Polymeric stabilized emulsions: steric effects and deformation in soft systems
Ofer Manor1, Thanh Tam Chau, Geoffrey Wayne Stevens
1Department of Mathematics and Statistics, University of Melbourne, Parkville 3010, Australia.
Langmuir : the ACS Journal of Surfaces and Colloids
|February 21, 2012
Summary
Polymeric stabilizers in emulsions are stabilized by drop deformation, not just polymer brush compression. This finding challenges the long-held understanding of steric stabilization for emulsion drops.
Area of Science:
- Colloid and Surface Science
- Materials Science
- Rheology
Background:
- Polymeric stabilizers are crucial in diverse applications, including pharmaceuticals, lubricants, food, and cosmetics.
- Current understanding attributes stabilization in rigid particulate systems to steric repulsion from compressed polymer coatings ('steric brush').
- This mechanism has guided polymer design for over 30 years.
Purpose of the Study:
- To investigate the stabilization mechanisms of adsorbed polymer layers on emulsion drops.
- To directly measure repulsive interactions between immobilized drops with adsorbed polymer layers.
- To challenge the prevailing model of steric stabilization in rigid systems.
Main Methods:
- Direct measurement of repulsive forces between immobilized emulsion drops with adsorbed polymer layers in aqueous electrolyte solutions.
- Analysis of interactions at varying collision speeds to differentiate hydrodynamic drainage effects.
- Application of simple continuum modeling to understand film drainage dynamics.
Main Results:
- Emulsion drop interactions are governed by both steric stabilization and significant drop deformation.
- At slow collision speeds, drop deformation, not polymer brush compression, dominates the repulsive force.
- At higher speeds, film drainage becomes sensitive to flow through the polymer brush.
Conclusions:
- The stability of emulsion drops is influenced by drop deformation, a factor overlooked in rigid particulate systems.
- For deformable drops, stability is less dependent on polymer molecular weight or size compared to rigid particles.
- This study necessitates a revised understanding of polymeric stabilization mechanisms in emulsions.
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