Dispersion stability
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Dispersions are unstable from the thermodynamic point of view; however, they can be kinetically stable over a large period of time, which determines their shelf life. This time span needs to be measured in order to ensure the best product quality to the final consumer. “Dispersion stability refers to the ability of a dispersion to resist change in its properties over time.” D.J. McClements.[1]
These destabilizations can be classified into two major processes:
- Migration phenomena : whereby the difference in density between the continuous and dispersed phase, leads to gravitational phase separation:
- Creaming, when the dispersed phase is less dense than the continuous phase (e.g. milk, cosmetic cream, soft drinks, etc.)
- Sedimentation, when the dispersed phase is denser than the continuous phase (e.g. ink, CMP slurries, paint, etc.)
- Particle size increase phenomena: whereby the size of the dispersed phase (drops, particles, bubbles) increases
- reversibly (flocculation)
- irreversibly (aggregation, coalescence, Ostwald ripening)
