2008讲稿(第7章)胶体化学概述.ppt

Gibbs Equation：（推导过程见书） （7－8） Г2（1）－Surface excess of solute， index（1）present the Gibbs surface is located atГ1＝0. a2－activity of solute； γ－surface tension of the solution. For dilute solution，a may be substituted by c . （7－9） or （7－10） The concentration of solute in σ is higher than that in the solution. It is positive adsorption of the solute in the σ phase. For then c↑→γ↓，Г2（1）0， For then c↑→γ↑，Г2（1）0， The concentration of solute in σ is lower than that in the solution. It is negative adsorption of the solute in the σ phase. 2．Adsorption of solute at surface of solution For dilute solution ，γ－c is a straight line . γ0－γ＝π＝Bc （7－11） B－a constant；c－concentration of the solution Taking Eq.（7－11）into Eq.（7－10） as （7－12） Г－c is also a straight line. For a high concentration of solution， γ－c presented by Szyszkowski equation： （7－13） a－constant； －amount of saturation of adsorption or limit of adsorption, when temperature is fixed that is a constant. For c is very low， ca， （7－14） For c is higher，ca， Г＝Гm （7－15） The amount of adsorption is constant, not changed with concentration of the solution. A monolayer of the solute is formed. －Gibbs layers Langmuir layer Monolayer formed by a substance that is insoluble in the liquid subphase. (2) Gibbs layers Monolayer formed by substances soluble in the bulk (oil or water) but adsorbe preferentially at the interface. (3) Langmuir-Blodgett(LB) layers (LB层) Langmuir layers are transferred to (转移到) a solid substrates. Blodgett transferred fatty ac