Making windows more flexible
A smart window material that is also flexible could revolutionize
architecture and vehicle design allowing control of heat and light to improve
efficiency as well as potentially opening new solutions to as yet unrecognized
problems.
Delia Milliron of the University of Texas at Austin, USA, and
colleagues have devised a low-temperature acid-catalyzed condensation of
polyniobate clusters process for making depositing a smart coating on to a
plastic substrate. The same approach also allows
"nanocrystal-in-glass" composites, i.e. tin-doped indium oxide (ITO)
nanocrystals embedded in NbOx glass to be prepared. The method gives
researchers an alternative to attempting to make transparent composites with
glass itself. The team has demonstrated their flexible electrochromic device,
which responds to a 4 volt input to lighten or darken the material and affect
the degree to which it transmits near-infrared radiation. The work was carried
out in collaboration with scientists at the European Synchrotron Radiation
Facility and CNRS in France, and Ikerbasque in Spain. [Milliron et al.,
Nature Mater. (2016) DOI: 10.1038/nmat4734]
The nanostructured material, niobium oxide, in common with those
made using sputtering techniques or by solution coating with high temperature
annealing at high temperature is amorphous but has a unique local arrangement
of linear chains of atoms. These chains allow ions to flow in and out of the
material. "There's relatively little insight into amorphous materials and
how their properties are impacted by local structure," Milliron explains.
"But, we were able to characterize with enough specificity what the local
arrangement of the atoms is, so that it sheds light on the differences in
properties in a rational way."
UT's Graeme Henkelman adds that the determination of the atomic
structure for amorphous materials is far more difficult than for crystalline
materials and so the team had to use a combination of X-ray scattering and
spectroscopic characterization to obtain an atomic structure that was
consistent with both experiment and computer simulations. "Such
collaborative efforts that combine complementary techniques are, in my view, the
key to the rational design of new materials," he suggests.
The same insights that have emerged from this work might also be
exploited in the design of other amorphous materials for a wide range of
engineering applications such as the development of supercapacitors for storing
electrical energy from sustainable but intermittent or periodic generation
sources such as wind and solar power.
The team's next challenge will be to optimize the flexible
material so that their low-temperature process makes substances that exceed the
performance of conventional electrochromic materials. "We want to see if
we can marry the best performance with this new low-temperature processing
strategy," Milliron says.
"The next step is to apply the newly developed low
temperature process to materials which have enhanced optical performance,"
Milliron told Materials Today. "Specifically, we want to be able to block
more infrared and tint the windows to a darker hue than is possible using the
materials that we used in our proof-of-concept study just published. We have
demonstrated enhanced optical coloration previously but it required multiple
high temperature processing steps, so we need to figure out how to use the low
temperature process on these other, improved materials.
David Bradley 7
September 2016 |
David Bradley blogs
at Sciencebase
Science Blog and tweets @sciencebase, he is author of the
popular science book "Deceived Wisdom".
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