  High energy density is always a key goal for developments of energy storage
or energetic materials (EMs). Except exploring novel EMs with high chemical
energy, it is also desirable if the traditional EMs could be assembled at a
higher density. However, it is very difficult to surpass their theoretical
maximum molecular packing density under ambient conditions, even though a
higher density could be achieved under ultra-high pressure (Gigapascals). Such
solid-state phase changes are reversible, and hence this high density packing
is not able to maintain under ambient conditions. Alternatively, in this
research, we demonstrated a molecular level compression effect by stacking of
2-D TAGP, resulting in a higher density packing of the HMX molecules with
changed conformation. The HMX crystal formed under compression in the solvent
has a unit cell parameter very close to the reported one observed under
pressure of 0.2 GPa. It shows that the compressed HMX molecules are trapped in
the TAGP layers, resulting in a higher density (e.g. 2.13 g cm-3) and also
higher heat of formation. The resulted HMX crystals are free of defects, and
unlike the pristine HMX, no polymorphic transition and melting point were
observed upon heating. Experiments and relevant calculations show that the best
resulted hybrid HMX crystal has a detonation velocity of 10.40 km s-1 and
pressure of 53.9 GPa, respectively. Its ground specific impulse reaches about
292 s, even much better than CL-20, making it a promising propellant component
for future space explorations.
