rheology of suspensions and emulsions

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Rheology of suspensions and emulsions:

Rheology of suspensions and emulsions

Rheology of suspensions:

Rheology of suspensions Factors considered are Viscosity of a suspension Change in flow properties of the suspension Spreading qualities of the lotion

Rheology of suspensions:

Rheology of suspensions Low shear rates – at storage conditions High shear rates – when container is shaken

Rheology of suspensions:

Rheology of suspensions Ideal suspending agent high viscosity at negligible shear rate Low viscosity at high shear rate Eg.Tragacanth, sodium alginate and sodium CMC

Rheology of suspensions:

Rheology of suspensions Suspending agent - should exhibit thixotropic and pseudoplastic behavior. Eg. 50:50 mixture of CMC and Micro Bentonite.

Rheology of emulsions:

Rheology of emulsions Performance of the emulsion – depends on flow properties Removal of an emulsion from a bottle or tube Flow of an emulsion through a hypodermic needle. Spreadability of an emulsion on the skin. Stress induced flow changes during manufacture (milling)

Rheology of emulsions:

Rheology of emulsions Dilute emulsions – Newtonian flow Concentrated emulsions – Non-newtonian flow

Rheology of emulsions:

Rheology of emulsions To modify the flow properties Viscosity of dispersed phase Viscosity of continuous phase Concentration of emulsifying agent

Rheology of emulsions:

Rheology of emulsions Dispersed phase Phase – volume ratio Particle size distribution Viscosity of the internal phase

Rheology of emulsions:

Rheology of emulsions Phase volume ratio volume concentration of dispersed phase Less than 0.05 – Newtonian More than 0.05 – pseudo plastic and plastic flow Approaches 0.74 – phase inversion

Rheology of emulsions:

Rheology of emulsions Particle size distribution Mean particle size reduced – more viscosity Wider particle size distribution – less viscosity

Rheology of emulsions:

Rheology of emulsions Viscosity of continuous phase Concentrated emulsions – higher viscosity - thickness of adjacent droplets is 100-200 A 0 Increasing shear – less viscosity – thickness decreases

Rheology of emulsions:

Rheology of emulsions Emulsifying agent affects particle flocculation and interparticle attractions. Concentration Physical properties of the film Electrical properties

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