ROTATIONAL DIFFUSION MEASUREMENTS OF SUSPENDED COLLOIDAL PARTICLES USING 2-DIMENSIONAL EXCHANGE NUCLEAR-MAGNETIC-RESONANCE

We present here an experimental and theoretical study of the applicati on of two-dimensional exchange nuclear magnetic resonance spectroscopy (NMR) to the investigation of the rotational diffusion of colloidal p articles. The theoretical discussion includes the nature of the NMR fr equency time-correlation function where the NMR interaction is represe nted by the chemical shift anisotropy (CSA). Time-correlation function s 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 suspe nsion of symmetric top particles containing an isotropic distribution of a single CSA interaction. Simulations of two-dimensional exchange s pectra for particles undergoing isotropic rotational diffusion are pre sented. We performed two-dimensional exchange NMR experiments on a col loidal suspension of spherical poly(methyl methacrylate) (PMMA) partic les which were synthesized with a 20% enrichment in C-13 at the carbon yl site. Rotational diffusion time-correlation functions determined fr om the experimental exchange spectra are consistent with the compositi on of the colloidal suspension. Detailed explanations of the syntheses of the enriched methyl C-13-(carbonyl)-methacrylate monomer and the s mall quantities of 20% enriched C-13-(carbonyl)-poly(methyl methacryla te) microspheres used for this study are presented. (C) 1996 American Institute of Physics.