Role of interfacial elasticity for the rheological properties of saponin-stabilized emulsions

Abstract

HypothesisSaponins are natural surfactants which can provide highly viscoelastic interfaces. This property can be used to quantify precisely the effect of interfacial dilatational elasticity on the various rheological properties of bulk emulsions. ExperimentsWe measured the interfacial dilatational elasticity of adsorption layers from four saponins (Quillaja, Escin, Berry, Tea) adsorbed on hexadecane-water and sunflower oil-water interfaces. In parallel, the rheological properties under steady and oscillatory shear deformations were measured for bulk emulsions, stabilized by the same saponins (oil volume fraction between 75 and 85 %). FindingsQuillaja saponin and Berry saponin formed solid adsorption layers (shells) on the SFO-water interface. As a consequence, the respective emulsions contained non-spherical drops. For the other systems, the interfacial elasticities varied between 2 mN/m and 500 mN/m. We found that this interfacial elasticity has very significant impact on the emulsion shear elasticity, moderate effect on the dynamic yield stress, and no effect on the viscous stress of the respective steadily sheared emulsions. The last conclusion is not trivial, because the dilatational surface elasticity is known to have strong impact on the viscous stress of steadily sheared foams. Mechanistic explanations of all observed effects are described.3 1. Introduction.

Origin of the extremely high elasticity of bulk emulsions, stabilized by Yucca Schidigera saponins

“…From the experimental results described so far we can conclude that the high shear elasticity of Yucca-stabilized emulsions, prepared with non-purified oil, is related to the presence of phytosterols in the oily phase which interact with the saponins from the aqueous phase and form elastic skin on the drop surface. However, as showed in our previous study (Tsibranska et al, 2020) the high interfacial elasticity (per se) can increase the shear elasticity of bulk emulsion by up to 4 times, as compared to the elasticity of emulsions with fluid adsorption layers. On the other hand, in the current study we found that the emulsion elasticity increased by ca.…”

“…an order of magnitude lower, at Φ SFO = 75 vol. % (Tsibranska et al, 2020). Another reference worthy to note is the elasticity of hexadecane emulsions, stabilized by Quillaja saponin extract QD with very high interfacial elasticity, which was ≈ 800 Pa at 75 vol %, whereas the FD-stabilized emulsions have emulsion elasticity of 4000 Pa at the same Φ SFO .…”

“…Dimitrova & Leal-Calderon, 2004;Arditty, Schmitt, Giermanska-Kahn, & Leal-Calderon, 2004;Bressy, Hébraud, Schmitt, & Bibette, 2003;Tsibranska et al 2020); and (2) The strength of the adhesion between the neighboring drops(Alben, Holtze, Tadros, & Schurtenberger, 2012;Becu, Manneville, & Colin, 2006) or bubbles(Denkov, Tcholakova, Hoehler, & Cohen-Addad, 2012;Princen, 2001;Politova et al, 2012). Below we analyze the available experimental results, both ours and of other authors, to clarify the relative importance of these two effects and of their combined action.…”

Aesculus hippocastanum L. as a Stabilizer in Hemp Seed Oil Nanoemulsions for Potential Biomedical and Food Applications

“…Different studies with various saponins groups have indicated the ability of these compounds to improve the emulsions' characteristics. Saponins increase the stability of emulsions containing crude oil [13], pure hydrocarbons such as hexadecane, and natural oils including sunflower oil [14], rice bran oil [15] and olive oil [16]. It was also found that the presence of saponins led to a significant decrease in emulsion droplet size; however, the saponins' impact on the droplets' zeta potential was ambivalent [17,18].…”

Shear modulus and yield stress of foams: contribution of interfacial elasticity

“…Even higher foam elastic modulus and yield stress values, not captured by the correlation between foam and interfacial viscoelastic properties, were found under conditions favoring protein aggregation and were attributed to lamellae spanning structures. Tsibranska et al 10 suggested the bulk elastic modulus of emulsions to scale with interfacial dilatational elastic modulus E A 4 5 mN m À1 as follows:…”