The extensive use of hydrophophobic alkyd resins in the coating industry is stimulating studies to obtain O / W emulsions by a catastrophic inversion process and to understand the influence of different variables in the fraction of water required for the inversion and the final droplet size. The highly viscous bio-based isosorbide polyester resin was synthesized from fatty acid (soybean oil), succinic acid and glycerol. The inversion is followed by conductivity, torque (Figure 1) and the light backscattering in order to compare the different signals and their performance to follow the inversion [1, 2]. The carboxylic functions of the resin can be neutralized with KOH. For the non-neutralized resin, a polydispersed distribution with an average diameter of 1 μm was reached at a final concentration of 3% by weight of surfactant and a flow rate of 0.5 ml / min of water. Under the same conditions, for neutralized resins, the droplet size is smaller (200-300 nm) and the emulsion has a narrow distribution. As the percentage of neutralization increases, the fraction of water at which inversion occurs also increases. The neutralization of the resin must incorporate a few small anionic amphiphilic molecules at the interface increasing the hydrophilicity of the system and widening the hysteresis zone [1]. The increase in the water flow rate (0.05-0.5 ml / min) increases the size of the droplets and decreases the "Phase Inversion Point". Increasing the surfactant concentration makes it possible to obtain smaller droplets, but emulsions with concentrations greater than 4% by weight exhibit asymptotic behavior [1]. Figure 1. Torque variation during catastrophic inversion of the bio-based polyester resin as function of the time during the water addition [1] Pierlot, C.; Ontiveros, J. F.; Royer, M.; Catté, M.; Salager, J.-L. Emulsification of Viscous Alkyd Resin by Catastrophic Phase Inversion with Nonionic Surfactant. Colloids Surf. Physicochem. Eng. Asp. 2018, 536, 113–124. [2] Catté, M.; Ontiveros, J. F.; Aramaki, K.; Pierlot, C. Catastrophic Emulsion Inversion Process of Highly Viscous Isosorbide Biobased Polyester Monitored in Situ by Torque and Light Backscattering. J. Oleo Sci. 2018, 67 (8), 925–931.