Experimental study on T<inf>2</inf> relaxation time of protons in water suspensions of iron-oxide nanoparticles: Effects of polymer coating thickness and over-low 1 / T<inf>2</inf>

The T2 relaxation time of protons in three sets of water suspensions of polymer coated Fe3 O4 particle clusters with effective diameter of the order of 102 nm is measured. It is found that with increasing the effective average coating thickness, the waiting time tw dependence of the measured T2 is weakened, but the T2 at tw = 0, T2 (0), remains almost without change, having the values of relaxation rate 1 / T2 (0) substantially lower than its static dephasing limit. The weakened tw dependence is a consequence of the weakened magnetostatic interaction, which induces cluster aggregation; the stable T2 (0) can be justified in the framework of existing theories; and the over-low 1 / T2 (0) is an interesting phenomenon, whose origin deserves further research. © 2009 Elsevier B.V. All rights reserved.