pH Effect on Properties of Surfactant-free Oil-in-water Emulsion Prepared with Oleic Acid

Size distribution, ζ potential, and yield of surfactant-free oil-in-water (O/W) emulsion prepared with oleic acid were measured at various pHs after seven days from the emulsification. We found that the size distribution is almost the same regardless of pH from 9 to 3. The magnitude of ζ potential and yield remains constant at pH from 9 to 6, and decreases at pH from 6 to 3. There is a correlation between the ζ potential and the yield, but no correlation between the ζ potential and the size, suggesting that the ζ potential relates to stability of oleic acid droplets in water rather than their size.