Understanding the Molecular Dynamics of Dual Crosslinked Networks by Dielectric Spectroscopy

The combination of vulcanizing agents is an adequate strategy to develop multiple networks that consolidate the best of different systems. In this research, sulfur (S), and zinc oxide ( ZnO) were combined as vulcanizing agents in a matrix of carboxylated nitrile rubber (XNBR). The resulting dual network improved the abrasion resistance of up to ~15% compared to a pure ionically crosslinked network, and up to ~115% compared to a pure sulfur-based covalent network. Additionally, the already good chemical resistance of XNBR in non-polar fluids, such as toluene and gasoline, was further improved with a reduction of up to ~26% of the solvent uptake. A comprehensive study of the molecular dynamics was performed by means of broadband dielectric spectroscopy (BDS) to complete the existing knowledge on dual networks in XNBR. Such analysis showed that the synergistic behavior that prevails over purely ionic vulcanization networks is related to the restricted motions of rubber chain segments, as well as of the trapped chains within the ionic clusters that converts the vulcanizate into a stiffer and less solvent-penetrable material, improving abrasion resistance and chemical resistance, respectively. This combined network strategy will enable the production of elastomeric materials with improved performance and properties on demand.

Highly Proton-Conducting Membranes Based on Poly(arylene ether)s with Densely Sulfonated and Partially Fluorinated Multiphenyl for Fuel Cell Applications

Series of partially fluorinated sulfonated poly(arylene ether)s were synthesized through nucleophilic substitution polycondensation from three types of diols and superhydrophobic tetra-trifluoromethyl-substituted difluoro monomers with postsulfonation to obtain densely sulfonated ionomers. The membranes had similar ion exchange capacities of 2.92 ± 0.20 mmol g−1 and favorable mechanical properties (Young’s moduli of 1.60–1.83 GPa). The membranes exhibited considerable dimensional stability (43.1–122.3% change in area and 42.1–61.5% change in thickness at 80 °C) and oxidative stability (~55.5%). The proton conductivity of the membranes, higher (174.3–301.8 mS cm−1) than that of Nafion 211 (123.8 mS cm−1), was the percent conducting volume corresponding to the water uptake. The membranes were observed to comprise isolated to tailed ionic clusters of size 15–45 nm and 3–8 nm, respectively, in transmission electron microscopy images. A fuel cell containing one such material exhibited high single-cell performance—a maximum power density of 1.32 W cm2 and current density of >1600 mA cm−2 at 0.6 V. The results indicate that the material is a candidate for proton exchange membranes in fuel cell applications.

Studies on the Processes of Electron Capture and Clustering of Benzyl Chloride by Ion Mobility Spectrometry

This paper presents the results of the study on the course of the benzyl chloride (BzCl) ionization process in a drift tube ion mobility spectrometer (DT IMS) in which nitrogen was used as the carrier gas. BzCl ionization follows the dissociative electron capture mechanism. The chloride ions produced in this process take part in the formation of cluster ions. Using DT IMS allows for estimation of the value of the electron attachment rate for BzCl and the equilibrium constant for the cluster ion formation. The basic experimental method used in this work was to analyze drift time spectra obtained for the introduction of the sample to the spectrometer with the drift gas. The theoretical interpretation of the results is based on the mathematical description of the ion transport. This description takes into account the phenomenon of diffusion, as well as the processes of formation and dissociation of ionic clusters occurring during the movement of ions in the drift section.

Gas-phase generation of dinuclear Au(I)-Au(II) complexes by laser desorption ionization mass spectrometry

Alkali metal chloroaurates(III) were analysed by laser desorption ionization mass spectrometry. Among a number of generated gas-phase ionic clusters, the unusual ions [MAu2Cl5]- (were M stands for Na, K, Rb, Cs) were detected. The spectra of metastable ions and quantum mechanics calculations show the presence of unprecedented Au(I)-Au(II) interactions in the clusters.

Formation and Evolution of Nanoscale Calcium Phosphate Precursors Under Biomimetic Conditions

Simulated body fluids that mimic human blood plasma are widespread media for in-vitro studies in an extensive array of research fields, from biomineralization to surface and corrosion sciences. We show that these solutions undergo dynamic nanoscopic conformational rearrangements on the timescale of minutes to hours, even though they are commonly considered stable or metastable. In particular, we find and characterize nanoscale inhomogeneities made of calcium phosphate (CaP) aggregates that emerge from homogeneous SBF within a few hours and evolve into prenucleation species (PNS) that act as precursors in CaP crystallization processes. These ionic clusters consist of about 2 nm large spherical building units that can aggregate into supra-structures with sizes of over 200 nm. We show that the residence times of phosphate ions in the PNS depend critically on the total PNS surface. These findings are particularly relevant for understanding non-classical crystallization phenomena, in which PNS are assumed to act as building blocks for the final crystal structure.<br>

Formation and Evolution of Nanoscale Calcium Phosphate Precursors Under Biomimetic Conditions

Simulated body fluids that mimic human blood plasma are widespread media for in-vitro studies in an extensive array of research fields, from biomineralization to surface and corrosion sciences. We show that these solutions undergo dynamic nanoscopic conformational rearrangements on the timescale of minutes to hours, even though they are commonly considered stable or metastable. In particular, we find and characterize nanoscale inhomogeneities made of calcium phosphate (CaP) aggregates that emerge from homogeneous SBF within a few hours and evolve into prenucleation species (PNS) that act as precursors in CaP crystallization processes. These ionic clusters consist of about 2 nm large spherical building units that can aggregate into supra-structures with sizes of over 200 nm. We show that the residence times of phosphate ions in the PNS depend critically on the total PNS surface. These findings are particularly relevant for understanding non-classical crystallization phenomena, in which PNS are assumed to act as building blocks for the final crystal structure.<br>

The many-body expansion for aqueous systems revisited: III. Hofmeister ion–water interactions

We report a Many Body Energy (MBE) analysis of aqueous ionic clusters containing kosmotropic and chaotropic anions and cations at the two opposite ends of the Hofmeister series to quantify how these ions alter the interaction between the water molecules in their immediate surroundings.