NMR Diffusometry and Dynamic NMR Microscopy Studies of Colloidal Systems
Doctoral thesis, 2004
In this thesis, the NMR diffusometry and dynamic NMR microscopy methods were shown to be useful techniques with a great potential for the study of colloidal systems. In Paper I-II, NMR diffusometry was used to study the behaviour of surfactant and polymer molecules that are normally important components in colloidal dispersions and emulsions. In Paper I, depletion flocculation of aqueous paraffin dispersions and hexadecane emulsions by non-ionic surfactant were studied by optical scanning and NMR diffusometry using the experimental design methodology. In Paper II, NMR diffusometry and dynamic light scattering were used to study the time evolution of the size and size distribution of cationic amylopectin samples, which were found to be strongly dependent on the sample preparation method.
Paper III-V concern the study of the colloidal particles themselves using both NMR diffusometry and dynamic NMR microscopy methods such as NMR velocimetry. In order to enable the dynamic NMR study of colloidal particles, a model system of a core-shell latex type containing a liquid core surrounded by a solid polymer shell was used. This system is ideally suited for NMR studies, in that it contains a liquid core that gives rise to an NMR signal while the polymer shell retains a hard sphere character of the particle as such. In Paper III the core-shell latex particles were found to be a suitable model system for NMR diffusometry studies of colloidal behaviour provided that great care was taken in the interpretation of the NMR results, in particular with respect to effects of sample polydispersity and the presence of oil in the polymer shell. Using the NMR-visible core-shell latex spheres as slowly diffusing tracer particles, we extended in Paper IV the NMR velocimetry technique down to the nanoscale domain, probing particle distances of sub-diameter length. Paper V explored the NMR velocimetry technique for the rheological study of a soft glassy system represented by a concentrated dispersion of NMR-visible core-shell latex particles. The system was found to exhibit a shear-rate dependent shear-thinning behaviour above the yield stress, and aging and rejuvenation effects were also observed.
dynamic NMR microscopy
core-shell latex particles