Review on nanofiber and applications
ECG653 Project Report
Submitted by
Xinan Zhou
zhouxinan0129@gmail.com
Fall 2008
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Abstract
Electrospinning has been recognized as an efficient technique for the fabrication of polymer
nanofibers. Various polymers have been successfully electrospun into ultrafine fibers in recent
years mostly in solvent solution and some in melt form. The development of smart nanotextiles has
the potential to revolutionize the functionality of our clothing and the fabrics in our surroundings.
Nanoscale manipulation results in new functionalities for intelligent textiles, including selfcleaning, sensing, actuating, and communicating. This is made possible by such developments as
new materials, fibers, and finishings; inherently conducting polymers; carbon nanotubes; and
antimicrobial nanocoatings. These additional functionalities have numerous applications,
encompassing healthcare, sports, military applications, and fashion. In this paper, a short review is
presented on the researches and developments related to polymer nanofibers including pabrication
processing, property characterization and applications.
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Introduction
When the diameters of polymer fiber materials are shrunkfrom micrometers (e.g. 10–100
to sub-microns or nanometers (e.g.
)
), there appear several amazing
characteristics such as very large surface area to volume ratio (this ratio for a nanofiber can be as
large as 103 times of that of a microfiber), flexibility in surface functionalities, and superior
mechanical performance (e.g. stiffness and ten- sile strength) compared with any other known form
of the material. These outstanding properties make the polymer nanofibers to be optimal candidates
for many important applications.
Electrospinning
Figure1. Schematic diagram to show polymer nanofibers by electrospinning.
A schematic diagram to interpret electrospinning of polymer nanofibers is shown in the figure
1. There are basically three components to fulfill the process: a high voltage supplier, a capillary
tube with a pipette or needle of small diameter, and a metal collecting screen. In the
electrospinning process a high voltage is used to create an electrically charged jet of polymer
solution or melt out of the pipette. Before reaching the collecting screen, the solution jet evaporates
or solidifies, and is collected as an interconnected web of small fibers. One electrode is placed into
the spinning solution/melt and the other attached to the collector. In most cases, the collector is
simply grounded. The electric field is subjected to the end of the capillary tube that contains the
solution fluid held by its surface tension. This induces a charge on the surface of the liquid. Mutual
charge repulsion and the contraction of the surface charges to the counter electrode cause a force
directly opposite to the surface tension. As the intensity of the electric field is increased, the
hemispherical surface of the fluid at the tip of the capillary tube elongates to form a conical shape
known as the Taylor cone. Further increasing the electric field, a critical value is attained with
which the repulsive electrostatic force overcomes the surface tension and the charged jet of the
fluid is ejected from the tip of the Taylor cone. The discharged polymer solution jet undergoes an
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instability and elongation process, which allows the jet to become very long and thin. Meanwhile,
the solvent evaporates, leaving behind a charged polymer fiber. In the case of the melt the
discharged jet solidifies when it travels in the air.
Fiber alignment
Most nanofibers obtained so far are in non-woven form, which can be useful for relatively
small number of applications such as filtration, tissue scaffolds, implant coating film, and wound
dressing. However, as we understand from traditional fiber and textile industry, only when
continuous single nanofibers or uniaxial fiber bundles are obtained can their applications be
expanded into unlimited. Nevertheless, this is a very tough target to be achieved for electrospun
nanofibers, because the polymer jet trajectory is in a very complicated three-dimensional
‘‘whipping’’ way caused by bending instability rather than in a straight line. Efforts are believed to
be being made in various research groups all over the world. Up to date, however, there is no
continuous long nanofiber yarn obtained and the publications related to aligned nanofibers are very
limited.
Figure2. (A) Set-up for controlling fibre deposition area using rings as auxiliary electrodes. (B) Electric field profile of the region between the syringe
needle and the collection plate with the ring as auxiliary electrodes (reprinted from Deitzel et al 2001b Polymer 42 8163, © 2001 with permission
from Elsevier). (C) Schematic diagram of parallel auxiliary electrode arrangement. (D) Electric field profile from the spinneret to the parallel auxiliary
electrodes (reprinted with permission from Li et al 2003, © American Chemical Society). (E) Schematic diagram of a knife-edge rotating disc as a
collector. (F) Electric field profile from the tip of the spinneret to the knife edge (reprinted with permission from Theron et al 2001).
Since both the manipulation of electric field and the use of a dynamic collector are the most
common methods of getting ordered fibre assemblies, the two methods have been combined to
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achieve greater order in the fibre assembly. Theron et al used a rotating disc collector to take
advantage of the rotating motion and the convergence of electric field lines toward the knife edge
of the disc to collect highly aligned fibres as shown in figure 2(E). For a typical electrospinning
process, the electrospinning jet undergoes bending instability which spreads over a larger area,
resulting in a large deposition area on a static collector. However, when a knife-edge disc was used,
the electrospinning jet converged towards the knife-edge of the disc as shown in figure 2(F), which
was subsequently aligned along the edge as it rotates (Theron et al 2001).
Nanoparticles: Composite Fibers and Finishings
Nanostructured composite fibers are one area where nanotechnology is already having a huge
impact within the textile industry. Composite fibers employ nanosized components such as
nanoparticles, graphite nanofibers, and CNTs to improve physical properties such as conductivity
and antistatic behavior. Table I lists some of the nano-sized species that are used to improve the
performance of textiles. These nanoparticles may be used to develop composite fibers as nanoscale
fillers or through a foam-forming process and may also be applied as finishings to the textile, for
example, spray-coating TiO2 for biological protective materials.
Applications
Sports
The sports industry has driven much research within the textile industry to help improve
athletic performance, personal comfort, and protection from the elements. Synthetics that were
once thought to be inferior to natural fabrics now boast high performance characteristics.
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Figure 3. (a) Carbon-loaded elastomer-sensorized garment
for kinesthetic monitoring developed at the University of
Pisa.
Figure3. (b) The Intelligent Knee Sleeve is a biofeedback
device using PPy sensors that monitors the wearer’s knee
joint motion. (Courtesy of CSIRO Textile and Fiber
Technology.)
Strain sensors made from piezoelectric materials may be used in
biomechanical analysis to provide wearable kinesthetic interfaces able to detect
posture, improve movement performance, and reduce injuries. The conductivity of
these textiles is affected by stress and strain applied to the fabric, which can be used
to assess physiological movements that impose strain or pressure on the material.
Garments integrating piezoresistive ICPs and conductor-loaded rubbers with strainsensing capabilities offer continuous monitoring of body kinematics and vital signs.
The advantage of this approach is that the tactile and flexible properties of the
textile are maintained, providing truly wearable fabrics. Such devices may be used
to teach athletes the correct way to perform movement skills by providing real-time
feedback about limb orientation. Examples of such devices are shown in Figure 3.
Figure 3a shows a carbon-loaded elastomersensorized garment developed at the
University of Pisa. The piezoresistive sensors are fabricated on a Lycra®/cotton
textile by masked smearing of the conducting mixture, which consists of a silicone
matrix filled with carbon black powder. The same polymer/conductor composite is
also used as material for the connection tracks between sensors and an acquisition
electronic unit, avoiding the stiffness of conventional metal wires. Figure 3b shows
the Intelligent Knee Sleeve, developed through a collaboration between the
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Intelligent Polymer Research Institute and Biomedical Science at the University of
Wollongong and CSIRO Textile and Fiber Technology. It is a biofeedback device
using PPy sensors that monitors the wearer’s knee joint motion during jumping and
landing to reinforce the correct landing technique. The PPy-coated fabric acts as a
strain gauge, with a wide dynamic range, and is connected to a microcontroller that
emits an audio tone when the knee bends beyond a pre-set angle. The device was
developed for sports where jumping-related knee injuries are common and may also
be used as a rehabilitation device following injury.
Fashion/Lifestyle
Figure4. Lumalive textile garment from Philips features flexible arrays of colored light-emitting diodes fully integrated into the
fabric. (Courtesy of Philips.).
Although technology may be hidden through invisible coatings and advanced
fibers, it can also be used to dramatically change the appearance of the textile,
giving new and dazzling effects. Luminex® is a fabric with fiber-optic strands
woven into it, which are then illuminated using light-emitting diodes (LEDs).
Luminex® has been incorporated into glowing clothes, safety garments, handbags,
furniture, and even a wedding dress. Another recent development is the Lumalive
fabric from Philips, featuring flexible arrays of colored LEDs fully integrated
within the fabric (Figure 4). These light-emitting textiles can carry dynamic
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messages, graphics, or multicolored images. Based on concepts of color and light
therapy, brightness and the color appearance of light are thought to affect mood; these
textiles are designed to enhance the observer’s mood and positively influence his or her
behavior.
Conclusion
Through this review, various concepts behind the nanofiber are described.
Fundamental aspect of fabrication of polymer nanofibers is given. Developments in
smart nanotextiles may affect many aspects of our daily lives and produce clothing
that is contextually aware. New materials integrating novel technologies enable
passive, noninvasive sensing of wearers and their environs. A major problem in
wearable computing at present is the interconnections, with conventional silicon
and metal components being highly incompatible with the soft textile substrate. By
integrating technology at the nanoscale, the tactile and mechanical properties of the
textile may be preserved, retaining the necessary wearable and flexible
characteristics that we expect from our clothing. Smart textiles must be flexible
enough to be worn for long periods of time without causing any discomfort in order
to become a viable and practical product.
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