Molecular Approach to the Effect of Interfacial Energy on Growth Habit of ε-HNIW

Abstract

The present work describes how consideration of the onset of supersaturation for 2D nucleation, σ2D, is very important for prediction of the growth habit of ε-hexanitrohexaazaisowurtzitane (ε-HNIW) when the edge energy decreases extremely in solution. From ethyl acetate, the spiral growth model without considering σ2D was shown to accurately predict the polyhedral morphology of ε-HNIW, where the {110}, {101}, {111̅}, {002}, and {101̅} faces are mainly constructed. However, that model was found to be inappropriate for predicting the bipyramidal morphology of ε-HNIW from methanol because the {101} face was anticipated to dominate, but a bipyramid shape is possible only if the {101} face grows faster and finally disappears. The present simulation results show that the edge energy of the {101} face is considerably reduced from methanol by forming a hydrogen bond. This gives rise to a decrease in the σ2D compared with the growth of ε-HNIW from ethyl acetate, which means that the {101} face has a relatively high probability to grow faster by 2D nucleation. As a consequence, a parameter of σ2D enables us to exclude the morphologically unimportant faces among flat-faces by determining which face tends to grow faster by 2D nucleation.