ISSN 0012-5016, Doklady Physical Chemistry, 2011, Vol. 441, Part 1, pp. 212–214. © Pleiades Publishing, Ltd., 2011. Original Russian Text © E.V. Moroz, J.A. Zakharova, V.G. Sergeyev, A.B. Zezin, 2011, published in Doklady Akademii Nauk, 2011, Vol. 441, No. 2, pp. 205–208. 212 The polyelectrolyte complexes with oppositely charged surfactants are formed spontaneously upon mixing of aqueous solutions of chemically comple- mentary components [1]. A fundamental feature of these complexes is the ability of surfactant ions bound electrostatically to a polyion to be packed in micelles, which are able to solubilize organic compounds of dif- ferent chemical nature. As has been shown previously [2], even small amounts of solubilized compounds can considerably affect the solubility of the complexes by changing the hydrophilic–hydrophobic balance of particles. In this paper, we report for the first time ternary complexes, either soluble or insoluble in aqueous solu- tions, containing multiwalled carbon nanotubes apart from the polyelectrolyte and the surfactant. As the polyelectrolyte, we used positively charged poly(N-ethyl-4-vinylpyridinium bromide)s prepared by quaternization of poly-4-vinylpyridine (polymer- ization degree 2500, manufactured by Polyscience, Inc., USA) with ethyl bromide in methanol. Accord- ing to IR spectroscopy, the degree of quaternization of the samples was 32 ± 5% (PEVP 32 ) and 83 ± 5% (PEVP 83 ). The polyelectrolyte concentration in the solution was expressed as the total base molar concen- tration of all the PEVP units (base-mol/L) including nonquaternized moieties. Sodium dodecyl sulfate (SDS, Serva, used as received) served as the anionic surfactant. The multiwalled carbon nanotubes (MNT), manu- factured by Nanocyl (Belgium) with an average diam- eter of 10 nm and a length of 1.5 μm were dispersed in aqueous solutions of SDS (20 or 40 mg of MNT in 20 mL of a 1% aqueous solution of SDS) by a 5-min ultrasonic treatment in an ice bath. Note that the ultrasonic treatment of nanotubes in micellar surfac- tant solutions is a known method for the preparation of stable nanotube dispersions (see, for example [3– 5]). After dispersion, the solutions were centrifuged on a MiniSpin microcentrifuge at 13000 rpm for 5 min. The nanotube concentration in the solution was deter- mined by spectrophotometry based on the absorption at 500 nm (ε = 42.2 L g –1 cm –1 [6]) on a Perkin-Elmer Lambda 25 spectrophotometer. The photomicro- graphs of binary and ternary complexes were obtained on a Leo912 AB Omega transmission electron micro- scope (TEM) (Carl Zeiss, Germany) (Fig. 1). Judging by the high contrast of the MNT surface, upon the ultrasonic dispersion in SDS, the tube surface becomes coated by a surfactant layer, whose charge ensures the dispersion stability of the tubes in aqueous solutions. In addition, it can be seen that the ultra- sonic treatment of the MNT in a micellar solution of SDS results in a noticeable decrease in the average tube length down to approximately 600 nm but almost does not affect their diameter. The dispersions remain stable even on dilution with water to a SDS concentra- tion of less than 1 × 10 –3 mol/L, which is much lower than the critical micelle concentration (the CMC of SDS in water at 25°C is 8 × 10 –3 mol/L [1]). The PEVP–SDS–MNT ternary complexes were obtained by dropwise addition (with vigorous stirring) of an aqueous MNT-SDS dispersion (1 to 2 g/L of nanotubes, [SDS] = 0.035 mol/L) to solutions of PEVP in the desired component ratio. The final con- centration of the polyions in the samples was 0.004– 0.016 base-mol/L. Alternatively, a solution of PEVP was rapidly added with stirring to a dilute MNT–SDS dispersion. In the series of samples obtained in this way, the final SDS concentration was 1.4 × 10 –3 mol/L and the MNT concentration was 45 mg/L. The result- ing ternary mixtures were kept for at least 24 h to reach equilibrium. The composition of the reaction mixture Z = [SDS]/[PEVP + ], where [SDS] is the molar concen- tration of surfactant ions and the [PEVP + ] is the molar concentration of quaternized PEVP units, was varied from 0 to 1.2. For separating large aggregates, which are below referred to as insoluble complexes, the reaction mix- tures were centrifuged at 13 000 rpm. The PEVP con- centration in the supernatants was determined by spectrophotometry. Since at λ 257 nm (the absorption maximum of PEVP) the absorption of the polymer is superimposed on the absorption of nanotubes, PHYSICAL CHEMISTRY Ternary Complexes Polyelectrolyte–Oppositely Charged Surfactant–Carbon Nanotubes: Formation and Properties E. V. Moroz, J. A. Zakharova, V. G. Sergeyev, and Corresponding Member of the RAS A. B. Zezin Received May 11, 2011 DOI: 10.1134/S0012501611090077 Moscow State University, Moscow, 119991 Russia