Mechanical and electrical properties of electrospun PVDF/MWCNT ultrafine fibers using rotating collector
© Wang et al.; licensee Springer. 2014
Received: 30 August 2014
Accepted: 16 September 2014
Published: 23 September 2014
Poly(vinylidene fluoride) (PVDF) ultrafine fibers with different proportions of multi-walled carbon nanotube (MWCNT) embedded have been fabricated using a modified electrospinning device with a rotating collector. With the increasing of MWCNT content, the β phase was noticeable enhanced, and the fibers became more elastic, which was manifested by Young's modulus decreased drastically. Furthermore, with adding the amounts of MWCNTs, the density of carbon nanotube (CNT)-CNT junctions among the fibers increased accordingly. When the MWCNT content was of 1.2 wt.%, a stable three-dimensional conducting network was formed. After this percolation threshold, the density of CNT-CNT junctions among the fibers tended to be a constant quantity, leading to a stabilized conductivity consequently. It is hoped that our results can be helpful for the fabrication of flexible devices, piezoelectric devices, force transducer, and so on.
Electrospinning is a simple and versatile technique for fabricating ultrafine fibers with diameters ranging from several micrometers down to a few nanometers. With outstanding properties such as large surface area, high length/diameter ratio, flexible surface functionality, and tunable surface morphologies, the electrospun fibers have an underlying application in optoelectronics, sensors, catalysis, textiles, filters, fiber reinforcement, tissue engineering, drug delivery, wound healing, etc. [1–7]. During electrospinning process, when the electric field force reaches a certain threshold value, polymer droplet overcomes the surface tension and forms a jet trickle from the capillary Taylor cone vertex. After a series of vigorous whipping and/or splitting motion due to fluid instability and electrically driven bending instability, the products are deposited commonly as a nonwoven fibrous web on a collector. In order to improve the further application of the as-spun fibers, numerous researchers and groups have engaged in fabricating morphology-controlled electrospun micro/nanofibers, and it is delighted to notice that apart from fiber membranes without orientation, other fibrous structures and organization (e.g., aligned fiber arrays, helical or wavy fibers, twisted fibrous yarns, patterned fibrous mats) based on not only polymers of synthetic or biological nature but also metals, metal oxides, ceramics, organic/organic, organic/inorganic, as well as inorganic/inorganic composite systems have been electrospun successfully via modified electrospinning process or collectors [8–10], which will extend further application of as-spun fibers in many fields.
As a semicrystalline polymer, poly(vinylidene fluoride) (PVDF) has aroused much attention due to its distinguished electroactive properties, nonlinear optical, strong corrosive, susceptibility, and high dielectric constant [11, 12], which make it useful in a variety of fields such as sensors, actuators, and energy transducers . PVDF consists of four different crystalline phases depending on the chain conformation of trans and gauche linkages: α, β, γ, and δ. Among these phases, the α phase is known as the most abundant form commercially available powders and films, and the β phase has the largest spontaneous polarization per unit cell and thus, exhibits the highest electroactive properties, responsible for most of PVDF's piezoelectric characters . It is reported that electrospinning and blending PVDF with carbon nanotubes (CNTs) can increase the β-phase content in PVDF .
So far, the study of PVDF/CNT composites mainly focuses on the following three aspects: (1) the dielectric property of the composites and its CNT dispersion and loading dependence ; (2) enhancement of the β-phase crystal formation of PVDF in the doping of CNTs and the related property alterations [17, 18]; (3) the electrical conductivity, its percolation behavior and other properties of the composites in the doping of CNTs [18–23]. Although numerous studies on PVDF/CNT nanofibrous composites have been published, new work in this field emerges consistently and continually. In the present work, well-aligned PVDF ultrafine fibers with different multi-walled carbon nanotube (MWCNT) contents (0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, and 2%) have been fabricated using a modified electrospinning device with a rotating collector. It is found that with the increasing content of MWCNTs from 0.6 to 2 wt.%, the β phase has been noticeable enhanced, and the composited fibers become much more elastic lying in the fact that Young's modulus decreased from 4.4 × 10-2 to 9.1 × 10-3 MPa. Moreover, with adding the amounts of MWCNTs, the density of CNT-CNT junctions among the fibers increased accordingly, forming a stable three-dimensional conducting network. After the three-dimensional network has been constructed (the percolation threshold) where MWCNT content was of 1.2 wt.%, the density of CNT-CNT junctions tend to be a constant quantity, resulting in a stabilized conductivity of the fibers.
Preparation of PVDF/MWCNT solution and electrospinning
To study the surface morphology and the size of electrospun fibers, a scanning electron microscope (SEM; JEOL JSM-6390, JEOL Ltd., Akishima-shi, Japan) and a transmission electron microscope (TEM; HITACHI H-9000, Hitachi, Ltd., Chiyoda-ku, Japan) were used. The crystalline phase or phases present in the composited fibers were identified by Fourier transform infrared (FTIR) spectroscopy using a Thermo Scientific Nicolet iN10 spectrometer (Thermo Fisher Scientific, Waltham, MA, USA), and absorbance data were processed for the wave number ranging from 600 to 1,600 cm-1. The X-ray diffraction patterns were recorded by a Bruker D8 Advance X-ray diffractometer (XRD; Bruker AXS, Inc., Madison, WI, USA). An electronic tensile testing machine (Jinan Hengrui machine Co. Ltd., Jinan, China) was used for the mechanical characterization of aligned electrospun fibrous membranes, and the electrical properties of the fibers were tested using a Keithley 6485 high-resistance meter system (Keithley Instruments, Inc., Cleveland, OH, USA).
Results and discussion
Figure 4b presents the relationship between Young's modulus and MWCNT contents for the electrospun PVDF/MWCNT fibers. With the content of carbon nanotubes increased from 0.6 to 2 wt.%, Young's modulus is decreased from 4.4 × 10-2 to 9.1 × 10-3 MPa, e.g., the products' elasticity has been drastically improved with the increasing of MWCNTs.
Here σ is the electrical conductivity of the PVDF/MWCNT composited fibers, p is MWCNT concentration, p c is the percolation threshold, and t is the critical exponent, which reflects dimensionality of the system and universality class of the problem. Usually, experimental results are fitted by plotting log σ vs. log (p - p c ) and incrementally varying p c until the best linear fit is obtained . In our experiments, the percolation threshold p c and critical exponent t (the slope of the linear relation of log σ to log (p - p c )) were of 1.2 and 4.08 wt.%, respectively, as shown in Figure 5b. Besides, it is reported that for the polymer/CNT composites, the exponent t is frequently associated with the conducting system dimensionality, namely, with values of t ≈ 1.3 (or slightly higher) representing a two-dimensional network while t ≈ 2 (or higher) a three-dimensional one . Here the values of t = 4.08 indicated a three-dimensional conducting network formed among PVDF/MWCNT composited fibers. As increasing the amounts of MWCNTs in the composites, the density of CNT-CNT junctions increased accordingly, with an enhancive conductivity till the MWCNT content of 1.2 wt.%. After the three-dimensional network had been constructed, the density of CNT-CNT junctions tended to be a constant, therefore, the conductivity of the PVDF/MWCNTs remained stabilized, and the value of log σ in Figure 5a was likely to form a platform after the percolation threshold.
In this paper, the ultrafine fibers of PVDF/MWCNTs were fabricated via a modified electrospinning technique. The mechanical and electrical properties of the as-spun fibers were enhanced evidently by incorporating MWCNTs into the PVDF fibers. With the increase of the MWCNT content, an enhancement of the β phase was observed. With the MWCNT mass proportion increased from 0.6 to 2 wt.%, Young's modulus of the composited fibers decreased from 4.4 × 10-2 to 9.1 × 10-3 MPa. At room temperature, the conductivity of the PVDF/CNT fiber membranes with MWCNT content of 0.6 wt.% was 1 × 10-14 S cm-1, however, for the 1.2 wt.% loaded, it changed into 1 × 10-6 S cm-1, and the critical exponent t was of 4.08, which proved that a three-dimensional conducting network constructed among PVDF/MWCNT fibers. After the network formed, the density of CNT-CNT junctions tended to a steady value, which led to the conductivity of the PVDF/MWCNT fibers forming a platform after the percolation threshold (MWCNT content of 1.2 wt.%). It is hoped that our results can be helpful for the fabrication of flexible devices, piezoelectric devices, force transducer, etc.
This work was supported by the Project of Shandong Province Higher Educational Science and Technology Program (J13LJ07), the National Natural Science Foundation of China (11144007), and the Program for Scientific Research Innovation Team in Colleges and Universities of Shandong Province, China.
- Lipomi DJ, Bao Z: Stretchable, elastic materials and devices for solar energy conversion. Energy Environ Sci 2011, 4: 3314–3328. 10.1039/c1ee01881gView ArticleGoogle Scholar
- Li D, Xia Y: Electrospinning of nanofibers: reinventing the wheel? Adv Mater 2004, 16: 1151–1170. 10.1002/adma.200400719View ArticleGoogle Scholar
- Lu X, Zhang W, Wang C, Wen TC, Wei Y: One-dimensional conducting polymer nanocomposites: synthesis, properties and applications. Prog Polym Sci 2011, 36: 671–712. 10.1016/j.progpolymsci.2010.07.010View ArticleGoogle Scholar
- Greiner A, Wendorff JH: Functional self-assembled nanofibers by electrospinning. Adv Polym Sci 2008, 219: 107–171.Google Scholar
- Reneker DH, Yarin AL: Electrospinning jets and polymer nanofibers. Polymer 2008, 49: 2387–2425. 10.1016/j.polymer.2008.02.002View ArticleGoogle Scholar
- Agarwal S, Wendorff JH, Greiner A: Use of electrospinning technique for biomedical applications. Polymer 2008, 49: 5603–5621. 10.1016/j.polymer.2008.09.014View ArticleGoogle Scholar
- Schiffman JD, Schauer CL: A review: electrospinning of biopolymer nanofibres and their applications. Polym Rev 2008, 48: 317–352. 10.1080/15583720802022182View ArticleGoogle Scholar
- Huang ZM, Zhang YZ, Kotaki M, Ramakrishna S: A review on polymer nanofibers by electrospinning and their applications in nanocomposites. Compos Sci Technol 2003, 63: 2223–2253. 10.1016/S0266-3538(03)00178-7View ArticleGoogle Scholar
- Sun B, Long YZ, Zhang HD, Li MM, Duvail JL, Jiang XY, Yin HL: Advances in three-dimensional nanofibrous macrostructures via electrospinning. Prog Polym Sci 2014, 39: 862–890. 10.1016/j.progpolymsci.2013.06.002View ArticleGoogle Scholar
- Sun B, Long YZ, Chen ZJ, Liu SL, Zhang HD, Zhang JC, Han WP: Recent advances in flexible and stretchable electronic devices via electrospinning. J Mater Chem C 2014, 2: 1209–1219. 10.1039/c3tc31680gView ArticleGoogle Scholar
- Furukawa T: Piezoelectricity and pyroelectricity in polymers. IEEE Trans Electr Insul 1989, 24: 375–394. 10.1109/14.30878View ArticleGoogle Scholar
- Koga K, Ohigashi HJ: Piezoelectricity and related properties of vinylidene fluoride and trifluoroethylene copolymers. J Appl Phys 1986, 59: 2142–2150. 10.1063/1.336351View ArticleGoogle Scholar
- Chen QX, Payne PA: Industrial applications of piezoelectricity polymer transducers. Meas Sci Technol 1995, 6: 249–267. 10.1088/0957-0233/6/3/001View ArticleGoogle Scholar
- Chang J, Dommer M, Chang C, Lin L: Piezoelectric nanofibers for energy scavenging applications. Nano Energy 2012, 1: 356–371. 10.1016/j.nanoen.2012.02.003View ArticleGoogle Scholar
- Huang S, Yee WA, Tjiu WC, Liu Y, Kotaki M, Boey YCF, Ma J, Liu T, Lu X: Electrospinning of polyvinylidene difluoride with carbon nanotubes: synergistic effects of extensional force and interfacial interaction on crystalline structures. Langmuir 2008, 24: 13621–13626. 10.1021/la8024183View ArticleGoogle Scholar
- Huang XY, Jiang PK, Kim C, Liu F, Yin Y: Influence of aspect ratio of carbon nanotubes on crystalline phases and dielectric properties of poly(vinylidene fluoride). Eur Polym J 2009, 45: 377–386. 10.1016/j.eurpolymj.2008.11.018View ArticleGoogle Scholar
- Yu SS, Zheng WT, Yu WX, Zhang YJ, Jiang Q, Zhao ZD: Formation mechanism of β-phase in PVDF/CNT composite prepared by the sonication method. Macromolecules 2009, 42: 8870–8874. 10.1021/ma901765jView ArticleGoogle Scholar
- Wang M, Shi JH, Pramoda KP, Goh SH: Microstructure, crystallization and dynamic mechanical behavior of poly(vinylidene fluoride) composites containing poly(methyl methacrylate)-grafted multiwalled carbon nanotubes. Nanotechnology 2007, 18: 235701–235701. 10.1088/0957-4484/18/23/235701View ArticleGoogle Scholar
- Liu ZH, Pan CT, Lin LW, Lai HW: Piezoelectric properties of PVDF/MWCNT nanofiber using near-field electrospinning. Sens Actuators A 2013, 193: 13–24.View ArticleGoogle Scholar
- Huang WW, Edenzon K, Fernandez L, Razmpour S, Woodburn J, Cebe P: Nanocomposites of poly(vinylidene fluoride)with multiwalled carbon nanotubes. J Appl Polym Sci 2010, 115: 3238–3248. 10.1002/app.31393View ArticleGoogle Scholar
- Simoes R, Silva J, Vaia R, Sencadas V, Costa P, Gomes J, Lancerros-mendez S: Low percolation transitions in carbon nanotube networks dispersed in a polymer matrix: dielectric properties, simulations and experiments. Nanotechnology 2009, 20: 035703–035703. 10.1088/0957-4484/20/3/035703View ArticleGoogle Scholar
- Chang CM, Liu YL: Electrical conductivity enhancement of polymer/multiwalled carbon nanotube (MWCNT) composites by thermally-induced defunctionalization of MWCNTs. ACS Appl Mater Interfaces 2011, 3: 2204–2208. 10.1021/am200558fView ArticleGoogle Scholar
- Chanmal C, Deo M, Rana A, Jog J, Ogale S: Strong electric field modulation of transport in PVDF/MWCNT nanocomposite near the percolation threshold. Solid State Commun 2011, 151: 1612–1615. 10.1016/j.ssc.2011.07.018View ArticleGoogle Scholar
- Edwards MD, Mitchell GR, Mohan SD, Olley RH: Development of orientation during electrospinning of fibres of poly(ϵ-caprolactone). Eur Polym J 2010, 46: 1175–1183. 10.1016/j.eurpolymj.2010.03.017View ArticleGoogle Scholar
- Dror Y, Salalha W, Khalfin RL, Cohen Y, Yarin AL, Zussman E: Carbon nanotubes embedded in oriented polymer nanofibers by electrospinning. Langmuir 2003, 19: 7012–7020. 10.1021/la034234iView ArticleGoogle Scholar
- Potschke P, Fornes TD, Paul DR: Rheological behavior of multiwalled carbon nanotube/polycarbonate composites. Polymer 2002, 43: 3247–3255. 10.1016/S0032-3861(02)00151-9View ArticleGoogle Scholar
- Du FM, Scogna RC, Zhou W, Brand S, Fischer JE, Winey KI: Nanotube networks in polymer nanocomposites: rheology and electrical conductivity. Macromolecules 2004, 37: 9048–9055. 10.1021/ma049164gView ArticleGoogle Scholar
- Bug ALR, Safran SA, Webman I: Continuum percolation of rods. Phys Rev Lett 1985, 54: 1412–1415. 10.1103/PhysRevLett.54.1412View ArticleGoogle Scholar
- Vigolo B, Coulon C, Maugey M, Zakri C, Poulin P: An experimental approach to the percolation of sticky nanotubes. Science 2005, 309: 920–923. 10.1126/science.1112835View ArticleGoogle Scholar
- Bauhofer W, Kovacs JZ: A review and analysis of electrical percolation in carbon nanotube polymer composites. Compos Sci Technol 2009, 69: 1486–1498. 10.1016/j.compscitech.2008.06.018View ArticleGoogle Scholar
- Kirkpatrick S: Classical transport in disordered media: scaling and effective-medium theories. Phys Rev Lett 1971, 27: 1722–1725. 10.1103/PhysRevLett.27.1722View ArticleGoogle Scholar
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