Size distribution of nanoparticle aggregates in an aqueous magnetic fluid based on atomic-force microscopy data
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MATERIALS
Size Distribution of Nanoparticle Aggregates in an Aqueous Magnetic Fluid Based on AtomicForce Microscopy Data A. V. Shuleninaa, b, M. V. Avdeeva, c, S. P. Besedina, d, V. V. Volkovd, A. Hajdue, E. Tombacz f, and V. L. Aksenova, b, c a
National Research Centre Kurchatov Institute, pl. Akademika Kurchatova 1, Moscow, 123182 Russia b Moscow State University, Moscow, Russia email: [email protected] c Joint Institute for Nuclear Research, ul. ZholioKyuri 6, Dubna, Moscow oblast, 141980 Russia d Shubnikov Institute of Crystallography, Russian Academy of Sciences, Leninskii pr. 59, Moscow, 119333 Russia e Semmelweis University, Budapest, Hungary f Szeged University, Szeged, Hungary Received August 10, 2011
Abstract—Atomicforce microscopy (AFM) has been applied in a fluid environment to determine the size distribution function of nanoparticle aggregates in an aqueous magnetic fluid with magnetite particles coated by polyacrylic acid for stabilization. It is proposed to use an external magnetic field to anchor aggregates on the substrate. The data are compared with the AFM data for dried precipitates of the system under consider ation, formed during evaporation of the liquid carrier under different conditions, as well as with the particle size distribution in the initial system obtained from smallangle Xray scattering data. DOI: 10.1134/S1063774512060144
INTRODUCTION Magnetic fluids (MFs) are stable colloidal solu tions of singledomain ferro or ferrimagnetic nano particles (magnetite particles are considered here). These objects combine fluidity and magnetic proper ties [1, 2], a circumstance significantly complicating their structure in comparison with other liquid col loids [3]. To prevent aggregation, particles in an MF are coated by a stabilizing layer of surfactants or ions. Currently, MFs are widely applied in technology [4, 5]. There has been interest in studying biocompatible MFs [6–12] in view of the prospects of their applica tion in medicine (contrast media in magnetoreso nance tomography; targeted drug delivery controlled by an external magnetic field; magnetic hyperthermia; etc.). Despite a relatively long history (the first MFs were synthesized in the 1960s), until now synthesis of concentrated (with a volume fraction of magnetic material ϕm > 1%), aqueous MFs without nanoparticle aggregation is a difficult problem [13]. The reason is that the standard procedures of nonelectrostatic (or steric) stabilization of MFs in nonpolar (hydrocar bons, hexane, benzene, decahydronaphthalene) and polar (alcohols) organic media are difficult to apply to dispersed aqueousbased media because of the strong interaction between the solvent and surfactant mole cules. Individual particles can be stabilized by an adsorbing charge on their surface (Massart method [14]); however, in this case MFs are unstable under physiological conditions with a neutral medium [15].
In recent years, some progress has been observed in methods for synthesizing concentrated aqueous MFs that combine to some extent ste
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