Using low-field NMR relaxation to optimise particulate dispersions

Formulation of particulate dispersions is a difficult industrial problem, with a multitude of system details influencing the final outcome. Solvent relaxation NMR is shown to help optimise the formulation of particulate dispersions of a range of widely used commercial silicas. Solvent at the particle interface is sensitive to details of the formulation, and it is shown that the average solvent spin-relaxation time in a dispersion can be used to monitor wetted surface area, sample sedimentation, and additive amounts; chemical syntheses and mechanical degradation of silicas are also monitored to optimise the dispersions. The experiments, which can be carried out on bench-top or on-line spectrometers, are not limited to silicas and can be generalised to other particles in a range of aqueous and non-aqueous dispersions, providing useful feedback to the formulator anywhere surfactants, polymers, pH, ionic strength, Hamaker constants, and surface charge play a role in stabilisation.