Rational design of O/W nanoemulsions based on the surfactant dodecyldiglyceryl ether using the normalized HLD concept and the formulation-composition map

Abstract

The 1-O-dodecyl diglycerol ether (C12Gly2) is a well-balanced bio-based surfactant whose amphiphilicity and emulsifying property have been studied within the Normalized Hydrophilic-Lipophilic-Deviation (HLDN) framework. Its Hydrophilic-Lipophilic tendency has been measured in saline and salt-free media by two methods. The classic one, is based on the identification of the optimal formulation (Winsor III) in a series of tubes containing a series of C12Gly2/Alkane/Water systems at equilibrium. The alternative method, much faster and more precise, is based on the phase inversion of the same systems under stirring, the HLDN value of which is gradually modified by changing the temperature or the salinity. C12Gly2 is found to be three times less sensitive to temperature and salinity variations than typical ethoxylated surfactants. By stirring C12Gly2/Alkane/Water systems, O/W or W/O emulsions are obtained depending on whether the alkane is long or short. The finest and the least stable emulsions (1 µm) are obtained with n-octane for which HLDN = 0. By systematically varying the Water-to-Oil Ratio (WOR) and the hydrophobicity of the oil, either direct O/W or reverse W/O emulsions are formed and are represented in a Formulation-Composition map. This map is a powerful tool to guide the formulator about which type of emulsion will be obtained depending on the composition of the SOW system and the emulsification protocol used i.e. the pathway in the map. In particular, it is possible to prepare stable and very fine emulsions (≈ 100 nm) by crossing the inversion border of the map favouring the splitting of the droplets and then moving away from it quickly to prevent the coalescence of the droplets.