- Rheological Properties of Emulsions reveal interactions between dispersed droplets and continuous phase.
- Rheological Properties of Emulsions is the study of flow and deformation of matter. In emulsions, rheology influences pourability, spreadability, stability, and user acceptability.
Flow Behavior Types:
- Newtonian: Viscosity remains constant (e.g., water, some dilute emulsions)
- Non-Newtonian:
- Pseudoplastic (shear-thinning): Viscosity decreases with shear (common in emulsions with polymers)
- Plastic: Shows yield stress before flowing
- Thixotropic: Viscosity decreases over time with shear, but recovers when shear is removed (ideal for creams and lotions)
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Importance in Emulsions:
- High viscosity reduces creaming and coalescence.
- Thixotropic emulsions are desirable for topical applications.
- Helps in product stability and aesthetic quality.
Viscosity Modifiers Used
- Natural polymers: Acacia, tragacanth
- Synthetic polymers: Carbopol, HPMC
- Clays: Bentonite
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Factors Affecting Emulsion Rheology:
- Droplet size and distribution
- Volume fraction of dispersed phase
- Type and concentration of emulsifiers
- Use of rheology modifiers (e.g., carbomers, cellulose derivatives)
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