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First, the stress-induced chain scission is addressed.  This is a very difficult problem to address, because of the relevance of a range of time and length scales.  In particular, quantum mechanics is necessary to treat the covalent bonds which will broken, but such methods cannot be used to treat the many atoms in the condensed phase system that are relevant to causing the stress that will break the bond.  To treat this problem, we are using the Quantum Mechanics/Molecular Mechanics (QM/MM) approach, in which a subsystem is treated with a quantum mechanical electronic structure method, while the rest of the system is treated with a more approximate molecular mechanics method. We are using the Charmm and Gaussian software packages for this purpose.  This work has led to the Masters Thesis of Ms. Gallia Painter.

Second, we have addressed a different phenomenon that we think is related to stress-induced chain scisson.  As granular materials flow, the particles rub against each other and can become electrostatically charged.  This effect has important implications in the petrochemical industry, such as in processes involving fluidized beds.

Surprisingly, the physical processes that underlie triboelectric charging are very poorly understood.  We believe that they are related to changes in the electronic structure (e.g., bond breaking) that occur as materials are rubbed (and thus stressed ) – in this way we believe that triboelectric charging is related to the stress-induced chain scission.  We have carried out a combined experimental and theoretical investigation of triboelectric charging in granular systems, where we show that particle size differences play an important role in the electrostatic charging.  Our experimental results and theoretical analysis show that smaller particles tend to charge negatively, and larger particles tend to charge positively.  These results have led to two publications: Forward, K. M., Lacks, D. J. and Sankaran, R. M., “Triboelectric charging of lunar regolith simulant”, J. Geophys. Res., in press; Forward, K. M., Lacks, D. J. and Sankaran, R. M., “Particle-size dependent bipolar charging of Martian regolith simulant”, Geophys. Res. Lett. 36 L13201 (2009).  Although the materials addressed in these papers are not directly relevant to the petrochemical industry, the conclusions and models we present are general and in fact relevant to the petrochemical industry.

Our work has implications beyond the petrochemical industry.  For example, our work has been featured in the general science magazine New Scientist, which says “Martian dust is particularly clingy. This was noticed more than a decade ago when surprisingly large amounts stuck to the wheels of NASA's Sojourner rover. Static electricity was thought to be to blame, but no one could explain how the particles became charged. Now a team led by Keith Forward [Lacks’s graduate student] of Case Western Reserve University in Cleveland, Ohio, have an answer.” (New Scientist, July 18, 2009).