Crystallization of ammonium perchlorate from solution confined to native and organically modified silica nanopores

Abstract

The crystallization of ammonium perchlorate from a methanol/water solution confined to native and organically modified silica nanopores is analyzed by differential scanning calorimetry. The effects of nanoconfinement on the salt crystallization are primarily due to the surface interactions with the nanopores’ walls. The process in the native nanopores occurs at markedly lower temperature and with much larger heat relative to the bulk, which is linked to adsorption of the salt ions on the surface of the native nanopores. The process in organically modified pores also demonstrates predominantly a surface effect, revealed in larger crystallization temperature and smaller crystallization heat relative to the bulk. This is proposed to be due to a phase separation of the methanol/water solution inside the hydrophobic nanopores, so that the crystallization occurs from the methanol phase. Additional insights into the crystallization process have been obtained by analysis of the isoconversional activation energies of the process.