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Coalescence in concentrated Pickering emulsions under shear
Catherine P Whitby1, Melinda Krebsz
1Ian Wark Research Institute, University of South Australia, Mawson Lakes, SA 5095, Australia. Catherine.Whitby@unisa.edu.au.
Soft Matter
|May 28, 2014
Summary
Concentrated emulsions stabilized by silica nanoparticles exhibit solid-like elasticity. Their breakdown is linked to salt concentration and particle interactions, with the nanoparticle layer acting as a mechanical barrier.
Area of Science:
- Materials Science
- Colloid and Surface Chemistry
- Rheology
Background:
- Concentrated emulsions are complex fluids with applications in food, cosmetics, and pharmaceuticals.
- Understanding the relationship between particle stabilization and emulsion rheology is crucial for formulation stability.
- Silanised silica nanoparticles offer tunable surface properties for emulsion stabilization.
Purpose of the Study:
- To investigate the rheological properties of concentrated oil-in-water emulsions stabilized by silanised silica nanoparticles.
- To determine the factors influencing the elasticity and breakdown of these emulsions.
- To explore the role of the nanoparticle interfacial layer in emulsion stability.
Main Methods:
- Rheological measurements (e.g., small-amplitude oscillatory shear) were performed on emulsions with varying salt concentrations and nanoparticle loadings.
- Microscopy techniques were employed to observe droplet morphology and interfacial layer characteristics.
- Analysis of the correlation between emulsion elasticity, salt concentration, and particle interactions.
Main Results:
- The emulsions exhibited high elasticity, behaving like solids under small strains.
- Emulsion breakdown and yielding occurred at larger deformations.
- Emulsion elasticity strongly correlated with salt concentration, indicating particle aggregation's role.
- Minimizing inter-particle attractive forces favored emulsion destabilization.
- Microscopy revealed anisotropic, wrinkled coalesced drops, suggesting the interfacial layer's barrier function.
Conclusions:
- Silanised silica nanoparticles effectively stabilize concentrated emulsions, imparting significant elasticity.
- Emulsion stability and rheological behavior are critically dependent on salt-induced particle aggregation and inter-particle forces.
- The nanoparticle interfacial layer acts as a mechanical barrier, influencing bulk emulsion destabilization mechanisms.
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