ISSN 10274510, Journal of Surface Investigation. Xray, Synchrotron and Neutron Techniques, 2013, Vol. 7, No. 6, pp. 1133–1136. © Pleiades Publishing, Ltd., 2013. Original Russian Text © A.A. Kaznacheevskaya, O.A. Kizima, L.A. Bulavin, A.V. Tomchuk, V.M. Garamus, M.V. Avdeev, 2013, published in Poverkhnost’. Rentgenovskie, Sinkhrotronnye i Neitronnye Issledovaniya, 2013, No. 12, pp. 21–24. 1133 INTRODUCTION Currently, cluster formation in fullerene solutions is a topical issue in colloidal chemistry [1]. The study of fullerene solutions is important from both funda mental (information about the cluster state of matter) and practical points of view. The applied interest in fullerene solutions is caused, in particular, by the bio activity of fullerenes; hence, it is necessary to search for watersoluble and stable forms of these highsym metry molecules. Despite the large number of experi mental and theoretical studies on this subject [2, 3], the nature of cluster formation, cluster structure, and the anomalous properties of fullerene solutions caused by the presence of clusters are still far from being com pletely understood. The purpose of our study is to clar ify this question. It was previously shown that the transition from a molecular solution to a cluster one occurs with time in the С 60 /Nmethylpyrrolidone (NMP) system [4]. One can state that an overwhelming number of the initially dissolved С 60 molecules finally aggregate into clusters (up to 500 nm in size), which remain stable for a long (at least, 1 yr) time. This system also exhibits an inter esting effect of cluster reorganization after adding some water [5, 6]: С 60 /NMP complexes are partially dissolved in the NMP/H 2 O mixture [7]. This effect depends on the age of the initial solution [6]. The reorganization of the cluster state (specifically, a significant decrease in the characteristic size of clus ters) can easily be detected by smallangle neutron scattering (SANS) [5, 6]. Concerning dynamic light scattering (DLS), which is used to record clusters in the final (cluster) С 60 /NMP solution, it was only reported that the characteristic size of the clusters tends to decrease after dilution of this system with water. We analyzed the change in the DLS spectra after adding water to С 60 /NMP based on quantitative reconstruction of the sizedistribution function of the clusters. To obtain a more pronounced DLS effect, water is added to a relatively fresh (two week old) ini tial solution. The data obtained are compared with the previous SANS results for rather old (more than one month) initial С 60 /NMP solutions. The purpose of this study was to reveal the degree of agreement between the data on the size characteristics of polydis perse clusters obtained by two different methods. EXPERIMENTAL To prepare the С 60 /NMP system, a fullerene of purity grade >99.5% (Fullerenovie Tekhnologii) was dissolved in NMP of purity grade >99.5% (Merck) and stirred for four days at room temperature. The concen tration (0.89 mg/mL) was determined from the adsorption coefficient in the UV–visible spectrum Reorganization of the Cluster State in a C 60 /NMethylpyrrolidone/Water Solution: Comparative Characteristics of Dynamic Light Scattering and SmallAngle Neutron Scattering Data A. A. Kaznacheevskaya a, b , O. A. Kizima a, c , L. A. Bulavin c , A. V. Tomchuk a, c , V. M. Garamus d , and M. V. Avdeev a a Frank Laboratory of Neutron Physics, Joint Institute for Nuclear Research, Dubna, 141980 Russia b Tula State University, Tula, 300012 Russia c Shevchenko National University, Kyiv, 03022 Ukraine d HelmholtzZentrum Geesthacht, 21502 Geesthacht, Germany Received February 11, 2013 Abstract—Data on dynamic light scattering from cluster solutions of C 60 fullerenes in Nmethylpyrrolidone (NMP) and its mixture with water are analyzed. Initial C 60 /NMP solutions kept for two weeks (i.e., fresher than those analyzed previously) are considered, where the effect of clusterstate reorganization after adding water is recorded more reliably. Based on the sizedistribution functions of the clusters, obtained from dynamic light scattering data, model curves of smallangle neutron scattering are calculated and compared with the experimental data. DOI: 10.1134/S102745101306030X