Polymer Nanostructures
Power
Supercapacitors are essential for the
effective development of electric vehicles. Currently, a number of small scale
high performance supercapacitors have become available commercially for use in
relatively low power electronic applications, but the challenge remains to scale
these up for exploitation in large vehicles. Work at Reading has led to the
development of a new low cost approach to the production of nitrogen containing
high surface area carbon nano-particles. When these are incorporated in to
prototype supercapacitors they exhibit power densities which are in excess of
current industry targets.
The Proton Exchange Membrane Fuel Cell
is now beginning to approach viability However, the costs associated with fuel
cell technology are still an order of magnitude too high for widespread
acceptance. The key fuel cell component in this type of power source is the
membrane-electrode assembly, comprising a thin film of proton-conducting ionomer
laminated on each side to a layer of transition-metal catalyst and thence to a
porous gas-diffusion electrode. Current work at Reading is focused on the
development of new types of the membrane materials with the aim on reducing
costs.
Smart materials
We have discovered how nano and micro
conducting particles can be dispersed in deformable media to yield materials
whose electrical conductivities remarkably increases rather than decreases upon
deformation. We are exploring the potential for these novel materials as sensors
and for use in smart textiles.
The development of molecular sized wires
has been a key target in the field of molecular electronics and current work at
Reading is making considerable inroads towards realising this target. The
approach taken is to polymerise within a nanostructured template with very well
defined porous columns. The approach has considerable flexibility and a range of
wires can be prepared.
Nanocomposites
There is world-wide interest in the
inclusion of nano-particles in synthetic polymers to enhance existing properties
and to define new ones. We are exploiting the expertise at Reading in
time-resolving x-ray and neutron scattering techniques to develop an
understanding of how nano-particles such as clays are mixed and exfoliated
within a polymer matrix during flow.
We have discovered how small quantities
of a low molar mass compound can be dispersed in polymers including
biodegradable systems to provide a self-assembling nanoscale framework which
directs the subsequent crystallisation to yield high levels of crystal
orientation. This control can have a marked influence on the properties of the
final material. We are exploring this new approach in a variety of materials
including those used for preparing medical implants and scaffolds.
Optical
Photonic crystals provide the analogous
properties for light as semi-conductors provide for electrons. Self-assembly is
seen as the key in this materials demanding area. We are developing novel
polymers for use in self-assembling photonic crystals for exploitation in the
visible and infra-red spectral regions.
Security is a vital area in today's
society and we have initiated a major programme to develop novel security
devices which use nano-structured surfaces to define the optical properties of
thin films. These are designed at the outset to have the potential for volume
manufacturing to facilitate use in protecting documents, ID cards and high value
goods.
Molecular Machines
We are working on the development of
nanoscale machines in which molecular components assemble into larger structures
and modify one another’s behaviour. Our best example of this so far is a
molecular tweezer which can grip a second molecule between its arms and induce
significant changes in the shape and spectroscopic characteristics of the second
molecule.
Molecular Pumps and Motors
Polyelectrolyte brushes, where
chemically charged polymers are grafted to a substrate in an aqueous
environment, exhibit an interesting transition between a collapsed and an
extended state induced by changing the pH. This transition offers a convenient
mechanism of converting chemical energy into mechanical energy to form various
nanoscale machines. See for example
www.polymercentre.org.uk/expert/features/0101.php for a possible design of a
nanoscale pump. We are currently involved in developing the theory for these new
exciting systems.
Nanoscale Templating
This is a relatively new method for the
production of nanostructured materials and employs surfactant molecules as
templating agents. Surfactant
templating utilises the 3D
aggregate structures (true liquid crystalline phases) formed by surfactant
molecules as moulds around which a solid material may subsequently be formed.
Electrodeposition of adherent nanostructured films from these templates has been
achieved. The surfactant method of nanostructuring has been shown to be useful
for the preparation of a wide variety of materials, such as many metals/metal
oxides/hydroxides and semiconductors, and ease of fabrication suggest that the
use of these materials in the fields of batteries, fuel cells and
electrochemical capacitors may be advantageous.
Block copolymers involve the bonding
together of two or more incompatible polymer chains, and are renowned for their
self-assembly into nanoscale periodic morphologies with wide-ranging symmetries.
In recent years, thin layers of block copolymer material have been used as
templates for etching patterns into various substrates. One intended application
is to etch nanoscale holes into silicon wafers in which ferromagnetic material
is deposited to form ultrahigh-density magnetic-storage devices. We are involved
in the theoretical modelling of such pattern formation and the prediction of its
symmetry in terms of the molecular characteristics of the block copolymer.
As an alternative to block copolymers,
we are also investigating the possible benefits of using binary polymeric
brushes to form patterned layers. In this case, two types of chemically
incompatible polymers are grafted to the substrate, and they self-assemble into
patterned morphologies. The mechanism is very similar to that of block
copolymers, but the immobility of the chains offers certain advantages.
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