Water Magnetic Relaxation in Superparamagnetic Colloid Suspensions: The Effect of Agglomeration
Superparamagnetic (SPM) nanoparticles in aqueous suspensions are known to shorten the nuclear magnetic relaxation of water protons. For transverse relaxation, this effect is enhanced when agglomeration of elementary SPM cores occurs. This feature is explained by considering the agglomerate as a large magnetized sphere, which at high field contributes strongly to the secular part of the transverse relaxivity. Longitudinal relaxation is modeled by analyzing diffusion through the permeable coating of the agglomerate as a virtual exchange between normal decaying modes and the bulk water. This model is used to interpret the flattening of the Nuclear Magnetic Relaxation Dispersion profiles during a chemically induced agglomeration of ferrite particles.
KeywordsZinc Anisotropy Ferrite Manganese Polysaccharide
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