Chapter 2
To distinguish simple and multiple emulsions, optical microscopy method is
also used. If the optical property difference between the water and oil phase is
significant enough, it is easy to find the type the emulsions under microscopy
observation. This method is often used in complicated water∕oil systems and will
be mentioned later.
2.2.3. Shear viscosity
Rheology properties of emulsion are obviously important physical attributes.
In qualitative terms, emulsions range from low viscosity milk-like Newtonian
liquids through thicker shear-thinning liquids, right up to thick, cream-like
materials with apparent yield stresses t8j.
As shear-thinning liquids, emulsions can be described by apparent shear
viscosity η, which is analogous to that of pure fluids as given by Newton’s law. η is
the proportionality coefficient between stress (τ∕z) and rate of strain (also shear
rate, yÿ), η = τjilγij.
Factors affecting the shear viscosity of an emulsion are, in order of relevance,
the viscosity of the continuous phase (∕7c), the dispersed phase content (φ), and
the mean size and size distribution Ofdroplets [2].
The viscosity increases with the dispersed phase content due to interactions
among droplets. For diluted colloidal dispersions (φ<0.02) the correction
10
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