Pronounced sponge-like nanostructure in propylammonium nitrate.

The bulk structure of the ionic liquid propylammonium nitrate (PAN) has been determined using neutron diffraction. Empirical potential structure refinement (EPSR) fits to the data show that PAN self-assembles into a quasi-periodic bicontinuous nanostructure reminiscent of an amphiphile L(3)-sponge phase. Atomic detail on the ion arrangements around the propylammonium cation and nitrate anion yields evidence of hydrogen bonding between ammonium and nitrate groups and of strong alkyl chain aggregation and interdigitation. The resultant amphiphilic PAN nanostructure is more pronounced than that previously determined for ethylammonium nitrate (EAN) or ethanolammonium nitrate (EtAN).