Types of Colloidal Systems PDF

Types of Colloidal Systems 3. Association (amphiphilic) colloids: Below CMC, amphiphiles adsorb at the air-water interface, forming monolayer at the surface. Adsorption increases with increasing amphiphile concentration; and surface tension decreases greatly. The interface becomes saturated...

Types of Colloidal Systems 3. Association (amphiphilic) colloids: Below CMC, amphiphiles adsorb at the air-water interface, forming monolayer at the surface. Adsorption increases with increasing amphiphile concentration; and surface tension decreases greatly. The interface becomes saturated with monomers and if excess amphiphiles are added, CMC is reached, and micelles start to form in the bulk phase. When reaching the CMC, surface tension remains constant because further additions of surfactant no longer result in a decrease in surface tension  Types of Colloidal Systems 3. Association (amphiphilic) colloids: When surface tension (γ) of a surfactant is plotted against the logarithm of the surfactant concentration (log c), the following plot is obtained: Surface Tension,  Dyne/cm CMC (LogC) Types of Colloidal Systems 3. Association (amphiphilic) colloids (cont’d): – Micelle shapes: a) Micelles in water: hydrocarbon chains face inward and the polar heads are associated with water b) Reverse Micelles in nonpolar liquids: polar heads face inward and the hydrocarbon chains are associated with the continuous nonpolar phase c) Laminar micelles: formed at higher amphiphile concentrations – Spherical micelles exist at concentration close to the CMC – At higher concentrations, laminar micelles are formed and exist in equilibrium with spherical micelles  Types of Colloidal Systems a) Spherical micelle in water b) Reverse micelle in an organic solvent c) Laminar micelle Types of Colloidal Systems 3. Association (amphiphilic) colloids (cont’d): – Amphiphiles may be anionic, cationic, nonionic, or ampholytic (zwitterionic) – If a micelle is formed of an anionic association colloid such as sodium lauryl sulfate, a certain number of sodium ions are attracted to the surface of the micelle, reducing the overall negative charge – The bound ions are termed counter ions or gegenions Micelle of an anionic surfactant in water Solubilization Association colloids such as micelles increase the solubility of insoluble or slightly soluble materials in the dispersion medium used This phenomena is known as solubilization Absorption, bioavailability, activity, and stability of materials may be modified by solubilization Nonionic surfactants are commonly used as solubilizers because of their low toxicity