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1. Self‐Diffusion of a Chemical Warfare Agent Simulant and Water in Nafion by Pulsed Field Gradient NMR 

   https://doi.org/10.1002/cite.202300010  

   Trusty, Blake ; Fang, Junchuan ; Angelopoulos, Anastasios ; Vasenkov, Sergey ( July 2023 , Chemie Ingenieur Technik)

   Pulsed field gradient (PFG) NMR at high magnetic field was used to study microscopic diffusion of dimethyl methyl phosphonate (DMMP), a common chemical warfare agent (CWA) simulant, and water in Nafion membranes. PFG NMR measurements were performed for a broad range of molecular displacements. The self‐diffusivities were measured as a function of the DMMP concentration for several fixed water concentrations. The measured data suggest that DMMP and water diffuse in different regions of Nafion. While water mostly diffuses in hydrophilic regions of the membrane, viz. water channels, DMMP diffusion is mostly limited to interfacial perfluoroether regions between these water channels and the semi‐crystalline matrix.

    

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2. Potentials and challenges of high-field PFG NMR diffusion studies with sorbates in nanoporous media

   https://doi.org/10.1007/s10450-020-00255-y  

   Baniani, Amineh ; Berens, Samuel J. ; Rivera, Matthew P. ; Lively, Ryan P. ; Vasenkov, Sergey ( August 2020 , Adsorption)

   High magnetic fields (up to 17.6 T) in combination with large magnetic field gradients (up to 25 T/m) were successfully utilized in pulsed field gradient (PFG) NMR studies of gas and liquid diffusion in nanoporous materials. In this mini-review, we present selected examples of such studies demonstrating the ability of high field PFG NMR to gain unique insights and differentiate between various types of diffusion. These examples include identifying and explaining an anomalous relationship between molecular size and self-diffusivity of gases in a zeolitic imidazolate framework (ZIF), as well as revealing and explaining an influence of mixing different linkers in a ZIF on gas self-diffusion. Different types of normal and restricted self-diffusion were quantified in hybrid membranes formed by dispersing ZIF crystals in polymers. High field PFG NMR studies of such membranes allowed observing and explaining an influence of the ZIF crystal confinement in a polymer on intra-ZIF self-diffusion of gases. This technique also allowed measuring and understanding anomalous single-file diffusion (SFD) of mixed sorbates. Furthermore, the presented examples demonstrate a high potential of combining high field PFG NMR with single-crystal Infrared Microscopy (IRM) for obtaining greater physical insights into the studied diffusion processes. 

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3. Role of nanoparticle size and surface chemistry on ion transport and nanostructure of perfluorosulfonic acid ionomer nanocomposites

   https://doi.org/10.1039/d1sm01573g  

   Domhoff, Allison ; Wang, Xueting ; Silva, Mayura S. ; Creager, Stephen ; Martin, Tyler B. ; Davis, Eric M. ( May 2022 , Soft Matter)

   Herein, we present a systematic investigation of the impact of silica nanoparticle (SiNP) size and surface chemistry on the nanoparticle dispersion state and the resulting morphology and vanadium ion permeability of the composite ionomer membranes. Specifically, Nafion containing a mass fraction of 5% silica particles, ranging in nominal diameters from 10 nm to >1 μm and with both sulfonic acid- and amine-functionalized surfaces, was fabricated. Most notably, an 80% reduction in vanadium ion permeability was observed for ionomer membranes containing amine-functionalized SiNPs at a nominal diameter of 200 nm. Further, these membranes exhibited an almost 400% increase in proton selectivity when compared to pristine Nafion. Trends in vanadium ion permeability within a particular nominal diameter were seen to be a function of the surface chemistry, where, for example, vanadyl ion permeability was observed to increase with increasing particle size for membranes containing unfunctionalized SiNPs, while it was seen to remain relatively constant for membranes containing amine-functionalized SiNPs. In general, the silica particles tended to exhibit a higher extent of aggregation as the size of the particles was increased. From small-angle neutron scattering experiments, an increase in the spacing of the hydrophobic domains was observed for all composite membranes, though particle size and surface chemistry were seen to have varying impacts on the spacing of the ionic domains of the ionomer. 

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4. Covalently functionalized uniform amino-silica nanoparticles. Synthesis and validation of amine group accessibility and stability

   https://doi.org/10.1039/c9na00772e  

   Miller, Peter J. ; Shantz, Daniel F. ( February 2020 , Nanoscale Advances)

   This paper describes the synthesis and characterization of colloidally stable, 18 nm silica nanoparticles that are functionalized with amine groups. Electron microscopy, small-angle X-ray scattering (SAXS), and dynamic light scattering show the amine grafting does not impact particle size. SAXS and DLS confirm the particles do not aggregate at 10 mg mL −1 and pH 2 for 30 days. Ninhydrin analysis, fluorescamine binding, and NMR studies of carboxylic acid binding show that the amines are present on the surface and accessible with maximum loading calculated to be 0.14 mmol g −1 . These materials should find a range of use in nanotechnology applications. 

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5. In situ quasi-elastic neutron scattering study on the water dynamics and reaction mechanisms in alkali-activated slags

   https://doi.org/10.1039/c9cp00889f  

   Gong, Kai ; Cheng, Yongqiang ; Daemen, Luke L. ; White, Claire E. ( May 2019 , Physical Chemistry Chemical Physics)

   null (Ed.)

   In this study, in situ quasi-elastic neutron scattering (QENS) has been employed to probe the water dynamics and reaction mechanisms occurring during the formation of NaOH- and Na 2 SiO 3 -activated slags, an important class of low-CO 2 cements, in conjunction with isothermal conduction calorimetry (ICC), Fourier transform infrared spectroscopy (FTIR) analysis and N 2 sorption measurements. We show that the single ICC reaction peak in the NaOH-activated slag is accompanied with a transformation of free water to bound water (from QENS analysis), which directly signals formation of a sodium-containing aluminum-substituted calcium–silicate–hydrate (C–(N)–A–S–H) gel, as confirmed by FTIR. In contrast, the Na 2 SiO 3 -activated slag sample exhibits two distinct reaction peaks in the ICC data, where the first reaction peak is associated with conversion of constrained water to bound and free water, and the second peak is accompanied by conversion of free water to bound and constrained water (from QENS analysis). The second conversion is attributed to formation of the main reaction product ( i.e. , C–(N)–A–S–H gel) as confirmed by FTIR and N 2 sorption data. Analysis of the QENS, FTIR and N 2 sorption data together with thermodynamic information from the literature explicitly shows that the first reaction peak is associated with the formation of an initial gel (similar to C–(N)–A–S–H gel) that is governed by the Na + ions and silicate species in Na 2 SiO 3 solution and the dissolved Ca/Al species from slag. Hence, this study exemplifies the power of in situ QENS, when combined with laboratory-based characterization techniques, in elucidating the water dynamics and associated chemical mechanisms occurring in complex materials, and has provided important mechanistic insight on the early-age reactions occurring during formation of two alkali-activated slags. 

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