化、多功能化的發(fā)展趨勢(shì)，對(duì)電子線路中元件的封裝密度提出了更高的要求。嵌入式無源元件技術(shù)能夠?qū)崿F(xiàn)對(duì)電容、電感等無源元件在印刷線路板內(nèi)部的嵌入式封裝，從而節(jié)省線路板表面空間、提高封裝密度。聚合物基復(fù)合電介質(zhì)材料因其在嵌入式電容器中的潛在應(yīng)用價(jià)值而日益受到人們的關(guān)注。雖然具有一定介電常數(shù)的陶瓷顆粒/聚合物型復(fù)合材料已經(jīng)獲得了初步應(yīng)用，但是由于這些材料的介電常數(shù)仍然偏低，并且由于較高陶瓷填料含量引起復(fù)合材料機(jī)械及工藝性能惡化，陶瓷顆粒/聚合物型復(fù)合材料仍不是理想的目標(biāo)材料。通過向聚合物基體內(nèi)添加導(dǎo)電顆粒，利用導(dǎo)電顆粒的滲流（逾滲）效應(yīng)提高復(fù)合材料介電常數(shù)的方法雖然能夠顯著地提高復(fù)合材料介電常數(shù)，但是隨之而來的是材料發(fā)生“絕緣體－導(dǎo)體”轉(zhuǎn)變會(huì)導(dǎo)致較高的電導(dǎo)率和急劇增大的損耗。同時(shí)在滲流閾值附近復(fù)合材料介電常數(shù)對(duì)導(dǎo)電顆粒含量過于敏感，相對(duì)滲流閾值的微小含量偏差就會(huì)引起介電性能的嚴(yán)重降低，造成介電性能可重復(fù)性差，增大了工藝控制的難度。本論文主要著眼于通過選擇材料體系、設(shè)計(jì)與控制材料微結(jié)構(gòu)兩種手段來降低滲流型復(fù)合材料的介電損耗。首先由研究導(dǎo)電填料的種類、形狀對(duì)聚合物基復(fù)合材料的介電性能影響規(guī)律入手，進(jìn)而提出通過在導(dǎo)電顆粒之間引入絕緣界面層來抑制由顆粒間的直流漏導(dǎo)所引起的高介電損耗，實(shí)現(xiàn)對(duì)滲流型復(fù)合材料介電性能的綜合優(yōu)化。在對(duì)高介電復(fù)合材料研究的基礎(chǔ)上，通過添加大尺寸鐵氧體顆粒，在滲流型復(fù)合電介質(zhì)材料內(nèi)部形成雙滲流結(jié)構(gòu)，進(jìn)一步實(shí)現(xiàn)了電容、電感特性在聚合物基復(fù)合材料中的集成。首先以半導(dǎo)體填料取代導(dǎo)體填料以降低漏電損耗，采用具有較大長(zhǎng)徑比的半導(dǎo)體Bi2S3納米棒為填料，以聚偏氟乙烯（Polyvinylidenefluoride,PVDF）為聚合物基體，制備了Bi2S3/PVDF復(fù)合材料。具有一定長(zhǎng)徑比的Bi2S3納米棒能夠顯著降低復(fù)合材料的滲流閾值，從而可以在低填料含量的條件下，使復(fù)合材料的介電常數(shù)得到提高。且Bi2S3納米棒的定向排列使得復(fù)合材料介電性能呈現(xiàn)出明顯的各向異性。但實(shí)驗(yàn)結(jié)果表明，棒狀顆粒滲流時(shí)彼此間有限的接觸面積造成滲流結(jié)構(gòu)較為脆弱，易受到外電場(chǎng)破壞；半導(dǎo)體Bi2S3能夠在一定程度上降低復(fù)合材料的電導(dǎo)率，同其它采用導(dǎo)電顆粒為填料的復(fù)合材料體系相比，Bi2S3/PVDF復(fù)合材料的電導(dǎo)率要低2～3個(gè)數(shù)量級(jí)。但是在降低介電損耗方面仍然沒有取得預(yù)期的理想效果。并且由于Bi2S3半導(dǎo)體本征電導(dǎo)率隨溫度升高而增加，該復(fù)合材料在高溫下（>100oC）漏導(dǎo)顯著增大，介電損耗快速增加。為了有效降低滲流型復(fù)合材料介電損耗，本論文提出了在導(dǎo)電顆粒間引入絕緣層來阻斷漏導(dǎo)通道，采用具有核殼結(jié)構(gòu)的Ag@C納米顆粒與環(huán)氧樹脂（Epoxy）進(jìn)行復(fù)合，發(fā)展了高介電、低損耗的新型Ag@C/Epoxy復(fù)合材料。首先采用水熱法，利用葡萄糖在高溫高壓下的催化特性還原出Ag納米顆粒，繼而通過葡萄糖在高活性Ag納米顆粒表面的聚合實(shí)現(xiàn)絕緣有機(jī)多聚糖殼層（記為C）對(duì)Ag納米顆粒的包覆，即Ag@C。該多聚糖殼層的厚度及導(dǎo)電性可以通過改變水熱反應(yīng)條件進(jìn)行調(diào)制，最終獲得直徑80~100nm的納米Ag顆粒，其外包覆層厚度可在4~120nm之間調(diào)節(jié)。將此核殼結(jié)構(gòu)納米顆粒與樹脂進(jìn)行液相共混，并隨后加入固化劑實(shí)現(xiàn)環(huán)氧樹脂的原位聚合，從而實(shí)現(xiàn)了納米顆粒在聚合物基體內(nèi)的均勻穩(wěn)定分散，并進(jìn)一步將此前軀體混合液以溶液澆鑄法成膜，最終獲得厚度80~100m的復(fù)合材料厚膜。對(duì)采用該方法制備復(fù)合材料介電性能進(jìn)行綜合表征，結(jié)果顯示，Ag@C/Epoxy復(fù)合材料的介電性能獲得了綜合優(yōu)化。該復(fù)合材料的介電常數(shù)在環(huán)氧樹脂基體的基礎(chǔ)上提高了約2個(gè)數(shù)量級(jí)（例如，采用殼層厚度8nm的Ag@C顆粒，在滲流閾值附近介電常數(shù)達(dá)到320），其介電損耗保持在Tanδ<0.04的較低水平。且介電常數(shù)隨填料含量、頻率、溫度、外電場(chǎng)強(qiáng)度變化顯示出良好穩(wěn)定性。在所測(cè)量范圍（如，100Hz~30MHz，20oC~120oC）內(nèi)均未顯示出介電松弛，復(fù)合材料擊穿場(chǎng)強(qiáng)達(dá)到107Vm-1。從而成功地實(shí)現(xiàn)了滲流型復(fù)合材料的高介電、低損耗、高穩(wěn)定性，并提出了相應(yīng)的理論模擬解釋。在此基礎(chǔ)上，繼續(xù)對(duì)納米顆粒中有機(jī)多聚糖層的厚度和電性能對(duì)Ag@C/Epoxy復(fù)合材料介電性能的影響進(jìn)行研究。結(jié)果表明，復(fù)合材料的介電性能對(duì)于Ag@C顆粒中有機(jī)多聚糖殼層厚度的變化較為敏感，顯示出明顯的納米尺寸效應(yīng)。因而通過調(diào)節(jié)有機(jī)多聚糖層的厚度，實(shí)現(xiàn)了對(duì)復(fù)合材料介電常數(shù)的調(diào)制，如在殼層厚度由4nm增加至13nm時(shí)，復(fù)合材料的介電常數(shù)可以在430至210之間進(jìn)行調(diào)節(jié)。有機(jī)多聚糖殼層電導(dǎo)率的增加將造成復(fù)合材料內(nèi)部漏電流增加，從而引起介電損耗增大，介電常數(shù)在滲流閾值以上隨成分變化的穩(wěn)定性嚴(yán)重下降，并引起介電常數(shù)隨溫度升高、以及外電場(chǎng)強(qiáng)度增加均出現(xiàn)一定程度下降。這進(jìn)一步證明，殼層良好的電絕緣特性對(duì)復(fù)合材料介電性能的提高有非常重要的意義。提出并實(shí)驗(yàn)證實(shí)了絕緣有機(jī)殼層在Ag@C/Epoxy復(fù)合材料中的主要作用機(jī)制：(1)作為Ag顆粒的表面改性劑提高了Ag顆粒與高分子基體間的相容性，保證了Ag@C納米顆粒的均勻分散；(2)作為Ag顆粒間的絕緣界面層，阻斷了Ag顆粒間的漏電通過，從而降低了復(fù)合材料內(nèi)部的漏電流；(3)其結(jié)構(gòu)上的完整性保證了在滲流閾值以上Ag顆粒之間仍被完全隔絕，微電容結(jié)構(gòu)得以保存，使得復(fù)合材料介電常數(shù)在滲流閾值以上仍然保持穩(wěn)定；從而使得Ag@C/Epoxy復(fù)合材料的介電性能得到綜合優(yōu)化。在高介電滲流型復(fù)合材料的基礎(chǔ)上，將滲流型復(fù)合材料的高介電特性與現(xiàn)有軟磁性復(fù)合材料相結(jié)合，提出了電容-電感（容感）兩性集成的一條新思路，即制備兼?zhèn)潆娙?電感兩性的聚合物基復(fù)合材料。選用具有一定磁性的導(dǎo)電Ni顆粒，以及具有高起始磁導(dǎo)率的鐵氧體顆粒作為改性填料，選用自身具有較高介電常數(shù)的PVDF作為聚合物基體，采用固相共混熱壓成型的簡(jiǎn)便方法制備了新型的Ni/鐵氧體/PVDF三相復(fù)合材料。利用大尺寸鐵氧體顆粒與小尺寸Ni顆粒的粒徑差，形成聚合物與Ni顆粒在鐵氧體顆粒間隙內(nèi)的擇優(yōu)分布，在聚合物復(fù)合構(gòu)型中形成聚合物與Ni顆粒同時(shí)發(fā)生滲流的所謂“雙滲流結(jié)構(gòu)”。大尺寸鐵氧體顆粒賦予復(fù)合材料較高的起始磁導(dǎo)率，小尺寸Ni顆粒在鐵氧體間隙內(nèi)的滲流效應(yīng)賦予復(fù)合材料以較高的介電常數(shù)。對(duì)復(fù)合材料所作的綜合磁、電性能表征證實(shí)，雙滲流結(jié)構(gòu)的三相復(fù)合材料同時(shí)具有較高的起始磁導(dǎo)率和介電常數(shù)。在Ni顆粒含量位于滲流閾值附近時(shí)，復(fù)合材料具有不同的容感特性：（1）當(dāng)控制復(fù)合材料中Ni顆粒的含量時(shí)，由于Ni顆粒之間尚未完全形成漏電通路，復(fù)合材料的介電損耗能夠控制在較低水平，從而使復(fù)合材料具有較為均衡的容感特性。與現(xiàn)有高溫共燒陶瓷基復(fù)合材料相比，本工作所制備的容感兩性材料具有基本相當(dāng)?shù)男阅?。由于聚合物基?fù)合材料具有無需高溫處理、工藝簡(jiǎn)單等優(yōu)勢(shì)，使其在容感兩性的集成應(yīng)用方面相較高溫共燒陶瓷基容感兩性復(fù)合材料具有一定優(yōu)勢(shì)；（2）當(dāng)控制復(fù)合材料中Ni顆粒的含量時(shí)，復(fù)合材料損耗急劇增加，使其不適合再作為容感集成無源元件介質(zhì)材料。但從另一方面講，較高的介電及磁損耗卻是電磁屏蔽材料最為重要的目標(biāo)參數(shù)，這使得的雙滲流結(jié)構(gòu)復(fù)合材料在電磁屏蔽領(lǐng)域具有潛在的應(yīng)用價(jià)值。關(guān)鍵詞：復(fù)合材料；介電常數(shù)；起始磁導(dǎo)率；嵌入式電容器；滲流

PreparationandPropertiesofPolymer-BasedCompositeswithHigh-Dielectric-ConstantYangShenABSTRACTEver-increasingdemandforhigherdensitycircuitsinelectronicshasgreatlyacceleratedtheminiaturizationandintegrationofchipelectroniccomponentswithhighperformanceandmulti-function,smallersize,highefficiencyandlowcost.Theembeddedpassivetechnologycansavetherealestateonthesurfaceoftheprinted-circuits-boards(PCBs)byembeddingthecapacitorsandinductorsinsidethePCBs.Polymercompositedielectricsarearousingincreasingattentionduetotheirpotentialapplicationinsomeembeddedcapacitors.Polymercompositesfilledwithceramicparticleshavebeenusedinsomeembeddedcapacitors.Still,thereismuchworktobedonetoimproveitslowdielectricconstantsanddeterioratedmechanicalandprocessingpropertiesduetothehighcontentofrigidceramicparticlesintheflexiblepolymermatrix.Byreplacingceramicparticleswithconductiveparticlesinthepolymercomposites,thepercolativepolymercompositescanbemadewiththedielectricconstantdramaticallyincreasedinthevicinityofthepercolationthresholdoftheconductiveparticles.Thisincreaseinthedielectricconstant,however,isalwaysaccompaniedbythealsogreatlyincreasedelectricalconductivityanddielectriclossduetothe“insulator-conductor”transitionhappenedatthepercolationpoint.Thistransitionalsoleadstoextremesensitivityofthedielectricconstanttothecontentoftheconductivefillers,i.e.,smalldeviationfromthepercolationthresholdcouldresultinseriousdropofthedielectricconstant,makingitratherdifficulttocontroltheparametersofthepreparationprocess.Thisthesisfocusedondecreasingthedielectriclossofthepercolativepolymercompositesbybothcarefullychoosingdifferentcombinationsoffillersandpolymermatrixandcontrollingthemicrostructureofthecomposites.Itstartedwiththeinvestigationoftheinfluenceoftheparametersoftheconductivefillers,i.e.,conductivityandshape,onthedielectricpropertiesofthepolymercomposites.Thenthedielectricpropertiesofthepercolativecompositeswereoptimizedbyintroducinginsulatinginterfaciallayersbetweenthefillers.Withtheoptimizationofthedielectricproperties,anoveldouble-percolatingstructurewasachievedinthepercolativecompositesbytheadditionofthelargesizedferriteparticles.Characteristicsofbothcapacitorsandinductorscanthusbeintegratedinthecompositesbythismeans.First,replacementofconductivefillerswithsemiconductivefillerswasproposedtoreducetheleakagecurrentinthepercolativecomposites.SemiconductiveBi2S3nanorodswithlargeaspectratiosandpolyvinylidenefluoride(PVDF)wereemployedtofabricatetheBi2S3/PVDFcomposites.TheBi2S3nanorodscouldsignificantlyreducethepercolationthresholdofthecompositesandtheirorientationinsidethematrixgaverisetotheanisotropyintheelectricalpropertiesofthecomposites.Forparticleswithlargeaspectratios,theirconnectionswitheachotherarepreferentiallyinatip-by-tippatternwhenpercolationhappens.Thus,thelimitedcontactingareabetweeneachtwonanorodsmadethepercolationstructureratherfragileandeasytobedestroyedbytheexternalelectricfield.SemiconductiveBi2S3couldreducetheconductivityofthecomposites.Comparedwiththecompositesfilledwithconductiveparticles,theconductivityoftheBi2S3/PVDFcompositesismuchlowerby2~3ordersofmagnitude.However,thesemiconductiveBi2S3fillersdidnotpresentidealresultsinreducingthedielectricloss.Thedielectriclossincreasedrapidlyattemperaturesover100oCduetotheincreaseintheintrinsicconductivityofthesemiconductiveBi2S3nanorods.Toefficientlysuppresstheleak-currentanddecreasedielectriclossofthecomposites,weproposedtoblocktheleakagepathbyintroducinganinsulatinglayerbetweenfillers.Core-shellstructuredAg@Cnanoparticleswerethenemployedtofabricatepolymercompositeswithepoxyaspolymermatrix.Core-shellstructuredAg@Cnanoparticlesweresynthesizedbyahydrothermalmethod.ThesilvernanoparticleswerefirstlyreducedbyglucosefromtheAgNO3solution,followedbythesubsequentdepositionoftheorganicdielectricshell(denotedasC)onitssurfacethroughthepolymerizationoftheglucose.Thethicknessandconductivityoftheorganicdielectricshellscanbemodulatedbyadjustingthehydrothermalparameters,resultinginahybridAg@Cnanoparticlewithasilvercoreof80~100nmandanorganicshellof4~120nm.Theseparticleswerethenmixedwithresinandhardenersuccessively.Thefollowingin-situpolymerizationoftheepoxystabilizedthenanoparticlesandgaverisetoahomogeneousdistributionoftheparticlesinsidethepolymermatrix.Finalcompositefilmsof80~100mwereobtainedbycastingthemixedsolutiononasiliconsubstrateandevaporatingsolvents.ThedielectricpropertiesoftheAg@C/Epoxycompositeswerecomprehensivelyoptimized.Forexample,areduceddielectricloss(Tanδ<0.04)wasachievedintheAg@C/EpoxycompositefilledwithAg@Cnanoparticleswiththeorganicshellof8nm,whilethedielectricconstantwasenhancedtoε=320.Moreover,thedielectricconstantremainedstablewiththevariationofenvironmentaltemperatureorelectricfrequency,andnodielectricrelaxationwasobservedintheexperimentalrange(e.g.,100Hz~30MHzand20oC~120oC).ThebreakdownfieldoftheAg@C/Epoxycompositeswasalsoenhancedbytheshellstoover107Vm-1.Thus,high-permittivity,lowdielectricloss,andhighstabilityhavebeensuccessfullyachievedinsuchnovelpercolativecomposites,whichwasalsoexplainedbythetheoreticalsimulations.Furtherstudyontheinfluenceofthethicknessoftheorganicshellsonthedielectricpropertiesofthecompositesclearlyshowedthesizeeffect,indicatingthatthedielectricconstantsofthecompositescouldbemodifiedbychangingtheshellthickness.Forexample,thedielectricconstantsofthecompositescouldbetunedfrom430~210byadjustingthethicknessoftheshellsintherangeof4~13nm.Besidesitsgeometricsize,theconductivityoftheorganicshellcouldalsoinfluencetheperformanceoftheAg@C/Epoxycomposites,inthesensethattheincreasedconductivitycouldleadtomoreleak-currentbetweenthesilvercores,hencehigherdielectricloss,andmakethecompositesmoresensitivetothedeviationofthefillercontentfromthepercolationthreshold.Thesefurtherdemonstratedthatagoodinsulatingfeatureoftheshellsplaysaveryimportantroleinenhancingthedielectricperformanceofthecomposites.ThisthesisproposedandverifiedthemainfunctionalmechanismsoftheinsultingorganicshellsintheAg@C/Epoxycomposites,i.e.,(1)theexcellentcompatibilityoftheorganicshellswiththepolymermatrixensuredthedispersionofthefillersinthematrix;(2)theyactedasinsulatinginter-layersbetweentheAgcorestoblocktheleakpathandthusreducedtheleakageanddielectriclossinthecomposites;(3)thecompletenessoftheshellsinthecompositesalsoendowedthecompositewithstabledielectricconstantsevenwhenthecontentoftheAg@Cnanoparticlesisbeyondthepercolationthreshold.AlltheseresultedinthecomprehensiveoptimizationofthedielectricpropertiesoftheAg@C/Epoxycomposites.Basedonthedielectricpercolativecomposites,anovelthree-phasepolymercompositewithbothhighdielectricconstantandhighinitialpermeabilitywasproposedbyintroducingferriteparticleswithhighinitialpermeabilityintothepercolativepolymercompositedielectrics.BothlargeferriteparticlesandsmallNiparticleswereemployedasfillersandwithPVDFaspolymermatrix.Thethree-phasecompositesofNi/ferrite/PVDFwerefabricatedbyasimplehot-pressingmethod.ThelargedifferencebetweentheparticlesizesfortheferriteandtheNifillersgaverisetoadouble-percolatingstructureinthecomposites.Thelargeferriteparticlesinthecompositenotonlyactasmagneticphase,endowingthecompositewithhighinitialpermeability,butalsopresentasahigh-volumefractiondiscrete(nonpercolating)phase,confiningpolymerandmetallicparticlesintoacontinuousdouble-percolatingstructureoflowvolumefractions.ThepercolationofNiparticlesinthegapsbetweentheferriteparticlesenhancedthedielectricconstantofthecompositestoaconsiderablevalue.