基础化学-chapter_5_2.ppt

II. Surfactant (表面活性剂) (Surface-active-agent) ? solute concentration (surfactant) A: Inorganic additives such as NaCl, KNO3. B: Organic additives such as alcohol(醇), aldehyde(醛), carboxylic acid(羧酸), and ester(酯). C: Surfactants such as soaps and detergents. The surface tension of a liquid can be affected by dissolved substances. §4. Surfactants and Associated colloid 1. Structure of surfactant molecules Amphiphile (两亲分子) Hydrophilic (亲水的) Hydrophobic (疏水的) or lipophilic (亲油的) head tail §4. Surfactants and Associated colloid sodium dodecyl sulfate (十二烷基硫酸钠) 2. Classification of surfactants Anionic: (阴离子表面活性剂) Cationic: (阳离子表面活性剂) Zwitterionic: (两性离子 表面活性剂) Nonionic: (非离子表面活性剂) R = C14, C16, or C18 Lecithin (卵磷脂) §4. Surfactants and Associated colloid §4. Surfactants and Associated colloid Increasing concentrations of surfactant Adsorption (吸附) of surfactant molecules to the surface Formation of full layer of surfactant molecules on the surface Formation of micelles (胶束) in the solution §4. Surfactants and Associated colloid ? solute concentration (surfactant) Organic substances have much lower surface tension than water, the surface tension of the solution is greatly reduced. III. Associated colloid A micelle (胶束) is a colloidal-sized particle formed in water by the association of surfactant molecules. The minimum concentration of surfactants at which the micelle starts to form is referred as critical micelle concentration (CMC, 临界胶束浓度). §4. Surfactants and Associated colloid The hydrophobic ends point inward one another, and the hydrophilic ends are on the outside of the micelle facing the water. §4. Surfactants and Associated colloid A colloid in which the dispersed phase consists of micelles is called an associated colloid (缔合胶体). The micelles could be spherical, rod-shaped, or layered depending on the structure and concentration of surfactants, temperature, and additives. water micelle oil Solubilization (增溶): The solubility of oil is enhanced in associat