Frederick Seitz Materials Research Laboratory

Urbana, IL, United States

Frederick Seitz Materials Research Laboratory

Urbana, IL, United States
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News Article | February 13, 2017
Site: www.cemag.us

Molybdenum disulfide (MoS ), which is ubiquitously used as a solid lubricant, has recently been shown to have a two-dimensional (2D) form that is similar to graphene. But, when thinned down to less than a nanometer thick, MoS demonstrates properties with great promise as a functional material for electronic devices and surface coatings. Researchers at the University of Illinois at Urbana-Champaign have developed a new approach to dynamically tune the micro- and nano-scale roughness of atomically thin MoS , and consequently the appropriate degree of hydrophobicity for various potential MoS -based applications. “The knowledge of how new materials interact with water is a fundamental,” explains SungWoo Nam, an assistant professor of mechanical science and engineering at Illinois. “Whereas the wettability of its more famous cousin, graphene, has been substantially investigated, that of atomically thin MoS — in particular atomically thin MoS2 with micro- and nano-scale roughness — has remained relatively unexplored despite its strong potential for fundamental research and device applications. Notably, systematic study of how hierarchical microscale and nanoscale roughness of MoS influence its wettability has been lacking in the scientific community.” “This work will provide a new approach to dynamically tune the micro- and nano-scale roughness of atomically thin MoS and consequently the appropriate degree of hydrophobicity for various potential MoS2-based applications,” says Jonghyun Choi, a mechanical engineering graduate student and first author of the article, “Hierarchical, Dual-Scale Structures of Atomically Thin MoS for Tunable Wetting,” appearing in the journal, Nano Letters. “These include waterproof electronic devices with superhydrophobicity with water contact angle greater than 150 degrees. It may also be useful for medical applications with reduced hydrophobicity (WCA less than 100 degrees) for effective contact with biological substances." According to the authors, this study, expands the toolkit to allow tunable wettability of 2D materials, many of which are just beginning to be discovered. “When deformed and patterned to produce micro- and nano-scale structures, MoS shows promise as a functional material for hydrogen evolution catalysis systems, electrodes for alkali metal-ion batteries, and field-emission arrays,” Nam adds. “The results should also contribute to future MoS -based applications, such as tunable wettability coatings for desalination and hydrogen evolution.” In addition to Nam and Choi, co-authors of the paper include graduate students Michael Cai Wang and Ali Ashraf (Illinois), Jihun Mun and Sang-Woo Kang (Korea Research Institute of Standards and Science, Korea). Experiments were carried out in part in the Frederick Seitz Materials Research Laboratory, the Micro + Nano Technology Laboratory, and the Beckman Institute Imaging Technology Group at Illinois.


Researchers have come up with a first-of-its-kind "lab on the skin," a low-cost, soft wearable device that adheres to the skin easily and measures sweat to determine how an individual is responding to physical activity. In a study published in the journal Science Translational Medicine, John Rogers and colleagues were able to show how a device no bigger than a quarter can analyze sweat to assess key biomarkers and help people decide if they need to make any adjustments while engaged in physical activity, like drinking more water, or tell if something is medically wrong. "The intimate skin interface created by this wearable, skin-like microfluidic system enables new measurement capabilities not possible with the kinds of absorbent pads and sponges currently used in sweat collection," said Rogers, who led the research team. Designed to be used one time for a few hours, "lab on the skin" is to be directly placed on the skin on the back or forearm. During physical activity, sweat is directed to the device, where it will wind through microscopic channels and into four compartments. These compartments are filled with chemical reagents and the resulting reaction will produce a color change that corresponds to levels of pH, lactate, chloride and glucose. To analyze the reactions, a smartphone app takes a photo of the device, analyzing the image. The device can even detect a biomarker for cystic fibrosis so the researchers are looking at broader applications for "lab on the skin" when it came to disease diagnosis. It can also store samples so it's possible to carry out subsequent analysis in the laboratory. Watch "lab on the skin" at work below! Rogers explained that sweat is a "rich, chemical broth" made up of numerous important chemical compounds that contain information on physiological health. With the researchers building upon Rogers and Yonggang Huang's work on skin-like stretchable electronics, they were able to come up with a way to carry out biochemical analysis in a simpler, more efficient manner. However, "lab on the skin" was not without its challenges. According to Huang, the research team had to develop a means of addressing sweat collection, flow, storage and analysis for a device that is thin, soft and flexible. But with the sweat analysis platform the researchers made, it is now possible for people to do on-the-spot checks on their health without requiring blood samples or bulky electronics. The development of "lab on the skin" was made possible by funding support from the National Institutes of Health, the National Research Foundation of Korea, University of Illinois at Urbana-Champaign's Frederick Seitz Materials Research Laboratory and L'Oréal. © 2017 Tech Times, All rights reserved. Do not reproduce without permission.


News Article | November 28, 2016
Site: www.eurekalert.org

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics. Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent gradient refractive index (GRIN) micro-optics by electrochemically etching preformed Si micro-structures, like square columns, PSi structures with defined refractive index profiles. "The emergence and growth of transformation optics over the past decade has revitalized interest in using GRIN optics to control light propagation," explained Paul Braun, the Ivan Racheff Professor of Materials Science and Engineering at Illinois. "In this work, we have figured out how to couple the starting shape of the silicon micro-structure and the etch conditions to realize a unique set of desirable optical qualities. For example, these elements exhibit novel polarization-dependent optical functions, including splitting and focusing, expanding the use of porous silicon for a wide range of integrated photonics applications. "The key is that the optical properties are a function of the etch current," Braun said. "If you change the etch current, you change the refractive index. We also think that the fact that we can create the structures in silicon is important, as silicon is important for photovoltaic, imaging, and integrated optics applications. "Our demonstration using a three-dimensional, lithographically-defined silicon platform not only displayed the power of GRIN optics, but it also illustrated it in a promising form factor and material for integration within photonic integrated circuits," stated Neil Krueger, a former PhD student in Braun's research group and first author of the paper, "Porous Silicon Gradient Refractive Index Micro-Optics," appearing in Nano Letters. "The real novelty of our work is that we are doing this in a three-dimensional optical element," added Krueger, who has recently joined Honeywell Aerospace as a Scientist in Advanced Technology. "This gives added control over the behavior of our structures given that light follows curvilinear optical paths in optically inhomogeneous media such as GRIN elements. The birefringent nature of these structures is an added bonus because coupled birefringent/GRIN effects provide an opportunity for a GRIN element to perform distinct, polarization-selective operations." According to the researchers, PSi was initially studied due to its visible luminescence at room temperature, but more recently, as this and other reports have shown, has proven to be a versatile optical material, as its nanoscale porosity (and thus refractive index) can be modulated during its electrochemical fabrication. "The beauty of this 3D fabrication process is that it is fast and scalable," commented Weijun Zhou at Dow. "Large scale, nanostructured GRIN components can be readily made to enable a variety of new industry applications such as advanced imaging, microscopy, and beam shaping." "Because the etching process enables modulation of the refractive index, this approach makes it possible to decouple the optical performance and the physical shape of the optical element," Braun added. "Thus, for example, a lens can be formed without having to conform to the shape that we think of for a lens, opening up new opportunities in the design of integrated silicon optics." Paul Braun is also the director of the Frederick Seitz Materials Research Laboratory at Illinois. In addition to Braun, Krueger, and Zhou, co-authors of the paper include Seung-Kyun Kang, Christian R. Ocier, Glennys Mensing, and John A. Rogers (University of Illinois), Aaron L. Holsteen and Mark L. Brongersma (Stanford University).


News Article | April 8, 2016
Site: www.nanotech-now.com

Abstract: Researchers from the University of Illinois at Urbana-Champaign have demonstrated a new approach to modifying the light absorption and stretchability of atomically thin two-dimensional (2D) materials by surface topographic engineering using only mechanical strain. The highly flexible system has future potential for wearable technology and integrated biomedical optical sensing technology when combined with flexible light-emitting diodes. "Increasing graphene's low light absorption in visible range is an important prerequisite for its broad potential applications in photonics and sensing," explained SungWoo Nam, an assistant professor of mechanical science and engineering at Illinois. "This is the very first stretchable photodetector based exclusively on graphene with strain-tunable photoresponsivity and wavelength selectivity." Graphene--an atomically thin layer of hexagonally bonded carbon atoms--has been extensively investigated in advanced photodetectors for its broadband absorption, high carrier mobility, and mechanical flexibility. Due to graphene's low optical absorptivity, graphene photodetector research so far has focused on hybrid systems to increase photoabsorption. However, such hybrid systems require a complicated integration process, and lead to reduced carrier mobility due to the heterogeneous interfaces. According to Nam, the key element enabling increased absorption and stretchability requires engineering the two-dimensional material into three-dimensional (3D) "crumpled structures," increasing the graphene's areal density. The continuously undulating 3D surface induces an areal density increase to yield higher optical absorption per unit area, thereby improving photoresponsivity. Crumple density, height, and pitch are modulated by applied strain and the crumpling is fully reversible during cyclical stretching and release, introducing a new capability of strain-tunable photoabsorption enhancement and allowing for a highly responsive photodetector based on a single graphene layer. "We achieved more than an order-of-magnitude enhancement of the optical extinction via the buckled 3D structure, which led to an approximately 400% enhancement in photoresponsivity," stated Pilgyu Kang, and first author of the paper, "Crumpled Graphene Photodetector with Enhanced, Strain-tunable and Wavelength-selective Photoresponsivity," appearing in the journal, Advanced Materials. "The new strain-tunable photoresponsivity resulted in a 100% modulation in photoresponsivity with a 200% applied strain. By integrating colloidal photonic crystal--a strain-tunable optomechanical filter--with the stretchable graphene photodetector, we also demonstrated a unique strain-tunable wavelength selectivity." "This work demonstrates a robust approach for stretchable and flexible graphene photodetector devices," Nam added. "We are the first to report a stretchable photodetector with stretching capability to 200% of its original length and no limit on detection wavelength. Furthermore, our approach to enhancing photoabsorption by crumpled structures can be applied not only to graphene, but also to other emerging 2D materials." ### In addition to Nam and Kang, study co-authors include Michael Cai Wang and Peter M. Knapp in the Department of Mechanical Science and Engineering at Illinois. The optical characterizations and partial device fabrication were carried out in the Frederick Seitz Materials Research Laboratory and the Micro and Nano Technology Laboratory at Illinois. For more information, please click If you have a comment, please us. Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.


News Article | January 20, 2016
Site: www.nanotech-now.com

Abstract: A new class of small, thin electronic sensors can monitor temperature and pressure within the skull - crucial health parameters after a brain injury or surgery - then melt away when they are no longer needed, eliminating the need for additional surgery to remove the monitors and reducing the risk of infection and hemorrhage. Similar sensors can be adapted for postoperative monitoring in other body systems as well, the researchers say. Led by John A. Rogers, a professor of materials science and engineering at the University of Illinois at Urbana-Champaign, and Wilson Ray, a professor of neurological surgery at the Washington University School of Medicine in St. Louis, the researchers publish their work in the journal Nature on January 18. "This is a new class of electronic biomedical implants," said Rogers, who directs the Frederick Seitz Materials Research Laboratory at Illinois. "These kinds of systems have potential across a range of clinical practices, where therapeutic or monitoring devices are implanted or ingested, perform a sophisticated function, and then resorb harmlessly into the body after their function is no longer necessary." After a traumatic brain injury or brain surgery, it is crucial to monitor the patient for swelling and pressure on the brain. Current monitoring technology is bulky and invasive, Rogers said, and the wires restrict the patent's movement and hamper physical therapy as they recover. Because they require continuous, hard-wired access into the head, such implants also carry the risk of allergic reactions, infection and hemorrhage, and even could exacerbate the inflammation they are meant to monitor. "If you simply could throw out all the conventional hardware and replace it with very tiny, fully implantable sensors capable of the same function, constructed out of bioresorbable materials in a way that also eliminates or greatly miniaturizes the wires, then you could remove a lot of the risk and achieve better patient outcomes," Rogers said. "We were able to demonstrate all of these key features in animal models, with a measurement precision that's just as good as that of conventional devices." The new devices incorporate dissolvable silicon technology developed by Rogers' group at the U. of I. The sensors, smaller than a grain of rice, are built on extremely thin sheets of silicon - which are naturally biodegradable - that are configured to function normally for a few weeks, then dissolve away, completely and harmlessly, in the body's own fluids. Rogers' group teamed with Illinois materials science and engineering professor Paul V. Braun to make the silicon platforms sensitive to clinically relevant pressure levels in the intracranial fluid surrounding the brain. They also added a tiny temperature sensor and connected it to a wireless transmitter roughly the size of a postage stamp, implanted under the skin but on top of the skull. The Illinois group worked with clinical experts in traumatic brain injury at Washington University to implant the sensors in rats, testing for performance and biocompatibility. They found that the temperature and pressure readings from the dissolvable sensors matched conventional monitoring devices for accuracy. "The ultimate strategy is to have a device that you can place in the brain - or in other organs in the body - that is entirely implanted, intimately connected with the organ you want to monitor and can transmit signals wirelessly to provide information on the health of that organ, allowing doctors to intervene if necessary to prevent bigger problems," said Rory Murphy, a neurosurgeon at Washington University and co-author of the paper. "After the critical period that you actually want to monitor, it will dissolve away and disappear." The researchers are moving toward human trials for this technology, as well as extending its functionality for other biomedical applications. "We have established a range of device variations, materials and measurement capabilities for sensing in other clinical contexts," Rogers said. "In the near future, we believe that it will be possible to embed therapeutic function, such as electrical stimulation or drug delivery, into the same systems while retaining the essential bioresorbable character." ### The National Institutes of Health, the Defense Advanced Research Projects Agency and the Howard Hughes Medical Institute supported this work. Rogers and Braun are affiliated with the Beckman Institute for Advanced Science and Technology at the U. of I. For more information, please click If you have a comment, please us. Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.


News Article | January 20, 2016
Site: www.cemag.us

A new class of small, thin electronic sensors can monitor temperature and pressure within the skull — crucial health parameters after a brain injury or surgery — then melt away when they are no longer needed, eliminating the need for additional surgery to remove the monitors and reducing the risk of infection and hemorrhage. Similar sensors can be adapted for postoperative monitoring in other body systems as well, the researchers say. Led by John A. Rogers, a professor of materials science and engineering at the University of Illinois at Urbana-Champaign, and Wilson Ray, a professor of neurological surgery at the Washington University School of Medicine in St. Louis, the researchers published their work in the journal Nature. “This is a new class of electronic biomedical implants,” says Rogers, who directs the Frederick Seitz Materials Research Laboratory at Illinois. “These kinds of systems have potential across a range of clinical practices, where therapeutic or monitoring devices are implanted or ingested, perform a sophisticated function, and then resorb harmlessly into the body after their function is no longer necessary.” After a traumatic brain injury or brain surgery, it is crucial to monitor the patient for swelling and pressure on the brain. Current monitoring technology is bulky and invasive, Rogers says, and the wires restrict the patent’s movement and hamper physical therapy as they recover. Because they require continuous, hard-wired access into the head, such implants also carry the risk of allergic reactions, infection and hemorrhage, and even could exacerbate the inflammation they are meant to monitor. “If you simply could throw out all the conventional hardware and replace it with very tiny, fully implantable sensors capable of the same function, constructed out of bioresorbable materials in a way that also eliminates or greatly miniaturizes the wires, then you could remove a lot of the risk and achieve better patient outcomes,” Rogers says. ”We were able to demonstrate all of these key features in animal models, with a measurement precision that’s just as good as that of conventional devices.” The new devices incorporate dissolvable silicon technology developed by Rogers’ group at the U. of I. The sensors, smaller than a grain of rice, are built on extremely thin sheets of silicon — which are naturally biodegradable — that are configured to function normally for a few weeks, then dissolve away, completely and harmlessly, in the body’s own fluids. Rogers’ group teamed with Illinois materials science and engineering professor Paul V. Braun to make the silicon platforms sensitive to clinically relevant pressure levels in the intracranial fluid surrounding the brain. They also added a tiny temperature sensor and connected it to a wireless transmitter roughly the size of a postage stamp, implanted under the skin but on top of the skull. The Illinois group worked with clinical experts in traumatic brain injury at Washington University to implant the sensors in rats, testing for performance and biocompatibility. They found that the temperature and pressure readings from the dissolvable sensors matched conventional monitoring devices for accuracy. “The ultimate strategy is to have a device that you can place in the brain — or in other organs in the body — that is entirely implanted, intimately connected with the organ you want to monitor and can transmit signals wirelessly to provide information on the health of that organ, allowing doctors to intervene if necessary to prevent bigger problems,” says Rory Murphy, a neurosurgeon at Washington University and co-author of the paper. “After the critical period that you actually want to monitor, it will dissolve away and disappear.” The researchers are moving toward human trials for this technology, as well as extending its functionality for other biomedical applications. “We have established a range of device variations, materials and measurement capabilities for sensing in other clinical contexts,” Rogers says. “In the near future, we believe that it will be possible to embed therapeutic function, such as electrical stimulation or drug delivery, into the same systems while retaining the essential bioresorbable character.” The National Institutes of Health, the Defense Advanced Research Projects Agency, and the Howard Hughes Medical Institute supported this work. Rogers and Braun are affiliated with the Beckman Institute for Advanced Science and Technology at the U. of I. Release Date: January 18, 2016 Source: University of Illinois


News Article | December 2, 2016
Site: www.cemag.us

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics. Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3D birefringent gradient refractive index (GRIN) micro-optics by electrochemically etching preformed Si micro-structures, like square columns, PSi structures with defined refractive index profiles. “The emergence and growth of transformation optics over the past decade has revitalized interest in using GRIN optics to control light propagation,” explains Paul Braun, the Ivan Racheff Professor of Materials Science and Engineering at Illinois. “In this work, we have figured out how to couple the starting shape of the silicon micro-structure and the etch conditions to realize a unique set of desirable optical qualities. For example, these elements exhibit novel polarization-dependent optical functions, including splitting and focusing, expanding the use of PSi for a wide range of integrated photonics applications. “The key is that the optical properties are a function of the etch current,” Braun says. “If you change the etch current, you change the refractive index. We also think that the fact that we can create the structures in silicon is important, as silicon is important for photovoltaic, imaging, and integrated optics applications. “Our demonstration using a three-dimensional, lithographically-defined silicon platform not only displayed the power of GRIN optics, but it also illustrated it in a promising form factor and material for integration within photonic integrated circuits,” states Neil Krueger, a former PhD student in Braun’s research group and first author of the paper, “Porous Silicon Gradient Refractive Index Micro-Optics,” appearing in Nano Letters. “The real novelty of our work is that we are doing this in a three-dimensional optical element,” adds Krueger, who has recently joined Honeywell Aerospace as a Scientist in Advanced Technology. “This gives added control over the behavior of our structures given that light follows curvilinear optical paths in optically inhomogeneous media such as GRIN elements. The birefringent nature of these structures is an added bonus because coupled birefringent/GRIN effects provide an opportunity for a GRIN element to perform distinct, polarization-selective operations.” According to the researchers, PSi was initially studied due to its visible luminescence at room temperature, but more recently, as this and other reports have shown, has proven to be a versatile optical material, as its nanoscale porosity (and thus refractive index) can be modulated during its electrochemical fabrication. “The beauty of this 3D fabrication process is that it is fast and scalable,” comments Weijun Zhou at Dow. “Large scale, nanostructured GRIN components can be readily made to enable a variety of new industry applications such as advanced imaging, microscopy, and beam shaping.” “Because the etching process enables modulation of the refractive index, this approach makes it possible to decouple the optical performance and the physical shape of the optical element,” Braun adds. “Thus, for example, a lens can be formed without having to conform to the shape that we think of for a lens, opening up new opportunities in the design of integrated silicon optics.” Paul Braun is also the director of the Frederick Seitz Materials Research Laboratory at Illinois. In addition to Braun, Krueger, and Zhou, co-authors of the paper include Seung-Kyun Kang, Christian R. Ocier, Glennys Mensing, and John A. Rogers (University of Illinois), Aaron L. Holsteen and Mark L. Brongersma (Stanford University).


News Article | November 28, 2016
Site: www.nanotech-now.com

Abstract: A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics. Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent gradient refractive index (GRIN) micro-optics by electrochemically etching preformed Si micro-structures, like square columns, PSi structures with defined refractive index profiles. "The emergence and growth of transformation optics over the past decade has revitalized interest in using GRIN optics to control light propagation," explained Paul Braun, the Ivan Racheff Professor of Materials Science and Engineering at Illinois. "In this work, we have figured out how to couple the starting shape of the silicon micro-structure and the etch conditions to realize a unique set of desirable optical qualities. For example, these elements exhibit novel polarization-dependent optical functions, including splitting and focusing, expanding the use of porous silicon for a wide range of integrated photonics applications. "The key is that the optical properties are a function of the etch current," Braun said. "If you change the etch current, you change the refractive index. We also think that the fact that we can create the structures in silicon is important, as silicon is important for photovoltaic, imaging, and integrated optics applications. "Our demonstration using a three-dimensional, lithographically-defined silicon platform not only displayed the power of GRIN optics, but it also illustrated it in a promising form factor and material for integration within photonic integrated circuits," stated Neil Krueger, a former PhD student in Braun's research group and first author of the paper, "Porous Silicon Gradient Refractive Index Micro-Optics," appearing in Nano Letters. "The real novelty of our work is that we are doing this in a three-dimensional optical element," added Krueger, who has recently joined Honeywell Aerospace as a Scientist in Advanced Technology. "This gives added control over the behavior of our structures given that light follows curvilinear optical paths in optically inhomogeneous media such as GRIN elements. The birefringent nature of these structures is an added bonus because coupled birefringent/GRIN effects provide an opportunity for a GRIN element to perform distinct, polarization-selective operations." According to the researchers, PSi was initially studied due to its visible luminescence at room temperature, but more recently, as this and other reports have shown, has proven to be a versatile optical material, as its nanoscale porosity (and thus refractive index) can be modulated during its electrochemical fabrication. "The beauty of this 3D fabrication process is that it is fast and scalable," commented Weijun Zhou at Dow. "Large scale, nanostructured GRIN components can be readily made to enable a variety of new industry applications such as advanced imaging, microscopy, and beam shaping." "Because the etching process enables modulation of the refractive index, this approach makes it possible to decouple the optical performance and the physical shape of the optical element," Braun added. "Thus, for example, a lens can be formed without having to conform to the shape that we think of for a lens, opening up new opportunities in the design of integrated silicon optics." ### Paul Braun is also the director of the Frederick Seitz Materials Research Laboratory at Illinois. In addition to Braun, Krueger, and Zhou, co-authors of the paper include Seung-Kyun Kang, Christian R. Ocier, Glennys Mensing, and John A. Rogers (University of Illinois), Aaron L. Holsteen and Mark L. Brongersma (Stanford University). For more information, please click If you have a comment, please us. Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.


News Article | August 30, 2016
Site: phys.org

Though cumbersome, the flat plate impact is the only way to precisely recreate the conditions inside a detonating explosive—and now researchers at the University of Illinois at Urbana-Champaign have recreated this in miniature on a tabletop. In the process, they have made important new contributions to the field of energetic materials by precisely recreating conditions inside a bomb and achieving new levels of accuracy in measuring them. Their results inform a topic known as the hot spot model of explosive initiation by revealing the dynamics of hot spot growth. That's important because their long-term goal with improved testing is to make safer explosives—and eliminating hot spots is one way to do that. Their report appears this week in the journal Applied Physics Letters. Dana D. Dlott, at the University of Illinois at Urbana-Champaign's School of Chemical Sciences and Frederick Seitz Materials Research Laboratory, explains the team's work this way: "Because we can do this so many times a day with a small-scale device on a benchtop that has highly sophisticated optical diagnostics, we see what is happening during the millionth of a second the charge is exploding, with unprecedented accuracy." He emphasized that their approach does not replace the conventional test methods. Rather, their instrument and small-scale tests contribute to understanding how bombs really behave. "Our apparatus allows us to look at the fundamental mechanisms of the initial events never before seen," he said. "This is an important verification of the hot spot model of explosive initiation, and also, it's important because we measured time scales and rates never before seen," added Will P. Bassett a graduate student and member of the research team. Much has been written about hot spots, but they are not often observed and the detailed dynamics of hot spot growth have not been explored before this study. Hot spots are a hot topic in bomb research because they play a crucial role in the phase cycle of explosions, and in controlling explosions and their aftereffects. "Depending on the impact duration, the growth spurts could be as fast as 300 nanoseconds and as slow as 13 microseconds," Bassett said. Their experiments use a pulsed laser to launch a tiny flat bullet 0.5 millimeter in diameter at speeds up to 12 times the speed of sound. This flyer plate impacts an explosive charge that is less than one millionth the size—it could fit inside an adult's hand—yet capable of producing precisely the same conditions as in a detonating explosive. The current work builds on the team's previous research into the complex chemical kinetics of bomb behavior. In it the team observed that the powdered form of a standard test explosive known as HMX material—a common prototypical test material and most powerful explosive in general use—explodes in two phases. First, there is an immediate, prompt explosion at impact. Second, a delayed explosion occurs 300 nanoseconds later—one nanosecond is one-billionth of a second. This new paper extends the work to reveal that initially a small part of the explosive started to react and this spatially limited reaction spread throughout the HMX. For next steps, the team will continue to validate its instrument and apply test results to improving safety outcomes of explosion science. Explore further: Powerful new explosive could replace today's state-of-the-art military explosive More information: "Shock Initiation of Explosives: Temperature Spikes and Growth Spurts," Will P. Bassett and Dana D. Dlott, Applied Physics Letters, Aug. 30, 2016. DOI: 10.1063/1.4961619


News Article | September 1, 2016
Site: www.scientificcomputing.com

Testing explosions is epic science. The most detailed studies of explosive charges have been conducted at national laboratories using a gun as big as a room to fire a flat bullet -- the flyer plate, typically 100 millimeters in diameter -- into an explosive charge inside a thick-walled chamber that contains the fierce blast. The tests require enormous facilities. Though cumbersome, the flat plate impact is the only way to precisely recreate the conditions inside a detonating explosive -- and now researchers at the University of Illinois at Urbana-Champaign have recreated this in miniature on a tabletop. In the process, they have made important new contributions to the field of energetic materials by precisely recreating conditions inside a bomb and achieving new levels of accuracy in measuring them. Their results inform a topic known as the hot spot model of explosive initiation by revealing the dynamics of hot spot growth. That's important because their long-term goal with improved testing is to make safer explosives -- and eliminating hot spots is one way to do that. Their report appears this week in the journal Applied Physics Letters, from AIP Publishing. Dana D. Dlott, at the University of Illinois at Urbana-Champaign's School of Chemical Sciences and Frederick Seitz Materials Research Laboratory, explains the team's work this way: "Because we can do this so many times a day with a small-scale device on a benchtop that has highly sophisticated optical diagnostics, we see what is happening during the millionth of a second the charge is exploding, with unprecedented accuracy." He emphasized that their approach does not replace the conventional test methods. Rather, their instrument and small-scale tests contribute to understanding how bombs really behave. "Our apparatus allows us to look at the fundamental mechanisms of the initial events never before seen," he said. "This is an important verification of the hot spot model of explosive initiation, and also, it's important because we measured time scales and rates never before seen," added Will P. Bassett a graduate student and member of the research team. Much has been written about hot spots, but they are not often observed and the detailed dynamics of hot spot growth have not been explored before this study. Hot spots are a hot topic in bomb research because they play a crucial role in the phase cycle of explosions, and in controlling explosions and their aftereffects. "Depending on the impact duration, the growth spurts could be as fast as 300 nanoseconds and as slow as 13 microseconds," Bassett said. Their experiments use a pulsed laser to launch a tiny flat bullet 0.5 millimeter in diameter at speeds up to 12 times the speed of sound. This flyer plate impacts an explosive charge that is less than one millionth the size -- it could fit inside an adult's hand -- yet capable of producing precisely the same conditions as in a detonating explosive. The current work builds on the team's previous research into the complex chemical kinetics of bomb behavior. In it the team observed that the powdered form of a standard test explosive known as HMX material -- a common prototypical test material and most powerful explosive in general use -- explodes in two phases. First, there is an immediate, prompt explosion at impact. Second, a delayed explosion occurs 300 nanoseconds later -- one nanosecond is one-billionth of a second. This new paper extends the work to reveal that initially a small part of the explosive started to react and this spatially limited reaction spread throughout the HMX. For next steps, the team will continue to validate its instrument and apply test results to improving safety outcomes of explosion science.

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