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Updated: Aug 30, 2025
Self-Nanoemulsification of Healthy Oils to Enhance the Solubility of Lipophilic Drugs
Published on: July 27, 2022
Minimum surfactant concentration required for inducing self-shaping of oil droplets and competitive adsorption
Jiale Feng1,2, Zhulieta Valkova3, E Emily Lin4
1Active and Intelligent Materials Lab, Department of Materials Science & Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 OFS, UK.
Abstract:
Surfactant choice is key in starting the phenomena of artificial morphogenesis, the bottom-up growth of geometric particles from cooled emulsion droplets, as well as the bottom-up self-assembly of rechargeable microswimmer robots from similar droplets. The choice of surfactant is crucial for the formation of a plastic phase at the oil-water interface, for the kinetics, and for the onset temperature of these processes. But further details are needed to control these processes for bottom-up manufacturing and understand their molecular mechanisms. Still unknown are the minimum concentration of the surfactant necessary to induce the processes, or competing effects in a mixture of surfactants when only one is capable of inducing shapes. Here we systematically study the effect of surfactant nature and concentration on the shape-inducing behaviour of hexadecane-in-water emulsions with both cationic (CTAB) and non-ionic (Tween, Brij) surfactants over up to five orders of magnitude of concentration. The minimum effective concentration is found approximately equal to the critical micelle concentration (CMC), or the solubility limit below the Krafft point of the surfactant. However, the emulsions show low stability at the vicinity of CMC. In a mixed surfactant experiment (Tween 60 and Tween 20), where only one (Tween 60) can induce shapes we elucidate the role of competition at the interface during mixed surfactant adsorption by varying the composition. We find that a lower bound of ∼75% surface coverage of the shape-inducing surfactant with C14 or longer chain length is necessary for self-shaping to occur. The resulting technique produces a clear visual readout of otherwise difficult to investigate molecular events. These basic requirements (minimum concentration and % surface coverage to induce oil self-shaping) and the related experimental techniques are expected to guide academic and industrial scientists to formulations with complex surfactant mixtures and behaviour.
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