FIELD-CYCLING PROTON NUCLEAR MAGNETIC RELAXATION-DISPERSION STUDY OF AQUEOUS COLLOIDAL SILICA SOLS

The magnetic-field dependence of tile water-proton spin-lattice relaxa tion rate 1/T-1 is reported for aqueous colloidal silica suspensions a s a function of temperature, particle size, silica concentration, and isotopical proton dilution. At low concentrations, it is found that T- 1 is essentially determined by a coupling of solvent protons with none xchangeable protons situated near the colloid surface. Comparison of N MRD and photon correlation spectroscopy measurements indicates that in terparticle interactions increase the NMR relaxation rates at low freq uencies. Finally, it is also shown that, in contrast to protein soluti ons, there is no evident link between the NMRD inflection frequency an d the correlation time of the rotational Brownian motion of the colloi dal particles. (C) 1995 Academic Press, Inc.