INVESTIGATION OF THE pH EFFECT ON THE STABILITY OF BIOCOMPATIBLE MAGNETIC FLUIDS USING TIME – DEPENDENT BIREFRIGENCE MEASUREMENTS

Gravina P. P. ¹ , Bakuzis A. F. ¹ , Neto S. ¹ , Azevedo R. B. ² , Morais P. C. ¹

1. Univesidade de Brasilia, Instituto de Fisica, Nucleo de Aplicada, 70919-970, Brasilia-DF, Brazil.

2. Univesidade de Brasilia, Instituto de Ciencias Biologicas, Departamento de Genetica e Morfologia, 70919-900, Brasilia-DF, Brazil.

Magnetic fluid (MF) stability has been laboriously studied and the guarantee of its maintenance plays a key role not only for the technological applications but also due to its recent use in the biomedical field [1 – 3]. One can investigate the MF stability by changing the temperature, external magnetic field, ionic strength, pH, coating layer, particle size, among others [4 – 7]. The exposure of a magnetic fluid sample to anyone of these variables as a function of time seems to be fundamental for the understanding of the colloidal stability, as investigated through the application of an external magnetic field [8]. Since biological systems are highly complex and present significant changes in pH from organelle it is extremely important to investigate how a pH variation affects the stability of biocompatible magnetic fluids. In this work we used the static magnetic birefringence technique to investigate how the pH variation affects the stability of an aqueous, citrate-coated, maghemite-based magnetic fluid as a function of time. The experimental setup used in our experiment has been already described in the literature [8 – 11]. The mean particle size (10.2 nm) and size-dispersity (0.21) of the sample were obtained from the transmission electron microscopy micrographs using a Joel 100CXII system. The particle volume fraction was obtained by combining bight the atomic absorption and the electron microscopy data. The samples were diluted from the stock sample down to the same particle concentration but at different final pH values. The measurements were performed at room temperature. The experimental data will be discussed in terms of the rotation of anisometric isolated nanoparticles, pre-existing agglomerates, and the formation of agglomerates as function of time for different pH values.

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