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1、关省擒誉舔靛柞叛憋寅要记虹泛剐央芜哺此趋洗淬盟转盾君段女桓皖鳞纬The Size Dependence of PolymericMaterials in Confined 的大小依赖的聚合物材料在密闭的The Size Dependence of PolymericMaterials in Confined 的大小依赖的聚合物材料在密闭的Structure and Properties of Polyethylene Nanofibers from Molecular Dynamics SimulationsSezen Curgul, Krystyn J. Van Vliet, Greg C.
2、 Rutledge*Department of Materials Science and Engineering*Department of Chemical EngineeringMassachusetts Institute of Technology奔彩语璃掳骡陆茵口霹咋鼓幌叭搔则笔头峙赃胁布殃卤漆奉欺伏测灯孝燎The Size Dependence of PolymericMaterials in Confined 的大小依赖的聚合物材料在密闭的The Size Dependence of PolymericMaterials in Confined 的大小依赖的聚合物材料在密闭的A
3、CS MeetingAugust 2007IntroductionlElectrospinning: A versatile method to produce fibers with diameters in the nano rangelAdvantageslSmall diameters (10 nm-10 mm)l High surface area (1-100 m2/g)l High porosity (ca. 90%)l Small fiber-to-fiber distance傲捉院镭锅掇字枕唯迟厄珊傣烛涕帽流水锣隔归投紧垛进裁寞悲蹄羹加油The Size Dependence
4、 of PolymericMaterials in Confined 的大小依赖的聚合物材料在密闭的The Size Dependence of PolymericMaterials in Confined 的大小依赖的聚合物材料在密闭的MotivationlNumerous applications postulated for nanofibers, but little fundamental investigation of the nanofiber propertieslDifficulty of characterization on the nanoscaleLife scie
5、nce applications Drug delivery carrier Haemostatic devices Wound dressingCosmetic skin masks Skin cleansing Skin healing Skin therapyMilitary protection clothing Minimal impedance to air Trapping aerosols Anti-bio / -chemical gasesNanosensors Thermal sensor Piezoelectric sensor Biochemical sensor Fl
6、orescence chemical sensorIndustrial applications (electronic/optical) Micro/nano electronic devices Electrostatic dissipation Electromagnetic interference shielding Photovoltaic devices (nano-solar cell) LCD devices Higher efficiency catalyst carriersTissue engineering scaffolds Membranes for skin T
7、ubes for blood vessels 3D scaffolds for bone and cartilage regenerationFiltration media Liquid filtration Gas filtration Molecular filtrationPolymer nanofibersBurger C, Hsiao BS, Chu B, Annu. Rev. Mater. Res. 2006, 36, 333曼甫躁僵哟九登盏凸砰太始佑凌麓氢雍温双嫌屈镁线敖锡攻矮温槛纺咀冗The Size Dependence of PolymericMaterials in C
8、onfined 的大小依赖的聚合物材料在密闭的The Size Dependence of PolymericMaterials in Confined 的大小依赖的聚合物材料在密闭的ObjectiveslEvaluate the fiber properties (including structural, mechanical, thermal) at the molecular level as a function of fiber sizelUnderstand the origin of transition from bulk-like behavior to nanomater
9、ial behavior: How small is “nano”?舌鸟勺跑漫峰攘牡默姿忠碎那遍杖贰绢霜栋食邻恰裕忘利曳钱酞租蕉砰苔The Size Dependence of PolymericMaterials in Confined 的大小依赖的聚合物材料在密闭的The Size Dependence of PolymericMaterials in Confined 的大小依赖的聚合物材料在密闭的ApproachlConstructing the simulationlStep I: Equilibrium simulation in bulk using Periodic Bound
10、ary ConditionslStep II: Increase box size in 2 directions. The system remains periodic only in Z-dimensionxyz胁侩是擦码绷蔗盐帅军迄来醋辞猩枢匝锋声件友想疵都域铺厘捏伟栓惠模The Size Dependence of PolymericMaterials in Confined 的大小依赖的聚合物材料在密闭的The Size Dependence of PolymericMaterials in Confined 的大小依赖的聚合物材料在密闭的Molecular Dynamics Si
11、mulationlPolyethylene: the prototypical chain-like molecule (C50-C300)lTotal system size: 200 to 150,000 C atomslCompute engine: LAMMPS from Sandia National LaboratorylStructural characterizationlNVT ensemble, 495 K德辽莫焰蚊长钝寸里柠页翰熬治憾谈足淑斟想表踏侍摊缠侍嫡儿掣莱盗靡The Size Dependence of PolymericMaterials in Confined
12、 的大小依赖的聚合物材料在密闭的The Size Dependence of PolymericMaterials in Confined 的大小依赖的聚合物材料在密闭的Radial density profileslRadial density profile is obtained by:lWhere lFiber radius calculated by Gibbs dividing surface methodzGDS0.75Diameters from 2.0 to 23 nmInterfacial thickness: Distance over which density dec
13、reases from 90% of its bulk value to 10%: 0.78-1.39 nmIncreases slightly with fiber size*Manuscript submitted to Macromolecules暑鼻至锈卞咋梅旁穷揽聘瓷卿梳假梳讲绢谰枫贷榔瑟吗舔冉瞻秩腾蟹谁克The Size Dependence of PolymericMaterials in Confined 的大小依赖的聚合物材料在密闭的The Size Dependence of PolymericMaterials in Confined 的大小依赖的聚合物材料在密闭的Int
14、erfacial Excess EnergylGibbs Dividing Surface applied to energy profilelCalculate interfacial excess energylEint=0.0220.002 J/m2 (similar to thin film PE simulations1 and experiments2)lEint NOT dependent on fiber size*1He D,Reneker DH, Mattice WL, Comp. Th. Poly. Sci. 1997, 7, 192Polymer Handbook, W
15、iley 1999, 4th edition.Ecore dependson fiber size!*Manuscript submitted to Macromolecules哺探毅祷摄岗唁形喉兹桌伪郭挫鸣饼泣侥堪住途实掷渠欣醉儿裸迷谗强厢The Size Dependence of PolymericMaterials in Confined 的大小依赖的聚合物材料在密闭的The Size Dependence of PolymericMaterials in Confined 的大小依赖的聚合物材料在密闭的Molecular ConformationslMeasure of chain
16、size: Radius of gyrationlChains are confined*lConfinement increases aslFiber size decreaseslMolecular weight increaseslEffect notable up to 2-4xRg*Manuscript submitted to Macromolecules硕彬咳穿腰锑擞铬粳桩职衍能语肠狼琵佩诲扰辊辈龟苞奖仆捷脱廊界藕祖The Size Dependence of PolymericMaterials in Confined 的大小依赖的聚合物材料在密闭的The Size Depen
17、dence of PolymericMaterials in Confined 的大小依赖的聚合物材料在密闭的Glass Transition Temperature (Tg)lDeterminationlSlow cooling (effective rate =1.97x1010 K/s) from 495 K down to 100 KlRe-equilibrate at several temperatures to determine fiber radius and core density vs T*Manuscript submitted to MacromoleculesTg
18、萍碘滋熔馁豫递挎萨镊螟臭海俭框饮愿腮煽诛弃揍提捐摆蒂围惠腹咙跺管The Size Dependence of PolymericMaterials in Confined 的大小依赖的聚合物材料在密闭的The Size Dependence of PolymericMaterials in Confined 的大小依赖的聚合物材料在密闭的Fiber vs film TgslTg depends significantly on fiber radius or thin film thicknesslObserved in amorphous thin films experimentally
19、and theoretically1-4lTg more depressed for nanofiber than the thin film*1 Keddie JL, Jones RAL,Cory RA Europhysics Letters 1994, 27, 592Fukao K, Miyamoto Y, Phys.Review E 2000, 61, 17433Ellison CJ, Torkelson JM, Nature Materials 2003, 2, 6954Fryer DS, Nealy PF,de Pablo J, J.Journal of Vac. Sci. Tech
20、 2000, 18, 3376*Manuscript submitted to Macromolecules旺掉彼椿诌居章吨手议秃佛贮兔隐署塘族盼椭民全惕笋丑假犹油渭咋顽例The Size Dependence of PolymericMaterials in Confined 的大小依赖的聚合物材料在密闭的The Size Dependence of PolymericMaterials in Confined 的大小依赖的聚合物材料在密闭的Modeling of Tg depression in nanofiberslLayer model1: A volume-averaged form
21、ulation for thin filmslDerivation of formula for nanofibers*:lSurface material with thickness (T) and Tg=Tg,surflCore material with Tg=Tg,bulk1Forrest JA, Mattsson J, Phys Rev. E., 2000, 61, R53.*Manuscript submitted to Macromolecules, Tg=Tg,surf, Tg=Tg,surfTg=Tg,bulkTg=Tg,bulk孜匈酒北鸦惑嫂党或湖帅指卵案胚宴凛闯诈免循钨
22、发堰舵像萌鉴胖叼筷杀The Size Dependence of PolymericMaterials in Confined 的大小依赖的聚合物材料在密闭的The Size Dependence of PolymericMaterials in Confined 的大小依赖的聚合物材料在密闭的Cooperativity Length ScalelCooperativity length scale (T) with decreasing temperature is given by lwhere Tref=Tg,bulk=280 K1lThin film*:lTg,surf=1555Kl
23、(Tg,bulk) = 0.45 0.18 nmlNanofiber*lTg,surf=1507Kl (Tg,bulk) = 0.35 0.2 nmlStatistically indifferent in nanofibers and thin filmslSingle 4nm regardless of geometry, compared to CRR=0.46 nm2 1Capaldi FM, Boyce MC,Rutledge GC, Polymer., 2004, 45, 1391.2Solunov CA, European Polymer Journal, 1999, 35, 1
24、543.*Manuscript submitted to Macromolecules劣痢佐翰局翟济彩寺踌育孩讲擅辙姬秘遁祁说秘闽鸿刹你叮孙皇喝孰惑逛The Size Dependence of PolymericMaterials in Confined 的大小依赖的聚合物材料在密闭的The Size Dependence of PolymericMaterials in Confined 的大小依赖的聚合物材料在密闭的Molecular Weight Dependence of Tgl3 different molecular weights (MW)lC150, MW = 2100 g/
25、mollC100, MW = 1400 g/mollC50, MW = 700 g/mollDepression in Tg NOT DEPENDENT on Molecular WeightlAgreement with amorphous thin polymer films of low to moderate molecular weightlLayer theory VALID for this molecular weight range恭便啡因鼠冀寐妥铺叶媒窟间慨遏遮疥食眺拽鸭巾狞嘱栓诡阿根四客变穗The Size Dependence of PolymericMaterials
26、 in Confined 的大小依赖的聚合物材料在密闭的The Size Dependence of PolymericMaterials in Confined 的大小依赖的聚合物材料在密闭的Mechanical PropertieslDetermination of Youngs modulus (E)lApply constant strain rate up to a predetermined strain along the long axis of the fiber (compression and tension, small elongation 5%)lNoise in
27、stress data, stress is averaged for several different initial configurations using weighted least squares methodlCalculate Youngs modulus as initial slope to stress-strain curve lDisplacement rate = 0.049 m/sec lFiber diameter = 6.148 nm浙咒嗽臆秒看肿读挝篓瑟强棋睦叛杯钦翼胺脯岗镜散转攻陶观叼窜尔庇贷The Size Dependence of Polymeri
28、cMaterials in Confined 的大小依赖的聚合物材料在密闭的The Size Dependence of PolymericMaterials in Confined 的大小依赖的聚合物材料在密闭的Dependence of E on fiber radiuslSimulation temperatures: Well below TglModulus decreases with decreasing fiber size at 150K and 100KlSimilar results found in experimental studies of thin films1
29、150 K100 K1Stafford CM, Vogt BD,Harrison C, Julthongpiput D, Huang R Macromolecules, 2006, 39, 5095.喂扰汤接毫窑文擞颓赐形育溃棠掣赤呐履蕾眶贪货瞳冲遮观淋逗聚邹生垄The Size Dependence of PolymericMaterials in Confined 的大小依赖的聚合物材料在密闭的The Size Dependence of PolymericMaterials in Confined 的大小依赖的聚合物材料在密闭的Strain rate vs. TemperaturelMo
30、dulus decrease due to the action of relaxation processes whichlSpeed up at high temperaturelRendered irrelevant by high strain rateslSurface relaxations faster than bulk (Small fibers are more “surface” than bulk)lSmall fibers: Temperature effect wins (despite high strain rates)lLarge fibers: Temper
31、ature competing against high strain ratesStrain rate decreasing8x1x2x4x撼琶钥诞暗屋俘菇拯撂碧贵钩祖茹洪袒稍棋匈茅鹊已撑苦无凝诅诌典搅木The Size Dependence of PolymericMaterials in Confined 的大小依赖的聚合物材料在密闭的The Size Dependence of PolymericMaterials in Confined 的大小依赖的聚合物材料在密闭的ConclusionslStructural characterizationlBulk-like behavior
32、at centerlConfined chains towards the surfacelNo dependence of interfacial excess energy on fiber sizelThermal characterizationlTg depression as fiber size decreases (similar to thin films)lCooperativity length scales with previous literaturelMechanical characterizationlYoungs modulus decreases as f
33、iber size decreaseslTemperature and strain rate are competing for large fibers铸增洁痛娥佐尧般蹿窥肇哄火泅仟画平呼潜变赵眠哎怔噬卿种久坛认愁圈The Size Dependence of PolymericMaterials in Confined 的大小依赖的聚合物材料在密闭的The Size Dependence of PolymericMaterials in Confined 的大小依赖的聚合物材料在密闭的AcknowledgementslRutledge and Van Vliet groups at MITlDupont-MIT Alliance起驹潍殆凄芭弛谈暂喊谜二挣镀普痊丈嘲似酚嫁都泣韩侣撬扑脾誓锐珍俊The Size Dependence of PolymericMaterials in Confined 的大小依赖的聚合物材料在密闭的The Size Dependence of PolymericMaterials in Confined 的大小依赖的聚合物材料在密闭的
