For polymer particle dispersions, traditional gas adsorption techniques (e.g. BET surface area) are insufficient to elucidate the structure of a wetted material, which may collapse during sample preparation steps (vacuum). To address this limitation of conventional surface area measurements, we are developing low-field NMR methods to characterize materials under inherent conditions, e.g. as a wetted slurry. The physical basis for these methods and example data sets for colloidal silica and polystyrene will be discussed to underscore the value of low-field NMR for challenging characterization problems. In the case of silica colloids, a linear relationship exists between colloid concentration<br/>(weight percent) and the measured spin-spin relaxation rate (1/T2) for a number of different commercially available colloids. For polystyrene the behavior is much different; essentially 1/T2 is invariant with concentration. The differences are consistent with the degree of hydrogen-bonding between the water and the surface. In line with others in the literature, we suggest that 1/T2 can be used to infer the wetted surface area of particle suspensions. The influence of surface chemistry upon this attribute will be described.

Low-field NMR relaxometry for characterizing wetted surface area in colloids and polymer particle dispersions

2019 Fall National Meeting

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