Ultrafast Dynamics of Nanotechnology Energetic Materials
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Ultrafast Dynamics of Nanotechnology Energetic Materials Hyunung Yu, Selezion A. Hambir and Dana D. Dlott School of Chemical Sciences, University of Illinois at Urbana-Champaign 600 S. Mathews Ave. Urbana, IL 61801 ABSTRACT Our work involves understanding the chemical reaction dynamics of nanotechnology energetic materials on the time and length scales of individual molecules or nanoparticles. These types of measurements provide insights into fundamental mechanisms and make a close connection to modern atomistic simulation methods. We are especially interested in the relationships between performance and nanostructure. We have developed a number of diagnostic instruments in our laboratory that can be used to probe chemical reaction dynamics, reaction propagation over short length scales, and explosive performance. Some recent results on energetic materials containing Al nanoparticles and either nitrocellulose (NC) or Teflon oxidizers are presented. INTRODUCTION About one year ago, the US Army Research Office began a Multidisciplinary University Research Initiative (MURI) program termed “Nano-engineered Energetic Materials” (NEEM). An award was made to a team of investigators from Pennsylvania State University (PSU), the University of Illinois at Urbana-Champaign (UIUC) and the University of Southern California (USC), to facilitate the development of methods for: (1) synthesizing energetic materials using methods that have the potential to control the structure on all length scales; (2) developing an experimental and theoretical understanding of the relationships between nanostructure and reactivity; and (3) characterizing the performance of these materials and evaluating their potential for propulsion or explosives applications. A flow chart of the program is shown in Fig. 1.
Figure 1. Flow chart of Nano-engineered Energetic Materials (NEEM) program at Pennsylvania State University (PSU), University of Illinois at Urbana-Champaign (UIUC) and the University of Southern California (USC). Chart courtesy of R. Yetter (PSU).
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In the Dlott group at UIUC, our part of the program is to understand the dynamics of NEEM materials using methods that can resolve processes occurring on short time and length scales. To understand these scales, imagine metal (fuel) nanoparticles embedded in a matrix of oxidizer [1-3]. Chemical reactions at the fuel/oxidizer interface, just a few nm thick, occur on the picosecond and nanometer scales. Chemical reactions that consume the nanoparticle occur on the length scale of the nanoparticle diameter, tens of nanometers and nanosecond time scales. Chemical reactions that propagate from one nanoparticle to another [4] occur in tens of nanoseconds and hundreds of nanometers. Transients that ultimately lead to steady state combustion or detonation occur on the length scales of tens to perhaps thousands of nanoparticles and time scales of nanoseconds to microseconds. In order to address these time and length scales, we have combined ultrashort pulse lasers (0.1 ps to 1
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