Modeling the Conductivity and Diffusion Permeability of a Track-Etched Membrane Taking into Account a Loose Layer.

The microheterogeneous model makes it possible to describe the main transport properties of ion-exchange membranes using a single set of input parameters. This paper describes an adaptation of the microheterogeneous model for describing the electrical conductivity and diffusion permeability of a track-etched membrane (TEM). Usually, the transport parameters of TEMs are evaluated assuming that ion transfer occurs through the solution filling the membrane pores, which are cylindrical and oriented normally to the membrane surface. The version of the microheterogeneous model developed in this paper takes into account the presence of a loose layer, which forms as an intermediate layer between the pore solution and the membrane bulk material during track etching. It is assumed that this layer can be considered as a "gel phase" in the framework of the microheterogeneous model due to the fixed hydroxyl and carboxyl groups, which imparts ion exchange properties to the loose layer. The qualitative and quantitative agreement between the calculated and experimental concentration dependencies of the conductivity and diffusion permeability is discussed. The role of the model input parameters is described in relation to the structural features of the membrane. In particular, the inclination of the pores relative to the surface and their narrowing in the middle part of the membrane can be important for their properties.

Superhydrophobic copper in biological liquids: Antibacterial activity and microbiologically induced or inhibited corrosion.

The bactericidal activity of copper and copper alloys is well appreciated and was already exploited in medical practice in 19th century. However, despite of being an essential nutrient required by organisms to perform life functions, excess copper is extremely toxic and detrimental to health. Recent studies have shown that superhydrophobic surfaces have a significant antibacterial potential for reduction of nosocomial infections. At the same time, the prolonged contact with biological liquids may cause a degradation of the superhydrophobic copper surface and corrosion with increasing egress of toxic copper ions. These aspects are poorly studied so far. In this paper, we analyze the evolution of the properties of both the superhydrophobic copper surface and the suspension of Escherichia coli bacteria during their prolonged contact and study the impact of such contact on the bactericidal activity of the surface. It is shown that by controlling the corrosion resistance and the wettability of the superhydrophobic copper substrate, it becomes possible to sustain the bactericidal action of copper substrates for a long time, simultaneously avoiding the excessive corrosive degradation and release of copper ions in the environment.

Streaming potential in cylindrical pores of poly(ethylene terephthalate) track-etched membranes: variation of apparent zeta potential with pore radius.

Streaming potential variation with pressure measured through poly(ethylene terephthalate) track-etched membranes of different pore sizes led to the determination of an apparent interfacial potential zetaa in the presence of 10-2 M KCl. The variation of zetaa with the pore radius r0 is interpreted by (i) the electric double layer overlap effect and (ii) the presence of a conductive gel layer. We propose a method which integrates both effects by assuming a simple model for the conductive gel at the pore wall. We observed the following three domains of pore size: (i) r0 > 70 nm, where surface effects are negligible; (ii) approximately 17 nm < r0 < 70 nm, where the pore/solution interface could be described as a conductive gel of thickness around 1 nm; (iii) r0 < approximately 17 nm, which corresponds to the region strongly damaged by the ion beam and is not analyzed here. The first one (zeta = -36.2 mV) corresponds to the raw material when etching has completely removed the ion beam predamaged region, which corresponds to the second intermediate domain (zeta = -47.3 mV). There the conductance of the gel layer deduced from the treatment of streaming potential data was found to be compatible with the number of ionic sites independently determined by the electron spin resonance technique.