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

Research output: Contribution to journalArticlepeer-review

Authors

  • Sonya Tsibranska
  • Slavka Tcholakova
  • Konstantin Golemanov
  • Nikolai Denkov
  • Simeon D. Stoyanov

Colleges, School and Institutes

External organisations

  • Sofia University
  • Unilever Research and Development
  • Wageningen University and Research Centre
  • University College London

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.

Bibliographic 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.

Details

Original languageEnglish
Pages (from-to)264-275
Number of pages12
JournalJournal of Colloid and Interface Science
Volume564
Publication statusPublished - 22 Mar 2020

Keywords

  • Emulsion, Emulsion rheology, Interfacial rheology, Saponin, Surface elasticity, Surface rheology