Novel transport phenomena through nanopores are expected to emerge as their diameters approach subnanometer scales. However, it has been challenging to explore such a regime experimentally. Here, this study reports on polymer subnanometer pores exhibiting unique selective ionic transport. 12 μm long, parallel oriented polymer nanopores are fabricated in polyethylene terephthalate (PET) films by irradiation with GeV heavy ions and subsequent 3 h exposure to UV radiation. These nanopores show ionic transport selectivity spanning more than 6 orders of magnitude: the order of the transport rate is Li+>Na+>K+>Cs+>>Mg2+>Ca2+>Ba2+, and heavy metal ions such as Cd2+ and anions are blocked. The transport can be switched off with a sharp transition by decreasing the pH value of the electrolyte. Structural measurements and molecular dynamics simulations suggest that the ionic transport is attributed to negatively charged nanopores with pore radii of ≈0.3 nm, and the selectivity is associated with the dehydration effect.

The great potential of nanoporous membranes for water filtration and chemical separation has been challenged by the trade-off between selectivity and permeability. Here we report on nanoporous polymer membranes with an excellent balance between selectivity and permeability of ions. Our membranes are fabricated by irradiating 2-μm-thick polyethylene terephthalate Lumirror® films with GeV heavy ions followed by ultraviolet exposure. These membranes show a high transport rate of K+ ions of up to 14 mol h−1 m−2 and a selectivity of alkali metal ions over heavy metal ions of >500. Combining transport experiments and molecular dynamics simulations with a polymeric nanopore model, we demonstrate that the high permeability is attributable to the presence of nanopores with a radius of ~0.5 nm and a density of up to 5 × 1010 cm−2, and the selectivity is ascribed to the interaction between the partially dehydrated ions and the negatively charged nanopore wall.

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Fluctuation of ion current, between a high conductance and a low conductance state, through biological ion channels and pores is assumed to arise from conformational changes between an "open" and a "closed" configuration. Here we offer an additional mechanism that arises from changes in ionization of fixed charges within, or at the mouth of, a channel or pore. Our hypothesis, which is based on measurements of ion selectivity alongside ion current, applies to pores through some synthetic membranes and through channels-such as those created by certain toxins-that remain (at least partially) open in the low conductance state. It may also explain the phenomena of "open channel noise" and "substate behavior" that characterize several endogenous ion channels and should be considered when modeling the behavior of such channels.

Membranes are widely used in modern technology. The demand for different types of membranes and membrane processes is increasing every year. This review summarizes the current state of the art and prospects of membrane science developments including membrane materials for gas separation, pervaporation, and pressure-driven membrane processes; ion-exchange, hybrid, and track-etched membranes; membranes for electrochemical sensors; and mathematical modeling of membrane separation processes and ion and water transport in membrane systems. Studies aimed at improving the selectivity and performance of membranes and their stability are surveyed. New approaches to the synthesis and modification of membranes as well as their advanced applications are discussed.

Understanding of the current density distribution over an electrically heterogeneous surface and its effect on ion transport represents an important issue in electrochemistry, composite materials, geophysics, and some other domains. We report an approach for three-dimensional (3D) modeling (with cylindrical symmetry) of transient ion transfer across a surface composed of conductive and nonconductive areas. In the model formulation and solution we use the electrical current stream function. It allows setting the integral boundary condition for electric current at a heterogeneous surface without any restrictions on the local current density distribution. A very good agreement is found between the numerical solution and the experimental transition time determined from chronopotentiograms. The use of a specially designed membrane allows computation without fitted parameters. We show that the application of specific simplifications for the current density distribution over the surface (uniform distribution throughout all the surface or its conductive area, neglect of tangential current density) results in essential deviations from experimental transition time.

A combination of a long exposure to ultraviolet (UV) radiation and the extraction of radiolysis and photolysis products from tracks makes it possible to create ion-selective membranes from polyethylene terephthalate (PET) films irradiated with heavy ions. These membranes exhibit high selectivity for singly charged cations and high transport characteristics in the electrodialysis mode. The aim of this study is to analyze the mechanisms of the transformation of latent tracks into a system of through pores of the subnanometer range in more detail. Polyethylene terephthalate films are irradiated with accelerated Xe and Bi ions with energy losses in the polymer of 11 and 18 keV/nm, respectively. The evolution of the free volume and the accumulation of carboxyl groups in the irradiated films at different stages of the treatment are studied using gravimetry, IR and UV spectroscopy, conductometry, and electron microscopy methods. It is found that the properties of the resulting membranes depend on several critical parameters, which include, in addition to temperature during extraction, the energy loss of the bombarding ion, the pH of the solution used for extraction, and ion fluence. Dramatic changes in the membrane properties are observed at ion fluences at which individual tracks begin to overlap.

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