| Abstract
| - Growth processes of hydrocarbon droplets (C6−C16: n-hexane, cyclohexane, n-octane, n-decane,n-dodecane, n-tetradecane, and n-hexadecane) in oil/water emulsions under surfactant-free conditionswere examined by dynamic light scattering (DLS) and freeze-fracture electron microscopy (FFEM). DLSresults showed that the growth rate of droplet size decreased with increase in hydrocarbon chain length.For example, n-hexane droplets grew within 1 h from submicrometer to micrometer droplets, whilen-hexadecane droplets with sizes of several tens of nanometers kept their dispersibility for 24 h. Wedetermined the growth processes as coalescence and molecular diffusion (Ostwald ripening) in terms ofthe Lifshitz−Slyozov−Wagner theory and the Smoluchowski equation. Furthermore, FFEM was used toexamine the growth mechanism in detail. Direct imaging of n-hexane and cyclohexane droplets by FFEMallowed us to observe very fine oil droplets (∼10 nm in diameter) though DLS could not detect thesedroplets, suggesting that fine droplets of shorter hydrocarbons such as n-hexane and cyclohexane growvia both molecular diffusion and coalescence processes in a very short time after preparation.
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