M. V. Avdeev, T. V. Tropin, Kh. T. Kholmurodov, M. Erdauletov

The area includes the investigation of the structural stability of liquid nanosystems, including magnetic nanosystems and systems related to biology, under various conditions. The main goal of the research is to compare the behavior and structural organization of the components of such systems in the bulk and at interphase boundaries using the small-angle scattering and liquid thermal neutron reflectometry together. The combined use of these techniques allows to reveal common features and differences in the behavior of particles and their complexes in bulk and at interphase boundaries. This information is needed for understanding and describing processes in multicomponent colloidal systems and for the synthesis of stable systems, including biomedical ones, with tunable properties. The research objects include representatives of major classes of liquid nanosystems: liquid dispersions of nanoparticles (including magnetic nanoparticles), solutions of organic polymers and nanoparticles in biological environment; solutions of biological polymers; lipid membranes. A separate emphasis in research is made on the investigation of the stability of colloidal systems with magnetic nanoparticles in the bulk and in near-surface layers when positioned in an external magnetic field. Methodological aspects cover: development of the hardware base for experiments on neutron reflectometry on horizontal samples, including those that contain a liquid phase; adaptation of specialized cells to study the designated types of systems using neutron scattering; enhancement of capabilities of small-angle neutron scattering.

Structural investigations of disperse systems, including systems concerning medical and biological developments, have been traditionally developed at FLNP. Thus, when using small-angle neutron scattering, a range of original approaches for implementing and interpreting experiments on contrast variation for disperse systems have been proposed. In particular, a technique of modified basis functions for contrast variation data processing in small-angle scattering experiments for nanosystems with inhomogeneous polydisperse particles, including magnetic particles, has been proposed. A multifunctional neutron reflectometer with a horizontal sample plane GRAINS at the modernized IBR-2 reactor has been operating at FLNP since 2013 (Fig. 1). The basic configuration of the reflectometer allows to study liquid objects at various interfaces.

Fig. 1. Schematic diagram of the GRAINS reflectometer

In the course of recent work, the impact of an external electric field on the adsorption of magnetic nanoparticles on planar interfaces from dielectric magnetic fluids has been studied. The latter are used as thermolyzing additives in high-voltage transformers. A magnetic fluid based on transformer oil with magnetite nanoparticles coated with a single layer of a surfactant (oleic acid) has been investigated. The magnetic fluid was in contact with a thin-film copper electrode deposited on single-crystal silicon. Neutron reflectometry (GRAINS reflectometer) reveals the production of several layers of magnetic nanoparticles on the electrode surface (Fig. 2). With increasing field strength, the near-surface structure experiences nontrivial changes in the layer-by-layer density distribution that is qualitatively consistent with previously discovered inhomogeneities that arise in the volume of dielectric magnetic fluids under the action of an external electric field.

Fig.2. Layer-by-layer analysis of the distribution of nanoparticles from a dielectric magnetic fluid on the planar surface of a copper electrode when exposed to an external electric field (perpendicular to the surface) according to neutron reflectometry data

The anti-amyloid activity of C60 and C70 fullerene dispersions in 1-methyl-2-pyrrolidone (NMP) has been discovered (Fig. 3). The investigations have been carried out in model aqueous solutions of amyloid fibrils obtained from lysozyme and insulin. A combined approach involving various experimental techniques has been used. To monitor the deaggregation activity of fullerenes, thioflavin T fluorescence analysis and atomic force microscopy (AFM) have been used. Both types of fullerene-based complexes have been shown to be very efficient in disrupting pre-developed fibrils and are characterized by low deaggregation concentration (DC50), ~22-30 µg/mL. Small-angle neutron scattering (SANS) has been used to control various stages of the fibril destruction process, including the determination of the size and morphology of aggregates. Based on the results obtained, a possible mechanism for the destruction of amyloid fibrils interacting with fullerene/NMP complexes has been proposed. These investigations are an important step in understanding the mechanism of destruction of protein amyloids using fullerenes in living organisms and also to provide valuable information on how macromolecules can be designed to destroy unwanted amyloid aggregates using various mechanisms.

Fig. 3. Destruction of amyloid fibrils upon interaction with fullerenes from dispersion in NMP. SANS data (YuMO, IBR-2), AFM and fluorescence control

The structure of binary liquid nanocarbon systems obtained by mixing a detonation nanodiamond hydrosol and aqueous dispersions of single-layer graphene oxide has been studied. Small-angle neutron scattering (SANS) data convincingly support the 2D structural organization of graphene oxide sheets, as well as the fact that they are composed of a single graphene-type layer (Fig. 4). The size and spatial distribution of nanocarbon clusters produced during the interaction of components in aqueous environment have been investigated. Based on the analysis of scattering data, it was concluded that individual nanodiamond particles, as well as their small fractal clusters are bound together with a uniform and random distribution along graphene planes that is confirmed by transmission electron microscopy (TEM) data of dried samples. The observed effect can significantly modify the structure of nanocarbon composites produced using nanodiamond and graphene oxide, aligning the graphene in a certain way during the drying of the mixture.

Fig. 4. (a) SANS on aqueous dispersions of graphene oxide, detonation nanodiamond and their mixture. The inset shows the TEM data. (b) The sensitivity of TEM and SANS techniques to the structure of thin graphene layers is shown separately. The occurrence of nanodiamonds on the surface of a graphene sheet increases both thickness and density in terms of SANS

Publications:

1. Karpets M., Rajnak M., Petrenko V., et al., Electric field-induced assembly of magnetic nanoparticles from dielectric ferrofluids on planar interface. Journal of Molecular Liquids, 362, 119773 (2022). Doi:10.1016/j.molliq.2022.119773
2. Siposova K., Petrenko V.I., Ivankov O.I., et al., Fullerenes as an Effective Amyloid Fibrils Disaggregating Nanomaterial, ACS Appl. Mater. Interfaces 12(29), 32410-32419 (2020). Doi:10.1021/acsami.0c07964
3. Tomchuk O.V., Avdeev M.V., Dideikin A.T., et al., Revealing the structure of composite nanodiamond–graphene oxide aqueous dispersions by small-angle scattering, Diamond Related Materials 103, 107670 (2020). Doi:10.1016/j.diamond.2019.107670