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A comprehensive electric field analysis of a multifunctional electrospinning platform
Journal of Electrostatics 71 (2013) 294e298
Contents lists available at SciVerse ScienceDirect
Journal of Electrostatics journal homepage: www.elsevier.com/locate/elstat
A comprehensive electric field analysis of a multifunctional electrospinning platform Erol Jentzsch a, *, Ömer Gül b, Ertan Öznergiz c a
Electrical & Electronics Faculty, Istanbul Technical University, Turkey Istanbul Technical University, Turkey c Yildiz Technical University, Turkey b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 30 August 2012 Accepted 4 December 2012 Available online 4 February 2013
The electric field is one of the most critical parameters in electrospinning process. This study provides a comprehensive electric field analysis of a multifunctional electrospinning platform performed by FEMM 4.2. In this paper firstly information about the electrospinning method is mentioned. Electric field distribution of the multifunctional electrospinning platform is analyzed in different voltage levels. The effect of the applied voltage between the needles and the collector on nanofibers is investigated which are collected on the chassis. Furthermore the analysis results clearly demonstrated the effect of electrostatic force on the multiple jets which are at the needle tips. Ó 2012 Elsevier B.V. All rights reserved.
Keywords: Electrospinning Electric field analysis Multifunctional electrospinning platform
1. Introduction Electrospinning is the most effective, cheap and simple method of producing polymer-based nanofibers [1e4]. Additionally electrospinning is a multi-disciplinary method which contains fluid dynamics, polymer chemistry, basic physics, electric physics, mechanical and textile engineering [5]. Electric field is one of the most crucial parameters in electrospinning process. Moreover it can be controlled by changing voltage, distance between the needle and the collector, type of the collector and the characteristics of the needle [6]. These parameters change the fiber morphology considerably. Taylor obtained that a minimum voltage of 6 kV, either positive or negative, is enough for the solution at the needle tip to turn into a Taylor Cone throughout jet initiation [7]. Higher voltages result in a more charge. Thus, this will accelerate the jet and a greater amount of solution will come out from the needle tip [8]. Changing the distance between the needle and the target will directly affect the flight time and electric field strength [8]. Mo et al. found that a less internal diameter of a needle lowers occlusion of needles as well as
* Corresponding author. Tel.: þ90 5556109527. E-mail addresses: [email protected], [email protected] (E. Jentzsch), [email protected], [email protected] (Ö. Gül), [email protected] (E. Öznergiz). 0304-3886/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.elstat.2012.12.007
beads on the nanofibers [9]. Depending on the application the type of the collector varies. There are several ways of calculating the electric field distribution. Ying Yang et al. [10] and Cuiru Yang et al. [11] for example used ANSOFT software to calculate electric field distribution in the xz plane. Carnell et al. [12] created an experimental set-up, calculated equipotential lines for different electrode spacings with a formula and noted that at every location electric field is perpendicular to the plotted equipotential lines. Angammana and Jayaram [13] used COMSOL Multiphysics in two dimensions while modeling the electric field distribution of single and multijet arrangements. Angammana and Jayaram [13] found experimentally that with an increase in voltage, the vertical angle of the straight jet portion increases and the vertical angle increases with an increase in the number of needles. Theron et al. [2] also obtained a similar result while modeling the multiple jets. In this study, electric field distribution of an existing multifunctional electrospinning platform is simulated with Finite Element Method Magnetics (FEMM) v4.2. The behavior of the electric field is investigated by applying different voltages between the needles and the collector. Electric field strength and potential variation between a needle and the collector are investigated. 2. Principle of the machine An electrospinning setup basically consists of three main parts as seen in Fig. 1 [5].
E. Jentzsch et al. / Journal of Electrostatics 71 (2013) 294e298
295
and applied voltage between the charging unit and the collector. In order to observe the effects of these parameters evidently, there is a need for a device where these parameters could be changed easily. In this context, the novel multifunctional electrospinning platform (MEP) is developed as seen in Fig. 2 [14]. 2.1. Parts of the machine In this section, information about the parts of the MEP will be given.
Fig. 1. A basic electrospinning mechanism.
2.1.1. Motors and collector types Depending on the application (filtration, vascular, woundcovering), the motor speed and collector type should be changed. At the preliminary stage, four types of collector are designed (see Fig. 3). The axial and forward-backward rotation features of the collector enable to obtain a more homogenized product. Wannatong et al. mentioned that there will be more time for the solvent to evaporate when a rotating collector is used [15]. Additionally this results in a more improved fiber morphology [8]. 2.1.2. Solution charging unit Another significant part of the MEP is the solution charging unit. Pool type and tip type chargers are available as shown in Fig. 4. 3. Electric field analysis Electric field is the area where there is an electric force caused by the presence of electric charges. When there is a charge between two points, it is meaningful to consider Coulomb’s law to account the interaction between them. But when there are more points included in the system, it is expedient to use electric field and potential together. The magnitude of the field is defined by the electric field strength of it [8].
F ¼ q$E
Fig. 2. Multifunctional electrospinning platform (MEP).
Electrospinning is the most effective method for producing nanofibers. In this method, the polymer material which is melt or in the form of solution is fed to the needles. Then high voltage is applied to the polymer which is sent to the needle tip through a pump. As soon as surface tension disappears polymer material accelerates from the needles to the collector. At that moment solvent evaporates rapidly and fiber becomes longer and thinner due to the increase in speed. Thicknesses of these nanofibers are usually between 60 and 300 nm. The properties of obtained nanofiber are affected by various parameters including solution viscosity, flow rate, collector type
(1)
Laplace’s equation for the electric field between the needles and the collector could be given as follows:
V2 u ¼ 0
(2)
Dirichlet boundary conditions could be given as follows:
u ¼ Va;
(3)
u ¼ 0;
(4)
FEMM is a multi-purpose analysis software which uses finite element analysis method when processing the simulation. After adding the system parts to the model considering the original dimensions of the machine the triangle-shaped finite elements were produced with the mesh generator of the software. In the next step
Fig. 3. (a) Plate type (b) Disc type (c) Cylinder type (d) Rod type.
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E. Jentzsch et al. / Journal of Electrostatics 71 (2013) 294e298
Fig. 4. (a) Tip type charger (b) Pool type charger.
Fig. 5. Voltage distribution and equipotential lines while feeding unit is 20 kV and collector is grounded.
the finite elements analyzer was run and the voltage distributions were achieved as color scales for different voltage levels of the collector. (See Figs. 5 and 6.) What is proposed here is applying different voltages to the collector changes the fiber morphology considerably.
While the velocity and the collection characteristics of the nanofiber material depend on the strength of electric field, Fig. 8 shows that applying a negative voltage to the collector results in a more effective electric field comparing to grounding the collector (Fig. 7).
Fig. 6. Voltage distribution and equipotential lines while feeding unit is 20 kV and collector is 5 kV.
E. Jentzsch et al. / Journal of Electrostatics 71 (2013) 294e298
297
Fig. 7. Electric field distribution while feeding unit is 20 kV and collector is grounded.
Fig. 8. Electric field distribution while feeding unit is 20 kV and collector is 5 kV.
The variation of electric field intensity amplitude with the changing distance on a line could be seen in Fig. 9. Here, the line is limited with endpoints A (321, 17) and B (320, 145) in millimeters taking the down left side as reference. As it is seen in Fig. 9, after a distance of 5 mm away from the needle, electric field density is visibly declining.
Hence, it can be concluded that the nanofiber material in the form of solution is accelerated by the electric field force just after the needle tip. When the collector is grounded, the continuous electric field strength is about 1.2e1.5 kV/cm. Moreover it is about 2 kV/cm when the collector potential is 5 kV.
Fig. 9. Variation of electric field intensity amplitude with the changing distance. (a) Feeding unit is 20 kV and collector is grounded. (b) Feeding unit is 20 kV and collector is 5 kV.
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E. Jentzsch et al. / Journal of Electrostatics 71 (2013) 294e298
4. Conclusions A comprehensive electric field analysis of a multifunctional electrospinning platform is performed. It is suggested that the problem of nanofiber collection on the chassis could be solved by applying a negative voltage to the collector. In this way, instead of fronting to the chassis, the polymer in the electric field fronts to the collector which has a lower potential. Despite having meaningful results by defining an axial depth as a three dimensional approach, a direct three dimensional simulation may yield more certain outcomes. At this point due to the complex geometric structure of the electrospinning platform, it could be difficult to model all the components in three dimensions in terms of numerical simulation. The components that cause this problem are holes, screws, washers and curved corners etc. Most three dimensional analysis programs could not divide these components into finite elements. Acknowledgment The authors would like to thank The Scientific And Technological Research Council Of Turkey (TUBITAK) for funding this research, Grant No: 108M045. References [1] C.J. Angammana, S.H. Jayaram, Analysis of the effects of solution conductivity on electrospinning process and fiber morphology, IEEE Trans. Ind. Appl. 47 (3) (2011) 1109e1117.
[2] S.A. Theron, A.L. Yarin, E. Zussman, E. Kroll, Multiple jets in electrospinning: experiment and modeling, Polymer 46 (9) (2005) 2889e2899. [3] J. Lyons, C. Li, F. Ko, Melt-electrospinning part I: processing parameters and geometric properties, Polymer 45 (22) (2004) 7597e7603. [4] J. Doshi, D.H. Reneker, Electrospinning process and applications of electrospun fibers, J. Electrostat. 35 (2e3) (1995) 151e160. [5] S. Kozanoglu, Nanofiber production technology by means of electrospinning method, M.Sc. Thesis, Istanbul Technical University, 2006. [6] C.J. Angammana, S.H. Jayaram, Investigation of the optimum electric field for a stable electrospinning process, IEEE Trans. Ind. Appl., Society Annual Meeting, 2010 pp. 1e6. [7] G. Taylor, Disintegration of water drops in an electric field, Proc. R. Soc. London A Mat. 280 (1964) 383e397. [8] S. Ramakrishna, An Introduction to Electrospinning and Nanofibers, World Scientific Publishing Co., Singapore, 2005. [9] X.M. Mo, C.Y. Xu, M. Kotaki, S. Ramakrishna, Electrospun P(LLA-CL) nanofiber: a biomimetic extracellular matrix for smooth muscle cell and endothelial cell proliferation, Biomaterials 25 (10) (2004) 1883e1890. [10] Y. Yang, Z. Jia, J. Liu, Q. Li, L. Hou, L. Wang, Z. Guan, Effect of electric field distribution uniformity on electrospinning, J. Appl. Phys. 103 (10) (2008). 104307e104307-11. [11] C. Yang, Z. Jia, J. Liu, Z. Xu, Z. Guan, L. Wang, Guiding effect of surface electric field of collector on deposited electrospinning fibers, IEEE Trans. Dielectr. Electr. Insul 16 (3) (2009) 785e792. [12] L.S. Carnell, E.J. Siochi, R.A. Wincheski, N.M. Holloway, R.L. Clark, Electric field effects on fiber alignment using an auxiliary electrode during electrospinning, Scripta Mater. 60 (6) (2009) 359e361. [13] C.J. Angammana, S.H. Jayaram, The effects of electric field on the multijet electrospinning process and fiber morphology, IEEE Trans. Ind. Appl. 47 (2) (2011) 1028e1035. [14] T. Gümüs¸, S. Güls¸en, Y. Kıyak, O. Erden, E. Öznergiz, A. Demir, Multifunctional Nanofiber Development Platform, vol. 3, Uludag Textile Exporters Union R&D Project Market, Bursa, 2010. [15] L. Wannatong, A. Sirivat, P. Supaphol, Effects of solvents on electrospun polymeric fibers: preliminary study on polystyrene, Polym. Int. 53 (11) (2004) 1851e1859.
Contents lists available at SciVerse ScienceDirect
Journal of Electrostatics journal homepage: www.elsevier.com/locate/elstat
A comprehensive electric field analysis of a multifunctional electrospinning platform Erol Jentzsch a, *, Ömer Gül b, Ertan Öznergiz c a
Electrical & Electronics Faculty, Istanbul Technical University, Turkey Istanbul Technical University, Turkey c Yildiz Technical University, Turkey b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 30 August 2012 Accepted 4 December 2012 Available online 4 February 2013
The electric field is one of the most critical parameters in electrospinning process. This study provides a comprehensive electric field analysis of a multifunctional electrospinning platform performed by FEMM 4.2. In this paper firstly information about the electrospinning method is mentioned. Electric field distribution of the multifunctional electrospinning platform is analyzed in different voltage levels. The effect of the applied voltage between the needles and the collector on nanofibers is investigated which are collected on the chassis. Furthermore the analysis results clearly demonstrated the effect of electrostatic force on the multiple jets which are at the needle tips. Ó 2012 Elsevier B.V. All rights reserved.
Keywords: Electrospinning Electric field analysis Multifunctional electrospinning platform
1. Introduction Electrospinning is the most effective, cheap and simple method of producing polymer-based nanofibers [1e4]. Additionally electrospinning is a multi-disciplinary method which contains fluid dynamics, polymer chemistry, basic physics, electric physics, mechanical and textile engineering [5]. Electric field is one of the most crucial parameters in electrospinning process. Moreover it can be controlled by changing voltage, distance between the needle and the collector, type of the collector and the characteristics of the needle [6]. These parameters change the fiber morphology considerably. Taylor obtained that a minimum voltage of 6 kV, either positive or negative, is enough for the solution at the needle tip to turn into a Taylor Cone throughout jet initiation [7]. Higher voltages result in a more charge. Thus, this will accelerate the jet and a greater amount of solution will come out from the needle tip [8]. Changing the distance between the needle and the target will directly affect the flight time and electric field strength [8]. Mo et al. found that a less internal diameter of a needle lowers occlusion of needles as well as
* Corresponding author. Tel.: þ90 5556109527. E-mail addresses: [email protected], [email protected] (E. Jentzsch), [email protected], [email protected] (Ö. Gül), [email protected] (E. Öznergiz). 0304-3886/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.elstat.2012.12.007
beads on the nanofibers [9]. Depending on the application the type of the collector varies. There are several ways of calculating the electric field distribution. Ying Yang et al. [10] and Cuiru Yang et al. [11] for example used ANSOFT software to calculate electric field distribution in the xz plane. Carnell et al. [12] created an experimental set-up, calculated equipotential lines for different electrode spacings with a formula and noted that at every location electric field is perpendicular to the plotted equipotential lines. Angammana and Jayaram [13] used COMSOL Multiphysics in two dimensions while modeling the electric field distribution of single and multijet arrangements. Angammana and Jayaram [13] found experimentally that with an increase in voltage, the vertical angle of the straight jet portion increases and the vertical angle increases with an increase in the number of needles. Theron et al. [2] also obtained a similar result while modeling the multiple jets. In this study, electric field distribution of an existing multifunctional electrospinning platform is simulated with Finite Element Method Magnetics (FEMM) v4.2. The behavior of the electric field is investigated by applying different voltages between the needles and the collector. Electric field strength and potential variation between a needle and the collector are investigated. 2. Principle of the machine An electrospinning setup basically consists of three main parts as seen in Fig. 1 [5].
E. Jentzsch et al. / Journal of Electrostatics 71 (2013) 294e298
295
and applied voltage between the charging unit and the collector. In order to observe the effects of these parameters evidently, there is a need for a device where these parameters could be changed easily. In this context, the novel multifunctional electrospinning platform (MEP) is developed as seen in Fig. 2 [14]. 2.1. Parts of the machine In this section, information about the parts of the MEP will be given.
Fig. 1. A basic electrospinning mechanism.
2.1.1. Motors and collector types Depending on the application (filtration, vascular, woundcovering), the motor speed and collector type should be changed. At the preliminary stage, four types of collector are designed (see Fig. 3). The axial and forward-backward rotation features of the collector enable to obtain a more homogenized product. Wannatong et al. mentioned that there will be more time for the solvent to evaporate when a rotating collector is used [15]. Additionally this results in a more improved fiber morphology [8]. 2.1.2. Solution charging unit Another significant part of the MEP is the solution charging unit. Pool type and tip type chargers are available as shown in Fig. 4. 3. Electric field analysis Electric field is the area where there is an electric force caused by the presence of electric charges. When there is a charge between two points, it is meaningful to consider Coulomb’s law to account the interaction between them. But when there are more points included in the system, it is expedient to use electric field and potential together. The magnitude of the field is defined by the electric field strength of it [8].
F ¼ q$E
Fig. 2. Multifunctional electrospinning platform (MEP).
Electrospinning is the most effective method for producing nanofibers. In this method, the polymer material which is melt or in the form of solution is fed to the needles. Then high voltage is applied to the polymer which is sent to the needle tip through a pump. As soon as surface tension disappears polymer material accelerates from the needles to the collector. At that moment solvent evaporates rapidly and fiber becomes longer and thinner due to the increase in speed. Thicknesses of these nanofibers are usually between 60 and 300 nm. The properties of obtained nanofiber are affected by various parameters including solution viscosity, flow rate, collector type
(1)
Laplace’s equation for the electric field between the needles and the collector could be given as follows:
V2 u ¼ 0
(2)
Dirichlet boundary conditions could be given as follows:
u ¼ Va;
(3)
u ¼ 0;
(4)
FEMM is a multi-purpose analysis software which uses finite element analysis method when processing the simulation. After adding the system parts to the model considering the original dimensions of the machine the triangle-shaped finite elements were produced with the mesh generator of the software. In the next step
Fig. 3. (a) Plate type (b) Disc type (c) Cylinder type (d) Rod type.
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Fig. 4. (a) Tip type charger (b) Pool type charger.
Fig. 5. Voltage distribution and equipotential lines while feeding unit is 20 kV and collector is grounded.
the finite elements analyzer was run and the voltage distributions were achieved as color scales for different voltage levels of the collector. (See Figs. 5 and 6.) What is proposed here is applying different voltages to the collector changes the fiber morphology considerably.
While the velocity and the collection characteristics of the nanofiber material depend on the strength of electric field, Fig. 8 shows that applying a negative voltage to the collector results in a more effective electric field comparing to grounding the collector (Fig. 7).
Fig. 6. Voltage distribution and equipotential lines while feeding unit is 20 kV and collector is 5 kV.
E. Jentzsch et al. / Journal of Electrostatics 71 (2013) 294e298
297
Fig. 7. Electric field distribution while feeding unit is 20 kV and collector is grounded.
Fig. 8. Electric field distribution while feeding unit is 20 kV and collector is 5 kV.
The variation of electric field intensity amplitude with the changing distance on a line could be seen in Fig. 9. Here, the line is limited with endpoints A (321, 17) and B (320, 145) in millimeters taking the down left side as reference. As it is seen in Fig. 9, after a distance of 5 mm away from the needle, electric field density is visibly declining.
Hence, it can be concluded that the nanofiber material in the form of solution is accelerated by the electric field force just after the needle tip. When the collector is grounded, the continuous electric field strength is about 1.2e1.5 kV/cm. Moreover it is about 2 kV/cm when the collector potential is 5 kV.
Fig. 9. Variation of electric field intensity amplitude with the changing distance. (a) Feeding unit is 20 kV and collector is grounded. (b) Feeding unit is 20 kV and collector is 5 kV.
298
E. Jentzsch et al. / Journal of Electrostatics 71 (2013) 294e298
4. Conclusions A comprehensive electric field analysis of a multifunctional electrospinning platform is performed. It is suggested that the problem of nanofiber collection on the chassis could be solved by applying a negative voltage to the collector. In this way, instead of fronting to the chassis, the polymer in the electric field fronts to the collector which has a lower potential. Despite having meaningful results by defining an axial depth as a three dimensional approach, a direct three dimensional simulation may yield more certain outcomes. At this point due to the complex geometric structure of the electrospinning platform, it could be difficult to model all the components in three dimensions in terms of numerical simulation. The components that cause this problem are holes, screws, washers and curved corners etc. Most three dimensional analysis programs could not divide these components into finite elements. Acknowledgment The authors would like to thank The Scientific And Technological Research Council Of Turkey (TUBITAK) for funding this research, Grant No: 108M045. References [1] C.J. Angammana, S.H. Jayaram, Analysis of the effects of solution conductivity on electrospinning process and fiber morphology, IEEE Trans. Ind. Appl. 47 (3) (2011) 1109e1117.
[2] S.A. Theron, A.L. Yarin, E. Zussman, E. Kroll, Multiple jets in electrospinning: experiment and modeling, Polymer 46 (9) (2005) 2889e2899. [3] J. Lyons, C. Li, F. Ko, Melt-electrospinning part I: processing parameters and geometric properties, Polymer 45 (22) (2004) 7597e7603. [4] J. Doshi, D.H. Reneker, Electrospinning process and applications of electrospun fibers, J. Electrostat. 35 (2e3) (1995) 151e160. [5] S. Kozanoglu, Nanofiber production technology by means of electrospinning method, M.Sc. Thesis, Istanbul Technical University, 2006. [6] C.J. Angammana, S.H. Jayaram, Investigation of the optimum electric field for a stable electrospinning process, IEEE Trans. Ind. Appl., Society Annual Meeting, 2010 pp. 1e6. [7] G. Taylor, Disintegration of water drops in an electric field, Proc. R. Soc. London A Mat. 280 (1964) 383e397. [8] S. Ramakrishna, An Introduction to Electrospinning and Nanofibers, World Scientific Publishing Co., Singapore, 2005. [9] X.M. Mo, C.Y. Xu, M. Kotaki, S. Ramakrishna, Electrospun P(LLA-CL) nanofiber: a biomimetic extracellular matrix for smooth muscle cell and endothelial cell proliferation, Biomaterials 25 (10) (2004) 1883e1890. [10] Y. Yang, Z. Jia, J. Liu, Q. Li, L. Hou, L. Wang, Z. Guan, Effect of electric field distribution uniformity on electrospinning, J. Appl. Phys. 103 (10) (2008). 104307e104307-11. [11] C. Yang, Z. Jia, J. Liu, Z. Xu, Z. Guan, L. Wang, Guiding effect of surface electric field of collector on deposited electrospinning fibers, IEEE Trans. Dielectr. Electr. Insul 16 (3) (2009) 785e792. [12] L.S. Carnell, E.J. Siochi, R.A. Wincheski, N.M. Holloway, R.L. Clark, Electric field effects on fiber alignment using an auxiliary electrode during electrospinning, Scripta Mater. 60 (6) (2009) 359e361. [13] C.J. Angammana, S.H. Jayaram, The effects of electric field on the multijet electrospinning process and fiber morphology, IEEE Trans. Ind. Appl. 47 (2) (2011) 1028e1035. [14] T. Gümüs¸, S. Güls¸en, Y. Kıyak, O. Erden, E. Öznergiz, A. Demir, Multifunctional Nanofiber Development Platform, vol. 3, Uludag Textile Exporters Union R&D Project Market, Bursa, 2010. [15] L. Wannatong, A. Sirivat, P. Supaphol, Effects of solvents on electrospun polymeric fibers: preliminary study on polystyrene, Polym. Int. 53 (11) (2004) 1851e1859.