P.Yu. Apel

Diode-like single-ion track membrane prepared by electro-stopping

The prepn. of an asym. membrane in poly(ethylene terephthalate) (PET) is described, using a combination of chem. and electro-stopping. For this purpose, a single-ion-irradiated PET film is inserted ...

Preparation of permeability-controlled track membranes on the basis of ‘smart’ polymers

The modification of polymer track membranes from polyethylene terephtalate (PET) and polypropylene (PP) was performed by radiation-induced graft polymerization of thermosensitive poly-N-isopropylacrylamide (poly-NIPAAM). The opening and closing of the pores was controlled by temperature and studied by the electric conductivity and water flow methods. The structure of the grafted membranes was investigated by scanning electron and atomic force microscopy.

Surfactant-enhanced control of track-etch pore morphology

Abstract The influence of surfactants on the process of chemical development of ion tracks in polymers is studied. Based on the experimental data, a mechanism of the surfactant effect on the track-etch pore morphology is proposed. In the beginning of etching the surfactant is adsorbed on the surface and creates a layer that is quasi-solid and partially protects the surface from the etching agent. However, some etchant molecules diffuse through the barrier and react with the polymer surface. This results in the formation of a small hole at the entrance to the ion track. After the hole has attained a few nanometers in diameter, the surfactant molecules penetrate into the track and cover its walls. Further diffusion of the surfactant into the growing pore is hindered. The adsorbed surfactant layer is not permeable for large molecules. In contrast, small alkali molecules and water molecules diffuse into the track and provide the etching process enlarging the pore. At this stage the transport of the surfactant into the pore channel can proceed only due to the lateral diffusion in the adsorbed layer. The volume inside the pore is free of surfactant molecules and grows at a higher rate than the pore entrance. After a more prolonged etching the bottle-like (or “cigar-like”) pore channels are formed. The bottle-like shape of the pore channels depends on the etching conditions such as alkali and surfactant concentration, temperature, and type of the surfactant. The use of surfactants enables one to produce track-etch membranes with improved flow rate characteristics compared with those having cylindrical pores with the same nominal pore diameters.

Effect of nanosized surfactant molecules on the etching of ion tracks: New degrees of freedom in design of pore shape

Abstract A new method to control the geometry of track-etch nano- and micropores is described. Surfactant molecules added to a solution used for etching out ion tracks, create a steric-hindrance effect which is responsible for the formation of “bottleneck” or “cigar-like” pores. New applications are made possible with these new pore geometries.

THE USE OF RADIATION-INDUCED GRAFT POLYMERIZATION FOR MODIFICATION OF POLYMER TRACK MEMBRANES

Abstract Track membranes (TM) made of poly(ethylene terephtalate) (PET) and polypropylene (PP) films have a number of peculiarities as compared with other ones. They have high mechanical strength at a low thickness, narrow pore size distribution, low content of extractables. However, TM have some disadvantages such as low chemical resistance in alkaline media (PET TM), the low water flow rate due to the hydrophobic nature of their surface. The use of radiation-induced graft polymerization makes it possible to improve the basic characteristics of TM. In this communication our results on the modification of PET and PP TM are presented. The modified membranes were prepared by radiation-induced graft polymerization from the liquid phase. Three methods of grafting were used: (a) the direct method in argon atmosphere; (b) the pre-irradiation of TM in air followed by grafting in argon atmosphere; (c) pre-irradiation in vacuum followed by grafting in vacuum without contacting oxygen. The aim of the work was to investigate some properties of TM modified by grafted poly(methylvinyl pyridine) (PMVP) and poly(N-isopropylacrylamide) (PNIPAAM). It was shown that the modification of TM with hydrophilic polymer results in the growth of the water flow rate. In the past few years many works have been devoted to the synthesis of new polymers – the so-called “intelligent” materials – such as PNIPAAM. However, it is very difficult to make thin membranes of this polymer. Recently, it has been proposed to manufacture composite membranes by grafting stimulus-responsive polymers onto TM. Following this principle, we prepared thermosensitive membranes by the radiation-induced graft polymerization of N-isopropylacrylamide (NIPAAM) onto PET TM. PET TM with the pore size of about 1 μm and pore density of 106 cm−2 were first inserted into a solution of NIPAAM containing inhibitor of homopolymerization (CuCl2) and then exposed to the γ-rays from a 60Co source. The transport properties of the grafted TM were investigated. The permeation of water through the TM was controlled by temperature. The grafted TM exhibited almost the same transition temperature (about 33°C) as that of PNIPAAM.

Electrolyte transport in charged single ion track capillaries

Abstract The pH and concentration dependence of the electric current through etched single ion tracks in poly (ethyleneterephthalate) (PET) membranes is investigated using KCl solutions. The pH dependence of the current is attributed to the dissociation of the immobile carboxylic end groups attached to the PET leading to charged pore walls. As consequence a counterion layer near the pore walls is formed with increased conductivity. At low KCl concentrations surface conductivity can be several orders of magnitude above the regular volume conductivity.

Heavy particle tracks in polymers and polymeric track membranes

Abstract The review describes the evolution and present state of the use of accelerated heavy ion beams for investigation of track radiation effects and track membrane production at FLNR JINR. The research and development activity on track membranes (TMs) included studies of track formation process, latent track structure, environmental effects, sensitization of tracks, track etching, methods of membrane testing, designing and constructing facilities for membrane production. Some results on the physics and chemistry of ion tracks in polymers are described with the emphasis on the experiments performed during the last few years.

Investigation of the radial pore-etching rate in a plastic track detector as a function of the local damage density around the ion path

Abstract An attempt is made to define the sensitivity of plastic track detectors on the basis of a new concept. The main feature of this (micro)concept is the relation between the radial etching rate of a heavy ion track and the local ion damage density by means of a continuous function. The energy dose depending on the radial distance from the ion path is taken as a measure of the local damage density. The corresponding etching rate has been measured by the conductometric method. The sharp rise of the radial etching rate with increasing dose explains the threshold character of the track registration and confirms the applicability of the existing threshold registration criteria for practical purposes. The dependence of the radial etching rate on the radial dose can be described by the multi-target model which explains the preferential etching by the collective activation of a given number of sensitive elements. The lower slope of the corresponding curve for gamma radiation demonstrates the substantial influence of the dose rate on this collective activation process.

Micro- and nanoporous materials produced using accelerated heavy ion beams

This brief overview demonstrates how the ion track-based technology for micro-structuring polymeric materials that has been practised for decades is shifting to the nanometre scale in research and development applications. We present selected results of studies that have focused on the development of new nanoporous materials, especially membranes, performed recently at the Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research (JINR).

Conductometric studies of multiply charged ion track structure in various polymers

Abstract The radial structure of the etchable tracks of multiply charged ions in polethylene terephthalate, polycarbonate, polyarylate and polypropylene is investigated using the conductometric method. It is found that the track of a highly ionizing particle in a polymer consists of a core in which intensive destruction occurs and a halo where the cross linking of macromolecules may predominate. A hypothesis is proposed that the cross linking of a polymer in the track halo is conditioned by the effect of the hydrogen ions and atoms which are generated in the track core due to the ion explosion spike mechanism and diffuse to the surrounding space.