Study Set Content:
The stability of a pharmaceutical emulsion is characterized by
the:
Absence of coalescence of the internal phase
• Absence of creaming
• Maintenance of elegance with respect to appearance, odor,
color, and other physical properties.
Instability of Pharmaceutical Emulsions:
• Flocculation and creaming
• Coalescence and breaking
• Miscellaneous physical and chemical changes
• Phase inversion
an o/w stabilized with sodium stearate can be
inverted to the w/o type by adding calcium chloride to form
calcium stearate.
Phase inversion
Substances can exist in any of 3 phases: gas, liquid or solid.
When two phases meet, the boundary between them is called
an
interface. or Interfacial Phenomena
It is the boundary between two phases
Interphase
Boundary between ari (gas or vapor) and either solid or
liquid phases.
Surface
Is a phenomenon in which the surface of a liquid act as a thin
elastic membrane when it is in contact with gas.
Surface Tension
Due to unbalanced intermolecular forces, (term is used only
when the liquid surface is in contact with gas such as the air)
Surface Tension
Surface Tension Units:
dyne/cm
Is the tension existing at the interface between two immiscible
liquids.
Interfacial Tension
It does not exist if the two liquids are miscible
Interfacial Tension
Interfacial Tension Units:
dyne/cm
Intermolecular Forces
Cohesive
Adhesive
Are forces which act between molecules of the same phase
(forces are between like molecules).
Cohesive Forces
Are forces which act between molecules of different phases
(forces are between unlike molecules).
Adhesive Forces
forces tend to increase the affinity of two phases
Adhesion
force tend to keep the phases separate while
Cohesion
At liquid surface 2 opposite forces:
Cohesive forces
Adhesive forces
(between liquid molecules and gas molecules) upward
force pull towards the air.
Adhesive forces
(between liquid molecules from sides and below) inward
force pull towards the bulk.
Cohesive forces
