Solvent diffusion mechanism of gun propellant revealed through molecular dynamics simulation

Abstract

Drying is an important operational unit in the preparation of nitrocellulose-based gun propellant, which affects the drying quality and drying rate of the product. The diffusion properties of solvents during the drying process determine the rate of internal solvent removal from the gun propellant, so the diffusion behaviors of ethanol and acetone in the gun propellant were investigated based on molecular dynamics simulations. Three models of single-, double- and triple-base gun propellant components were established, and the interactions between the solvent and the components of gun propellant were investigated by radial distribution function, hydrogen bonding and interaction energy calculations, and the free volumes, diffusion coefficients and the activation energies of the solvents were used to describe the solvent diffusion performances. The results showed that the interaction between ethanol and the components of the gun propellant was mainly hydrogen bonding, and the interaction between acetone and the components was mainly van der Waals forces. When the mass ratio of ethanol and acetone is 1:1, the interaction energy between ethanol and the components is greater due to the presence of strong hydrogen bonding, which resulted in a higher diffusion activation energy of ethanol. However, since the molecular volume of ethanol is higher than that of acetone, it makes the diffusion coefficient of ethanol larger. Compared with single-base gun propellant, after adding nitroglycerin and nitroguanidine, the free volume fraction decreases, the sum of the interaction energies between the solvent and the components in gun propellant increases, and the diffusion activation energy increases. Hence, this present work regarding the study of solvent diffusion mechanism of gun propellant can provide theoretically guiding suggestion to the actual drying process and manufacture of gun propellant.