Rapid and robust sensing of nerve agent (NA) threats is necessary for real-time field detection to facilitate timely countermeasures. Unlike conventional phosphotriesterases employed for biocatalytic NA detection, this work describes the use of a new, green, thermally stable, and biocompatible zirconium metal–organic framework (Zr-MOF) catalyst, MIP-202­(Zr). The biomimetic Zr-MOF-based catalytic NA recognition layer was coupled with a solid-contact fluoride ion-selective electrode (F-ISE) transducer, for potentiometric detection of diisopropylfluorophosphate (DFP), a F-containing G-type NA simulant. Catalytic DFP degradation by MIP-202­(Zr) was evaluated and compared to the established UiO-66-NH2 catalyst. The efficient catalytic DFP degradation with MIP-202­(Zr) at near-neutral pH was validated by 31P NMR and FT-IR spectroscopy and potentiometric F-ISE and pH-ISE measurements. Activation of MIP-202­(Zr) using Soxhlet extraction improved the DFP conversion rate and afforded a 2.64-fold improvement in total percent conversion over UiO-66-NH2. The exceptional thermal and storage stability of the MIP-202/F-ISE sensor paves the way toward remote/wearable field detection of G-type NAs in real-world environments. Overall, the green, sustainable, highly scalable, and biocompatible nature of MIP-202­(Zr) suggests the unexploited scope of such MOF catalysts for on-body sensing applications toward rapid on-site detection and detoxification of NA threats.

The fracture-healing behavior of model physically associating triblock copolymer gels was investigated with experiments coupling shear rheometry and particle tracking flow visualization. Fractured gels were allowed to rest for specific time durations, and the extent of strength recovered during the resting time was quantified as a function of temperature (20−28°C) and gel concentration (5−6 vol %). Measured times for full strength recovery were an order of magnitude greater than characteristic relaxation times of the system. The Arrhenius activation energy for post-fracture strength recovery was found to be greater than the activation energy associated with stress relaxation, most likely due to the entropic barrier related to the healing mechanism of dangling chain reassociation with network junctions. S oft materials with well-defined mechanical properties are important in a variety of industrial and biomedical applications, including high toughness elastomers for seals and dampers, 1 hydrogels for synthetic cartilage, 2 hemostatic materials for wound dressing, 3 injectable materials for regenerative medicine, 4,5 and superabsorbent polymer hydrogels for applications as diverse as drug delivery to cement internal curing agents. 6 To exhibit optimum performance in these applications, the material's mechanical response to large applied deformations and their ability to heal following damage must be well understood. However, these nonlinear mechanical properties are difficult to characterize for soft materials using traditional experimental techniques. Standard tension and compression mechanical tests require self-supported samples and are thus not appropriate for materials that have fast relaxation times or contain large amounts of solvent.Recent work has shown shear rheometry to be an effective technique for characterizing the nonlinear deformation and fracture of soft materials. 7−10 To correlate the measured rheological response with the sample's macroscale behavior (e.g., formation of a fracture plane), rheophysical experiments are performed to simultaneously measure the local velocity profile during shear by employing a variety of techniques, including optical particle tracking, 11 ultrasonic velocimetry, 12 and NMR. 13 In this letter, we describe a rheophysical methodology for quantifying the fracture and self-healing behavior of a soft material. A temperature-dependent, physically associating polymer gel will be utilized as a model soft material. Shear rheometry coupled with an optical particle tracking system was used to directly observe the shear-induced formation and subsequent healing of the fracture plane within the material. Compared to the characteristic stress relaxation behavior, fracture-healing occurred over much greater time scales but with similar temperature dependence. Activation energy for healing was found to be greater than for relaxation, most likely due to the entropic barrier required for a chain to reassociate with a network junction.The model soft material is composed of triblock co...

No abstract