This document discusses several theoretical aspects of suspensions, including wetting, particle-particle interactions, and sedimentation. It describes wetting in terms of contact angles and affinity between solids and liquids. Particle interactions are explained using DLVO theory, which considers attractive van der Waals forces and repulsive electrostatic forces. The Schulze-Hardy rule relates the concentration of electrolytes needed for coagulation to ion valence. Sedimentation principles are also covered, such as the factors that influence rate of sedimentation according to Stokes' law.

1. T h e o r e t i c a l A s p e c t s
Suspension
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S V B ’ s C o l l e g e o f P h a r m a c y

2. S L I D E 2
SUSPENSION
Theoretical
aspects
Wetting
Wet Point
Flow point
P’cle- P’cle
Interaction
DLVO Theory
Schulze –
Hardy Rule
Sedimentation
Sedimentation
Volume
Degree of
Flocculation
Electro kinetic
Properties.
A a n c h a l . M , R u c h i r a . I
S V B ’ s C o l l e g e o f P h a r m a c y

3. Theoretical Aspect
1. Wetting
• Ability of a liquid to maintain contact with a solid surface,
resulting from intermolecular interaction.
• If there is strong affinity observed between Solid & Liquid 
Formation of Film over surface of solid.
• If weak affinity  Liquid cannot displace the air which leads
to Existence of Contact Angle (Results from IF tension)
If angle > 90  Complete floating (Hydrophobic solids)
If angle = 90  Partial Wetting
If angle < 90  Complete wetting (Hydrophilic solids)
Wetting
To exhibit complete wetting
Addition of Surfactants below CMC
Reduces Interfacial tension by
adsorbing itself
A a n c h a l . M , R u c h i r a . I
S V B ’ s C o l l e g e o f P h a r m a c y

4. Theoretical aspects
Wetting
Wet Point Flow point
Powder on glass plate
Add vehicle drop-wise &
mix thoroughly
End point formation of
coherent mass (ml/100g)
Measure additives in
beaker
Add vehicle drop-wise &
mix thoroughly
Mixture to flow in
uniform shear (ml/100g)
A a n c h a l . M , R u c h i r a . I
S V B ’ s C o l l e g e o f P h a r m a c y

5. Particle- Particle Interaction
DLVO Theory Derjaguin
Landau
Verwey
Overbeek
.
• Electrolyte concentration:
Low High
repulsive forces attractive forces
predominate predominate
• Brownian motion  frequent collision  stability
• Distance b/w the particles influence particle -particle interaction.
• One can determine amount of electrolyte required to stabilize the system
A a n c h a l . M , R u c h i r a . I
S V B ’ s C o l l e g e o f P h a r m a c y

6. Particle Particle Interaction
DLVO Theory
• 2 types of interactions
1) Attraction 2) Repulsion
A a n c h a l . M , R u c h i r a . I
S V B ’ s C o l l e g e o f P h a r m a c y

7. DLVO Theory
• DLVO theory – stability of particles depend upon total potential
energy function (VT)
VT = VA + VR
where,
VA – Vander Waals attractive forces
VR – Repulsive potential
• VA – Depends upon -chemical nature
-size of particles
• VR – Depends upon -density
-surface area
-thickness of double layer

8. Secondary Minimum
• Flocculated
• Observed when particles are separated by 1000 -2000 A
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S V B ’ s C o l l e g e o f P h a r m a c y

9. Primary maximum
• Activation barrier which must be exceeded for aggregation.
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S V B ’ s C o l l e g e o f P h a r m a c y

10. Primary minimum
• Deflocculated
• Aggregated state
• Lowest energy
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S V B ’ s C o l l e g e o f P h a r m a c y

11. Deflocculated
Particles carry finite charge
Repulsion
Sedimentation low
These forces create a high
potential barrier.
During storage
Sedimentation
Close contact
Hard cake formation
Flocculated
Particles (loosely
structured) reside at
secondary minimum
Separated by a distance of
1000- 2000 A
Experience high energy
barrier but easy to
redisperse
A a n c h a l . M , R u c h i r a . I
S V B ’ s C o l l e g e o f P h a r m a c y

12. Particle- Particle Interaction Schulze- Hardy Rule
To overcome Repulsive forces & permit coagulation
There is requirement of proper concentration of Electrolytes
Depends on Valence of ions of opposite charge
Concentration of ions required for coagulation :
Monovalent > Bivalent > Trivalent
E.g. NaNO3 > Ca (NO3)2 > Al (NO3)2
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S V B ’ s C o l l e g e o f P h a r m a c y

13. Theoretical aspects
3. Sedimentation
v = (d1 - d2) g d 2
18η.
Factors influencing Sedimentation :-
• Particle Size = Spherical, Independent –
If size decreases to half, sedimentation decreases by 4
• Viscosity = High Viscosity – High stability – Less crystal growth
(Hinders re- dispersibility)
• Density = Similar to Viscosity
Can be
prevented using
Stokes Law
A a n c h a l . M , R u c h i r a . I
S V B ’ s C o l l e g e o f P h a r m a c y

14. Theoretical aspects
Sedimentation
Sedimentation Parameters :-
• Sedimentation Volume (F) = Vu / Vo
Vu = Ultimate volume of Sediment
V0 = Original sediment
Gives qualitative account of flocculation.
• Degree of Flocculation (β) = F (flocculated) / F∞ (deflocculated)
The value says about the formation of flocs in a system.
A a n c h a l . M , R u c h i r a . I
S V B ’ s C o l l e g e o f P h a r m a c y

15. Thank You