Download Cutting-edge chemistry

Cutting-edge chemistry
The chemistry of alien atmospheres
Have you ever wondered what a distant planet is made
of? Contented yourself with Wallace & Gromit’s cheese
hypothesis? Daniel Johnson wants you to think again
velocity of a body (the same effect that makes the siren
of a passing ambulance rise and fall in pitch).
The spectrometer has been in service since 2006;
astronomers have been using the Doppler shift to find
exoplanets for years. So what’s new?
© nasa
Well, previously astronomers measured the Doppler
shift in a star’s spectrum caused by the planet’s
gravitational field. The much heavier star barely moves,
spinning in a small circle at only a few kilometres per
hour. But Birkby and her team flipped this around, using
the Doppler shift caused by the planet’s motion around
the star (around 400,000 km h-1).
Black holes
and revelations
Britain’s first astronaut,
Helen Sharman, wrote
about the science of alien
planets and black holes
when the first planet from
another galaxy was
discovered in the Milky
Way: http://bit.ly/16xbYVj
6 | The Mole | September 2013
Astronomers using the European Southern
Observatory’s Very Large Telescope (VLT) have
developed a new method that could allow us to analyse
the make-up of exoplanets (planets outside of our solar
system) in greater detail than ever before. According to
results presented this summer, the new technique will
allow astronomers to ‘search for water on hundreds of
worlds without space-based telescopes’.
Hunting for water meant looking at longer wavelengths
where the Earth’s atmosphere starts to obstruct what
they are looking for. High in Chile’s Atacama Desert, the
VLT is ideally placed to minimise atmospheric effects,
but still the spectrum received a combination of signals:
from the exoplanet, the star itself and some distortion
owing to our atmosphere. However, the Doppler effect
shifted the exoplanet’s contribution while the rest
of the spectrum stayed the same. This is where the
spectrometer comes in. Its extremely high resolution
can distinguish individual water lines in the spectrum,
allowing the overall pattern to be identified.
A needle in a spectral haystack
An analogy for the process is this: imagine you’re
looking for a needle in a haystack. Unfortunately, the
needle is moving. You must discount the hay (the
spectrum of the star and atmospheric distortion) and
find the moving needle (the water signal). Your one
advantage? You know what the needle looks like.
The implications? It will be easier to look for planets that
may harbour those green aliens, for a start. Furthermore,
having improved the technique for water, the team, led
‘Of course we were delighted when we saw the signal jump
by Jayne Birkby of Leiden University, Netherlands, may
out at us,’ said Birkby, conveying her excitement that this
now move on to other atmospheric molecules such as
technique could be used ‘to look for Earth-twin planets’.
O2, CO2 and CH4.
The researchers can now move on to looking for more
Old principles, new method
atmospheric molecules, building up a picture of the
The method itself is a lesson in how old principles can
atmospheres and histories of thousands of exoplanets.
be combined to make huge advances. The technique
It raises the tantalising prospect of one day finding a
uses a high-resolution infrared spectrometer mounted
planet with a similar atmosphere to our own, where life
on the VLT. Just as important is the relationship between may have existed or even exists today. Then things really
the Doppler shift of electromagnetic radiation and the
get exciting.
www.rsc.org/TheMole
Electronic
tattoos
Flexible electronics
Emma Stoye investigates a super-stretchy conductor
© Joseph Xu/ University of Michigan
US researchers have made the stretchiest electrical
conductor yet using gold nanoparticles embedded in
an elastic polymer. The new material can stretch to over
five times its size while still conducting well enough to
power small devices.
Find out how temporary
tattoos containing flexible
electronics can be used to
monitor racing car drivers
with this article from
Chemistry World:
http://rsc.li/1ctlxsy
Finding materials that can conduct when stretched is
a huge challenge within flexible electronics. Existing
approaches, which involve coiling wires, liquid inks or
embedding conductive particles in stretchy materials,
have achieved limited success. The biggest hurdle,
says lead scientist Nicholas Kotov from the University of
Michigan, is combining two properties that counteract
each other. ‘If we increase the stretchability of a
material we automatically decrease the conductivity
because we are increasing the gap between the
conducting elements,’ he says. ‘On the other hand,
adding more conductive elements increases stiffness
and reduces stretchability.’
Nanoparticles
Kotov and his group have overcome this trade-off using
spherical gold nanoparticles dispersed through sheets
of polyurethane. When this approach has been tried
with other conductors, such as carbon nanotubes,
conductivity drops as the material is stretched. But
instead of spreading further apart when the material
is stretched, the gold nanoparticles form a branching
network of conductive chains so conductivity stays high.
‘We knew from our experience with nanoparticles in
solutions that a lot of particles have the ability to selforganise – it’s intrinsic to nanoscale matter,’ says Kotov.
‘Our approach worked really well – because of this self-
organisation we were able to get high conductivity and
amazing stretchability.’ He also says nanoparticles other
than gold could be used in the same way.
The new super-stretchy
material can still conduct
electricity when stretched
to five times its original size
Without stretching, the material has a high conductance
of 11,000 S cm-1. When stretched to over twice their
original length, conductance is 2400 S cm-1. It even
conducts when stretched to 5.8 times its length at
35 S cm-1, which is still enough to power some small
devices. This is a significant improvement on existing
stretchy carbon nanotube containing conductors, few of
which can even stretch more than twice their length, let
alone maintain conductivity.
Applications
There are several potential applications for such an elastic
conductor. Kotov says it could feature in flexible gadgets
or soft robots, and his group are currently trying to use it
to create soft, stretchable medical implants and sensors,
in particular for use in the brain.
© Joseph Xu/ University of Michigan
John Rogers, a nanofabrication expert at the University of
Illinois, Urbana-Champaign, US, agrees this is a promising
development. ‘These types of conducting materials could
provide new options in engineering design,’ he says.
‘The next steps will be to determine routes for integrating
these materials into functional systems and assessing
their performance compared to alternatives.’
www.rsc.org/TheMole
Scanning electron
microscopy image of the
flexible conductor when
it's stretched 110%
September 2013 | The Mole | 7