Stoke's Law calculates rate of destabilization of an emulsion by equating gravitational force with the opposing hydrodynamic force. Stoke's Law can be used to predict emulsion stability.

1. Stoke’s Law
Photo
courtesy
of
Patrick
Willems
on
Flickr
Prof. Abd Karim Alias
Universiti Sains Malaysia

2. Stoke's Law calculates rate of destabilization of an
emulsion by equating gravitational force with the opposing
hydrodynamic force:
where V = velocity of separation (or rate of creaming), cm/sec;
g = acceleration of gravity (980 cm/sec);
r = droplet radius (cm);
d1 = density of disperse phase (g/cm3);
d2 = density of continuous phase (g/cm3);
µ = viscosity of the continuous phase (g/cm.sec) (µ = 0.01 at 20 °C)
Stoke’s Law
2gr2 (d1 – d2)
9µ

3. You are making orange soda from
an orange flavor emulsion. The density of the
orange oil is 0.85 g/cm3, the density of a 10%
sugar solution is 1.04 g/cm3, the average
particle radius is 3.0 micron, and µ = 0.01 g/
cm·sec. What is V? Will the emulsion remain
stable?
Stoke’s Law
PROBLEM 1
2gr2 (d1 – d2)
9µ
Photo
courtesy
of
Brent
Moore
on
Flickr

4. You homogenize the beverage mix so that
the particle radius is decreased to 0.3 micron.
What is V? Will the emulsion remain stable?
Stoke’s Law
PROBLEM 2
2gr2 (d1 – d2)
9µ
Photo
courtesy
of
Brent
Moore
on
Flickr

5. You add brominated vegetable oil to the
orange oil so the overall density is 0.95 g/
cm3 . What is V for particle radius 3.0 micron?
For 0.3 micron? Will the emulsion remain
stable?
Stoke’s Law
PROBLEM 3
2gr2 (d1 – d2)
9µ
Photo
courtesy
of
Brent
Moore
on
Flickr

6. For the above problems, which approach
stabilized the emulsion more -- decreasing
particle size or increasing density of the
dispersed phase?
Stoke’s Law
PROBLEM 4
2gr2 (d1 – d2)
9µ
Photo
courtesy
of
Brent
Moore
on
Flickr