Abstract
Hypothesis: Saponins 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. Experiments: We 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%). Findings: Quillaja 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 viscoelasticity is known to have strong impact on the viscous stress of steadily sheared foams. Mechanistic explanations of all observed effects are described.
Original language | English |
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Pages (from-to) | 264-275 |
Number of pages | 12 |
Journal | Journal of Colloid and Interface Science |
Volume | 564 |
DOIs | |
Publication status | Published - 22 Mar 2020 |
Bibliographical note
Funding Information:This work was supported by Unilever R&D Vlaardingen, the Netherlands , and by Operational Program “Science and Education for Smart Growth” 2014-2020, co-financed by European Union through the European Structural and Investment Funds , Grant BG05M2OP001-1.002-0012 “Sustainable utilization of bio-resources and waste of medicinal and aromatic plants for innovative bioactive products”. S. Tsibranska is grateful to Operational program “Science and Education for Smart Growth”, project BG05M2OP001-2.009-0028 for the financial support for her scientific visit to Unilever R&D Vlaardingen, the Netherlands. Appendix A
Publisher Copyright:
© 2019 Elsevier Inc.
Keywords
- Emulsion
- Emulsion rheology
- Interfacial rheology
- Saponin
- Surface elasticity
- Surface rheology
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Biomaterials
- Surfaces, Coatings and Films
- Colloid and Surface Chemistry