Radiation Measurements 43 (2008) S552 – S559 www.elsevier.com/locate/radmeas Surfactant-controlled etching of ion track nanopores and its practical applications in membrane technology P.Yu. Apel a , ∗ , I.V. Blonskaya a , S.N. Dmitriev a , T.I. Mamonova a , O.L. Orelovitch a , B. Sartowska b , Yu. Yamauchi a a Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, 141980 Dubna, Russia b Institute of Nuclear Chemistry and Technology, Dorodna Street 16, 03-195 Warsaw, Poland Abstract The effect of surfactants on chemical development of ion tracks in polymers has been studied. It has been shown that surface-active agents added to an alkaline etching solution adsorb on the polymer surface at the pore entrances. This reduces the etch rate, which leads to the formation of pores tapered toward the surface. Self-assembly of surfactant molecules at the pore entrance creates a barrier for their penetration into the etched-out nanopores, whereas hydroxide ions diffuse freely. Due to this, the internal pore volume grows faster than the pore surface diameter. The ability to control pore shape is demonstrated with the fabrication of profiled nano- and micropores in polyethylene terephthalate, polycarbonate. Some earlier published data on small track-etched pores in polycarbonate (in particular, the pore diameter vs. etching time curves measured conductometrically) have been revised in light of the above findings. Adding surfactants to chemical etchants makes it possible to optimize the structure of track membranes, thus improving their retention and permeation properties. Asymmetric membranes with thin skin retention layers have been produced and their performance studied. © 2008 Elsevier Ltd. All rights reserved. PACS: 61.80jh; 68.35.Fx; 68.90.+g; 81.40.Wx Keywords: Ion tracks; Polymers; Chemical etching; Nanopores; Micropores; Surfactant; Adsorption; Self-assembly; Membranes; Ultrafiltration; Microfiltration 1. Introduction When etching ion tracks, in particular in polymers, various surfactants are often added to the solution, to improve wetting and obtain more uniform etching (Petersen, 1970; Enge et al., 1975). While the influence of small-molecule surfactants is restricted to a wetting function, larger surfactant molecules have a much more complex effect, which has been overlooked for decades. In the present report, we consider the dramatic effect of surface-active species on the pore formation process, when chemically etching ion-irradiated polymers. We explain how the presence of a surfactant (i) alters the kinetics of the pore growth; (ii) can have a remarkable effect on the shape of the etched channel; (iii) can be employed for the production of nano- and microporous materials with special properties. ∗ Corresponding author. Tel.: +7 49621 63544; fax: +7 49621 28933. E-mail address: apel@nrmail.jinr.ru (P.Yu. Apel). 1350-4487/$ - see front matter © 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.radmeas.2008.04.057 To understand the process of track etching in the presence of surfactants, one has to take into account the following facts: 1. Surfactant molecules adsorb on surfaces and alter their susceptibility to chemical attack. 2. Molecules of most surfactants are a few nanometers in size, comparable to the radius of the preferentially etched track core. 3. The diffusion rate of the nanosized surfactant molecules in the restricted volume of the etched pore can differ sig- nificantly from the diffusion rate of the smaller molecules responsible for chemical etching. Starting from the above statements, we will consider below the surfactant-enhanced track etching process and its potential applications.