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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: 4r 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