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Electrospinning of beta silicon carbide nanofibers
Materials Letters 63 (2009) 2361–2364
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m a t l e t
Electrospinning of beta silicon carbide nanofibers Harvey A. Liu, Kenneth J. Balkus Jr. ⁎ The University of Texas at Dallas, Department of Chemistry and the Alan G. MacDiarmid NanoTech Institute, Richardson, TX 75083-0688, USA
a r t i c l e
i n f o
Article history: Received 13 May 2009 Accepted 4 August 2009 Available online 9 August 2009 Keywords: Silicon carbide Nanofibers Electrospinning
a b s t r a c t Silicon carbide exhibits many unique properties such as its mechanical robustness, chemical inertness, and thermal stability, which make the material appealing for many applications. Some of these applications include its use as a support for nanocomposites or as a high temperature filter material. The ability to fabricate nanofibers of SiC could enhance its utility in these applications. In the current study, nanofibers of β-SiC have been fabricated through the technique of concentric electrospinning. This method demonstrates the ability to fabricate uniform SiC nanofibers with a diameter ranging from 1 to 2 nm, the smallest to date. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Silicon carbide has been acclaimed for many of its characteristics such as its mechanical robustness, chemical inertness, and thermal stability. Due to the many unique properties of silicon carbide, different morphologies of this material have been fabricated, including: thin films [1,2], rods [3,4], and fibers [5,6]. For example, fibers with a diameter of 1–3 μm were fabricated through wet-type electrospinning [6]. A more recent study in the electrospinning of silicon carbide by Eick et al. demonstrated the ability to fabricate composite fibers with diameters as small as 20 nm, though the majority of the fibers observed were much larger, some of which exceeded 100 nm in diameter. In addition to the wide variation in the diameter of these fibers, a silica shell formed with a SiC core caused by the atmospheric oxygen and impurities in the furnace [5]. A fibrous morphology provides many unique favorable properties; the most prevalent is the increase in surface to volume ratio, which expands the utility of a material to various applications. Nanofibers of silicon carbide in particular offer potential applications as a support material for nanocomposites [7], substrates for catalysis [8–10], and as well as high temperature filters [6]. Electrospinning of the polycarbosilane followed by curing and pyrolysis has proven to be a successful approach to fabricating SiC fibers [5,6]. However, the resulting SiC fibers exhibited a wide range of fiber diameters as well as nonuniform and impure structures. In the present study, we utilized a polycarbosilane as a precursor, but employ the technique of concentric, or core–shell, electrospinning to fabricate uniform nanofibers. By employing concentric electrospinning we
demonstrated the first fabrication method to attain consistently uniform silicon carbide fibers with diameters in the range of 1–2 nm. There has been growing interest in the method of electrospinning, especially in the area of ceramic materials. This method has been utilized in the fabrication of submicron to nanosized fibers composed of various materials including polymers [11], ceramics [12–18], and composites[19], which have found application in areas such as tissue engineering [20,21], catalysis [22], composite materials [19], supercapacitors [23,24], drug delivery [25], as well as self-healing materials [26]. In the past few years, a variation of conventional electrospinning has been developed, known as coaxial or concentric electrospinning, and has resulted in the fabrication of fibrous materials that previously could not have been achieved [27–29]. A schematic of concentric electrospinning is shown in Fig. 1. Similar to conventional electrospinning, concentric electrospinning utilizes an external electrostatic force, which is applied to a polymer melt [27]. Upon excess electrostatic force, the polymer melt forms a Taylor cone and undergoes a whipping action, stretching the polymer solution and forming a nonwoven mat [10]. The technique of coaxial electrospinning allows for the formation of fibers for materials that cannot be electrospun through conventional spinning. Typically, a polymer that is easily electrospun is fed through the outer sheath and a material that is difficult to spin is fed through the core. The outer sheath material serves to contain the inner core and form the fiber morphology. After the fabrication of these coaxial fibers, post-fabrication methods can be performed on the inner material which may include either annealing and/or washing away of the outer sheath to reveal the inner fibrous material. 2. Experimental
⁎ Corresponding author. Tel.: +1 972 883 2659; fax: +1 972 883 2925. E-mail address: [email protected] (K.J. Balkus). 0167-577X/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2009.08.009
In the present study, high molecular weight polystyrene was used for the fabrication of the outer sheath while polycarbosilane
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Fig. 1. Schematic of concentric electrospinning setup.
(SMP-10, Starfire Systems Inc.) (Fig. 2a) was fed through the core as the silicon carbide precursor. The concentric electrospinning setup was assembled through the insertion of a 22 gauge needle through an 18 gauge needle. The flow rate through the outer and inner needle was independently regulated with a syringe pump (7802CO, KD Scientific Inc., USA). In a typical synthesis, a 15 wt.% polystyrene in chloroform melt was fed through the outer sheath at a rate of 7× 10− 2–1×10− 1 mL/min and the silicon carbide precursor, SMP-10, was used as received and fed through the inner core at a rate of 8× 10− 3 mL/min. A 10 kV charge was applied to the needle tip, which was adjusted to be 25 cm from the grounded rotating drum wrapped with foil as the collecting surface.
3. Results and discussion Scanning electron micrographs (SEM) of the as-spun core shell fibers are shown in Fig. 2b–c. The average diameter of the core–shell fibers typically ranged from 10 to 20 μm (Fig. 2b), however, fibers as small as 2 μm were observed as well (Fig. 2c). The fibers were spun into a freestanding sheet and cured in an oven overnight at 100 °C for 12 h followed by heating to 200 °C for 24 h to cure the polycarbosilane. The as-spun core–shell fibers as a free-standing sheet exhibited a slight yellow tint from the polycarbosilane precursor embedded in the core (Fig. 2d). It can be seen in the SEM micrograph (Fig. 2c) that some fibers
Fig. 2. (a) Molecular structure of polycarbosilane (b,c) SEM micrographs of the as-spun core–shell fibers (d) digital image of free-standing sheet of fibers.
H.A. Liu, K.J. Balkus Jr. / Materials Letters 63 (2009) 2361–2364
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Fig. 3. XRD of crystallized β-SiC nanofibers showing miller indices.
Fig. 5. TEM of crystallized β-SiC.
were fractured, due to the brittle nature of polystyrene, though the fibers were robust enough to handle (Fig. 2d). SEM imaging of the cured fibers revealed no changes in the morphology of the fibers from the curing process. The film was then washed in chloroform and centrifuged repeatedly to wash away the polystyrene outer sheath. The resulting cured fibers were then transferred to a graphite crucible and subjected to pyrolysis in a high temperature vacuum furnace under an inert gas atmosphere (Red Devil™, R. D. Webb Company, Inc.). The pyrolysis procedure was executed under argon gas according to published processing procedures [30]. The fibers were heated from room temperature to 650 °C at a rate of 1 °C/min, then from 650 °C to 850 °C at 3 °C/min. The oven was then held at 850 °C for 1 h whereupon heating was stopped and cooled to below 100 °C before the sample was recovered. The pyrolysis treatment results in the recovery of amorphous (glassy) silicon carbide, which was confirmed by X-ray diffraction. Further heat treatment was used in order to convert the glassy silicon carbide to polycrystalline β-SiC. The crystallization was conducted in a high temperature vacuum oven under argon where the sample was heated from room temperature to 1600–1650 °C at an approximate rate of 2–3 °C/min. The sample was held at this temperature for 6 h to crystallize the fibers. The X-ray diffraction pattern of the crystallized SiC nanofibers is shown in Fig. 3. Trace amounts of the hexagonal α-SiC are seen accompanied by a strong diffraction pattern for β-SiC (Fig. 3) In addition to SiC, trace amounts of graphite were also seen, represented by a peak appearing at approximately 26°. The appearance of graphite is likely from the graphite crucible and/or the graphitic insulation of the furnace. SEM micrographs of the crystalline β-SiC reveal uniform nanofibers with diameters approximately 10 nm in size (Fig. 4).
Comparisons of the fibers before the washing and pyrolysis of the electrospun composite fibers show a large difference in the diameter size. This is expected since the polystyrene was fed through the needle at a much higher rate than the silicon carbide precursor, and thus a smaller volume of the precursor was actually present in the core of the composite fibers. Transmission electron microscopy (TEM) of the crystallized silicon carbide is shown in Fig. 5, and is in good agreement with SEM micrographs. Sample preparation was carried out by physically grinding the large crystals and sonication followed by fishing with a lacey carbon TEM grids. The TEM images revealed similar structures as the SEM micrographs. Bundles were seen throughout the lacey carbon grid consisting of entangled nanofibers less than 1–2 nm in diameter. The discrepancy between the fiber diameter observed in the SEM and TEM was attributed to the Pd/Au coating for SEM imaging. In a typical Pd/Au coating, approximately 10 nm of the conductive metal was sputtered, accounting for the increased diameter observed in the SEM micrographs. In addition to the electrospinning of β-SiC with the SMP-10 precursor, we have also attempted to electrospin the hexagonal α-SiC. This was done by seeding the polycarbosilane precursor polymer with crystals of the hexagonal α-SiC during the electrospinning process. The curing, pyrolysis, and crystallization were performed in the same manner as the non-seeded precursor. However, there were no significant change in ratio of the α-SiC to the β-SiC nanofibers. 4. Conclusion The ability to fabricate uniform nanofibers of β-SiC 1–2 nm in diameter has been demonstrated via the technique of concentric
Fig. 4. SEM micrographs of crystallized β-SiC.
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electrospinning. These represent the smallest SiC nanofibers produced to date. The strategy demonstrated here to form nanofibers of silicon carbide can be applied to the preparation of other carbide fibers. Future work is focused on electrospinning the hexagonal α-SiC fibers, which may have more versatile applications. Acknowledgement Financial support for this work was provided by the Robert A. Welch Foundation and SPRING. References [1] Zorman CA, Fleischman AJ, Dewa AS, Mehregany M, Jacob C, Nishino S, et al. J Appl Phys 1995;78:5136. [2] Davis RF. Phys Rev B Condens Matter Mater Phys 1993;185:1. [3] Pei LZ, Tang YH, Zhao XQ, Chen YW. J Mater Sci 2007;42:5068. [4] Kholmanov IN, Kharlamov A, Barborini E, Lenardi C, Li Bassi A, Bottani CE, et al. J Nanosci Nanotechnol 2002;2:453. [5] Eick BM, Youngblood JP. J Mater Sci 2009;44:160. [6] Shin DG, Riu DH, Kim HE. J Ceram Process Res 2008;9:209. [7] Kamalakaran R, Lupo F, Grobert N, Scheu T, Jin-Phillipp NY, Ruhle M. Carbon 2004;42:1. [8] Herricks TE, Kim SH, Kim J, Li D, Kwak JH, et al. J Mater Chem 2005;15:3241. [9] Dersch R, Steinhart M, Boudriot U, Greiner A, Wendorff JH. Polym Adv Tech 2005;16:276. [10] Reneker DH, Yarin AL. Polymer 2008;49:2387.
[11] Reneker DH, Chun I. Nanotechnology 1996;7:216. [12] Li D, Wang Y, Xia Y. Nano Lett 2003;3:1167. [13] Macias M, Chacko A, Ferraris JP, Balkus Jr KJ. Microporous Mesoporous Mater 2005;86:1. [14] Madhugiri S, Sun B, Smirniotis PG, Ferraris JP, Balkus Jr KJ. Microporous Mesoporous Mater 2004;69:77. [15] K. J. Balkus, J. P. Ferraris, S. Madhugiri, U.S. Patent 7, 390, 452, 2008. [16] K. J. Balkus, J. P. Ferraris, S. Madhugiri, A. S. Scott, U.S. Patent 20040137225, 2004. [17] Madhugiri S, Zhou W, Ferraris JP, Balkus Jr KJ. Microporous Mesoporous Mater 2003;63:75. [18] K. J. Balkus Jr, C. Xiong, M. Macias-Guzman, Mater Res Soc Symp Proc Mater Res Soc, Boston, MA, 2005; 863, L5. 14.1. [19] Huang ZM, Zhang YZ, Kotaki M, Ramakrishna S. Compos Sci Technol 2003;63: 2223. [20] Khanam N, Mikoryak C, Draper RK, Balkus Jr KJ. Acta Biomater 2007;3:1050. [21] Yoshimoto H, Shin YM, Terai H, Vacanti JP. Biomaterials 2003;24:2077. [22] Jia H, Zhu G, Vugrinovich B, Kataphinan W, Reneker DH, Wang P. Biotechnol Prog 2002;18:1027. [23] Kim C, Ngoc BTN, Yang KS, Kojima M, Kim YA, Kim YJ, et al. Adv Funct Mater 2007;19:2341. [24] Kim C, Yang KS, Lee WJ. Electrochem Solid-State Lett 2004:7. [25] Kenawy ER, Bowlin GL, Mansfield K, Layman J, Simpson DG, Sanders EH, et al. J Control Release 2002;81:57. [26] Liu HA, Gnade BE, Balkus Jr KJ. Adv Funct Mater 2008;18:3620. [27] Li D, Babel A, Jenekhe SA, Xia Y. Adv Mater 2004;16:2062. [28] Li D, McCann JT, Xia Y. Small 2005;1:83. [29] I. G. Loscertales, J. E. D. GÛmez, M. Lallave, J. M. Rosas, J. Bedia, J. RodrÌguez-Mirasol, et al., Mater Res Soc Symp Proc Mater Res Soc, Boston, MA, 2006; 948, pp. 83–90. [30] Starfire Systems, http://www.starfiresystems.com/download.cfm/SMP_10_Curing _and_Pyrolysis.pdf?AssetID=164. 2008; 1–6.
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m a t l e t
Electrospinning of beta silicon carbide nanofibers Harvey A. Liu, Kenneth J. Balkus Jr. ⁎ The University of Texas at Dallas, Department of Chemistry and the Alan G. MacDiarmid NanoTech Institute, Richardson, TX 75083-0688, USA
a r t i c l e
i n f o
Article history: Received 13 May 2009 Accepted 4 August 2009 Available online 9 August 2009 Keywords: Silicon carbide Nanofibers Electrospinning
a b s t r a c t Silicon carbide exhibits many unique properties such as its mechanical robustness, chemical inertness, and thermal stability, which make the material appealing for many applications. Some of these applications include its use as a support for nanocomposites or as a high temperature filter material. The ability to fabricate nanofibers of SiC could enhance its utility in these applications. In the current study, nanofibers of β-SiC have been fabricated through the technique of concentric electrospinning. This method demonstrates the ability to fabricate uniform SiC nanofibers with a diameter ranging from 1 to 2 nm, the smallest to date. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Silicon carbide has been acclaimed for many of its characteristics such as its mechanical robustness, chemical inertness, and thermal stability. Due to the many unique properties of silicon carbide, different morphologies of this material have been fabricated, including: thin films [1,2], rods [3,4], and fibers [5,6]. For example, fibers with a diameter of 1–3 μm were fabricated through wet-type electrospinning [6]. A more recent study in the electrospinning of silicon carbide by Eick et al. demonstrated the ability to fabricate composite fibers with diameters as small as 20 nm, though the majority of the fibers observed were much larger, some of which exceeded 100 nm in diameter. In addition to the wide variation in the diameter of these fibers, a silica shell formed with a SiC core caused by the atmospheric oxygen and impurities in the furnace [5]. A fibrous morphology provides many unique favorable properties; the most prevalent is the increase in surface to volume ratio, which expands the utility of a material to various applications. Nanofibers of silicon carbide in particular offer potential applications as a support material for nanocomposites [7], substrates for catalysis [8–10], and as well as high temperature filters [6]. Electrospinning of the polycarbosilane followed by curing and pyrolysis has proven to be a successful approach to fabricating SiC fibers [5,6]. However, the resulting SiC fibers exhibited a wide range of fiber diameters as well as nonuniform and impure structures. In the present study, we utilized a polycarbosilane as a precursor, but employ the technique of concentric, or core–shell, electrospinning to fabricate uniform nanofibers. By employing concentric electrospinning we
demonstrated the first fabrication method to attain consistently uniform silicon carbide fibers with diameters in the range of 1–2 nm. There has been growing interest in the method of electrospinning, especially in the area of ceramic materials. This method has been utilized in the fabrication of submicron to nanosized fibers composed of various materials including polymers [11], ceramics [12–18], and composites[19], which have found application in areas such as tissue engineering [20,21], catalysis [22], composite materials [19], supercapacitors [23,24], drug delivery [25], as well as self-healing materials [26]. In the past few years, a variation of conventional electrospinning has been developed, known as coaxial or concentric electrospinning, and has resulted in the fabrication of fibrous materials that previously could not have been achieved [27–29]. A schematic of concentric electrospinning is shown in Fig. 1. Similar to conventional electrospinning, concentric electrospinning utilizes an external electrostatic force, which is applied to a polymer melt [27]. Upon excess electrostatic force, the polymer melt forms a Taylor cone and undergoes a whipping action, stretching the polymer solution and forming a nonwoven mat [10]. The technique of coaxial electrospinning allows for the formation of fibers for materials that cannot be electrospun through conventional spinning. Typically, a polymer that is easily electrospun is fed through the outer sheath and a material that is difficult to spin is fed through the core. The outer sheath material serves to contain the inner core and form the fiber morphology. After the fabrication of these coaxial fibers, post-fabrication methods can be performed on the inner material which may include either annealing and/or washing away of the outer sheath to reveal the inner fibrous material. 2. Experimental
⁎ Corresponding author. Tel.: +1 972 883 2659; fax: +1 972 883 2925. E-mail address: [email protected] (K.J. Balkus). 0167-577X/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2009.08.009
In the present study, high molecular weight polystyrene was used for the fabrication of the outer sheath while polycarbosilane
2362
H.A. Liu, K.J. Balkus Jr. / Materials Letters 63 (2009) 2361–2364
Fig. 1. Schematic of concentric electrospinning setup.
(SMP-10, Starfire Systems Inc.) (Fig. 2a) was fed through the core as the silicon carbide precursor. The concentric electrospinning setup was assembled through the insertion of a 22 gauge needle through an 18 gauge needle. The flow rate through the outer and inner needle was independently regulated with a syringe pump (7802CO, KD Scientific Inc., USA). In a typical synthesis, a 15 wt.% polystyrene in chloroform melt was fed through the outer sheath at a rate of 7× 10− 2–1×10− 1 mL/min and the silicon carbide precursor, SMP-10, was used as received and fed through the inner core at a rate of 8× 10− 3 mL/min. A 10 kV charge was applied to the needle tip, which was adjusted to be 25 cm from the grounded rotating drum wrapped with foil as the collecting surface.
3. Results and discussion Scanning electron micrographs (SEM) of the as-spun core shell fibers are shown in Fig. 2b–c. The average diameter of the core–shell fibers typically ranged from 10 to 20 μm (Fig. 2b), however, fibers as small as 2 μm were observed as well (Fig. 2c). The fibers were spun into a freestanding sheet and cured in an oven overnight at 100 °C for 12 h followed by heating to 200 °C for 24 h to cure the polycarbosilane. The as-spun core–shell fibers as a free-standing sheet exhibited a slight yellow tint from the polycarbosilane precursor embedded in the core (Fig. 2d). It can be seen in the SEM micrograph (Fig. 2c) that some fibers
Fig. 2. (a) Molecular structure of polycarbosilane (b,c) SEM micrographs of the as-spun core–shell fibers (d) digital image of free-standing sheet of fibers.
H.A. Liu, K.J. Balkus Jr. / Materials Letters 63 (2009) 2361–2364
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Fig. 3. XRD of crystallized β-SiC nanofibers showing miller indices.
Fig. 5. TEM of crystallized β-SiC.
were fractured, due to the brittle nature of polystyrene, though the fibers were robust enough to handle (Fig. 2d). SEM imaging of the cured fibers revealed no changes in the morphology of the fibers from the curing process. The film was then washed in chloroform and centrifuged repeatedly to wash away the polystyrene outer sheath. The resulting cured fibers were then transferred to a graphite crucible and subjected to pyrolysis in a high temperature vacuum furnace under an inert gas atmosphere (Red Devil™, R. D. Webb Company, Inc.). The pyrolysis procedure was executed under argon gas according to published processing procedures [30]. The fibers were heated from room temperature to 650 °C at a rate of 1 °C/min, then from 650 °C to 850 °C at 3 °C/min. The oven was then held at 850 °C for 1 h whereupon heating was stopped and cooled to below 100 °C before the sample was recovered. The pyrolysis treatment results in the recovery of amorphous (glassy) silicon carbide, which was confirmed by X-ray diffraction. Further heat treatment was used in order to convert the glassy silicon carbide to polycrystalline β-SiC. The crystallization was conducted in a high temperature vacuum oven under argon where the sample was heated from room temperature to 1600–1650 °C at an approximate rate of 2–3 °C/min. The sample was held at this temperature for 6 h to crystallize the fibers. The X-ray diffraction pattern of the crystallized SiC nanofibers is shown in Fig. 3. Trace amounts of the hexagonal α-SiC are seen accompanied by a strong diffraction pattern for β-SiC (Fig. 3) In addition to SiC, trace amounts of graphite were also seen, represented by a peak appearing at approximately 26°. The appearance of graphite is likely from the graphite crucible and/or the graphitic insulation of the furnace. SEM micrographs of the crystalline β-SiC reveal uniform nanofibers with diameters approximately 10 nm in size (Fig. 4).
Comparisons of the fibers before the washing and pyrolysis of the electrospun composite fibers show a large difference in the diameter size. This is expected since the polystyrene was fed through the needle at a much higher rate than the silicon carbide precursor, and thus a smaller volume of the precursor was actually present in the core of the composite fibers. Transmission electron microscopy (TEM) of the crystallized silicon carbide is shown in Fig. 5, and is in good agreement with SEM micrographs. Sample preparation was carried out by physically grinding the large crystals and sonication followed by fishing with a lacey carbon TEM grids. The TEM images revealed similar structures as the SEM micrographs. Bundles were seen throughout the lacey carbon grid consisting of entangled nanofibers less than 1–2 nm in diameter. The discrepancy between the fiber diameter observed in the SEM and TEM was attributed to the Pd/Au coating for SEM imaging. In a typical Pd/Au coating, approximately 10 nm of the conductive metal was sputtered, accounting for the increased diameter observed in the SEM micrographs. In addition to the electrospinning of β-SiC with the SMP-10 precursor, we have also attempted to electrospin the hexagonal α-SiC. This was done by seeding the polycarbosilane precursor polymer with crystals of the hexagonal α-SiC during the electrospinning process. The curing, pyrolysis, and crystallization were performed in the same manner as the non-seeded precursor. However, there were no significant change in ratio of the α-SiC to the β-SiC nanofibers. 4. Conclusion The ability to fabricate uniform nanofibers of β-SiC 1–2 nm in diameter has been demonstrated via the technique of concentric
Fig. 4. SEM micrographs of crystallized β-SiC.
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electrospinning. These represent the smallest SiC nanofibers produced to date. The strategy demonstrated here to form nanofibers of silicon carbide can be applied to the preparation of other carbide fibers. Future work is focused on electrospinning the hexagonal α-SiC fibers, which may have more versatile applications. Acknowledgement Financial support for this work was provided by the Robert A. Welch Foundation and SPRING. References [1] Zorman CA, Fleischman AJ, Dewa AS, Mehregany M, Jacob C, Nishino S, et al. J Appl Phys 1995;78:5136. [2] Davis RF. Phys Rev B Condens Matter Mater Phys 1993;185:1. [3] Pei LZ, Tang YH, Zhao XQ, Chen YW. J Mater Sci 2007;42:5068. [4] Kholmanov IN, Kharlamov A, Barborini E, Lenardi C, Li Bassi A, Bottani CE, et al. J Nanosci Nanotechnol 2002;2:453. [5] Eick BM, Youngblood JP. J Mater Sci 2009;44:160. [6] Shin DG, Riu DH, Kim HE. J Ceram Process Res 2008;9:209. [7] Kamalakaran R, Lupo F, Grobert N, Scheu T, Jin-Phillipp NY, Ruhle M. Carbon 2004;42:1. [8] Herricks TE, Kim SH, Kim J, Li D, Kwak JH, et al. J Mater Chem 2005;15:3241. [9] Dersch R, Steinhart M, Boudriot U, Greiner A, Wendorff JH. Polym Adv Tech 2005;16:276. [10] Reneker DH, Yarin AL. Polymer 2008;49:2387.
[11] Reneker DH, Chun I. Nanotechnology 1996;7:216. [12] Li D, Wang Y, Xia Y. Nano Lett 2003;3:1167. [13] Macias M, Chacko A, Ferraris JP, Balkus Jr KJ. Microporous Mesoporous Mater 2005;86:1. [14] Madhugiri S, Sun B, Smirniotis PG, Ferraris JP, Balkus Jr KJ. Microporous Mesoporous Mater 2004;69:77. [15] K. J. Balkus, J. P. Ferraris, S. Madhugiri, U.S. Patent 7, 390, 452, 2008. [16] K. J. Balkus, J. P. Ferraris, S. Madhugiri, A. S. Scott, U.S. Patent 20040137225, 2004. [17] Madhugiri S, Zhou W, Ferraris JP, Balkus Jr KJ. Microporous Mesoporous Mater 2003;63:75. [18] K. J. Balkus Jr, C. Xiong, M. Macias-Guzman, Mater Res Soc Symp Proc Mater Res Soc, Boston, MA, 2005; 863, L5. 14.1. [19] Huang ZM, Zhang YZ, Kotaki M, Ramakrishna S. Compos Sci Technol 2003;63: 2223. [20] Khanam N, Mikoryak C, Draper RK, Balkus Jr KJ. Acta Biomater 2007;3:1050. [21] Yoshimoto H, Shin YM, Terai H, Vacanti JP. Biomaterials 2003;24:2077. [22] Jia H, Zhu G, Vugrinovich B, Kataphinan W, Reneker DH, Wang P. Biotechnol Prog 2002;18:1027. [23] Kim C, Ngoc BTN, Yang KS, Kojima M, Kim YA, Kim YJ, et al. Adv Funct Mater 2007;19:2341. [24] Kim C, Yang KS, Lee WJ. Electrochem Solid-State Lett 2004:7. [25] Kenawy ER, Bowlin GL, Mansfield K, Layman J, Simpson DG, Sanders EH, et al. J Control Release 2002;81:57. [26] Liu HA, Gnade BE, Balkus Jr KJ. Adv Funct Mater 2008;18:3620. [27] Li D, Babel A, Jenekhe SA, Xia Y. Adv Mater 2004;16:2062. [28] Li D, McCann JT, Xia Y. Small 2005;1:83. [29] I. G. Loscertales, J. E. D. GÛmez, M. Lallave, J. M. Rosas, J. Bedia, J. RodrÌguez-Mirasol, et al., Mater Res Soc Symp Proc Mater Res Soc, Boston, MA, 2006; 948, pp. 83–90. [30] Starfire Systems, http://www.starfiresystems.com/download.cfm/SMP_10_Curing _and_Pyrolysis.pdf?AssetID=164. 2008; 1–6.