Composite polytetrafluoroethylene–poly(4-vinylpyridine) membranes for protection against phosphonate-based cholinesterase inhibitors

An expanded polytetrafluoroethylene (ePTFE) membrane was modified with an interpenetrating network of cross-linked poly(4-vinylpyridine) (PVP), a pH-responsive, nucleophilic polymer. Stirred reactor testing performed in buffered acidic conditions confirmed that PVP is a suitable catalyst to break down diisopropyl fluorophosphate (DFP), a commonly used nerve agent surrogate. The presence of the PVP interpenetrating network on the ePTFE membrane was established using Raman spectroscopy and thermogravimetric analysis. Goniometric measurements of average contact angles greater than 120° performed post-modification confirmed that the ePTFE membrane retained its hydrophobic properties. Utility of the ePTFE/PVP membrane was assessed by subjecting samples to DFP vapor permeation using the vial-in-vial method. The pH response of modified membranes having PVP loadings high enough to enable penetration of water was tested using cyclic voltammetry and electrochemical impedance spectroscopy. Changes in peak current and electron transfer resistance, R _ET, corresponding with pH revealed that the ePTFE/PVP membranes are potential candidates for self-decontamination and electrochemical sensing. Finally, nanoscale characterization of the responsive membranes using atomic force microscopy was performed via the Derjaguin approximation, which treats the surface-confined polymer as a brush. Analysis established that the average brush length increased from 60 to 70 nm in response to a pH decrease from 7 to 4.