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Sensitivity and the available free space per molecule in the unit cell
Miroslav Pospíšil1, Pavel Vávra, Monica C Concha
1Faculty of Mathematics and Physics, Charles University, Ke Karlovu 3, 12116 Prague 2, Czech Republic.
Journal of Molecular Modeling
|January 14, 2011
Summary
This study links molecular free space (ΔV) to impact sensitivity in energetic materials. Larger ΔV generally increases sensitivity, though specific chemical structures like nitramines show weaker dependence.
Area of Science:
- Materials Science
- Physical Chemistry
- Crystallography
Background:
- Impact sensitivity is a critical safety parameter for energetic materials.
- Molecular compressibility and packing efficiency are known to influence sensitivity.
- Previous studies suggested a preliminary link between free space and sensitivity.
Purpose of the Study:
- To quantitatively investigate the relationship between available free space per molecule (ΔV) and impact sensitivity.
- To define and calculate the intrinsic molecular volume (V(int)) using electronic density contours.
- To establish a predictive model for impact sensitivity based on molecular packing.
Main Methods:
- Calculating ΔV as the difference between effective volume (V(eff)) and intrinsic molecular volume (V(int)).
- Defining V(int) based on the 0.003 au electronic density contour.
- Correlating measured impact sensitivities with calculated ΔV values for various compounds.
Main Results:
- A general trend of increasing impact sensitivity with larger ΔV was observed.
- Packing coefficients derived from the V(int) definition align with crystallographic data.
- Nitramines and organic azides exhibit a weak dependence on ΔV, suggesting dominant initiation mechanisms.
Conclusions:
- Available free space per molecule (ΔV) is a significant factor influencing impact sensitivity.
- The electronic density contour method provides a reliable measure of V(int).
- The study enables rough estimations of impact sensitivity for unknown compounds.
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