Rotational diffusion measurements of suspended colloidal particles using two-dimensional exchange nuclear magnetic resonance

We present here an experimental and theoretical study of the application of two-dimensional exchange nuclear magnetic resonance spectroscopy ~NMR! to the investigation of the rotational diffusion of colloidal particles. The theoretical discussion includes the nature of the NMR frequency time-correlation function where the NMR interaction is represented by the chemical shift anisotropy ~CSA!. Time-correlation functions for the isotropic rotational diffusion of a suspension of colloidal particles containing single and multiple sites are derived in addition to time-correlation functions for the rotational diffusion of a suspension of symmetric top particles containing an isotropic distribution of a single CSA interaction. Simulations of two-dimensional exchange spectra for particles undergoing isotropic rotational diffusion are presented. We performed two-dimensional exchange NMR experiments on a colloidal suspension of spherical poly~methyl methacrylate! ~PMMA! particles which were synthesized with a 20% enrichment in C at the carbonyl site. Rotational diffusion time-correlation functions determined from the experimental exchange spectra are consistent with the composition of the colloidal suspension. Detailed explanations of the syntheses of the enriched methyl C-~carbonyl!-methacrylate monomer and the small quantities of 20% enriched C-~carbonyl!-poly~methyl methacrylate! microspheres used for this study are presented. © 1996 American Institute of Physics. @S0021-9606~96!00301-5#