Multimodal O/W emulsion structuration characterization using water and emulsion thickening ranges

To ensure the stability of emulsions, a thickening agent is often used to induce a higher viscosity of the continuous aqueous phase and reduce the possibility of gravitational separation(1). In some cases, these agents require a base to increase the thickening of emulsions and this process can be observed by following the viscosity as a function of the pH(2). Our work attempts to show the link between gelation process and emulsion stability investigated through the use of two innovative measurement techniques at the mesoscopic scale: micro-rheology by ultrasounds and electrical complex dielectric characterization by contactless radiofrequency spectroscopy. The first one allows to better understand the emulsion structuration through the measurement of the visco-elastic properties(3). The second one is used to get information about polarizability of the mixing and conductivity of the continuous phase(4). A comparison is done between the aqueous phase (water + Carbopol® CETD 2050: gel phase) and the equivalent emulsion (aqueous phase + oil: Isopropyl Palmitate + surfactants: Eumulgin® SMO 20/Cutina® GMS V), for different pH by changing the amount of base (Triethanolamine). Both are made on the same pH range (3.5 – 6) to emphasize steric behavior rather than the electrical one. The mesoscopic characterizations highlight the impact of oil on the gelation state. They also show the limits of pH adjustments on increasing viscosity and electronic repulsion between oil droplets, which are stability-promoting factors. The results are completed by complementary classical characterizations such as conductivity, rheological and optical microscopy measurements, to correlate them with documented macroscopic knowledge(5). (1) Piorkowski D.T., et al, 2014 (2) Abdolmaleki K., et al, 2016 (3) Gauthier V., et al, 2017 (4) Dinh T.H.N., et al, 2016 (5) Gutowski I., et al, 2008