Charles McLaren, a Ph.D. candidate in materials science and engineering at Lehigh, arrived last fall for a semester of research at the University of Marburg in Germany with his language skills lagging significantly behind his scientific prowess.
“It was my first trip to Germany, and I barely spoke a word of German,” he confessed.
With the help of his new German colleagues, he got past the point-and-eat phase of the international experience in no time. “The group members there were very welcoming. They showed me around and helped me learn enough vocabulary to order some food, at least.”
The main purpose of McLaren’s exchange study in Marburg was far from culinary, however. He was there to learn more about a complex process involving transformations in glass that occur under intense electrical and thermal conditions. New understanding of these mechanisms could lead the way to more energy-efficient glass manufacturing, and even glass supercapacitors that leapfrog the performance of batteries now used for electric cars and solar energy.
“This technology is relevant to companies seeking the next wave of portable, reliable energy,” said Himanshu Jain, the T. L. Diamond Distinguished Chair in Materials Science and Engineering at Lehigh and director of its International Materials Institute for New Functionality in Glass.
“A breakthrough in the use of glass for power storage could unleash a torrent of innovation in the transportation and energy sectors, and even support efforts to curb global warming.”
In his doctoral research, McLaren discovered that applying a direct current field across glass reduced its melting temperature. In lab experiments, he and Jain placed a block of glass between a cathode and anode, and then exerted steady pressure on the glass while gradually heating it. Together with colleagues at the University of Colorado, the Lehigh researchers reported their results last fall in Applied Physics Letters.
The implications for the finding were intriguing. In addition to making glass formulation possible at lower temperatures and reducing energy needs, designers using electrical current in glass manufacturing would have a tool to make precise manipulations not possible with heat alone.
“You could make a mask for the glass, for example, and apply an electrical field on a micron scale,” said Jain. “This would allow you to deform the glass with high precision, and soften it in a far more selective way than you could with heat, which gets distributed throughout the glass.”
Though McLaren and Jain had isolated the phenomenon and determined how to dial up the variables for optimal results, they did not yet fully understand the mechanisms behind it. McLaren and Jain had been following the work of Bernard Roling at the University of Marburg, who had discovered some remarkable characteristics of glass using electro-thermal poling, a technique that employs both temperature manipulation and electrical current to create a charge in normally inert glass. The process imparts useful optical and even bioactive qualities to glass.
Roling invited McLaren to spend a semester at Marburg to analyze the behavior of glass under electro-thermal poling, to see if it would reveal more about the fundamental science underlying what McLaren and Jain had observed in their Lehigh lab.
A high-speed avalanche
McLaren’s work in Marburg revealed a two-step process in which a thin sliver of the glass nearest the anode, called a depletion layer, becomes much more resistant to electrical current than the rest of the glass as alkali ions in the glass migrate away. This is followed by a catastrophic change in the layer, known as dielectric breakdown, which dramatically increases its conductivity. McLaren likens the process of dielectric breakdown to a high-speed avalanche, and uses spectroscopic analysis with electro-thermal poling as a way to see what is happening in slow motion.
“The results in Germany gave us a very good model for what is going on in the electric field-induced softening that we did here. It told us about the start conditions for where dielectric breakdown can begin,” said McLaren.
“Charlie’s work in Marburg has helped us see the kinetics of the process,” Jain said. “We could see it happening abruptly in our experiments here at Lehigh, but we now have a way to separate out what occurs specifically with the depletion layer.”
Learn more: NEW CURRENTS IN GLASS STUDIES
From protecting our most valuable works of art to enabling smartphone displays, glass has become one of our most important materials. Making it even more versatile is the next challenge. Developing new glass compositions is largely a time-consuming, trial-and-error exercise. But now scientists have developed a way to decode the glass “genome” and design different compositions of the material without making and melting every possibility.
Their report appears in ACS’ journal Chemistry of Materials.
Despite the fact that humans have been making glass since antiquity, the material is still unpredictable. Scientists don’t yet fully understand how the structure of glass affects its properties such as density, crack resistance and melting temperatures. This knowledge gap hinders progress in developing new products, such as lighter windows for more fuel-efficient cars. A major complicating factor is that just about any element can be incorporated into glass, which means a near-endless list of possible compositions, each with a different set of properties. Glass types have been made by trial-and-error, but this process takes a lot of time. Morten M. Smedskjaer of Aalborg University and colleagues at Corning Incorporated wanted to come up with a faster way to develop new glass compositions for large-scale use.
The researchers combined a range of computer models, from the empirical to those grounded in physics, to explore what they call the glass genome — the possible combinations of materials and their resulting properties. Using these models, glass makers will be able to predict how various glass compositions will behave in the real world, and optimize them for industrial production much faster than before.
Australian researchers at the University of Adelaide have developed a method for embedding light-emitting nanoparticles into glass without losing any of their unique properties – a major step towards ‘smart glass’ applications such as 3D display screens or remote radiation sensors.
This new “hybrid glass” successfully combines the properties of these special luminescent (or light-emitting) nanoparticles with the well-known aspects of glass, such as transparency and the ability to be processed into various shapes including very fine optical fibres.
The research, in collaboration with Macquarie University and University of Melbourne, has been published online in the journal Advanced Optical Materials.
“These novel luminescent nanoparticles, called upconversion nanoparticles, have become promising candidates for a whole variety of ultra-high tech applications such as biological sensing, biomedical imaging and 3D volumetric displays,” says lead author Dr Tim Zhao, from the University of Adelaide’s School of Physical Sciences and Institute for Photonics and Advanced Sensing (IPAS).
“Integrating these nanoparticles into glass, which is usually inert, opens up exciting possibilities for new hybrid materials and devices that can take advantage of the properties of nanoparticles in ways we haven’t been able to do before. For example, neuroscientists currently use dye injected into the brain and lasers to be able to guide a glass pipette to the site they are interested in. If fluorescent nanoparticles were embedded in the glass pipettes, the unique luminescence of the hybrid glass could act like a torch to guide the pipette directly to the individual neurons of interest.”
Although this method was developed with upconversion nanoparticles, the researchers believe their new ‘direct-doping’ approach can be generalised to other nanoparticles with interesting photonic, electronic and magnetic properties. There will be many applications – depending on the properties of the nanoparticle.