Study Set Content:
explains solid particle-liquid vehicle interaction
Electrical double layer theory
Considerations For Suspension Formulation
1. Wettability
2. Particle interaction and behavior
3. Electrokinetics
4. Aggregation
5. Sedimentation
easily wetted by water or polar liquids, can increase viscosity of water suspensions
Hydrophilic substances
Repel water, easily wetted by nonpolar liquid
Hydrophobic substances
decrease solid-liquid interfacial tension
Requires wetting agent or use of surfactants
can also improve wetting
Lanolin derivatives
Use of dispersing agents (hydrophilic polymers)
Na CMC
bentonite
colloidal silica
nonwetting, sensitive to (+) salts
Lyophobic
wetting
Lyophilic
Lyophilic e.g. gum →
gum → large amts of electrolytes
large amts of electrolytes to
salting out effects
salting out effects to
reversible precipitation with dilution
valence of the ions having a charge opposite to that of hydrophobic particles determines the effectiveness of electrolyte in particle aggregation
Schulze-Hardy rule
The aggregation value or efficiency increases with
valence of ions.
Aggregation Phenomena
1. Floccule/open network aggregate
2. Coagulate/closed aggregate
3. Deaggregated or dispersed form
aggregates settle quickly
Floccule/open network aggregate
individual particles are dispersed as discrete entitie
Deaggregated or dispersed form
tight packing arising from surface film bonding
Coagulate/closed aggregate
redispersible
Floccule/open network aggregate
far apart to avoid caking
Floccule/open network aggregate
