Temperature-dependent stability of water-in-undecanol emulsions

The stability of water-in-undecanol emulsions to sedimentation and coalescence as a function of temperature is described. By monitoring the release of water and oil by the emulsions, the stability of emulsions prepared in the absence of stabilisers and in the presence of either hydrophobic silica particles or octanoic acid molecules is characterised. We show that the destabilisation phenomena observed for the solid-stabilised emulsions reflects the breakdown of emulsions prepared in the absence of stabilisers. The extent of coalescence in the solid-stabilised emulsions undergoes a transition at a temperature about 10 °C above the melting point of undecanol and the stability of the emulsion to sedimentation passes through a maximum at about the same temperature. We attribute the low stability of these emulsions to coalescence at temperatures up to 10 °C above the melting point of undecanol to the formation of a solid-like layer of alcohol at the drop surface, similar to the surface crystallisation phenomena of medium chain length alcohols at planar oil–water interfaces. The addition of octanoic acid to these emulsions does not affect the surface crystallisation.