Experimental

Bottom-gate transistors were prepared on clean glass substrates.The bottom electrodes were applied by shadow-mask evaporation ofa thin chromium adhesion layer and gold. Subsequently, poly(vinyli-dene fluoride/trifluoroethylene) (P(VDF/TrFE); 65/35 mol-%) ran-dom copolymer was applied by spin casting from filtered 2-butanonesolutions. These devices were annealed in a vacuum oven at 138 °C toenhance the crystallinity. Gold or samarium source–drain electrodeswere created by using shadow-mask evaporation with a wire to createa channel of typically 10 to 40 lm in length and 4 to 6 mm inwidth. Pure [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) or a4/1 wt.-% blend with poly[2-methoxy-5-(2′-ethyl-hexyloxy)-p-phenyl-enevinylene] (MEH-PPV) polymer was spin cast onto the layer stackfrom chlorobenzene in a N2 filled glovebox. The PCBM solutions hada concentration of 30 g L–1 and the blend solutions were 15 g L–1. Theblend devices were annealed at 90 °C. Field-effect measurements ontransistors were performed in dark and vacuum using a Keithley 4200semiconductor analyzer. Polymer layer thicknesses were determinedusing a Dektak profilometer. The programming operation experimentin Figure 4 was performed with an Agilent 8114A pulse generator.Any capacitive charge obtained by the programming pulses was re-moved before the read-out measurement, by connecting all three elec-trodes for 3 min.

Received: March 17, 2005Final version: June 10, 2005

Published online: September 22, 2005

–[1] C. D. Dimitrakopoulos, P. R. L. Malenfant, Adv. Mater. 2002, 14, 99.[2] G. H. Gelinck, H. E. Huitema, E. van Veenendaal, E. Cantatore,

L. Schrijnemakers, J. B. P. H. van der Putten, T. C. T. Geuns,M. Beenhakkers, J. B. Giesbers, B.-H. Huisman, E. J. Meijer,E. Mena Benito, F. J. Touwslager, A. W. Marsman, B. J. E.van Rens, D. M. de Leeuw, Nat. Mater. 2004, 3, 106.

[3] R. C. G. Naber, C. Tanase, P. W. M. Blom, G. H. Gelinck, A. W.Marsman, F. J. Touwslager, S. Setayesh, D. M. de Leeuw, Nat. Mater.2005, 4, 243.

[4] K. N. N. Unni, R. de Bettignies, S. Dabos-Seignon, J. M. Nunzi,Mater. Lett. 2005, 59, 1165.

[5] R. Schroeder, L. A. Majewski, M. Voigt, M. Grell, IEEE ElectronDevice Lett. 2005, 26, 69.

[6] M. Matsumura, Y. Nara, J. Appl. Phys. 1980, 51, 6443.[7] A. Dodabalapur, H. E. Katz, L. Torsi, R. C. Haddon, Science 1995,

269, 1560.[8] A. Dodabalapur, H. E. Katz, L. Torsi, R. C. Haddon, Appl. Phys.

Lett. 1996, 68, 1108.[9] K. Tada, H. Harada, K. Yoshino, Jpn. J. Appl. Phys., Part 2 1996, 35,

L944.[10] R. Martel, V. Derycke, C. Lavoie, J. Appenzeller, K. K. Chan,

J. Tersoff, Ph. Avouris, Phys. Rev. Lett. 2001, 87, 256 805.[11] J. A. Misewich, R. Martel, P. Avouris, J. C. Tsang, S. Heinze, J. Ters-

off, Science 2003, 300, 783.[12] E. J. Meijer, D. M. de Leeuw, S. Setayesh, E. Van Veenendaal, B.-H.

Huisman, P. W. M. Blom, J. C. Hummelen, U. Scherf, J. Kadam,T. M. Klapwijk, Nat. Mater. 2003, 2, 678.

[13] R. J. Chesterfield, C. R. Newman, T. M. Pappenfus, P. C. Ewbank,M. H. Haukaas, K. R. Mann, L. L. Miller, C. D. Frisbie, Adv. Mater.2003, 15, 1278.

[14] J. K. J. van Duren, V. D. Mihailetchi, P. W. M. Blom, T. van Wou-denbergh, J. C. Hummelen, M. T. Rispens, R. A. J. Janssen, M. M.Wienk, J. Appl. Phys. 2003, 94, 4477.

[15] M. W. J. Prins, S. E. Zinnemers, J. F. M. Cillessen, J. B. Giesbers,Appl. Phys. Lett. 1997, 70, 458.

[16] T. D. Anthopoulos, C. Tanase, S. Setayesh, E. J. Meijer, J. C. Hum-melen, P. W. M. Blom, D. M. de Leeuw, Adv. Mater. 2004, 16, 2174.

Anisotropic Polyion-Complex Gels viaTemplate Polymerization**

By Yukari Shigekura, Yong Mei Chen,Hidemitsu Furukawa, Tatsuo Kaneko,Daisaku Kaneko, Yoshihito Osada, andJian Ping Gong*

Tissues in living organisms include a large amount of waterand are in a soft and wet gel-like state. These gels have a well-ordered structure, which plays a crucial role in the normalfunctioning of the living organisms.[1–5] For example, myosinshows a liquid-crystalline (LC) structure in sarcomere, whichcontributes to the formation and smooth motion of musclefibers.[4] Lipid bilayers show a phase transition between a LCstate and a gel state.[5] In the LC state, the lipid bilayersallow the efficient transport of molecules. However, the mostcommonly synthesized gels are amorphous, and rarely dothey possess a well-ordered structure. Thus, there have beenseveral attempts at replicating the functionality of living or-ganisms by introducing well-ordered structures into synthe-sized gels.[6–16] In our previous work, gels with an orderedstructure were synthesized by the copolymerization of thewater-soluble and hydrophobic monomers, acrylic acid (AA)and crystalline stearyl acrylate (SA).[9,10] It was found that thegels have a memory for shapes owing to the order–disordertransitions of SA-rich domains in water. Furthermore, by thecopolymerization of LC 11-(4′-cyanobiphenyloxy) undecylacrylate (11CBA) and AA monomers, poly(11CBA-co-AA)LC hydrogels were synthesized.[11–15] Poly(11CBA-co-AA)gels swollen in water display a smectic A state.[11–14] Thesegels also show anisotropic shrinking in one direction as thetemperature increases.[15] This behavior is an example of the

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–[*] Prof. J. P. Gong, Y. Shigekura, Dr. Y. M. Chen, Prof. H. Furukawa,

D. Kaneko, Prof. Y. OsadaDivision of Biological Sciences, Graduate School of ScienceHokkaido UniversitySapporo 060-0810 (Japan)E-mail: gong@sci.hokudai.ac.jpProf. J. P. GongSORST, JSTSapporo 060-0810 (Japan)Dr. Y. M. ChenCreative Research Initiative ‘SOUSEI’Hokkaido UniversitySapporo 001-0021 (Japan)Dr. T. KanekoDepartment of Molecular ChemistryGraduate School of EngineeringOsaka UniversitySuita 565-0871 (Japan)

[**] We thank Prof. H. Orihara for his advice and help with the measure-ment of birefringence. This research was financially supported by aGrant-in-Aid for the Creative Scientific Research from the Ministryof Education, Science, Sports, and Culture of Japan.

anisotropic motion of gels caused by LC structure. Also, Fin-kelmann and co-workers have succeeded in synthesizingsmectic A elastomers with uniform homeotropic orienta-tion.[16]

Here, we report a novel anisotropic gel formed by thetemplate (matrix) polymerization of cationic monomer N-[3-(N,N-dimethylamino)propyl]acrylamide methyl chloride quar-ternary (DMAPAA-Q) with anionic mesogen poly(2,2′-di-sulfonyl-4,4′-benzidine terephthalamide) (PBDT). PBDT, awater-soluble, rigid-rod, synthetic polyelectrolyte,[17,18] hasa nematic state with a lower critical concentration, C*LC of2.8 wt.-%.[19] PDMAPAA-Q has a flexible main-chain struc-ture and does not show any LC phase by itself. The polyion-complex gels show birefringence even when the concentrationof LC molecules is as low as 0.02 wt.-%. To the best of ourknowledge, such an anisotropic polyion-complex gel, whichshows birefringence with a very small amount of mesogen,has never been synthesized before. This template-polymeriza-tion method for making anisotropic polyion-complex gels rep-resents a new way to introduce optical anisotropy into synthe-sized gels by using a small amount of dopant.

Figure 1a shows the reaction scheme for template polymer-ization. In this reaction, polyion-complex gels have beensynthesized using an anionic completely rigid-rod macromole-cule, PBDT, as the template, with cationic DMAPAA-Q asthe monomer. N,N′-methylenebisacrylamide (MBAA) is usedas the crosslinker. The gels have been synthesized in bulk be-tween two glass plates without surface treatment for orienta-tion. In the present study, all of the gels have been preparedat a PBDT concentration of 2 wt.-%, which is lower than itsC*LC (2.8 wt.-%). The concentration of the DMAPAA-Qmonomer was 2 M, and thus the charge of DMAPAA-Q inthe feed was twenty-six times as high as that of PBDT. Under

these conditions, the monomer solution containing PBDT be-fore gelation is amorphous (isotropic), exhibiting a dark im-age under crossed polarizing microscopy, as shown in Fig-ure 1b. However, the synthesized polyion-complex gel showsa strong birefringence under crossed polarizing microscopy, asshown in Figure 1c, although the gel is highly transparent,as shown in the right panel in Figure 1a. This birefringence isa result of microscopic domains, which are randomly orientedin the bulk. The maximum size of oriented domains showingthe same color under the crossed polarizing microscope isabout 1 mm, as shown in Figure 1c. However, the DMAPAA-Q gel without PBDT shows no birefringence; thus, this bire-fringence is caused by the presence of a small amount ofPBDT introduced through template polymerization.

The gel swells to twenty times its size after equilibriumswelling in water, however, the birefringence is retained, asshown in Figure 1d. The sizes of the oriented domains becomelarger upon swelling. The concentration of PBDT in the swol-len gel, CLC, is only 0.14 wt.-%, which is 1/20 of the C*LC foraqueous PBDT. This result means that only a small amount ofLC macromolecules are necessary for birefringence in a cross-linked hydrogel formed by template polymerization. When aneutral acrylamide monomer is used instead of DMAPAA-Qfor the same polymerization reaction, no birefringence is ob-served. This implies that the formation of a polyion complexis important.

The swelling degree of the polyion-complex gels, Q, as afunction of crosslinker concentration in the feed, m= [MBAA]/[DMAPAA-Q], is shown in Figure 2a. On decreasing the den-sity of the crosslinker, the gels become more swollen. When mis decreased to 0.5 mol-%, Q can be as large as 200. The con-centration of PBDT in the polyion-complex gels as a functionof m is shown in Figure 2b. As m decreases, CLC of the swollen

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Gelation S Swelling

(a)

(b) (c) (d)

SO3Na

NaO3S

NHCOHN CO

n

+

CH2CH

CONH (CH2)3N+

CH3

CH3

CH3 Cl

-

Template

Polymerization

MBAA

PBDT PAA-Q

CLC=2wt.%<C*LC CLC=2wt.-% CLC=0.14wt.-%

500µm 500µm 500µm

DMA

Figure 1. Template polymerization of polyion-complex gels. a) Scheme for polymerization of gels. The photograph in the right panel shows the appear-ance of a gel polymerized from 2 M DMAPAA-Q and 2 mol-% MBAA in the presence of 2 wt.-% PBDT after equilibrium swelling in a large amount ofwater. b) Crossed polarizing microscope image of a 2 wt.-% PBDT aqueous solution before polymerization. c) Crossed polarizing microscope imageof an as-prepared gel; CLC is 2 wt.-%. d) Crossed polarizing microscope image of the equilibrium swollen gel in water; CLC is 0.14 wt.-%.

gels decreases due to an increase in Q. However, all the swol-len polyion-complex gels still show birefringence, as shownin Figure 2c. It is noted that CLC of the most swollen gel(Q = 200) is 0.02 wt.-%, and this concentration represents only1/140 of C*LC. It is quite interesting that polyion-complex gelssynthesized from PBDT and DMAPAA-Q show birefringenceeven at such low CLC. Furthermore, when DMAPAA-Q ispolymerized in the presence of PBDT with no MBAA, a whitesol is obtained, which shows no birefringence. Also, when wesimply added cationic PDMAPAA-Q to the mesogen PBDT, awhite precipitate was obtained, and birefringence was not ob-served. This means that the crosslinker prevents macroscopicphase separation, which occurs by the formation of a polyioncomplex.

Birefringence,

Dn = n� – n⊥ (1)

of polyion-complex gels and the PBDT aqueous solution hasbeen determined using a crossed polarizing microscope with aBerek compensator,[20] as shown in Figure 3a. It is found thatDn of the polyion-complex gels is as large as that of PBDTaqueous solutions around C*LC, although the CLC of polyion-complex gels is much lower than for PBDT aqueous solutions.This means that the large Dn of the polyion-complex gelsis caused not only by the orientation of PBDT but also bythe cooperative orientation of PDMAPAA-Q with PBDT.PDMAPAA-Q may align along PBDT, with PBDT acting as a

seed for the orientation during template polymerization, anda kind of anisotropic structure is formed in the polyion-com-plex gels.

Here, let us consider the effect of PBDT on template poly-merization. For rigid-rod LC molecules, the critical volumefraction for showing LC nature, �*, is defined by Flory’s lat-tice theory as,[21,22]

�� � 8X

1� 2X

� �≈

8X

(2)

Here, X is axial ratio and is defined by the equation,

X = L/D (3)

where L is the length of the molecule and D is the width ofthe molecule. The C*LC of PBDT is 2.8 wt.-%, so that �* forPBDT is 0.028. When this value of �* is substituted intoEquation 2, X for PBDT is calculated to be 286. For the swol-len polyion-complex gels of PBDT and PDMAPAA-Q, thelowest CLC is about 0.02 wt.-% and �* for the gel is 0.0002.Thus X for these gels is estimated to be 40 000 by substituting0.0002 in Equation 2. This X is 140 times larger than the valuefor PBDT in water, 286. Therefore, if this anisotropy is causedby the LC nature of PBDT, an extraordinarily large X shouldbe developed during template polymerization, simply basedon Flory’s theory.

We will now suggest a more detailed description of themechanism for template polymerization, as illustrated in Fig-

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101

102

103

10-1

100

101

Q

ν (mol.-%)

10-2

10-1

100

101

10-1

100

101

CL

C(w

t.-%

)

ν (mol.-%)

CLC

*

as-prepared

swollen

(a) (b)

(c)

0.5 1 2

(mol.-%)

500µm 500µm 500µm

ν

Figure 2. Effect of crosslinker concentration in the feed, m = [MBAA]/[DMAPAA-Q], on the properties of polyion-complex gels. a) Equilibrium swellingdegree of the gels, Q, as a function of m. b) Concentration of LC molecules (PBDT) in the gels, CLC, as a function of m. Open circles indicate the as-pre-pared gels and closed circles are for the equilibrium swollen gels. C*LC indicates the lower critical concentration at which a PBDT aqueous solution be-comes a nematic liquid crystal phase. c) Crossed polarizing microscope images of the swollen gels at different m.

ure 3b. Before gelation, the polyanions are randomly orientedand the pregel solution shows an amorphous (isotropic) statebecause the concentration of LC macromolecules is lowerthan C*LC. When template polymerization starts, the cationicpolymer emerges and forms an ion complex with anionic LCmacromolecules. By the formation of such ion complexes, theeffective volume fraction of the LC molecules becomes large.Since the ion complexes are oriented by electrostatic repul-sion and by connection to each other during polymerization,the axial ratio of the ion complex may become large enoughto show birefringence as a result of orientation effects. Prog-ress of the crosslinking reaction prevents macroscopic phaseseparation induced by the formation of the ion complex. Be-cause of this crosslinking effect, the synthesized polyion-com-plex gels are highly transparent. Actually, when DMAPAA-Qis polymerized in the presence of PBDT with no MBAA, awhite sol is obtained. The orientation of the gel network isfixed by the crosslinking reaction, which proceeds at the sametime as template polymerization. Because of this fixing of theorientation, the polyion-complex gels can maintain birefrin-gence after swelling in a large amount of solvent. By these

processes, a novel kind of oriented gel is synthesized by thepolymerization of a cationic monomer with anionic macro-molecule templates.

In conclusion, anisotropic polyion-complex gels have beensynthesized via the template polymerization of cationicmonomer DMAPAA-Q with an anionic mesogen PBDT tem-plate. The polyion-complex gels show birefringence even at0.02 wt.-% PBDT, which is 1/140 of the lower critical concen-tration of the nematic phase in PBDT aqueous solution. Thistemplate polymerization route is seen to be a novel method forobtaining optically anisotropic hydrogels using a very smallamount of dopant. It would be interesting to determine the rea-sons for the formation of such an ordered structure, and furtherstudies are ongoing to elucidate the mechanistic details.

Experimental

Preparation of PDMAPAA-Q Gels Containing PBDT: PBDT is awater-soluble polymer with a rigid-rod-like main-chain structure. Itwas synthesized by an interfacial polycondensation reaction. The de-

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(a)

(b) swelling

10-6

10-5

10-4

10-3

10-2

10-2

10-1

100

101

∆n

CLC

(wt.-%)

polyion-complex gels

PBDT aqueous solution

C*LC

+ + + +

++++ -----

+ + +

+ + + +

+

- --- -

+

++

+ +

++

+-- - - -

- - - - - + + + +

+ + + +

+

+

+

+ +

++

+

- - - - -

- - - - - - - - - -

-- - - - - + + + +

++ + + -- - - -

+ + +

+ + + +

+ - - - - - +

++

+ +

+ +

+-- - - -

- - - - - + + + +

+ + + +

+ + + +

++++ -----

+ + +

+ + + +

+- ---- +

++

+ +

+ +

+-- - - -

- - - - -+ + + +

+ + + +

Figure 3. a) Birefringence, as expressed by Equation 1, of polyion-complex gels and PBDT aqueous solutions as a function of PBDT concentration, CLC.b) Illustration of the template-polymerization mechanism for polyion-complex gels with LC structure prepared by using a very small amount of LC mol-ecules.

tails of this procedure have been published previously [18]. An aque-ous solution of PBDT has a LC nature above 2.8 wt.-% (C*LC). DMA-PAA-Q (Kohjin Co. Ltd.) was used as the monomer without furtherpurification. MBAA (Junsei Chemical Co. Ltd.) was recrystallizedwith ethanol and used as a crosslinker. Acrylamide (AAm) (JunseiChemical Co. Ltd.) was recrystallized with chloroform and used as theneutral monomer. Potassium persulfate (KPS) (Wako Pure ChemicalIndustries Ltd.) was recrystallized with water and used as the initiator.Water was deionized and purified with 0.22 lm and 5 lm membranefilters before use. 2 wt.-% PBDT, 2 mol L–1 DMAPAA-Q (or AAm),0.5, 1, or 2 mol-% (to DMAPAA-Q) MBAA, and 0.1 mol-% KPSwere dissolved in water. These solutions were poured into reactioncells consisting of a pair of glass plates with a 2 mm spacing. Radicalpolymerization was performed at 60 °C. After gelation, the productswere immersed in a large amount of water and allowed to reach anequilibrium state for a week.

Measurements: The swelling degree of the gels, Q, is defined here asthe weight ratio of a swollen to a dried gel [23]. The dried gels wereobtained by keeping them in a desiccator for 12 h and in a vacuumoven at 60 °C for 6 h.

Optical-microscopy observation was performed using a crossed po-larizing microscope (Olympus, BH-2) at room temperature. Samplegels were placed on glass plates and the upper free surfaces were ob-served. Birefringence, Dn, was measured by a crossed polarizing mi-croscope with a Berek compensator [20]. In the measurement, manymicroscopic domains randomly oriented in the bulk were observed.Thus, we chose one of large domains and selected the orientation di-rection by turning the sample under the crossed polarizing micro-scope. Under these conditions, Dn was measured from the retardation.Average Dn was determined by measuring Dn several times for eachsample.

Received: April 1, 2005Final version: July 27, 2005

Published online: September 29, 2005

–[1] Y. M. Evdokimov, T. V. Nasedkina, V. I. Salyanov, N. S. Badaev,

Mol. Biol. 1996, 30, 219.[2] M. Duvert, Y. Bouligand, C. Salat, Tissue Cell 1984, 16, 469.[3] M. Spencer, W. Fuller, M. H. F. Wilkins, G. L. Brown, Nature 1962,

194, 1014.[4] C. M. Coppin, P. C. Leavis, Biophys. J. 1992, 63, 794.[5] H. I. Petrache, N. Gouliaev, S. Tristram-Nagle, R. Zhang, R. M. Su-

ter, J. F. Nagle, Phys. Rev. E 1998, 57, 6.[6] M. Hayakawa, T. Onda, T. Tanaka, K. Tsujii, Langmuir 1997, 13,

3595.[7] K. Tsujii, M. Hayakawa, T. Onda, T. Tanaka, Macromolecules 1997,

30, 7397.[8] R. Kishi, M. Sisido, S. Tazuke, Macromolecules 1990, 23, 3868.[9] Y. Osada, A. Matsuda, Nature 1995, 376, 219.

[10] M. Uchida, M. Kurosawa, Y. Osada, Macromolecules 1995, 28, 4583.[11] T. Kaneko, K. Yamaoka, J. P. Gong, Y. Osada, Macromolecules

2000, 33, 412.[12] T. Kaneko, K. Yamaoka, J. P. Gong, Y. Osada, Macromolecules

2000, 33, 4422.[13] K. Yamaoka, T. Kaneko, J. P. Gong, Y. Osada, Macromolecules

2001, 34, 1470.[14] K. Yamaoka, T. Kaneko, J. P. Gong, Y. Osada, Langmuir 2003, 19,

8134.[15] T. Kaneko, K. Yamaoka, Y. Osada, J. P. Gong, Macromolecules

2004, 37, 5385.[16] E. Nishikawa, J. Yamamoto, H. Yokoyama, H. Finkelmann, Macro-

mol. Rapid Commun. 2004, 25, 611.[17] E. J. Vandenberg, W. R. Diveley, L. J. Filar, S. R. Pater, H. G. Barth,

J. Polym. Sci., Part A: Polym. Chem. 1989, 27, 3745.[18] N. Sarkar, L. D. Kershner, J. Appl. Polym. Sci. 1996, 62, 393.[19] T. Funaki, T. Kaneko, K. Yamaoka, Y. Ohsedo, J. P. Gong, Y. Osada,

Y. Shibasaki, M. Ueda, Langmuir 2004, 20, 6518.

[20] M. Born, E. Wolf, Principles of Optics, Cambridge University Press,Cambridge, UK 1959.

[21] P. J. Flory, Proc. R. Soc. London A 1956, 234, 60.[22] P. J. Flory, Proc. R. Soc. London A 1956, 234, 73.[23] H. Furukawa, J. Mol. Struct. 2000, 554, 11.

Self-Crimping BicomponentNanofibers Electrospun fromPolyacrylonitrile and ElastomericPolyurethane**

By Tong Lin,* Hongxia Wang, and Xungai Wang

Bicomponent polymer fibers combine the properties of twodifferent polymers to produce materials with new and im-proved properties that do not exist in either polymer fiber byitself.[1] They are often prepared by extruding the two poly-mers from the same spinneret, and the fibers are normallyclassified by their fiber cross-section structure as side-by-side,sheath–core, “islands-in-the-sea”, citrus fibers, segmented-pietypes, etc.[2] Bicomponent fibers have been used extensivelyin textile-related areas. For example, curly side-by-side “artifi-cial wool” has been produced for textile applications in thepast. Recently, metal–insulator–semiconductor bicomponentfibers have been reported, and these show potential for appli-cation as optoelectronic fibers or textiles.[3] Although existingfiber-making techniques are able to produce different cross-sectional shapes and geometries in bicomponent polymer fi-bers, the fiber diameters are limited to the micrometerscale.[4,5] Preparing bicomponent polymer fibers with muchsmaller diameters, especially with diameters on the order ofnanometers, has been a challenge.

The electrospinning process is an established method forproducing continuous polymer fibers with diameters on thenanometer scale.[6] In the electrospinning process, a polymersolution is charged with a high electrical voltage. A polymerdroplet at the tip of a nozzle is attracted by an electrical field,forming a so-called “Taylor cone”. At the tip of the cone,when the droplet overcomes restrictions due to surface ten-sion, a polymer jet is ejected. The charged jet then undergoesbending instability, alternatively referred to as “whipping in-stability”,[7] stretching itself to form very fine filaments. Solu-tion evaporation from the filament results in dry or semi-drynanofibers, which are deposited randomly on the collector

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–[*] Dr. T. Lin, H. Wang, Prof. X. Wang

Faculty of Science and Technology, Deakin UniversityGeelong, Victoria 3217 (Australia)E-mail: Tong.Lin@deakin.edu.au

[**] We thank Dr. Weidong Yang at CSIRO Manufacturing and Infra-structural Division for insightful discussions on the preparation ofthe microfluidic device and electrospinning process.