Polyamide is the key material in modern membrane desalination; however, its well-known and incompletely understood drawback is its low tolerance to chlorine, the most efficient in-line disinfectant. Here we report a first investigation of the mechanism and kinetics of chlorine attack using electrochemical impedance spectroscopy (EIS) that directly probes changes in ion permeation upon chlorination at different pH values, focusing on its early stages and low chlorine concentrations (15–197 ppm). EIS results partly conform to an established two-stage mechanism that proceeds as N-chlorination followed by either C-chlorination in acidic conditions or amide bond scission in alkaline conditions. However, early time kinetics in acidic conditions shows inconsistencies with this model, explained by possible effects of direct ring chlorination and finite polymer relaxation rates. The findings indicate that (a) N-chlorination reduces membrane polarity and ion permeability, while C-chlorination has an opposite effect; (b) chlorination in acidic conditions must involve other reactions, such as direct ring chlorination, in addition to N-chlorination and Orton rearrangement; and (c) the ultimate chemical transformations (C-chlorination or amide bond scission) result in an irreversible increase in membrane polarity and loss of ion rejection. The results highlight the potential of EIS as a powerful and sensitive tool for studying chemical degradation of ion-selective materials that may assist in developing new chlorine-resistant membranes.

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CMOS-like circuits in bioelectronics translate biological to electronic signals using organic electrochemical transistors (OECTs) based on organic mixed ionic-electronic conductors (OMIECs). Ambipolar OECTs can reduce the complexity of circuit fabrication, and in bioelectronics have the major advantage of detecting both cations and anions in one device, which further expands the prospects for diagnosis and sensing. Ambipolar OMIECs however, are scarce, limited by intricate materials design and complex synthesis. Here we demonstrate that judicious selection of p- and n-type materials for blend-based OMIECs offers a simple and tunable approach for the fabrication of ambipolar OECTs and corresponding circuits. These OECTs show high transconductance and excellent stability over multiple alternating polarity cycles, with ON/OFF ratios exceeding 103 and high gains in corresponding inverters. This work presents a simple and versatile new paradigm for the fabrication of ambipolar OMIECs and circuits with little constraints on materials design and synthesis and numerous possibilities for tunability and optimization towards higher performing bioelectronic applications.

An approach is suggested to describe the solvophobic effects in various solvents, qualitatively and quantitatively. We analyzed the relationships between the Gibbs energies and enthalpies of solvation of alkanes in various solvents on the basis of existing experimental data. It is shown that for a large group of solvents, there is a linear correlation between the two quantities. Other solvents, primarily self-associated, show deviations from this line. These deviations are always positive, leading to a decrease in solubility, and can be used as a measure of the strength of the solvophobic effects. It is also shown that the solvophobic effects is not the only factor determining the solubility, even for alkane solutes. The magnitudes of contributions of the solvophobic effect into the Gibbs energies of solvation of various compounds in monohydric alcohols are determined. These magnitudes are found to be linearly correlated with a characteristic molecular volume of a solute. The slope of correlation grows up with the concentration of hydrogen bonds in the liquid solvent.

Polyamide reverse osmosis (RO) membranes have been a "golden standard" in water desalination, with an aromatic polyamide layer providing an excellent balance between salt rejection and water permeability. Yet, there still are gaps in understanding the salt transport in RO, closely related to the nature and formation of membrane charge and its effect on ion permeation. We report here a systematic investigation that examines the correlation between the nominal membrane charge, determined by ion-binding methods, and key ion permeation characteristics, salt permeability, and membrane conductivity, at different pH values. In the mid-pH range, the most important in the desalination practice, observed relations between the conductivity, salt permeability and nominal charge show a much weaker dependence than the Donnan model predicts. This indicates that fixed charged groups inside polyamide films are largely deactivated, thereby the membrane behaves as effectively neutral or weakly charged. However, a substantial charge may form at extreme acidic and basic pH via uptake of H + and OH − ions, which increases ion uptake and conductivity, promoting polymer swelling and weakening salt rejection. Overall, the results strongly suggest that fixed charges weakly affect salt rejection in RO, and it is dominated by dielectric and steric mechanisms.