2. Thixotropy
It is non-Newtonian and time dependent behaviour and shear
thinning system.
Definition: It is defined as isothermal and comparatively slow
recovery of a system whose consistency is lost through
shearing.
Thixis means
Stiring or Shake
Tropy means
Changes
3. • Example of thixotropic materials :
Suspension
emulsion
lotion
cream
Penicilline G IM injection
yoghurt
mayonnaise.
4. Thixotropic systems usually contain asymmetric particles.
• At rest, this structure confers some degree of rigidity on
system and resembles a gel.
• Once the shear is applied, particles become alligned
and material undergoes gel to sol transformation and
exibits shear thinning.
• On removal of stress, progressive restoration of
consistency as asymmetric particles come into contact
with one another by Brownian movement.
6. • In Newtonian system, the
upcurve and downcurve are
identical and superimposible.
• In case of Non-newtonian
systems, the downcurve can be
displaced relative to the
upcurve.
• With shear-thinning systems
(Pseudoplastic), the down
curve(lower consistency) is
frequently displaced to left of the
upcurve, indicating a breakdown
of structure.
7. In case of plastic (bingham) bodies, two approaches are frequently
used to estimate degree of thixoptopy
1. First is to determine structural breakdown with time at a constant
rate of shear.
2. Second approach is to determine the structural breakdown due to
increasing shear rate
Measurement of Thixotropy
8. Anti-thixotropy or Negative thixotropy
In this thixotropy, viscosity of system is increased on applying of
shearing stress and when we remove shearing steers, it regain
its viscosity.
e.g. magnesia magma
11. D esirable property in liquid pharmaceutical systems
■ Suspensions
■ Emulsions
■ Lotions
■ C reams
■ O intments
■ Parenteral suspensions used for intramuscular
depot therapy
Thixotropy in Formulation: Applications
12. Thixotropy in Formulation
■Well formulated thixotropic suspension do not settle out
readily in the container, becomes liquid on gentle shaking
and remain long enough for a dose to be dispensed.
■With respect to suspension stability, there is a relationship
between the degree of Thixotropy and rate of sedimentation;
the greater the Thixotropy, lower the rate of settling
13. ■ C oncentrated parenteral suspensions containing
40% to 70 % w /v of procaine penicillin G in w ater found
to have high inherent Thixotropy and w ere found to be
shear thinning.
■Suspension on passing through hypodermic needle
breakdow n of structure occurred,again recovering of
consistency.
■ Formation of depot drug delivery systems at the site
of intramuscular injection,drug w as slow ly removed
and made available to the body.
