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DISPERSIONS - I
Classification by Size
True Solutions (“Molecular Dispersions”)
 (molecules, ions) in gas, liquid (solutions)
 < 1 nm, diffuse easily
Fine Dispersions (Colloidal Dispersions )
 micelles, microemulsions, some suspensions (e.g.
colloidal silver), “polymers”, smoke, films & foams
 1 to 500 nm, diffuse slowly, separated by ultrafiltration
Coarse Dispersions
 most pharmaceutical suspensions and emulsions, dust,
powder, cells, sands
 >500 nm, do not diffuse, separated by filtration
Thermodynamic Classification
•Lyophilic colloids
•Lyophobic colloids
Lyophilic Colloidal Systems
Dispersions that spontaneously form
from macroscopic phases, and are
thermodynamically stable with respect
to both enlargement of particles
through their aggregation and
disintegration to individual molecules
Property: equilibrium size distribution (do not change in time)
Formation of Lyophilic Colloids
Phase
Dispersion
Solution
•Increase in surface area (unfavorable)
•Increase in number of particles (favorable)
Spontaneous dispersion condition:
4r 2  15  30kT
Block Copolymer Micelle
CH 3
HO
CH 2 CH 2 O
CH CH 2 O
m/2
CH 2 CH 2O H
m/2
n
P
Free Drug
cmc
Micelle
Unimer
•Pluronic
Microemulsions
Surfactant
Water Pool
Protein
Organic Solvent
Block Ionomer Complexes
Lamellas
Vesicles
Poly(ethylene oxide)
Poly(methacrylate anion)
Poly(ethylene oxide)
Kabanov et al. (1998) JACS 119