Photonic crystals in biology - NanoTR-VI

PP andPoster Session, Thursday, June 17Theme F686 - N1123Optimization of Surface Modified Polymer/MWCNTs Nanofibers as Reinforcement inNanocomposites111UElif ÖzdenUP P*, Yusuf MencelioluP Melih PapilaP1PFaculty of Engineering and Natural Sciences, Sabanci University, Istanbul 34956, TurkeyAbstract -The focus of this study is to fabricate composite nanofibers containing MWCNTs and to incorporate them in making reinforced andtoughened nanocomposites. A systematic understanding of the electrospinning process parameters for composite nanofibers was obtained andan emprical relationship between the parameters and the average fiber diameter was established by response surface methodology (RSM).Mechanical tests under flexural loads are reported to demonstrate the effect of the composite nanofiber reinforcement.Nano- to submicron-scale fibers are also recently exploredfor their reinforcing ability in composites. Carbon nanotubes(CNTs) have been widely considered as a filler material dueto their unique electrical and mechanical properties such aselectrical conductivity, high specific strength and stiffness[1]. There are numerous attempts to fabricate CNTsembedded electrospun polymeric nanofiber webs, to enhancemechanical properties of the nanofibrous structure [2,3].However, these composite nanofibers have not beenembedded into polymer matrices to produce nanocomposites.As reported in our previous work [4], surface reactive P(Stco-GMA)nanofibers are promising materials in reinforcingand toughening of the epoxy resin. For its extension,multiwalled carbon nanotubes (MWCNTs) reinforcedpolymer composite fiber webs have been fabricated using theelectrospinning technique.The solutions of P(St-co-GMA)/DMF at various MWCNTsconcentrations (1% wt, 1,5% and 2 % wt) were prepared andstirred magnetically for 24 hour to obtain homogeneity. SincePSt has aromatic ring, long term stabilization of MWCNTs inelectrospinning polymer solution has been successfullyachieved during nanofiber formation, which was alsoprovided by the Dynamic Light Scattering (DLS) analysis.An electrical bias potential (via Gamma High Voltage ES30P-20W) was applied to the polymer solutions contained in2-ml syringe, which has an alligator clip attached to thesyringe needle (diameter 300 m). The applied voltage wasadjusted to 15kV, while the grounded collector was placed at10 cm away from the syringe needle. A syringe pump(NewEra NE-1000 Syringe Pump) was used to maintain asolution flow rate of 30 l/hr during electrospinning.The three level factorial design of experiments wasimplemented to investigate and identify the significance oftwo process parameters (one is the polymer concentration andthe other is the MWCNTs concentration) on the average fiberdiameter, as seen in Figure 1. The morphologies and the fiberdiameters of PSt-co-GMA/MWCNTs fibrous webs wereevaluated by scanning electron microscope (SEM - LEO1530VP). A quantitative relationship between the polymerand the MWCNTs concentration parameters and the averagefiber diameter was sought by response surface methodology(RSM). SEM images demonstrated that P(St-co-GMA)/MWCNTs composite nanofibers were considerablythinner (200 - 550 nm) than P(St-co-GMA) nanofibers (400 –800 nm). This is attributed to the shear thinning effectassociated with the MWCNTs. Due to the shear thinningbehavior, shear viscosity decreased and resulted in reducedfiber diameter along with the increase on conductivity.Considering homogeneity of webs, uniformity and lowvariance in nanofiber diameter, electrospinning solution at30% polymer concentration and 1% MWCNTs concentrationwas preferred.In order to assess the mechanical performance due to theP(St-co-GMA)/MWCNTs composite fibers, they were firstcut into 12 mm x 50 mm pieces. Next, the fiber mats wereembedded into the epoxy resin per our procedure [4].Thermal-mechanical properties of the neat epoxy and thecomposite nanofiber reinforced nanocomposites wereinvestigated by using a dynamic mechanical thermal analyzer(Netzsch DMA 242). The storage moduli of the 30 wt% PStco-GMA/MWCNTs(1 wt%) composite nanofiber, atreinforced nanocomposites are about 20 times higher than theneat epoxy, at weight fraction of the nanofibers being as lowas 2% at 80 C. Mechanical response of nanowebs, at variousMWCNTs and polymer concentration, embedded into epoxyis also underway.Figure 1. The morphology of fibers at applied voltage 15 kV atpolymer concentrations from 25% to 30% wt and MWCNTsconcentrations from 1% to 2% wt with a constant tip-to-collectordistance of 15 cm.*Corrresponding author: HTelifozden@su.sabanciuniv.eduT[1] Treacy, M. M. J.; Ebbesen, T. W.; Gibson, J. M. 1996Exceptionally High Young’s Modulus Observed for IndividualCarbon Nanotubes. Nature, 381, 678–680.[2] Seoul C.; Kim Y.T.; Baek C.K;, 2003, Electrospinning ofPoly(vinylidene fluoride)/Dimethylformamide Solutions withCarbon Nanotubes, Journal of Polymer Science: Part B: PolymerPhysics, Vol. 41, 1572–1577.[3] Sen R.;, Zhao B.; Perea D.; Haddon R. C.; 2004 Preparation ofSingle-Walled Carbon Nanotube Reinforced Polystyrene andPolyurethane Nanofibers and Membranes by Electrospinning, NanoLetters, 4 (3), 459-464.[4] Ozden E.; Menceloglu Y.; Papila M. "ElectrospunPolymer/MWCNTs Nanofiber Reinforced Composites“Improvement of Interfacial Bonding by Surface ModifiedNanofibers”" , 2009 MRS Fall Meeting Symposium FF proceedings.6th Nanoscience and Nanotechnology Conference, zmir, 2010 740