Abstract
In self-emulsification higher-energy micrometre and sub-micrometre oil droplets are spontaneously produced from larger ones and only a few such methods are known. They usually involve a one-time reduction in oil solubility in the continuous medium via changing temperature or solvents or a phase inversion in which the preferred curvature of the interfacial surfactant layer changes its sign. Here we harness narrow-range temperature cycling to cause repeated breakup of droplets to higher-energy states. We describe three drop breakup mechanisms that lead the drops to burst spontaneously into thousands of smaller droplets. One of these mechanisms includes the remarkable phenomenon of lipid crystal dewetting from its own melt. The method works with various oil–surfactant combinations and has several important advantages. It enables low surfactant emulsion formulations with temperature-sensitive compounds, is scalable to industrial emulsification and applicable to fabricating particulate drug carriers with desired size and shape.
Highlights
In self-emulsification higher-energy micrometre and sub-micrometre oil droplets are spontaneously produced from larger ones and only a few such methods are known
We show its applicability to a number of different systems
We studied a large series of oil-in-water emulsions of linear alkanes, with chain length varying from C14 to C20 and melting temperatures varying between Tm 1⁄4 6 °C for C14 and 37 °C for C20
Summary
In self-emulsification higher-energy micrometre and sub-micrometre oil droplets are spontaneously produced from larger ones and only a few such methods are known They usually involve a one-time reduction in oil solubility in the continuous medium via changing temperature or solvents or a phase inversion in which the preferred curvature of the interfacial surfactant layer changes its sign. For nonpolar oils with larger molecules, often encountered in practice, the phase inversion self-emulsification techniques were developed[11,12,13,14] The latter methods rely on change of the preferred interfacial curvature on change of the temperature or surfactant concentration. In the current study we describe an efficient and scalable process of self-emulsification in which we harness small temperature fluctuations to cause repeated spontaneous bursting of the dispersed drops into smaller droplets, in the processes of drop freezing and melting. We have confirmed that the studied phenomenon is rather general, as it has been observed with numerous oil–surfactant combinations, where the oily phase could be alkanes of different chain lengths, alcohols or triglycerides
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