Colloids PDF

Lecture contents 1. Types of dispersed systems (molecular, colloidal, and coarse dispersions). 2. Colloidal dispersions (definition and applications). 3. Classification of colloidal dispersion. 4. Preparation of colloidal dispersion. 5. Purification of colloidal dispersion. 6. Properties of coll...

Lecture contents 1. Types of dispersed systems (molecular, colloidal, and coarse dispersions). 2. Colloidal dispersions (definition and applications). 3. Classification of colloidal dispersion. 4. Preparation of colloidal dispersion. 5. Purification of colloidal dispersion. 6. Properties of colloids. 7. Stability of colloids  Dispersed systems Consists of: 1. Particulate matter (dispersed phase)  solid, liquid or gas. 2. Dispersion medium (continuous medium)  solid, liquid or gas. Classification: according to particle size 1] MOLECULAR 2] COLLOIDAL 3] COARSE DISPERSION DISPERSION DISPERSION < 1 nm. 1 nm-500 nm (up to 1 μ) > 1000 nm. Undergo rapid diffusion Very slow diffusion e.g. Don’t diffuse e.g. e.g. O2 & glucose. colloidal silver solution. Suspension & Emulsion. Particles invisible in Particles visible by Particles are visible electron microscope. electron microscope. under ordinary microscope. Pass through Pass through Not pass through filter paper semipermeable filter paper but not or semipermeable membranes & semipermeable Membrane. filter paper. membrane.  Colloidal dispersions Applications: colloidal systems are used as pharmaceutical excipients, vehicles, carriers, or product components. A. Therapy: small size, good absorption & better action. 1. Colloidal silver iodide, silver chloride & silver protein are effective germicides & not cause irritation as ionic silver salts. 2. Colloidal copper used in cancer. 3. Colloidal gold used as diagnostic agent. 4. Colloidal mercury used in syphilis. B. Solubility: insoluble drugs (sulfonamides, phenobarbitone)  colloidal systems (+ surfactant)  micellar solubilization C. Targeting of drug to specific organ: drug entrapped liposomes, niosomes, nanoparticles, microemulsions targeted to liver, spleen. D. Stability: 1. Dispersion of surfactants  association colloids   stability & solubility of certain compounds in aqueous & oily pharmaceutical preparations e.g. water soluble vitamins A, D & K, also essential oils & phenols of low H2O solubility. 2. Efficiency of certain substances is  when used in colloidal form due to large surface area e.g. efficiency of kaolin in adsorbing toxin in GIT & efficiency of aluminum hydroxide as antacid. 3. Dispersion of macromolecules (gelatin)  tablet Coating synthetic polymers (HPMC).  Official preparations: 1. Iron dextran inj (B.P): form non-ionic hydrophilic soloutions  anemia treatment. 2. Iron sorbitol inj (B.P): sorbitol, dextran, citric acid, iron. 3. Blood plasma substitutes as dextran, PVP, & gelatin are hydrophilic colloids used to restore or maintain blood volume.  Classification of colloids: 1. Based on charge: (+), (-). 2. Based on state of matter: solid, liquid, or gas. 3. Based on interaction of dispersed particles with dispersion medium: A. Lyophilic (solvent loving): dispersed phase has Hydrophilic & high affinity for dispersion medium hydrophobic B. Lyophobic (solvent hating): dispersed phase used when dispersion has low affinity for dispersion medium medium is C. Association (amphiphilic). aqueous A. Lyophilic colloids:  Colloidal particles interact to an considerable extent with the molecules of the dispersion medium (solvent loving).  Obtained spontaneously by dissolving the material in solvent (due to the high affinity)  material that form lyophilic colloid in a certain solvent may not do so in another solvent, e.g. 1. Acacia + water  lyophilic colloid (hydrophilic type). 2. Acacia + benzene  no lyophilic colloid formed.  Preparation & purification is easy.  Lyophilic colloid prepared with/without charge (acacia colloid [+].  Iso-electric point  neutral charge).. (benzene, ethylmethyl gelatin rubber ketone)  High viscosity of lyophilic colloids (may form a gel at high conc.).  The sols are quite stable as the solute particle surrounded by 2 stability factors: A. -ve or +ve charge. B. Layer of solvent, solvating layer represent a protective layer that prevent adherence & coagulation of particles.  The dispersed phase does not precipitate easily (need neutralization of charge & removal of H2O layer) 1. Addition of liquid less polar than H2O (acetone or alcohol) with small amount of electrolytes facilitate coagulation due to dehydration of particles  if dispersion medium is separated from the dispersed phase, the sol can be reconstituted by simply remixing with the dispersion medium. So, these sols are called reversible sols. 2. Similarly charged hydrophilic colloid easily mixed with no precipitation, while that of different charge interact together with precipitation (e.g. antigen antibody reaction). B. Lyophobic colloids:  Colloidal particles have very little or no attraction for the dispersion medium (solvent hating)  solvent don’t form a sheath on particle  thermodynamically unstable dispersion.  Colloidal particles: inorganic particles (e.g. gold, silver, sulfur….) dispersed in H2O. 1. These colloids are easily precipitated on the addition of small amounts of electrolytes, by heating or by shaking 2. Less stable as the particles surrounded only with a layer of +ve or –ve charge which lead to repulsion between particles. 3. Once precipitated, it is not easy to reconstitute the sol by simple mixing with the dispersion medium. Hence, these sols are called irreversible sols.  Viscosity of the dispersion medium doesn’t  by the presence of the dispersed particles.  Not obtained simply i.e. need special method for preparation (dispersion method or condensation method). C. Association colloids:  Certain molecules or ions termed amphiphile (surface active agent SAA) are characterized by 2 distinct regions of opposing solution affinities within the same molecules or ions  having affinity for both polar & non-polar solvents.  At  conc.: amphiphiles exist separately (subcolloidal size).  At  conc.: form aggregates or micelles (50 or more monomers) (colloidal size)  As with lyophilic sols, its formation is spontaneous, provided that the conc. Improve of amphiphile in solution exceeds CMC. Drug solubility &  Amphiphiles may be: precipitate absorption Only 1. Anionic (e.g., Na. lauryl sulfate has CMC range of 1-2%) Drug tightly external 2. Cationic (e.g., cetyl triethylammonium bromide) bind by use. 3. Nonionic (e.g., polyoxyethylene lauryl ether) laminar  internal & external use. micelles,  absorption, 4. Ampholytic (zwitterionic) e.g., dimethyl dodecyl & action ammoniom propane sulfonate.  Krafft point (Kt): “defined as temperature at which solubility of surfactant is equal to the CMC”.  Surfactant Applications: 1. Prevent hydrolytic/ oxidative decomposition. 2. Improving solubility of poorly soluble drugs by micellar solubilization.  Comparison of properties of colloidal sol: Thank you 13