RUSSIAN JOURNAL OF EARTH SCIENCES VOL. 7, ES4003, doi:10.2205/2005ES000177, 2005

Conclusion

[33]  The results of this study show that during the synthesis of polymer films the nanoparticles of magnetite are distributed over the matrix in the heterogeneously manner. They remain almost noninteracting and supermagnetic in the vicinity of the surface of the film, yet in the film itself they produce layers with chain structures, parallel to the film plane, similar to those developed in magnetotactic bacteria. The stability of these chain structures is controlled by the dipole-dipole interaction among the nanoparticles, performed via the polymer matrix at the expense of the elastic energy of the envelopes of the organic matter separating the particles. The result of this mechanism is the possibility of the formation of a specific domain structure and the fixing of the natural remanent magnetization in the ensemble of the superparamagnetic nanoparticles. As follows from the paper by Jianbao et al. [2000], along with the growth of the pressure applied to the maghemite particles covered by surfactant envelopes, the blocking temperature increased significantly in association with the growing magnetic interaction among the particles. In a composite material, its matrix ensured not only the solidity of the material but was also responsible for stress distribution at the expense of the interaction between the matrix and the filling material at the phase contacts. As to the nanocomposite material discussed, where nanoparticles were synthesized in situ in a nonmagnetic polymer matrix, the polymer elastic forces produce stress at the particle surface, similar to the external pressure. This stress arising in the space between the particles, filled with polymer molecules, leads to the growth of microstress in the particles themselves, recorded by X-ray diffraction. The further convergence of the particles and the elastic energy of the matrix create conditions favorable for high magnetic interaction among the superparamagnetic particles, which fixes magnetization with blocking temperature of about 300o C.

[34]  Shcherbakov et al. [1997] calculated the contribution of the elastic energy of envelopes from two-layer lipid membranes, 6 nm thick, to the stability of the chain structure of single-domain magnetite particles in magnetotactic bacteria. This problem can be transformed to a chain of superparamagnetic particles, separated by a PVA matrix, and this artificial system can be ranked as an analog of the biofilm produced by a colony of Fe-bacteria at the surface of minerals, where the bacteria become static. This result is important also for a new view for the formation of chemical remanent magnetization in nature, controlled by solutions. For instance, the laboratory experiments with amorphous ferric hydroxide, placed in the environment consisting of underground water, the samples of which had been collected from the overlying Cubero Sandstone, and the bacteria obtained from subsurface core samples (250 m below the ground surface) from the Morrison Formation, showed the substantial microbe recovery of the Fe(III) ions to their Fe(II) form [Fredrikson et al., 1998]. The primary reduction products of amorphous iron hydroxide (30% to 84%), produced during the incubation of 3 to 25 days, were siderite grains, 1  m m to 3  m m in size, vivianite crystals, 5-10  m m long and 0.5-1  m m wide, and the aggregates of magnetite grains of a few nanometers. The substantial magnetic interaction among magnetite particles in the aggregates of this kind might have been caused or intensified by the organic material of the cells. As follows from the results of this study, this interaction might have contributed to the stable natural remanent magnetization in the ambient geomagnetic field without the growth of the particles necessary for the record of the magnetic field that existed during the time of their formation.


RJES

Citation: Gendler, T. S., A. A. Novakova, and E. V. Smirnov (2005), Specific magnetic structure forming in polymer nanocomposites containing magnetite nanoparticles, Russ. J. Earth Sci., 7, ES4003, doi:10.2205/2005ES000177.

Copyright 2005 by the Russian Journal of Earth Sciences

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