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We report oscillations of current which accompany anodic deposition from Mn(II) solutions in a neutral acetic buffer and also cathodic birnessite deposition from alkaline permanganate solutions. We demonstrate that for both processes, oscillations appear at high enough overpotentials. The current oscillations are affected by solution convection. The results of rotating disc electrode experiments favor mixed control, with higher diffusion contribution in case of cathodic deposition. Electron microscopy combined with electron and X-ray diffraction and coulometric analysis is applied to assign oscillations to certain morphological features of the deposits. A pronounced difference in microstructure is found for anodic and cathodic deposits formed under oscillating growth conditions: "anodic" birnessite consists of parallel layers of small crystals, whereas "cathodic" birnessite is globular. This difference is interpreted with account for specific crystallographic features. Namely, the more ordered birnessite lattice formed by reduction of permanganate favors a preferentially lateral growth of thin lamellas, in contrast to birnessite having a pronounced interplane distortion, formed in the course of anodic deposition. We assign the periodic current decrease to diffusion limitations in growing porous layers and assume that the subsequent current increase in each period corresponds to dendrite-like growth of a low number of crystals located in the outer diffusion layer. [ABSTRACT FROM AUTHOR]

Abstract: Membranes of a Simplex type with diffusion layers from sulfoethyl cellulose (SEC) and chitosan were investigated. Aromatic poly (amide imide) (PAI-O) synthesized by the low-temperature polycondensation from dicarboxyphenylphtalimide dichloranhydride and 4,4′-diaminodiphenyl ether was used for the support preparation of the composite membrane. Porous support films with an average pore size in the skin layer of 8 nm, were obtained from PAI-O under conditions of a phase-inversion process. Transport characteristics of membrane samples obtained were tested in processes of the aqueous ethanol pervaporation. All membranes are selective in the isolation of water from 96 wt% ethanol solution. In the case of the SEC layer at the top of composite membrane the selectivity is very high and a water concentration in the permeate reaches 100 wt%. The most selective membranes contained PEC based on counter-ions with the same degree of substitution of hydroxyl groups. The structure and morphological features of multilayer films studied by X-ray diffraction method, scanning electron microscopy and energy-dispersive X-ray microanalysis were discussed in view of a ratio of ionogenic groups of polyelectrolytes and a concentration of their solutions. The boundary of the counterion layers was visualized, as well as the polyelectrolyte complex (PEC). A formation of the PEC layer in the film obtained on a glass plate was shown to occur with the ordering of chitosan chains resulting both hydrated and anhydrous polymorphs, while the formation of the same film on the PAI-O substrate led only to the anhydrous form of chitosan.Graphical abstract: [ABSTRACT FROM AUTHOR]

The structure of porphyrin-fullerene dyad ZnDHD6ee monolayers formed on the surface of aqueous subphase in a Langmuir trough and transferred onto solid substrates has been studied. The data obtained are interpreted using simulation of the structure of isolated molecules and their packing in monolayer and modeling of diffraction patterns from molecular aggregates having different sizes and degrees of order. Experiments on the formation of condensed ZnDHD6ee monolayers are described. The structure of these monolayers on a water surface is analyzed using π-A isotherms. The structure of the monolayers transferred onto solid substrates is investigated by electron diffraction and atomic force microscopy. The unit-cell parameters of two-dimensional domains, which are characteristic of molecular packing in monolayers and deposited films, are determined. Domains are found to be organized into a texture (the molecular axes are oriented by the [001] direction perpendicular to the substrate). The monolayers contain a limited number of small 3D domains. [ABSTRACT FROM AUTHOR]