What are the components of a disperse system?
Dispersed phase + dispersion medium.
Particle size ranges?
Colloidal: 1 nm – 0.5 μm
Fine: 0.5–10 μm
Coarse: >0.5 μm (susp & emul)
Define suspension.
Solid particles (1–50 μm) dispersed in a liquid with minimal solubility.
Desired properties of suspensions?
Slow settling, easy redispersion, constant particle size, no grittiness, pours easily.
Flocculated vs Deflocculated?
Flocculated: loose, fast sedimentation, easy to redisperse, prevents caking
Deflocculated: slow settling but forms hard cake
Examples of flocculating agents?
Bentonite, MC, sodium alginate, tragacanth.
Wetting agents used?
Alcohol, glycerin, propylene glycol.
Preservatives used?
Benzoic acid, methyl paraben.
Main methods of prep?
Dispersion, precipitation, double decomposition, extemporaneous.
Label required for suspensions?
“Shake well before use.”
What are magmas and milks?
Aqueous suspensions of insoluble inorganic drugs.
Difference between magma & milk?
Magma: thick, viscous
Milk: oral suspension (e.g., Milk of Magnesia)
Define emulsion.
Two immiscible liquids, one dispersed as droplets in the other using emulsifiers.
Types of emulsions?
O/W, W/O, multiple (w/o/w, o/w/o), microemulsion.
O/W emulsion characteristics?
Water is continuous phase; water >45%; hydrophilic emulsifier.
W/O emulsion characteristics?
Oil is continuous phase; used for protective/emollient preparations.
What is a microemulsion?
Transparent, thermodynamically stable, droplet size 100–1000 Å, ↑ absorption.
Surface Tension Theory?
Surfactants ↓ interfacial tension → easier droplet breakup.
Oriented-Wedge Theory?
Emulsifier orientation determines O/W or W/O.
Interfacial Film Theory?
Emulsifier forms a film around droplets → prevents coalescence.
Natural emulsifying agents?
Acacia, tragacanth, pectin, gelatin, egg yolk.
Finely divided solids used as emulsifiers?
Bentonite, veegum, Mg hydroxide.
Synthetic emulsifiers (examples)?
Anionic: SLS
Cationic: Benzalkonium chloride
Nonionic: Tween, Span, PEG
HLB range for O/W?
8–18
