Viscosity and density of organophosphorus liquids and their aqueous solutions

Abstract

Dimethyl methyl phosphonate (DMMP) and diisopropyl methyl phosphonate (DIMP) are surrogates for chemical warfare agents (CWAs). Their density and viscosity need to be known to design and interpret theoretically laboratory tests describing how CWAs interact with contaminated surfaces. Aqueous CWA solutions form when they come in contact with liquid or evaporated water. Quantifying densities and viscosities of such solutions is important for both interpreting relevant laboratory or field tests and designing decontamination and remediation protocols. Here, densities and viscosities of commercially available DMMP and DIMP and their aqueous solutions are measured. The effect of temperature on viscosity of DIMP and DMMP is quantified. Aqueous solutions for both DMMP and DIMP do not behave as ideal. Their viscosities peak at the mole fractions of xDMMP≈0.35 and xDIMP≈0.3. The infrared absorption spectroscopy suggests that this non-ideality is primarily due to the interaction between the P = O groups of the organophosphorus liquids and the hydroxyl groups of water. Those finding will help understanding the structure and designing predictive molecular models for CWAs, their surrogates, and their aqueous solutions. Reported data can also be directly used in simplified models describing the fate of chemical weapon agents and their surrogates in various practical scenarios.