(501d) Influence of Nanoconfinement on the Degradation of CL-20 and HMX

Nanoconfinement refers to a state in which materials are confined to regions below 100 nm in a single dimension, resulting in dramatic deviations from their typical bulk behavior. In particular, the melting point of materials under nanoconfinement are typically reduced. A common approach to investigate nanoconfinement is to load materials into a controlled pore glass (CPG), usually via melting. For example, the melting point depression of pentaerythritoletranitrate (PETN) and trinitrotoluene (TNT) was shown by McKenna and co-workers [1, 2] to decrease by ~22 and 27 ^oC, respectively, upon nanoconfinement within CPGs whose interior pore diameter was 8.1 nm. Similar results, although to a lesser extent, were observed for CPGs with larger pore diameters up to 70 nm. The goal of the current work is to perform a thermal analysis of hexanitrohexaazaisowurtzitane (CL-20) and cyclotetramethylenetetranitramine (HMX) upon nanoconfinement within CPGs. The samples were loaded into two different CPG nanoporous materials for the calorimetric study. Currently, the melting temperature of CL-20, even under nanoconfinement, remains elusive due to decomposition. We had initially hypothesized that nanoconfined CL-20 would yield a reduction in its melting point to a temperature before the onset of decomposition. However, nanoconfined CL-20 is found to decompose at lower temperatures than in the bulk material resulting in the onset temperature for decomposition decreasing with decreasing pore size. The results suggest an increase in CL-20’s sensitivity upon nanoconfinement. Future works aim to characterize the degradation behavior of CL-20, HMX, and a mixture of CL-20 and HMX in nanoconfinement.

[1] B. Xu, X. Di and G.B. McKenna, "Melting of pentaerythritol tetranitrate (PETN) nanoconfined in controlled pore glasses (CPG)," J. Thermal Analysis and Calorimetry, 113, 539-543 (2013).

[2] X. Di, B. Xu and G.B. McKenna, "The melting behavior of trinitrotoluene nanoconfined in controlled pore glasses," J. Thermal Analysis and Calorimetry, 113, 533-537 (2013).