Time Factor in Service Tension Measurement

Abstract

IN recent years various authors¹ have applied static methods to the study of the slow changes which occur in the surface tension of aqueous solutions of some long-chain compounds; and in general the possibility that the accumulation of solute on the surface by diffusion from bulk solution might be responsible for the drift in tension is dismissed on the grounds that the periods of time involved may be as much as 10⁹ times greater than those anticipated on classical diffusion theory. My recent quantitative studies of the adsorption process² using vibrating jets of aqueous alcohol solutions have confirmed that diffusion to the surface is complete within 10^-4 to 10^-1 sec. over the available range of chain-length and concentration, and similar results have been obtained with aqueous solutions of short-chain carboxylic acids. It seems clear that changes in tension over periods of hours, or even days, which occur in solutions of appreciable concentration (and which are usually smaller than the initial fall from the pure water value which occurs during development of the surface layer) are the result of rearrangements in the equilibrium adsorbed layer rather than of diffusion¹.