*Article* **Interfacial Properties and Emulsification of Biocompatible Liquid-Liquid Systems**

**Katarzyna Dziza 1, Eva Santini 1, Libero Liggieri 1,\*, Ewelina Jarek 2, Marcel Krzan 2, Thilo Fischer <sup>3</sup> and Francesca Ravera <sup>1</sup>**


Received: 19 March 2020; Accepted: 10 April 2020; Published: 17 April 2020

**Abstract:** A comparative study is reported on the interfacial properties of a set of surfactants and is discussed in terms of the effects on the features of the corresponding oil-water emulsions. The surfactants are saponin, Tween 80 and citronellol glucoside (CG), while the oil is Miglyol 812N—A Medium Chain Triglyceride (MCT) oil. Due to their high biocompatibility, all these compounds are variously utilized in food, cosmetic or pharmaceutical products. Among the surfactants, which are all soluble in water, CG presents also an important solubility in oil, as shown by the measured partition coefficient. For these systems, dynamic and equilibrium interfacial tensions and dilational viscoelasticity are measured as a function of the surfactant concentration and analyzed according to available adsorption models. In order to compare these results with the time evolution of the corresponding emulsions, the actual surfactant concentration in the matrix phase of the emulsion is accounted for. This may differ significantly from the nominal concentration of the solutions before dispersing them, because of the huge area of droplets available for surfactant adsorption in the emulsion. Using this approach allows the derivation of the correlations between the observed emulsion behavior and the actual surfactant coverage of the droplet interface.

**Keywords:** interfacial tensions; dilational rheology; biocompatible emulsions; partition coefficient; Tween 80; saponin; citronellol glucoside; MCT oil; Miglyol 812N
