Ultrafast Proton Conduction in an Aqueous Electrolyte Confined in Adamantane-like Micropores of a Sulfonated, Aromatic Framework.

Sulfonated, cross-linked porous polymers are promising frameworks for aqueous high-performance electrolyte-host systems for electrochemical energy storage and conversion. The systems offer high proton conductivities, excellent chemical and mechanical stabilities, and straightforward water management. However, little is known about mass transport mechanisms in such nanostructured hosts. We report on the synthesis and postsynthetic sulfonation of an aromatic framework (SPAF-2) with a 3D-interconnected nanoporosity and varying sulfonation degrees. Water adsorption produces the system SPAF-2H20. It features proton exchange capacities up to 6 mequiv g-1 and exceptional proton conductivities of about 1 S cm-1. Two contributions are essential for the highly efficient transport. First, the nanometer-sized pores link the charge transport to the diffusion of adsorbed water molecules, which is almost as fast as bulk water. Second, continuous exchange between interface-bound and mobile species enhances the conductivities at elevated temperatures. SPAF-2H20 showcases how to tailor nanostructured electrolyte-host systems with liquid-like conductivities.

Quantification of photooxidative defects in weathered microplastics using 13C multiCP NMR spectroscopy.

Weathering of microplastics made of commodity plastics like polystyrene, polypropylene and polyethylene introduces polar polymer defects as a result of photooxidation and mechanical stress. Thus, hydrophobic microplastic particles gradually become hydrophilic, consisting of polar oligomers with a significant amount of oxygen-bearing functional groups. This turnover continuously changes interactions between microplastics and natural colloidal matter. To be able to develop a better understanding of this complex weathering process, quantification of the corresponding defect proportions is a first and essential step. Using polystyrene, 13C enriched at the α position to 23%, we demonstrate that 13C cross polarisation (CP) NMR spectroscopy allows for probing the typical alcohol, peroxo, keto and carboxyl defects. Even the discrimination between in- and end-chain ketones, carboxylic acids and esters as well as ketal functions was possible. Combined with multiCP excitation, defect proportions could be determined with excellent accuracy down to 0.1%. For materials with 13C in natural abundance, this accounts for a detection limit of roughly 1%. The best trade-off between measurement time and accuracy for the quantification of the defect intensities for multiCP excitation was obtained for CP block lengths shorter than 250 µs and total build-up times longer than 2 ms. Further measurement time reduction is possible by using multiCP excitation to calibrate intensities obtained from series of 13C CP MAS NMR spectra. As photooxidation is an important degradation mechanism for microplastics in the environment, we expect these parameters to be transferable for probing defect proportions of weathered microplastics in general.

Reorientational dynamics in highly asymmetric binary low-molecular mixtures-A quantitative comparison of dielectric and NMR spectroscopy results.

Previously, we scrutinized the dielectric spectra of a binary glass former made by a low-molecular high-Tg component 2-(m-tertbutylphenyl)-2'-tertbutyl-9,9'-spirobi[9H]fluorene (m-TPTS; Tg = 350 K) and low-Tg tripropyl phosphate (TPP; Tg = 134 K) [Körber et al., Phys. Chem. Chem. Phys. 23, 7200 (2021)]. Here, we analyze nuclear magnetic resonance (NMR) spectra and stimulated echo decays of deuterated m-TPTS-d4 (2H) and TPP (31P) and attempt to understand the dielectric spectra in terms of component specific dynamics. The high-Tg component (α1) shows relaxation similar to that of neat systems, yet with some broadening upon mixing. This correlates with high-frequency broadening of the dielectric spectra. The low-Tg component (α2) exhibits highly stretched relaxations and strong dynamic heterogeneities indicated by "two-phase" spectra, reflecting varying fractions of fast and slow liquid-like reorienting molecules. Missing for the high-Tg component, such two-phase spectra are identified down to wTPP = 0.04, indicating that isotropic reorientation prevails in the rigid high-Tg matrix stretching from close to Tg TPP to Tg1 wTPP. This correlates with low-frequency broadening of the dielectric spectra. Two Tg values are defined: Tg1 (wTPP) displays a plasticizer effect, whereas Tg2 (wTPP) passes through a maximum, signaling extreme separation of the component dynamics at low wTPP. We suggest understanding the latter counter-intuitive feature by referring to a crossover from "single glass" to "double glass" scenario revealed by recent MD simulations. Analyses reveal that a second population of TPP molecules exists, which is associated with the dynamics of the high-Tg component. However, the fractions are lower than suggested by the dielectric spectra. We discuss this discrepancy considering the role of collective dynamics probed by dielectric but not by NMR spectroscopy.