Experimental study on T2 relaxation time of protons in water suspensions of iron-oxide nanoparticles: Effects of polymer coating thickness and over-low 1/T2

The T-2 relaxation time of protons in three sets of water suspensions of polymer coated Fe3O4 particle clusters with effective diameter of the order of 10(2) nm is measured. It is found that with increasing the effective average coating thickness, the waiting time t(w) dependence of the measured T-2 is weakened, but the T-2 at t(w) = 0, T-2(0), remains almost without change, having the values of relaxation rate 1/T(2)d(0) substantially lower than its static dephasing limit. The weakened t(w) dependence is a consequence of the weakened magnetostatic interaction, which induces cluster aggregation; the stable T-2(0) can be justified in the framework of existing theories; and the over-low 1/T-2(0) is an interesting phenomenon, whose origin deserves further research. (C) 2009 Elsevier B.V. All rights reserved.