Effect Of pH On The Rate Of Surface Tension Lowering.

摘要

The sodium salts of the fatty acids hydrolyze in water solution, and the free acid formed associates with fatty acid ions to form acid soap. The extent of hydrolysis is partially controlled by the pH of the solution in that the formation of acid soap is repressed by the addition of free base and enhanced by the addition of free acid. It has been shown that a finite time is necessary for a newly formed surface to reach surface equilibrium by diffusion of the surface-active components contained in the bulk solution to the interface. If acid soap is surface active, it is probable that the rate of surface tension lowering is a function of pH since the rate of diffusion of acid soap would be different from that of single ions. On the other hand, surface-active agents which do not hydrolyze should have rates of surface tension lowering which are independent of pH if the electrolyte effect of the added acid or base can be neglected. In this research the effect of pH on the rate of surface tension lowering of pure sodium myristate, dodecylamine hydrochloride, and sodium dodecyl sulfate was determined. These compounds exhibit a hydrolysis alkalinity, a hydrolysis acidity, and no hydrolysis, respectively. jg p.2.