Delivered by Ingenta toRensselaer Polytechnic Institute

IP 1281132688Wed 23 Jun 2010 180354

REVIEW

Copyright copy 2010 American Scientific Publishers

All rights reserved

Printed in the United States of America

Journal ofNanoscience and Nanotechnology

Vol 10 5507ndash5519 2010

Electrospinning of Nanomaterials and Applications in

Electronic Components and Devices

Jianjun Miao124 Minoru Miyauchi4 Trevor J Simmons24Jonathan S Dordick134lowast and Robert J Linhardt1234lowast

1Departments of Chemical and Biological Engineering 2Chemistry and Chemical Biology 3Biology4Center for Nanotechnology and Center for Biotechnology and Interdisciplinary Studies

Rensselaer Polytechnic Institute Troy NY 12180 USA

Electrospinning of nanomaterial composites are gaining increased interest in the fabrication ofelectronic components and devices Performance improvement of electrospun components resultsfrom the unique properties associated with nanometer-scaled features high specific surfaceareas and light-weight designs Electrospun nanofiber membrane-containing polymer electrolytesshow improved ionic conductivity electrochemical stability low interfacial resistance and improvedchargendashdischarge performance than those prepared from conventional membranes Batteries withnon-woven electrospun separators have increased cycle life and higher rate capabilities than oneswith conventional separators Electrospun nanofibers may also be used as working electrodes inlithium-ion batteries where they exhibit excellent rate capability high reversible capacity and goodcycling performance Moreover the high surface area of electrospun activated carbon nanofibersimproves supercapacitor energy density Similarly nanowires having quasi-one-dimensional struc-tures prepared by electrospinning show high conductivity and have been used in ultra-sensitivechemical sensors optoelectronics and catalysts Electrospun conductive polymers can also per-form as flexible electrodes Finally the thin porous structure of electrospun nanofibers provides forthe high strain and fast response required for improved actuator performance The current reviewexamines recent advances in the application of electrospinning in fabricating electronic componentsand devices

Keywords Carbon Nanofiber Electrode Separator Electrolyte Nanowire SupercapacitorsActuator Lithium Ion Battery

CONTENTS

1 Introduction 5507

11 Electrospinning History and Overview 5507

12 Electrospinning in Energy Applications 5509

13 Electrospinning Methods and Principles 5510

2 Applications of Electrospinning Preparing Electrical

Components and Devices 5510

21 Electrospun Insulators Separators and Electrolytes 5510

22 Electrospun Electrodes 5511

23 Wires and Nanowires 5513

24 Supercapacitors 5515

25 Actuators 5516

3 Challenges and Open Questions 5517

4 Conclusion and Prospects 5518

Acknowledgments 5518

References and Notes 5518

lowastAuthors to whom correspondence should be addressed

1 INTRODUCTION

11 Electrospinning History and Overview

Electrospinning first appeared in 1934 as a new patented

process for spinning small diameter fibers12 Prototype

electrospinning devices were capable of collecting threads

of aligned fibers By 1969 Taylor developed a jet form-

ing process3 and not long after the impact of experimental

parameters on electrospun fiber structuresproperties was

established4 resulting in polyethylene and polypropylene

melts that could be electrospun into fibers56 Very little

additional work on electrospinning was undertaken until

the early 1990s when electrospinning was applied to a

broad range of polymers yielding porous fibers Increased

popularity of the term electrospinning coincided with a

dramatic increase in the number of annual publications

at the beginning of the 21st Century78 Many polymers

J Nanosci Nanotechnol 2010 Vol 10 No 9 1533-48802010105507013 doi101166jnn20103073 5507

Delivered by Ingenta toRensselaer Polytechnic Institute

IP 1281132688Wed 23 Jun 2010 180354R

EVIEW

Electrospinning of Nanomaterials and Applications in Electronic Components and Devices Miao et al

have been electrospun into fiber mats and membranes

New technologies have been introduced for electrospin-

ning such as double needle electrospinning (Fig 1(a))

which can fabricate fibers from two different compo-

nents simultaneously such as polymers or polymers and

solids combinations or solndashgels9 The resulting fibers

Jianjun Miao received his BS degree in Chemical Engineering from East China University

of Science and Technology (ECUST) in 2001 and PhD degree in Chemical Engineering

from University of Connecticut in 2009 He joined Professor Linhardtrsquos group at Rensselaer

Polytechnic Institute as a postdoctoral fellow in 2009 His research interests include electro-

spinning nanostructured materials bionanomaterials and nanostructure-based devices He

has published nine peer-reviewed papers in the area of materials chemistry

Minoru Miyauchi received his MD in 1999 from Nagoya Institute of Technology in Japan

And then he joined CHISSO Co Ltd as an engineer in fiber division His responsibility

was mainly RampD of synthetic fibers for industry In 2008 he started to study at Professor

Linhardt group as a visiting researcher from CHISSO

Trevor J Simmons earned his BS in Chemical Science from SUNY Stony Brook in 2004

and a PhD in Chemistry from Rensselaer Polytechnic Institute (RPI) in Troy NY in 2008

under the guidance of Dr Pulickel M Ajayan and Dr Robert J Linhardt He has primarily

worked in academics but also has recently worked as a nanotechnology consultant with a

cellulose-based energy storage company Research interests focus on carbon nanomaterials

chemistry in nanotechnology cellulosic materials energy storage and engineering novel

applications in these areas but he maintains a wide-range of interests in chemistry physics

biotechnology and materials science He has published several peer-reviewed papers in the

area of carbon nanotubes and cellulosic materials He currently works as a postdoctoral

investigator for the Coordinacion para la Investigacion y Aplicacion de la Ciencia y la

Tecnologıa (CIACyT) which is part of the Universidad Autonoma de San Luis Potosı

(UASLP) in San Luis Potosı Mexico He also conducts investigations as a visiting scholar at RPI with Dr Linhardt and

works as a consultant for the Paper Battery Company of Troy NY

Jonathan S Dordick received his BA degree in Biochemistry and Chemistry from

Brandeis University and his PhD in Biochemical Engineering from the Massachusetts Insti-

tute of Technology He has held chemical engineering faculty appointments at the University

of Iowa (1987ndash1998) where he also served as the Associate Director of the Center for Bio-

catalysis and Bioprocessing and Rensselaer Polytechnic Institute (1998ndashpresent) where he

is the Howard P Isermann Professor of Chemical and Biological Engineering and Professor

of Biology and Director of the Center for Biotechnology and Interdisciplinary Studies

Professor Dordick has received numerous awards including the American Chemical Soci-

etyrsquos Marvin Johnson and Elmer Gaden Awards the International Enzyme Engineering

Award the Iowa Section Award of the ACS and an NSF Presidential Young Investigator

Award in 1989 and he has been elected as a Fellow of the American Association for the

Advancement of Science and the American Institute of Medical and Biological Engineers

have a corendashsheath composition which contain cores and

sheaths made of different materials A flexible polymer

usually resides in the sheath while another polymer with

a unique property such as low solubility or conductiv-

ity (eg poly(34-ethylenedioxythiophene) (PEDOT)) is

located in the core10 Nanomaterials such as nanoparticles

5508 J Nanosci Nanotechnol 10 5507ndash5519 2010

Delivered by Ingenta toRensselaer Polytechnic Institute

IP 1281132688Wed 23 Jun 2010 180354

REVIEW

Miao et al Electrospinning of Nanomaterials and Applications in Electronic Components and Devices

Robert J Linhardt received his PhD degree from the Johns Hopkins University (1979)

and was a postdoctoral student with Professor Robert Langer at the Massachusetts Institute

of Technology (1979ndash1982) and served on the faculty of University of Iowa from 1982ndash

2003 He is currently the Ann and John H Broadbent Jrrsquo59 Senior Constellation Professor

of Biocatalysis and Metabolic Engineering at Rensselaer Polytechnic Institute holding joint

appointments in the Departments of Chemistry and Chemical Biology Biology and Chemi-

cal and Biological Engineering His honors include the American Chemical Society Horace

S Isbell and Claude S Hudson Awards and the AACP Volwiler Research Achievement

Award His research focuses on glycobiology glycochemistry and glycoengineering Since

his arrival at Rensselaer Dr Linhardt has been actively involved in the emerging field of

nano-biotechnology focused on developing an artificial Golgi and paper-based energy stor-

age devices Professor Linhardt has published nearly 500 peer-reviewed manuscripts and

holds over 30 patents

or nanotubes can also be encapsulated in the core struc-

ture When p and n semiconductor materials are fab-

ricated into such a coaxial structure the contact area

between pndashn heterojunctions are maximized by reduc-

ing fiber diameter which for example can be used to

improve solar cell performance11 Electrospinning of abun-

dant and renewable natural biopolymers such as cellu-

lose and chitin is becoming an increasingly active area of

research However there are very few suitable solvents for

such biopolymers which significantly limits their use in

electrospinning Room temperature ionic liquids (RTILs)

nonvolatile solvents with high thermal stability that can

dissolve both highly polar and nonpolar polymers12ndash15

offer a potential solution to the poor solubility associated

with polysaccharides such as cellulose that limits their

application to electrospinning Unlike spinning a polymer

solution in volatile solvents which quickly evaporate in

the low pressure surrounding the fiber jet non-volatile

RTILs must be removed using a miscible co-solvent coag-

ulation bath to solidify polymer fiber

12 Electrospinning in Energy Applications

The search for alternative and stable sources of energy

is a growing and vital concern Although ldquocleanrdquo power

sources like nuclear wind solar and fuel cells have

been around for many years significant hurdles remain in

exploiting these sources on large enough scale to solve

the emerging energy crisis As a consequence increased

attention has focused on applying electrospinning in the

preparation of porous fiber mats as electronic components

including electrodes and separators and devices such as

batteries and supercapacitors (Fig 1(b)) Electrospun fiber

mats are capable of improving battery power increasing

energy density of capacitors and fuel cell and solar cell

efficiency Poly(olefin) microporous membranes are widely

used as commercial separators for Li-ion batteries16 and

although these conventional separators have a number of

suitable properties ie chemical stability tunable thick-

ness and mechanical strength17 their low porosity and

poor wettability resulting from the large polarity differ-

ence between non-polar poly(olefin) separator and highly

polar liquid electrolyte lead to increased cell resistance

limiting the performance of Li-ion batteries18 Electro-

spun fiber mats have extremely high specific areas as a

result of their high porosity making them a good can-

didate for battery membranes By introducing a polar

block to diblock polymers such as sulfonated styrene

Corendashshell nanofibers

Syringe pump

Core solution

Shell solutionHigh voltage

Electrically groundedcollecting plate

Core

Fiber structureS

hell

She

ll

(a)

(b)

Fig 1 (a) Schematic of electrospinning apparatus In spinning of corendash

shell (sheath) fibers both pumps are used with a coaxial needle assembly

in the spinneret In single solution electrospinning only a single pump

containing core solution is spun through a single needle (b) Performance

characteristics of powerenergy storage devices Reproduced with per-

mission from [76] R Kotz and M Carlen Electrochim Acta 45 2483

(2000) copy 2000 Elsevier

J Nanosci Nanotechnol 10 5507ndash5519 2010 5509

Delivered by Ingenta toRensselaer Polytechnic Institute

IP 1281132688Wed 23 Jun 2010 180354R

EVIEW

Electrospinning of Nanomaterials and Applications in Electronic Components and Devices Miao et al

have been electrospun into fiber mats and membranes

New technologies have been introduced for electrospin-

ning such as double needle electrospinning (Fig 1(a))

which can fabricate fibers from two different compo-

nents simultaneously such as polymers or polymers and

solids combinations or solndashgels9 The resulting fibers

Jianjun Miao received his BS degree in Chemical Engineering from East China University

of Science and Technology (ECUST) in 2001 and PhD degree in Chemical Engineering

from University of Connecticut in 2009 He joined Professor Linhardtrsquos group at Rensselaer

Polytechnic Institute as a postdoctoral fellow in 2009 His research interests include electro-

spinning nanostructured materials bionanomaterials and nanostructure-based devices He

has published nine peer-reviewed papers in the area of materials chemistry

Minoru Miyauchi received his MD in 1999 from Nagoya Institute of Technology in Japan

And then he joined CHISSO Co Ltd as an engineer in fiber division His responsibility

was mainly RampD of synthetic fibers for industry In 2008 he started to study at Professor

Linhardt group as a visiting researcher from CHISSO

Trevor J Simmons earned his BS in Chemical Science from SUNY Stony Brook in 2004

and a PhD in Chemistry from Rensselaer Polytechnic Institute (RPI) in Troy NY in 2008

under the guidance of Dr Pulickel M Ajayan and Dr Robert J Linhardt He has primarily

worked in academics but also has recently worked as a nanotechnology consultant with a

cellulose-based energy storage company Research interests focus on carbon nanomaterials

chemistry in nanotechnology cellulosic materials energy storage and engineering novel

applications in these areas but he maintains a wide-range of interests in chemistry physics

biotechnology and materials science He has published several peer-reviewed papers in the

area of carbon nanotubes and cellulosic materials He currently works as a postdoctoral

investigator for the Coordinacion para la Investigacion y Aplicacion de la Ciencia y la

Tecnologıa (CIACyT) which is part of the Universidad Autonoma de San Luis Potosı

(UASLP) in San Luis Potosı Mexico He also conducts investigations as a visiting scholar at RPI with Dr Linhardt and

works as a consultant for the Paper Battery Company of Troy NY

Jonathan S Dordick received his BA degree in Biochemistry and Chemistry from

Brandeis University and his PhD in Biochemical Engineering from the Massachusetts Insti-

tute of Technology He has held chemical engineering faculty appointments at the University

of Iowa (1987ndash1998) where he also served as the Associate Director of the Center for Bio-

catalysis and Bioprocessing and Rensselaer Polytechnic Institute (1998ndashpresent) where he

is the Howard P Isermann Professor of Chemical and Biological Engineering and Professor

of Biology and Director of the Center for Biotechnology and Interdisciplinary Studies

Professor Dordick has received numerous awards including the American Chemical Soci-

etyrsquos Marvin Johnson and Elmer Gaden Awards the International Enzyme Engineering

Award the Iowa Section Award of the ACS and an NSF Presidential Young Investigator

Award in 1989 and he has been elected as a Fellow of the American Association for the

Advancement of Science and the American Institute of Medical and Biological Engineers

have a corendashsheath composition which contain cores and

sheaths made of different materials A flexible polymer

usually resides in the sheath while another polymer with

a unique property such as low solubility or conductiv-

ity (eg poly(34-ethylenedioxythiophene) (PEDOT)) is

located in the core10 Nanomaterials such as nanoparticles

5508 J Nanosci Nanotechnol 10 5507ndash5519 2010

Delivered by Ingenta toRensselaer Polytechnic Institute

IP 1281132688Wed 23 Jun 2010 180354

REVIEW

Miao et al Electrospinning of Nanomaterials and Applications in Electronic Components and Devices

Robert J Linhardt received his PhD degree from the Johns Hopkins University (1979)

and was a postdoctoral student with Professor Robert Langer at the Massachusetts Institute

of Technology (1979ndash1982) and served on the faculty of University of Iowa from 1982ndash

2003 He is currently the Ann and John H Broadbent Jrrsquo59 Senior Constellation Professor

of Biocatalysis and Metabolic Engineering at Rensselaer Polytechnic Institute holding joint

appointments in the Departments of Chemistry and Chemical Biology Biology and Chemi-

cal and Biological Engineering His honors include the American Chemical Society Horace

S Isbell and Claude S Hudson Awards and the AACP Volwiler Research Achievement

Award His research focuses on glycobiology glycochemistry and glycoengineering Since

his arrival at Rensselaer Dr Linhardt has been actively involved in the emerging field of

nano-biotechnology focused on developing an artificial Golgi and paper-based energy stor-

age devices Professor Linhardt has published nearly 500 peer-reviewed manuscripts and

holds over 30 patents

or nanotubes can also be encapsulated in the core struc-

ture When p and n semiconductor materials are fab-

ricated into such a coaxial structure the contact area

between pndashn heterojunctions are maximized by reduc-

ing fiber diameter which for example can be used to

improve solar cell performance11 Electrospinning of abun-

dant and renewable natural biopolymers such as cellu-

lose and chitin is becoming an increasingly active area of

research However there are very few suitable solvents for

such biopolymers which significantly limits their use in

electrospinning Room temperature ionic liquids (RTILs)

nonvolatile solvents with high thermal stability that can

dissolve both highly polar and nonpolar polymers12ndash15

offer a potential solution to the poor solubility associated

with polysaccharides such as cellulose that limits their

application to electrospinning Unlike spinning a polymer

solution in volatile solvents which quickly evaporate in

the low pressure surrounding the fiber jet non-volatile

RTILs must be removed using a miscible co-solvent coag-

ulation bath to solidify polymer fiber

12 Electrospinning in Energy Applications

The search for alternative and stable sources of energy

is a growing and vital concern Although ldquocleanrdquo power

sources like nuclear wind solar and fuel cells have

been around for many years significant hurdles remain in

exploiting these sources on large enough scale to solve

the emerging energy crisis As a consequence increased

attention has focused on applying electrospinning in the

preparation of porous fiber mats as electronic components

including electrodes and separators and devices such as

batteries and supercapacitors (Fig 1(b)) Electrospun fiber

mats are capable of improving battery power increasing

energy density of capacitors and fuel cell and solar cell

efficiency Poly(olefin) microporous membranes are widely

used as commercial separators for Li-ion batteries16 and

although these conventional separators have a number of

suitable properties ie chemical stability tunable thick-

ness and mechanical strength17 their low porosity and

poor wettability resulting from the large polarity differ-

ence between non-polar poly(olefin) separator and highly

polar liquid electrolyte lead to increased cell resistance

limiting the performance of Li-ion batteries18 Electro-

spun fiber mats have extremely high specific areas as a

result of their high porosity making them a good can-

didate for battery membranes By introducing a polar

block to diblock polymers such as sulfonated styrene

Corendashshell nanofibers

Syringe pump

Core solution

Shell solutionHigh voltage

Electrically groundedcollecting plate

Core

Fiber structureS

hell

She

ll

(a)

(b)

Fig 1 (a) Schematic of electrospinning apparatus In spinning of corendash

shell (sheath) fibers both pumps are used with a coaxial needle assembly

in the spinneret In single solution electrospinning only a single pump

containing core solution is spun through a single needle (b) Performance

characteristics of powerenergy storage devices Reproduced with per-

mission from [76] R Kotz and M Carlen Electrochim Acta 45 2483

(2000) copy 2000 Elsevier

J Nanosci Nanotechnol 10 5507ndash5519 2010 5509

Delivered by Ingenta toRensselaer Polytechnic Institute

IP 1281132688Wed 23 Jun 2010 180354

REVIEW

Miao et al Electrospinning of Nanomaterials and Applications in Electronic Components and Devices

Robert J Linhardt received his PhD degree from the Johns Hopkins University (1979)

and was a postdoctoral student with Professor Robert Langer at the Massachusetts Institute

of Technology (1979ndash1982) and served on the faculty of University of Iowa from 1982ndash

2003 He is currently the Ann and John H Broadbent Jrrsquo59 Senior Constellation Professor

of Biocatalysis and Metabolic Engineering at Rensselaer Polytechnic Institute holding joint

appointments in the Departments of Chemistry and Chemical Biology Biology and Chemi-

cal and Biological Engineering His honors include the American Chemical Society Horace

S Isbell and Claude S Hudson Awards and the AACP Volwiler Research Achievement

Award His research focuses on glycobiology glycochemistry and glycoengineering Since

his arrival at Rensselaer Dr Linhardt has been actively involved in the emerging field of

nano-biotechnology focused on developing an artificial Golgi and paper-based energy stor-

age devices Professor Linhardt has published nearly 500 peer-reviewed manuscripts and

holds over 30 patents

or nanotubes can also be encapsulated in the core struc-

ture When p and n semiconductor materials are fab-

ricated into such a coaxial structure the contact area

between pndashn heterojunctions are maximized by reduc-

ing fiber diameter which for example can be used to

improve solar cell performance11 Electrospinning of abun-

dant and renewable natural biopolymers such as cellu-

lose and chitin is becoming an increasingly active area of

research However there are very few suitable solvents for

such biopolymers which significantly limits their use in

electrospinning Room temperature ionic liquids (RTILs)

nonvolatile solvents with high thermal stability that can

dissolve both highly polar and nonpolar polymers12ndash15

offer a potential solution to the poor solubility associated

with polysaccharides such as cellulose that limits their

application to electrospinning Unlike spinning a polymer

solution in volatile solvents which quickly evaporate in

the low pressure surrounding the fiber jet non-volatile

RTILs must be removed using a miscible co-solvent coag-

ulation bath to solidify polymer fiber

12 Electrospinning in Energy Applications

The search for alternative and stable sources of energy

is a growing and vital concern Although ldquocleanrdquo power

sources like nuclear wind solar and fuel cells have

been around for many years significant hurdles remain in

exploiting these sources on large enough scale to solve

the emerging energy crisis As a consequence increased

attention has focused on applying electrospinning in the

preparation of porous fiber mats as electronic components

including electrodes and separators and devices such as

batteries and supercapacitors (Fig 1(b)) Electrospun fiber

mats are capable of improving battery power increasing

energy density of capacitors and fuel cell and solar cell

efficiency Poly(olefin) microporous membranes are widely

used as commercial separators for Li-ion batteries16 and

although these conventional separators have a number of

suitable properties ie chemical stability tunable thick-

ness and mechanical strength17 their low porosity and

poor wettability resulting from the large polarity differ-

ence between non-polar poly(olefin) separator and highly

polar liquid electrolyte lead to increased cell resistance

limiting the performance of Li-ion batteries18 Electro-

spun fiber mats have extremely high specific areas as a

result of their high porosity making them a good can-

didate for battery membranes By introducing a polar

block to diblock polymers such as sulfonated styrene

Corendashshell nanofibers

Syringe pump

Core solution

Shell solutionHigh voltage

Electrically groundedcollecting plate

Core

Fiber structureS

hell

She

ll

(a)

(b)

Fig 1 (a) Schematic of electrospinning apparatus In spinning of corendash

shell (sheath) fibers both pumps are used with a coaxial needle assembly

in the spinneret In single solution electrospinning only a single pump

containing core solution is spun through a single needle (b) Performance

characteristics of powerenergy storage devices Reproduced with per-

mission from [76] R Kotz and M Carlen Electrochim Acta 45 2483

(2000) copy 2000 Elsevier

J Nanosci Nanotechnol 10 5507ndash5519 2010 5509

Delivered by Ingenta toRensselaer Polytechnic Institute

IP 1281132688Wed 23 Jun 2010 180354R

EVIEW

Electrospinning of Nanomaterials and Applications in Electronic Components and Devices Miao et al

the resulting electrospun fiber membranes afford separa-

tors with excellent affinity for liquid electrolytes increas-

ing ionic conductivity and battery performance The high

internal surface area large pore volume and long fiber

length of conducting electrospun membranes also make

them suitable as electrodes in Li-ion batteries Transi-

tion metal oxide (particles or nanoparticles) loaded onto

carbon nanofibers (CNF) facilitate more complete access

of Li ions to the inner sites of anodes decreasing Li-

ion diffusion distance and significantly increasing the rate

of electron transport Nano-structured LiCoO2 electrodes

afford a higher initial discharge capacity of sim140 (mAh)g

than conventional powder-based and film-based electrodes

However due to surface reactions of electrodes a large

loss of electrode capacity is observed during the chargendash

discharge process By electrospinning inorganic coaxial

fibers having a highly crystalline LiCoO2 core and a

low crystalline MgO shell electrodes may be obtained in

which LiCoO2 cannot directly contact electrolyte These

electrodes exhibit improved electrochemical properties

including excellent reversibility small impedance growth

and better cyclability9

The many applications and unique features of

electrospinning has been reviewed in a number

of publications719ndash21 This review provides an overview

of the application of electrospinning to the preparation of

electronic components and devices The text presents a

brief introduction of the mechanisms and methodology for

electrospinning and the application of electrospinning to

the preparation of separators electrodes nanowires super-

capacitors and actuators Finally the challenges for future

developments in electrospinning are briefly discussed

13 Electrospinning Methods and Principles

A typical electrospinning apparatus consists of a syringe

syringe pump spinneret collector and high voltage power

supply In single solution spinning a solution of solute in

volatile solvent is pumped through a nozzle Two solu-

tions are used in coaxial spinning where a core solution

is pumped through a needle at the same time a sheath

solution is pumped through the space between the noz-

zle and needle (Fig 1(a)) A potential of 10ndash50 kV is

applied between the spinneret where the spinning solu-

tion is located and the collector plate In electrospinning

with non-volatile solvents a co-solvent coagulation bath

is interposed between the spinneret and collector plate

The spinneret and collector are electrically conducting

and separated at an optimum distance When high volt-

age is applied the solution becomes highly charged and

as a result the solution droplet at the tip of the needle

will experience two major types of electrostatic forces

the repulsion between the surface charges and Coulombic

force exerted by the external electric field When a criti-

cal voltage is reached these electrostatic forces cause the

pendant droplet of polymer fluid to deform into a conical

structure called a Taylor cone Once the applied voltage

surpasses the critical value at which repulsive electrostatic

forces overcome the surface tension of the pendant droplet

a fiber jet is ejected from the apex of the Taylor cone and

accelerated towards the grounded collector or co-solvent

bath The fiber jet undergoes a whipping motion and

continuously elongates under this electrostatic repulsion

Instability can occur if the applied voltage is below the

critical value causing the jet to break up into droplets or

form a spray Such phenomenon is called Rayleigh insta-

bility Therefore the formation of nanofibers is determined

by many operating parameters such as applied voltage

solution concentration viscosity surface tension conduc-

tivity and flow rate The structure of the resulting fiber

can be tuned by carefully modifying these parameters

2 APPLICATIONS OF ELECTROSPINNINGPREPARING ELECTRICAL COMPONENTSAND DEVICES

21 Electrospun Insulators Separatorsand Electrolytes

Electrospun polymers such as polyvinylidenedifluoride

(PVDF) and polyacrylonitrile (PAN) and their deriva-

tives can be used as nanofiber mats in separators of

Li-ion batteries providing a nanoporous structure lead-

ing to increased ionic conductivity of a membrane soaked

with liquid electrolyte Aligned electrospun PVDF fibrous

membranes can enhance the tensile strength and mod-

ulus of membranes by improving interfiber compaction

under hot pressing Such electrospun membranes may have

important applications as battery separators

Uniform electrospun PVDF membrane thickness and

fiber diameter can be obtained by using high poly-

mer concentrations and electrospinning at high volt-

age This improves mechanical strength and provides the

PVDF separator with charge and discharge capacities

that exceed commercial polypropylene separators while

resulting in little capacity loss (Fig 2)2223 However

the high crystallinity of PVDF results in low conduc-

tivity The use of diblock polymers reduce crystallinity

while retaining a high dielectric constant which offers

one approach for improving resulting battery performance

Electric double-layer (EDL) capacitors (also known

as ultra or supercapacitors) prepared with electrospun

nonwoven poly(vinylidene fluoride-hexafluoropropylene)

(PVDF-PHFP) membrane separators and 1-ethyl-3-methyl

immidazolium tetrafluoroborate (emim[BF4]) RTIL elec-

trolyte exhibit excellent specific capacity and cycling

efficiency24

Electrospun PAN nonwoven fibers show higher porosi-

ties with lower Gurley values (high air permeability) and

increased wettabilities compared to conventional separa-

tors Furthermore cells with separators of PAN nonwovens

5510 J Nanosci Nanotechnol 10 5507ndash5519 2010

Delivered by Ingenta toRensselaer Polytechnic Institute

IP 1281132688Wed 23 Jun 2010 180354

REVIEW

Miao et al Electrospinning of Nanomaterials and Applications in Electronic Components and Devices

(a)

(b)

Fig 2 Cyclic voltammograms for the cells with separator

(a) CelgardTM 2400 (polypropylene) and (b) EPM884 (PVDF) at sweep

rate 01 mVsminus1 Reproduced with permission from [23] K Gao et al

Mater Sci Eng B 131 100 (2006) copy 2006 Elsevier

show enhanced cycle lifeperformance higher rate capa-

bilities and smaller diffusion resistance than cells with

conventional separators (Fig 3)2526

Polymer electrolytes have a number of advantages over

liquid electrolytes such as limited internal shorting and

low electrolyte leakage One of most widely used methods

to prepare polymer electrolytes is the immobilization of

1 M lithium hexafluorophosphate (LiPF6 within ethylene

carbonate (EC)dimethyl carbonate (DMC) in electrospun

fiber membranes27 An increased interest in improving the

performance of Li-ion polymer batteries has resulted from

the rapid expansion in the industrial demand for these

batteries Improved performance has relied on gel poly-

mer electrolytes (GPEs) such as those based on electro-

spun PVDF-graft-poly-tert-butylacrylate (g-tBA) nanofiber

(a)

(b)

Fig 3 (a) Results of discharge capacity tests for the cells with the Cel-

gard membrane and the PAN nonwovens Reproduced with permission

from [25] T H Cho et al J Power Sources 181 155 (2008) copy 2008

Elsevier (b) Results of rate capability test for the cells with PE PP PAN

No 1 and PAN No 2 separators Reproduced with permission from [26]

T H Cho et al Electrochem Solid State Lett 10 A159 (2007) copy 2007

The Electrochemical Society

membranes These GPEs show improved ionic conductiv-

ity electrochemical stability lower interfacial resistance

and improved cycle performance compared to neat PVDF

nanofiber membranes resulting from the reduced crys-

tallinity of tBA-grafted PVDF28

Electrospun PVDF-PHFPsilica composite nanofiber-

based polymer electrolytes were comparatively better than

those prepared through the direct addition of silica27 Dye-

sensitized solar cell (DSSC) devices also use polymer elec-

trolytes based on electrospun PVDF-PHFP nanofibers and

show power conversion efficiency greater than 529

22 Electrospun Electrodes

Electrospinning is an excellent method for the fabrica-

tion of inorganic fibers within a templated polymer For

J Nanosci Nanotechnol 10 5507ndash5519 2010 5511

Delivered by Ingenta toRensselaer Polytechnic Institute

IP 1281132688Wed 23 Jun 2010 180354

REVIEW

Miao et al Electrospinning of Nanomaterials and Applications in Electronic Components and Devices

(a)

(b)

Fig 2 Cyclic voltammograms for the cells with separator

(a) CelgardTM 2400 (polypropylene) and (b) EPM884 (PVDF) at sweep

rate 01 mVsminus1 Reproduced with permission from [23] K Gao et al

Mater Sci Eng B 131 100 (2006) copy 2006 Elsevier

show enhanced cycle lifeperformance higher rate capa-

bilities and smaller diffusion resistance than cells with

conventional separators (Fig 3)2526

Polymer electrolytes have a number of advantages over

liquid electrolytes such as limited internal shorting and

low electrolyte leakage One of most widely used methods

to prepare polymer electrolytes is the immobilization of

1 M lithium hexafluorophosphate (LiPF6 within ethylene

carbonate (EC)dimethyl carbonate (DMC) in electrospun

fiber membranes27 An increased interest in improving the

performance of Li-ion polymer batteries has resulted from

the rapid expansion in the industrial demand for these

batteries Improved performance has relied on gel poly-

mer electrolytes (GPEs) such as those based on electro-

spun PVDF-graft-poly-tert-butylacrylate (g-tBA) nanofiber

(a)

(b)

Fig 3 (a) Results of discharge capacity tests for the cells with the Cel-

gard membrane and the PAN nonwovens Reproduced with permission

from [25] T H Cho et al J Power Sources 181 155 (2008) copy 2008

Elsevier (b) Results of rate capability test for the cells with PE PP PAN

No 1 and PAN No 2 separators Reproduced with permission from [26]

T H Cho et al Electrochem Solid State Lett 10 A159 (2007) copy 2007

The Electrochemical Society

membranes These GPEs show improved ionic conductiv-

ity electrochemical stability lower interfacial resistance

and improved cycle performance compared to neat PVDF

nanofiber membranes resulting from the reduced crys-

tallinity of tBA-grafted PVDF28

Electrospun PVDF-PHFPsilica composite nanofiber-

based polymer electrolytes were comparatively better than

those prepared through the direct addition of silica27 Dye-

sensitized solar cell (DSSC) devices also use polymer elec-

trolytes based on electrospun PVDF-PHFP nanofibers and

show power conversion efficiency greater than 529

22 Electrospun Electrodes

Electrospinning is an excellent method for the fabrica-

tion of inorganic fibers within a templated polymer For

J Nanosci Nanotechnol 10 5507ndash5519 2010 5511

Delivered by Ingenta toRensselaer Polytechnic Institute

IP 1281132688Wed 23 Jun 2010 180354R

EVIEW

Electrospinning of Nanomaterials and Applications in Electronic Components and Devices Miao et al

example electrospun LiCoO2 nanofibers have been used

as a cathode for Li-ion batteries resulting in improved

diffusion and increased migration of Li+ cation30 TiO2

nanofibers have been used in dye-sensitized solar cells31ndash34

These electrospun electrodes have a porous structure that

enhances the penetration of the viscous polymer gel elec-

trolyte Carbon nanofibers (CNFs) such as carbon nano-

tubes as well as conventional nano-scale carbon fibers have

also been fabricated from polymer solutions for use as

anode material for Li-ion batteries and as electrodes of

supercapacitors35ndash38

221 Electrodes of Li-ion Batteries

So far silicon (Si) has the highest theoretical capac-

ity sim4200 mAh gminus1 which is much greater than the

one of graphite and metal oxides3940 Therefore Si has

always been considered as an ideal anode material for

next-generation rechargeable Li-ion batteries with high-

capacity Dispersion of Si nanoparticles (Si NPs) in a

quasi-one-dimensional nanoporous CNF matrix is one of

approaches to make such high capacityconductivity elec-

trodes The CNF matrix holds Si NPs aggregation to

provide a continuous electron transport pathway as well

as large number of active sites for charge-transfer reac-

tions which eliminate the need for polymer binder Thus

CNFSi nanocomposites can offer a large accessible sur-

face area (Fig 4) therefore a high reversible capacity and

relatively good cycling performance at high current density

can be obtained35

Although transition metal oxides also exhibit promis-

ing electrochemical behavior they suffer from poor

cycling performance due to their agglomeration and

mechanical instabilities which are mainly caused by

large volume changes and aggregation during lithium

insertionextraction processes This results in increased dif-

fusion lengths and electrical disconnection from the cur-

rent collectors To solve these critical issues the porous

CNFs may be chosen as matrix to incorporate nano-sized

transition metal oxides since CNFs have very high inter-

nal surface areas large pore volumes and long fiber

lengths which facilitate more access of Li-ions to the inner

sites of anodes decrease Li-ion diffusion distance there-

fore significantly increase electron transport rate41 For

examples CarbonMnOx nanofiber anodes exhibit large

reversible capacity excellent capacity retention and good

rate capability in the absence of a binder polymer36

CNFFe3O4 composites also exhibit excellent electrochem-

ical performance with a high reversible capacity and excel-

lent rate capability38 High-purity CNFs electrospun from

PAN solutions exhibit a large accessible surface area

derived from the nanometer-sized fiber diameter high car-

bon purity (without binder) a relatively high electrical

conductivity high structural integrity thin web macromor-

phology large reversible capacity (sim450 mAh gminus1 and a

Fig 4 SEM images of PANPLLASi (1736) precursor nanofibers

(AndashC) and their corresponding porous CSi composite nanofibers (DndashF)

Reproduced with permission from [35] L W Ji and X W Zhang Elec-trochem Commun 11 1146 (2009) copy 2009 Elsevier

relatively linear voltage profile37 Nanostructured LiCoO2

fiber electrodes with faster diffusion of Li+ cations pre-

pared by electrospinning afford a higher initial discharge

capacity of 182 (mAh)g compared with that of con-

ventional powder and film electrodes (sim140 (mAh)g)30

Electrospun LiCoO2 nanofibers also have been used to

resolve instability induced by lithium intercalation and

de-intercalation and maintain the three-dimensional archi-

tecture of Li-ion batteries However a large loss of

capacity of fiber electrodes was still observed during

the chargendashdischarge process due to surface reactions

of electrodes To improve electrochemical stability sur-

face modification of the cathode material is necessary

and effective Coating of metal oxides on surface of

LiCoO2 particle or film as a shell material can prevent

these active electrode materials from directly contacting

the electrolyte and enhance the electrochemical stabil-

ity For example coating of lithium phosphorous oxyni-

tride onto the three-dimensional structure improved rate

capability and higher reversibility42 The fabrication of

inorganicndashinorganic coaxial fibers using electrospinning

technology is useful in this regard By co-electrospinning

a highly crystalline LiCoO2 core and a low crystallinity

MgO shell coaxial fibers were prepared exhibiting excel-

lent reversibility smaller impedance growth and better

5512 J Nanosci Nanotechnol 10 5507ndash5519 2010

Delivered by Ingenta toRensselaer Polytechnic Institute

IP 1281132688Wed 23 Jun 2010 180354

REVIEW

Miao et al Electrospinning of Nanomaterials and Applications in Electronic Components and Devices

cyclability with improved electrochemical properties9 A

three-dimensional network architecture of anatase TiO2

and spinel Li4Ti5O12 has also been reported TiO2 nano-

fibers have poor cycle performance but Li4Ti5O12 exhibits

stable three-dimensional network architectures and shows

reversible electrochemical cycling Li4Ti5O12 may have

excellent potential for three-dimensional battery applica-

tions as a zero-strain insertion material43 A quasi-one-

dimensional array of Li1+V3O8 nanosheets prepared by

electrospinning combined with a solndashgel route gave higher

chargendashdischarge capacities and better cycle performance

compared to separated Li1+V3O8 nanosheets (Fig 5)44

Generally electrodes made from conducting polymers

are also composed of an insulating polymer or sul-

fonated polymer as binder The insulating polymer low-

ers the electrical conductivity of the resulting electrodes

however polymers used as both binder and dopant that

are sulfonated can increase electrical and electrochemical

properties4546 Electrospun polypyrrole (PPy)sulfonated

poly(styrene-ethylene-butylenes-styrene) (S-SEBS) fibers

can enhance electrochemical capacity due to the high dop-

ing level of S-SEBS and the ease of charge-transfer reac-

tions due to its high electrical conductivity47

Manganese-oxide (MnO) nanofibers prepared by elec-

trospinning PMMA gels with manganese salts shows

reversible electrochemical activity in lithium cells48 Nano-

sized nickel oxide (NiO) has also shown promise as

an anode material with excellent electrochemical per-

formance for lithium ion batteries49 Interestingly sin-

gle walled carbon nanotube-reinforced NiO nanofibers

have higher reversible capacity and lower capacity

loss than do conventional NiO electrodes50 Hollow

LiNi08Co01Mn01O2ndashMgO coaxial fibers have been pre-

pared with polyvinylpyrrolidone (PVP) and these fibers

show a high discharge capacity and excellent cycle

stability51 Co3O4 nanofibers have also shown high

Fig 5 The cycle life of the 1D arrays (a) and Li1+V3O8 nanosheets

(b) at a current density of 40 mA gminus1 Reproduced with permission from

[44] Y X Gu et al J Mater Chem 16 4361 (2006) copy 2006 Royal

Society of Chemistry

reversible capacity due to the high surface area of these

nanofibers52

222 Solar Cell and Fuel Cell Electrodes

High efficiency of light-to-energy conversion with dye-

sensitized solar cells (DSSCs) requires a high surface

area for the sensitized electrode53 DSSCs based on

nano-crystalline TiO2 have been intensively investigated

because of their low cost and reasonably high efficiency

Electrospun TiO2 fiber mats with large surface areas

enhance the light-harvesting capability of the adsorbed

dye TiO2 nanofibers are prepared by electrospinning of

a PVPTiO2 mixture The TiO2 nanofibers are then fab-

ricated into thick membrane electrodes to enhance elec-

tron percolation through interconnected nanofibers and to

improve the ability of absorption of low energy photons

thereby gradually increasing photocurrent and light har-

vesting efficiency as well as dye loading325455 The TiO2

electrodes used in DSSCs are electrospun directly onto

different substrates including a fluorine-doped tin oxide

(FTO) transparent conducting oxide substrate55 In this

manner the porous electrospun TiO2 electrode can be pen-

etrated efficiently with the viscous polymer gel electrolyte

due to its porous structure After treatment with aqueous

TiCl4 solution a short-circuit photocurrent was improved

and performance was enhanced by more than 3033 Plat-

inum nanoparticles supported on nanoporous carbon fiber

mats exhibit high activity and stability as electrocatalysts

in the oxidation of methanol in methanol fuel cells This

reduced the amount of platinum used and the associated

cost of this expensive catalyst56

23 Wires and Nanowires

The construction of nanomaterials particularly quasi-

one-dimensional nanowires mainly involves hydrothermal

methods solndashgel processes nanowire techniques vapor

growth template methods and electrospinning Wires and

nanowires fabricated by electrospinning potentially repre-

sent important building blocks for nanoscale chemical sen-

sors optoelectronics and photoluminescence since they

can potentially function as miniaturized devices as well as

electronic interconnects The large surface-to-volume ratio

and high electronndashhole conductivity along the quasi-1D

structure and high aspect ratio of nanowires makes them

ideal candidates for use as ultrasensitive chemical sensors

solar cells and fuel cell electrodes

231 Chemical Sensors

The pndashn type transition of nano-structured metal oxides

are important in sensing mechanisms involved in chem-

ical detection of charge-transfer interactions between a

sensor and the absorbed chemical species that modify

the electrical resistance of a sensor57 Size-related effects

J Nanosci Nanotechnol 10 5507ndash5519 2010 5513

Delivered by Ingenta toRensselaer Polytechnic Institute

IP 1281132688Wed 23 Jun 2010 180354R

EVIEW

Electrospinning of Nanomaterials and Applications in Electronic Components and Devices Miao et al

of nanomaterials are also important with respect to free

charge carriers Electrospun SnO2 and MoO3 nanowires

show increased stability faster response time and higher

sensitivity than thin film structures of the same materials

in detecting H2S and NH3 respectively58 ZnO nanowires

prepared in an electrospinning process have been used to

detect ethanol vapor at concentrations as low as 10 ppm

at 220 C59 WO3 nanofibers behave as a semiconductor

when heated and their electrical resistance varies when

exposed to NO2 gas60 TiO2polyvinyl acetate composite

nanofibers also show exceptional sensitivity to NO2 when

electrospun onto Pt electrodes61

Tin-doped indium oxide electrospun nanowires show

a 107-fold enhancement in conductance compared to the

matrix without doping With such high conductance quasi-

one-dimensional nanowire FETs should be useful in build-

ing highly sensitive chemical and biological sensors of

reduced device dimensions62

232 Optoelectronics

Twisted electrospun ZnONiO nanofiber yarn (Fig 6)

act as pndashn heterojunctions exhibiting rectifying

currentndashvoltage (IndashV ) characteristics63 Highly aligned

multi-layers of TiO2 nanowire arrays with conjugated

polymers show more than 70 improvement com-

pared to non-woven TiO2 nanowire in power conversion

(a)

(d) (e) (1)

(2)

(b) (c)

Fig 6 Optical microscope image of (a) and (b) twisted pndashn junction NiOZnO nanofiber yarns annealed at 873 K and (c) tapered pndashn junction

NiOZnO nanofiber yarns annealed at 873 K (d) SEM image of NiO nanofiber yarn annealed at 873 K (e) Schematic diagram for the formation of (1)

tapered nanofiber pndashn junction yarn (2) twisted nanofiber pndashn junction yarn For both junctions the white yarn is an n-type ZnO while the gray yarn

is a p-type NiO Reproduced with permission from [63] A F Lotus et al J Appl Phys 106 014303 (2009) copy 2009 American Institute of Physics

due to enhanced charge collection and transport rate64

Aluminum-doped ZnO (AZO) is a low cost and non-

toxic transparent and conductive alternative to indium

tin oxide (ITO)65 Single electrospun nanowires of AZO

show a highly sensitive photoresponse under below-gap

light illumination compared to AZO films Well-oriented

quasi-one-dimensional CuO nanofibers are intrinsic p-typesemiconductors and when assembled in field-effect

transistors (FET) serve as a potentional building blocks

for low cost logic and switching circuits66 Necklace-like

PbTiO3 nanowires exhibit high surface photovoltage under

the action of an external electrical field which is useful

for optoelectric applications such as field effect controlled

devices6768

233 Photoluminescene

Hetero-structured electrospun Ag nanoparticle-loaded ZnO

nanowires exhibit enhanced UV photoresponse due

to enhanced separation of photogenerated electronndashhole

pairs69 Quasi-one-dimensional CaWO4 and CaWO4Tb3+

nanowires and nanotubes show strong blue and green

emissions upon excitation as a result of quantum con-

finement effects Tb3+ ions show characteristically strong

emissions due to an efficient energy transfer from

the WO2minus4 group to the Tb3+ ions70 Europium-doped

(YBO3Eu3+ nanowires show photoluminescence71 and

5514 J Nanosci Nanotechnol 10 5507ndash5519 2010

Delivered by Ingenta toRensselaer Polytechnic Institute

IP 1281132688Wed 23 Jun 2010 180354

REVIEW

Miao et al Electrospinning of Nanomaterials and Applications in Electronic Components and Devices

Erbium-doped silicon and Germanium oxide nanofibers

are strongly emissive in the near infrared72 Aligned CdS

nanowires embedded in polymer nanofibers show linearly

polarized emissions73

234 Catalysts

Surface modified TiO2 anatase nanofibrous membranes

with incorporated Pt Pd and Ru nanoparticles show cat-

alytic properties that have been exploited in continuous

flow for Suzuki coupling reactions with short reaction

times and no need for separation74 Electrospun Pt and

PtRh nanowires show higher catalytic activities in a poly-

mer electrolyte membrane fuel cell anode than the con-

ventional Pt nanoparticle catalysts like carbon-supported

Pt or Pt black75 This improvement is due to the quasi-one-

dimensional pathway for electron transfer that dramatically

reduces the number of boundaries between the catalytic

nanoparticles

24 Supercapacitors

Supercapacitors (Fig 7) are well known as attractive

energy storage systems that exhibit high power den-

sity rapid chargingdischarging capacity and long cycle

life Potential applications range from small-scale mobile

devices to medium-scale electric vehicles to large-scale

power grid storage While the high power density of

supercapacitors compares favorably to batteries superca-

pacitors have a much lower energy density (Fig 1(b))76

Higher capacitance values and higher operating voltages

are critical to improve the energy density of supercapac-

itors The simplest way to obtain higher capacitance val-

ues of electrical double-layer capacitors is to increase the

ndash+

++ +

++

+

+

+

++

+

++

+

+

+

+

ndashndash

ndash

ndashndash

ndash

ndashndash

ndash

ndashndash

ndashndash

ndash

ndashndash

ndash

ndash

ndash ndash

ndash++

+

+

++

+

++

++

+

+

+

+

+

+

+

++

++

++

ndashndashndash

ndash

ndash

ndash

ndash

ndash

ndash

ndash

ndashndash

ndash

ndash

ndash

ndashndash

ndash

ndash

ndash

d = ~1 μm

Activated carbon ElectrodeSeparatorElectrolyte

Fig 7 Schematic diagram of electric double layer capacitor

(supercapacitor)

surface area of the supercapacitor electrodes and electro-

spun nanofibers can provide just such a property Activated

CNFs fabricated by electrospinning serve as excellent

candidates for supercapacitor electrodes Activated CNFs

have been fabricated from a variety of polymers77ndash79

which have high carbon yield including PAN poly(imide)

(PI) polybenzimidazol (PBI)8081 polyamic acid (PAA)

and isotropic pitch precursor (IPP) These polymer solu-

tions were electrospun into nanofibers and then stabilized

and carbonized at high temperature to obtain activated

CNFs Activated CNFs have high surface areas due to the

nanofiber morphology and porous structures on the fiber

surface82

Blending polymers and other additives with base poly-

mers has been studied to improve electrical conductivity

of activated CNFs Activated CNFs from PANcellulose

acetate composite solution showed increased conductiv-

ity due to the high oxygen content of cellulose acetate83

Activated carbon fibers from PANmulti-walled nanotubes

(MWNT)84 PANVO585 activated CNFMWNT coated

with polypyrrole86 and PANAg87 nanoparticle compos-

ites show improved conductivity due to the addition

of conductive materials andor coating with conductive

polymers Thinner fiber diameters were also examined

in PANMWNT and PANAg nanoparticle systems to

improve electrical conductivity and to enhance electro-

chemical performance Fiber diameter depends on several

electrospinning parameters such as solution concentration

applied voltage flow rate and solution conductivity The

diameter of an electrospun fiber decreases with increasing

the solution conductivity88 By adding conductive MWNT

or Ag nanoparticles into solution a greater tensile force

may be available in the presence of an electric field

Similar results were reported in systems of PANZinc

chloride and PANNickel nitrate8990 The higher surface

area resulting from thinner diameters produces improved

capacitance Physical activation of nanofibers is also pos-

sible using silica91 Silica embedded into nanofibers is

removed from carbon materials by immersing in hydroflu-

oric acid with the resulting carbon fiber showing a 30-fold

higher BET surface area which results in improved

capacitance

CNFs prepared from PANNickel acetate solution results

in a Ni-embedded carbon composite with more than three-

fold higher capacitance and improved electrochemical

stability92 Ni in CNFs works as an active species and

imparts a surface polarity to the fiber surface thus enhanc-

ing dipole affinity towards the anion and causing capaci-

tance to increase

The conductive polymer PEDOT was fabricated into

a fiber by electrospinning from ethylenedioxythiophene

(EDOT)PVP solution93 PVP is commonly added into

solutions as a matrix to improve electrospinnability After

electrospinning EDOT in the fiber is polymerized to

J Nanosci Nanotechnol 10 5507ndash5519 2010 5515

Delivered by Ingenta toRensselaer Polytechnic Institute

IP 1281132688Wed 23 Jun 2010 180354R

EVIEW

Electrospinning of Nanomaterials and Applications in Electronic Components and Devices Miao et al

PEDOT by heating The resulting PEDOT nanofiber

showing high conductivity and high surface area can be

used as electrodes in flexible supercapacitors

Composites that enhance EDL capacitors and

pseudo-capacitors based on a Faradaic mechanism have

been studied Adding hydrous ruthenium oxide to carbon

generates the composite however by using this approach

it is difficult to obtain both the formation of mesoporous

and well-dispersed metal particles Ruthenium embed-

ded CNFs have been formed through electrospinning

of PANRuthenium acetylacetonate solution94 These

CNFs had both increased mesopore size and contained

well-dispersed Ruthenium particles The specific capaci-

tance increased from 140 Fg to 391 Fg because of the

combination of electrical double-layer capacitance and

pseudo-capacitance based on ruthenium oxidation

25 Actuators

Actuators can take electrical and other energy and con-

vert it into a mechanical motion However large strain

and quick response times still remain the most impor-

tant challenges in actuator design Large strain can be

obtained by enhancing mechanical properties and flexi-

ble electrospun fiber templates can be used to improve

strain This is because a large amount of electrolyte can

be localized in the porous structure of electrospun fiber

mats Good ion mobility is also possible in such fiber

mats thereby increasing the response speed of the actuator

and by simply reducing the fiber diameter in electrospin-

ning the response speed can be enhanced Unique thermal

response-type actuators can also be prepared by electro-

spinning A liquid crystalline main-chain polymer with a

photoactive moiety can also be electrospun into a highly

oriented fiber

251 Electrospun Fibers Coated withConductive Polymers

Among the many materials suitable for actuators con-

ducting polymers have received considerable attention as

promising candidates for actuator design owing to their

moderately high actuation strain at low operational volt-

ages below 1 V95ndash97 Despite being good candidates for

designing actuators the brittleness and poor elongation at

break98 of conducting polymers limit their active appli-

cability in devices Recent reports show the potential of

hydrogels being used as efficient candidates for actua-

tor applications owing to their stimuli responsive behav-

ior following a change in pH temperature or solvent

composition99100 A simple and versatile approach has

been described for the fabrication of flexible conducting

polymer actuators using hydrogel nanofibers as a tem-

plate An electrospun polyvinyl alcohol (PVA) nanofiber

mat containing a flexible conducting polymer actuator

prepared by in situ polymerization of aniline has been

reported101 The resulting structure has a large surface area

and high porosity that promotes facile diffusion of ions to

ensure efficient electrochemical reactions A higher strain

could also be obtained as a result of the enhanced mechan-

ical properties of this nanofiber mat (Fig 8)

(a)

(b)

(c)

Act

uatio

n st

rain

(

)

4

3

2

1

0

ndash1

4

3

2

1

0

ndash1

ndash2

ndash3

0

ndash02 00 02

Potential (V)

Cur

rent

(m

A)

04 06

Strip

Rolled

08

100

40 sec

10 sec

5 sec

4 sec

Scan rate (mVsec)

Res

pons

e sp

eed

(sec

ndash1)

200 300

020

015

010

005

000

400

Inter-layerspace

100 μm

Fig 8 (a) An FE-SEM image showing the rolled-up structure of

the PVAPANI hybrid mat The inset shows a cross-sectional image

of the rolled-up structure (b) A graph showing the variation in strain

and the subsequent response speed for the rolled up structure with

increasing scan rate (c) Cyclic voltammogram of the rolled-up structure

and the single strip measured at a scan rate of 5 mVs (Electrolyte =1 M methane sulfonic acid) Reproduced with permission from [101]

Y A Ismail et al Sens Actuator B-Chem 136 438 (2009) copy 2009

Elsevier

5516 J Nanosci Nanotechnol 10 5507ndash5519 2010

Delivered by Ingenta toRensselaer Polytechnic Institute

IP 1281132688Wed 23 Jun 2010 180354R

EVIEW

Electrospinning of Nanomaterials and Applications in Electronic Components and Devices Miao et al

PEDOT by heating The resulting PEDOT nanofiber

showing high conductivity and high surface area can be

used as electrodes in flexible supercapacitors

Composites that enhance EDL capacitors and

pseudo-capacitors based on a Faradaic mechanism have

been studied Adding hydrous ruthenium oxide to carbon

generates the composite however by using this approach

it is difficult to obtain both the formation of mesoporous

and well-dispersed metal particles Ruthenium embed-

ded CNFs have been formed through electrospinning

of PANRuthenium acetylacetonate solution94 These

CNFs had both increased mesopore size and contained

well-dispersed Ruthenium particles The specific capaci-

tance increased from 140 Fg to 391 Fg because of the

combination of electrical double-layer capacitance and

pseudo-capacitance based on ruthenium oxidation

25 Actuators

Actuators can take electrical and other energy and con-

vert it into a mechanical motion However large strain

and quick response times still remain the most impor-

tant challenges in actuator design Large strain can be

obtained by enhancing mechanical properties and flexi-

ble electrospun fiber templates can be used to improve

strain This is because a large amount of electrolyte can

be localized in the porous structure of electrospun fiber

mats Good ion mobility is also possible in such fiber

mats thereby increasing the response speed of the actuator

and by simply reducing the fiber diameter in electrospin-

ning the response speed can be enhanced Unique thermal

response-type actuators can also be prepared by electro-

spinning A liquid crystalline main-chain polymer with a

photoactive moiety can also be electrospun into a highly

oriented fiber

251 Electrospun Fibers Coated withConductive Polymers

Among the many materials suitable for actuators con-

ducting polymers have received considerable attention as

promising candidates for actuator design owing to their

moderately high actuation strain at low operational volt-

ages below 1 V95ndash97 Despite being good candidates for

designing actuators the brittleness and poor elongation at

break98 of conducting polymers limit their active appli-

cability in devices Recent reports show the potential of

hydrogels being used as efficient candidates for actua-

tor applications owing to their stimuli responsive behav-

ior following a change in pH temperature or solvent

composition99100 A simple and versatile approach has

been described for the fabrication of flexible conducting

polymer actuators using hydrogel nanofibers as a tem-

plate An electrospun polyvinyl alcohol (PVA) nanofiber

mat containing a flexible conducting polymer actuator

prepared by in situ polymerization of aniline has been

reported101 The resulting structure has a large surface area

and high porosity that promotes facile diffusion of ions to

ensure efficient electrochemical reactions A higher strain

could also be obtained as a result of the enhanced mechan-

ical properties of this nanofiber mat (Fig 8)

(a)

(b)

(c)

Act

uatio

n st

rain

(

)

4

3

2

1

0

ndash1

4

3

2

1

0

ndash1

ndash2

ndash3

0

ndash02 00 02

Potential (V)

Cur

rent

(m

A)

04 06

Strip

Rolled

08

100

40 sec

10 sec

5 sec

4 sec

Scan rate (mVsec)

Res

pons

e sp

eed

(sec

ndash1)

200 300

020

015

010

005

000

400

Inter-layerspace

100 μm

Fig 8 (a) An FE-SEM image showing the rolled-up structure of

the PVAPANI hybrid mat The inset shows a cross-sectional image

of the rolled-up structure (b) A graph showing the variation in strain

and the subsequent response speed for the rolled up structure with

increasing scan rate (c) Cyclic voltammogram of the rolled-up structure

and the single strip measured at a scan rate of 5 mVs (Electrolyte =1 M methane sulfonic acid) Reproduced with permission from [101]

Y A Ismail et al Sens Actuator B-Chem 136 438 (2009) copy 2009

Elsevier

5516 J Nanosci Nanotechnol 10 5507ndash5519 2010

Delivered by Ingenta toRensselaer Polytechnic Institute

IP 1281132688Wed 23 Jun 2010 180354

REVIEW

Miao et al Electrospinning of Nanomaterials and Applications in Electronic Components and Devices

252 Porous Electrospun Fiber Mats EnhanceIon Mobility

Aligned electrospun cellulose fibers have been obtained by

electrospinning using a wet-drawn stretching method102

Electrospun cellulose film-based electroactive paper

(EAPap) displayed a three-fold larger in-plane piezoelec-

tric charge constant than a similar spin cast cellulose

film The well-aligned cellulose fibers and well-developed

crystallinity of the electrospun cellulose film and the large

number of micro-cavities between layers improve the

performance of this actuator Nanofiber mats have been pre-

pared by electrospinning a sulfonated tetrafluoroethylene-

based fluoropolymerndashcopolymer (NafionTM103 When

these mats are saturated with ionic liquids they show

approximately three-fold improvement in ionic conductiv-

ity compared to conventional film-type membranes Also

these fabricated fiber mat-based transducers showed higher

strain speed of 134 per second which is 52 faster than

the film-based actuators (Fig 9)

Electrospun nanometer sized fibers should exhibit much

faster response times than commercially available micron

size fibers104 When submicron diameter PAN fibers were

prepared by electrospinning changing the pH caused

more than a 100 response improvement over conven-

tional fibers of diameters 10ndash50 m Thin polyacrylamide

(PAAM) gel fibers also show enhanced response times

253 Photo-Cross-Linkable Liquid CrystalMain-Chain Polymers

For mechanical actuators a response to external stimuli is

required Main-chain liquid crystal elastomers (MCLCEs)

show large response to changes in temperature especially

in the vicinity of a phase transition Liquid crystalline

main-chain polymers with photoactive moieties have been

electrospun into highly oriented fibers using in situ UV

Fig 9 Strain response of two similar transducers built on NafionTM mat

and film Reproduced with permission from [103] C Nah et al ComposSci Technol 68 2960 (2008) copy 2008 Elsevier

Fig 10 Thermoelastic curves on cooling with different preload Repro-

duced with permission from [105] S Krause et al Macromol RapidCommun 28 2062 (2007) copy 2007 Wiley-VCH Verlag GmbH amp Co

KGaA

curing105 The resulting thin film mats show excep-

tional mechanical properties such as large temperature-

dependent changes in length and a nonlinear stressndashstrain

relation (Fig 10)

3 CHALLENGES AND OPEN QUESTIONS

There has been tremendous surge in the development of

electrospinning technology and applications since the year

2000 but there are still several issues not yet resolved

First more experimental studies and theoretical model-

ing are needed to achieve greater control over the size

and morphology of electrospun fibers and a better under-

standing of the correlation between electronic properties

and the spun fiber morphology Additionally the diversity

and scope of materials that can be used with an electro-

spinning process must be greatly expanded Some non-

spinnable conducting polymers can be electrospun with

other spinnable polymers in the form of corendashshell struc-

tures or as coatings of a conducting polymer on the surface

of another polymer fiber mat The number of corendashshell

structures must be expanded for electrospinning technol-

ogy to meet expanding application demands Melt elec-

trospinning and in-flight polymerization electrospinning

are still rather nascent technologies and will require sig-

nificant development Also the current scale of standard

electrospinning equipment cannot meet the widespread

manufacturing demand Although using multi-spinneret

techniques can achieve high mass throughput the cost

of this new equipment may prevent its increased use in

manufacturing As these techniques are perfected and new

processes developed electrospinning may become more

critical in the fields of nanotechnology and bioengineering

J Nanosci Nanotechnol 10 5507ndash5519 2010 5517

Delivered by Ingenta toRensselaer Polytechnic Institute

IP 1281132688Wed 23 Jun 2010 180354R

EVIEW

Electrospinning of Nanomaterials and Applications in Electronic Components and Devices Miao et al

4 CONCLUSION AND PROSPECTS

Current advances in electrospinning technology are

providing important evidence for new potential roles of

electrospun materials in energy conversion and storage

applications The electrospun porous fiber mats used as a

separator in Li-ion batteries will improve ion-conductivity

thereby enhancing battery efficiency The use of elec-

trospun porous fiber mats as electrodes in both Li-ion

batteries and supercapacitors will undoubtedly improve

the cycle life and increase rate capabilities and capaci-

tance Porous fibers also have good mechanical strength

and will certainly improve the performance of polymer

actuators Electrospinning also offers a technique to pre-

pared nanoscale electrical components for the construc-

tion of nanodevices and nanomachines Electrospinning

using RTILs as biopolymer solvents represent ldquogreenrdquo

electrospinning techniques as biopolymers are renewable

and recyclable and RTILs are non-volatile and also eas-

ily recycled Such ldquogreenrdquo technology makes electrospin-

ning a sustainable and environmentally friendly processing

method

Acknowledgments We gratefully acknowledge

Chisso Corporation Tokyo Japan and the Rensselaer

Nanotechnology Center for their support of our research

on electrospinning

References and Notes

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5518 J Nanosci Nanotechnol 10 5507ndash5519 2010

Delivered by Ingenta toRensselaer Polytechnic Institute

IP 1281132688Wed 23 Jun 2010 180354

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mol Rapid Commun 28 2062 (2007)

Received 29 October 2009 Accepted 8 March 2010

J Nanosci Nanotechnol 10 5507ndash5519 2010 5519