Eco-friendly explosives?
Lawrence Livermore National Laboratory (LLNL) researchers have added 'green' solvents to an explosive called TATB (1,3,5-triamino-2,4,6-trinitrobenzene). As a result, these explosives may soon get a little greener and a little more precise. As said the project's principal investigator, 'Improving crystal quality and purity leads to explosive materials that are safer (less likely to react violently) when subjected to mechanical impact or heat.' These explosives are used by the U.S. Department of Energy, but also by its Department of Defense and the mining industry. But read more...
You can see above some of the molecules added to the TATB explosive. "Fluoride ionic liquid as a novel super-efficient solvent can lead to high-quality single crystals of technologically important materials. The molecules in red, white, blue and gray are the explosive, TATB. The green balls (fluoride anions) and the gray and blue sticks (cations), act as the solvent. The rocks in the background are TATB crystals." (Credit:LLNL) Here is a link to a larger version of this figure.
This project, supported under the DoE's Transformational Materials Initiative (TMI), was performed at LLNL's High Explosives Application Facility (HEAF) by an interdisciplinary team of researchers belonging to the CMELS Directorate (Chemistry, Materials, Earth and Life Sciences). Some of the researchers involved are Larry Fried, the project's principal investigator, Amitesh Maiti and Phil Pagoria.
Now, let's look at modern explosives. "Most explosives belong to a general class of materials called molecular crystals, which have become important building blocks in a number of other applications ranging from drugs, pigments, agrochemicals, dyes and optoelectronics. Many of these materials, including TATB, are bound together by a strong network of hydrogen-bonds. This extended network often makes these materials nearly insoluble in common organic solvents, leading to poor quality and limited size crystals, which in turn hinders progress in many technological applications."
So the research team looked "for a suitable alternative, which happened to be ionic liquids -- a special type of molten salt that becomes liquid under the boiling point of water (100 degrees Celsius)." However, there is an almost infinite number of solutions to choose from. "To narrow the choices down, Amitesh Maiti used state-of-the-art quantum mechanical simulations to identify a special class of ionic liquids containing fluoride anions that are highly effective in dissolving hydrogen-bonded materials such as TATB."
The team then tested successfully these solvents. But what could be possible applications for these solvents -- besides explosives? "The solvents and the dissolution process developed by the TMI team have applications in other fields as well, such as the production of polymers (plastics) or molecular solids (pharmaceuticals, paints, propellants, explosives). For instance, the team found that fluoride ionic liquids are highly effective in dissolving cellulose (plant fiber), a versatile bio-renewable polymeric material with many applications."
This research work has been published in the Physical Chemistry Chemical Physics under the name "Solvent screening for a hard-to-dissolve molecular crystal" (Volume 10, Issue 33, Pages 5050-5056). Here is the beginning of the abstract. "Materials with a high-degree of inter- and intra-molecular hydrogen bonding generally have limited solubility in conventional organic solvents. This presents a problem for the dissolution, manipulation and purification of these materials. Using a state-of-the-art density-functional-theory based quantum chemical solvation model we systematically evaluated solvents for a known hydrogen-bonded molecular crystal. This, coupled with direct solubility measurements, uncovered a class of ionic liquids involving fluoride anions that possess more than two orders of magnitude higher solvation power as compared with the best conventional solvents."
And here is a link to the HTML version of this paper, with an excerpt from the conclusions. "Possible chemical modifications notwithstanding, the ultimate goal of our project was to generate high-quality crystals from the solution. More specifically, the aim was to achieve large defect-free crystallites, which was expected to lead to a better-formulated material for energetic applications. [We have compared] scanning electron micrograph (SEM) images of commercially available TATB with our new material re-crystallized from an IL solution. The superior quality of the newly re-crystallized TATB is clearly evident.
Sources: Lawrence Livermore National Laboratory news release, August 28, 2008; and various websites
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