NMR properties of poly(dimethyl siloxane) colloids as new contrast agents for NMR imaging

By connecting the field-gradient spin-echo theory to spin-spin relaxation, we have found that the relationship between the tube-reptation model and sp in-spin relaxation can be represented by G(t) = exp[-(t/T-2)(n)] in which n = 1 and 0.5 for regimes IV and III, respectively. In our experiments, the spin-spin relaxation of linear poly(dimethyl siloxane) (PDMS) agrees with G (t) = expr[-(t/T-2)] while that of crosslinked PDMS coincides with G(t) = e xp[-(t/T-2)(0.5)]. These results reflect that in the time interval 8-800 ms the dynamics of linear PDMS are in regime IV (governed by reptation motion s) and those of the crosslinked PDMS are in regime III (dominated by wriggl ing motions). The Line-shapes of NMR spectra of crosslinked PDMS are consis tent with the Lorentzian rather than the Gaussian model. This can be accoun ted for by supposing that the PDMS chains between crosslinks have liquid-li ke motions even though crosslinked PDMS is a solid. The liquid-like motions of crosslinked PDMS could be regarded as wriggling motions described by th e tube-reptation model. In addition, the experimental results of diameter d istribution, viscosity, NMR image and spin-lattice relaxation are presented in this work. (C) 2000 Society of Chemical Industry.