PHM2213 practical
106733862
PHM2213 Physical Pharmacy 2
Emulsion properties
Note
This practical will use oil-in-water emulsions prepared earlier.
Objective
To determine the pH of emulsions, stability of the emulsion against heat and the
occurrence of phase inversion of the emulsions, and their viscosities. These properties
will be related to the types of surfactants used for emulsification and emulsion
stability.
Introduction
Stability of emulsions depends on many factors. For instance the zeta potential of oil
droplets is influenced by the pH of the medium. The determination of emulsion
properties helps in predicting the stability. The rate of creaming in an emulsion or the
rate of sedimentation of dispersed solids, observed in phase separation, are related to
viscosity of the medium, as given by Stoke’s equation.
Experimental procedure
1. pH measurement
Measure the pH of each emulsion at 30C. Repeat measurement. Record the
reading and the type of pH meter used.
Table 1 pH of oil emulsions measured at 30C.
Type of emulsion
pH-1
Emulsion 1
Emulsion 2
Emulsion 3
Emulsion 4
pH-2
pH-average
2. Heat stability
Weigh 200 g emulsion in a 200 ml glass beaker. Using a hot plate and a magnetic
stirrer, increase the temperature gradually from 30C to 70C. Observe if there is a
change in the appearance of the emulsion.
Table 2 Stability of emulsions against heat
Type of emulsion
Phase inversion
(Y/N)
Emulsion 1
Emulsion 2
Emulsion 3
Emulsion 4
Prepared by: Kausar Ahmad
Date created: 13-May-2004
Date of revision: 16-December-2004
Page 1 of 2
Observations
PHM2213 practical
106733862
3. Viscosity measurement
Measure the viscosity of each emulsion using all spindles. Take readings after 60
seconds. Record the type of viscometer used, shear rates applied by using the
different spindles and tabulate your results.
Table 3 Viscosities of oil emulsions
Spindle
Shear rate
No.
(rpm)
Emulsion 1
1
2
3
4
Type of emulsion
Emulsion 2
Emulsion 3
Emulsion 4
Write a report and submit one week after the practical.
Relate your findings in this practical to earlier work and answer the following in
your discussion:
1. What is the reason for the different pH observed?
2. Upon heating the emulsion:
a. Is the emulsion stable?
b. Has a phase inversion occurred?
i. If yes, at what temperature the emulsion appeared to destabilise?
How do you justify this?
ii. If no, why not?
3. Why is there a difference in the viscosity measurement when using different
types of spindles?
4. What do you think will happen to the viscosity if the concentration of the oil
phase is increased?
5. Is there a relationship between viscosity and particle size?
6. What is the effect of ageing on emulsion properties?
Prepared by: Kausar Ahmad
Date created: 13-May-2004
Date of revision: 16-December-2004
Page 2 of 2