In this paper, the crystallization mechanism of hydrogenated castor oil (HCO) is studied. In contrast to what occurs for a classical emulsion crystallization, the surfactant present in the aqueous phase is shown to enable an aqueous phase driven crystallization forming nonspherical, sometimes highly elongated, crystals. The presence of surfactant appears to be crucial, as it increases the solubility of HCO and sustains crystal growth of aqueous crystals. This is demonstrated by linking the formation of these nonspherically shaped crystals with a required relatively high solubility obtained by adding surfactant. The solubilized HCO concentration versus the crystal shapes is presented for four different surfactants as a function of the surfactant concentration: amine oxide, sodium and monoethylamine linear alkylbenzenesulfonate and sodium dodecyl sulfate. Furthermore, under certain conditions the emulsified HCO is shown to completely crystallize in the aqueous phase, even if at the start of the crystallization only part of the HCO is solubilized. This illustrates the presence of a HCO transport mechanism continuously transporting HCO from emulsion to the aqueous phase to the growing crystals.
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