Agent-to-Simulant Relationships for Vapor Emission from Absorbing Materials

Abstract

When using a simulant to predict the behavior of a chemical warfare agent (CWA), it is not always possible to sufficiently match all relevant properties, and the use of an agent-to-simulant relationship is required. The objective of the agent-to-simulant relationship developed here is to enable the prediction of vapor emission rate of a CWA from a polymer given an experimental measurement of the vapor emission rate of a simulant from the polymer. Vapor emission experiments for the CWA sulfur mustard (HD) and the simulants methyl salicylate (MeS) and 2-chloroethyl ethyl sulfide (CEES) absorbed in the polymers silicone and polydimethylsiloxane (PDMS) were carried out to verify the theoretical predictions. It was found that the agent-to-simulant relationship holds if the initial dimensionless concentration distributions and Biot numbers in the polymer are similar for the agent and simulant. The mathematical agent-to-simulant relationship also provides guidance on the critical properties to match in simulant selection.

Vapor Sorption–Desorption Phenomena of HD and GB Simulants from Polyurethane Thin Films on Aluminum Oxide via a Quartz Crystal Microbalance

“…Desorption diffusion coefficients from this work fell within the range of HD and GB simulant values reported for other polymer systems and was also similar to literature values of HD and GB agents from alkyds and polyurethanes. − ,− While some variation between values is expected due to differences in polymer substrates and their permeability, ,, the results from the QCM method used in this work generally aligned well with previous studies. Of note, the desorption coefficients were several orders of magnitude larger than the sorption coefficients.…”

“…A CWA simulant exposure time of 60 min was chosen for consistency with other studies. 7,13 As evident from Figure 2, the resonant Though not readily apparent, the frequency for the bare aluminum oxide sensor without polyurethane coating did decrease slightly upon exposure to DMMP. While few studies have used DCP as a simulant, DMMP is known to irreversibly adsorb to the surface of aluminum oxide.…”

“…A CWA simulant exposure time of 60 min was chosen for consistency with other studies. 7 , 13 As evident from Figure 2 , the resonant frequency significantly decreased upon injection of the CWA simulant into the sample reservoir, indicating vapor uptake. Though not readily apparent, the frequency for the bare aluminum oxide sensor without polyurethane coating did decrease slightly upon exposure to DMMP.…”

“…Much of the literature on CWAs has focused on detection and decontamination, ,, while relatively few studies have studied the mass uptake and transport of CWAs into polymers and paints. ,,− More often, these studies instead use less toxic CWA simulants to model the sorption and desorption behavior of an agent. ,− In these works, desorption diffusion coefficients are usually determined by exposing a surface to a liquid chemical agent or simulant for about an hour, removing the liquid, and then measuring vapor off-gassing from the surface as a function of mass loss over time. ,,,− Desorption diffusion coefficients for HD and GB vapor from polyurethane and alkyd films were generally on the order of 10 –10 to 10 –11 cm 2 /s, respectively. , Likewise, the desorption diffusion coefficients for HD simulants ranged from 10 –7 to 10 –10 cm 2 /s, while GB simulant values ranged from 10 –9 to 10 –15 cm 2 /s. ,,− The range of values for the desorption diffusion coefficients across the literature is attributed primarily to differences in the types of polymer substrates as the uptake and mass transport of CWAs and CWA simulants in each substrate will vary depending on the intermolecular attractions and permeability of the system. ,, …”