Colloids instability
Colloidal systems, here nanoemulsions, are thermodynamically unstable dispersion. There are five distinct known instability mechanisms: coalescence, Ostwald ripening, flocculation, creaming and sedimentation.
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Ostwald ripening, diffusion of dispersed phase from small droplet to large ones, is known as the main destabilisation mechanism of nanoemulsions. However, Brownian motion induced coalescence has been neglected.
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Using a range of oils (with different solubility) and various surfactant aqueous solutions, it is shown that Ostwald ripening results in an initial decrease in average droplet size (number of small droplets decreases) and when the small droplet disappear, the average droplet size increases.
At low surfactant concentration, with not sufficient surface coverage, Brownina motion induced coalescence results in formation of larger droplets, and right skewed droplet size distribution.
