Pharmaceutical suspension is a
internal phase is
internal phase consisting of insoluble
throughout the suspending
aid of single
external phase (suspending medium)
some instance, may be
or oily liquid for non oral
Degree of flocculation (
Degree of flocculation: is the ratio of the sedimentation volume of the flocculated
suspension F, to the sedimentation volume of the deflocculated suspension, F¥
ß = F / F¥
When the total volume of both the flocculated and the deflocculated suspensions
ß = (Vu)
The minimum value of ß is
; this is the case when the sedimentation volume of
the flocculated suspension is equal to the sedimentation volume of deflocculated
ß is more fundamental parameter than F since it relates the volume of flocculated
sediment to that in a deflocculated system
The zeta potential is defined as the difference in potential between
the surface of the tightly bound layer (shear plane) and electro
neutral region of the solution.
The ions that gave the particle its charge, are called potential
Immediately adjacent to the surface of the particle is a layer of tightly
bound solvent molecules, together with some ions oppositely charged
to the potential determining ions.
These two layers of ions at the interface constitute a double layer of
electric charge (shear plane).
Zeta potential governs the degree of repulsion between the adjacent,
similarly charged, dispersed particles.
If the zeta potential is reduced below a certain value, the attractive
forces exceed the repulsive forces, and the particles come together.
This phenomenon is known as flocculation.
Particles carry charge may acquire it from
as well as
during process like
crystallization, grinding processing, ionization of functional group
of the particle, adsorption of ions from solution e.g. ionic
In flocculated suspension, formed
(loose aggregates) will cause increase
in sedimentation rate due to increase in size of
Hence, flocculated suspensions sediment more rapidly. Here, the sedimentation
depends not only on the size of the
but also on the porosity of
flocculated suspension the loose structure of the rapidly
tends to preserve in the sediment, which contains an appreciable amount of
The volume of final sediment is thus relatively large and is easily
Even the smallest particles are involved in
, so the supernatant appears clear
In deflocculated suspension, individual particles are
rate of sedimentation is slow. which prevents entrapping of liquid medium which
makes it difficult to re
disperse by agitation.
This phenomenon called ‘
’ or ‘claying’. In deflocculated suspension,
larger particles settle fast and smaller remain in supernatant liquid
so supernatant appears cloudy