THE MAXIMUM BUBBLE PRESSURE METHOD OF MEASURING SURFACE-TENSION, REVISITED

The maximum bubble pressure method can give precise and accurate values of the equilibrium surface tension as well as of the dynamic surface tension at clearly defined bubble ages as given by the bubble intervals. Each bubble samples a fresh, substantially clean surface and the sensitivity can be mdyn cm-1. The dynamic measurements can give a unique survey of the evolution of the surface tension and therefore of adsorption, over 5 orders of magnitude of time. The origin, main forms, some interesting embodiments and recent experimental improvements of this method are reviewed including a manostat which permits making the measurement over hours and an extension of the method to stirred systems. Accurate results may require corrections for the effect of gravity on large bubbles and for the capillary effect of cell walls. The value of Schrödinger's simple equation is pointed out in connection with the former and a graphical method is presented for estimating the latter on the basis of published exact solutions of the capillarity equation. Finally the problem of relating the age of the bubble to the transport properties of the sorptive is discussed. Because part of the surface of the post-maximum-pressure, i.e. growing and detaching, bubble must remain to close off the capillary, the formation of this surface should be considered the initial part of the age of the new bubble. This first, explosive stage of the life of a bubble is important for concentrated (millimolar) solutions and seems too complicated for any detailed analysis at present. It is insignificant for dilute (micromolar) solutions. The remainder of the bubble's life, the calm stage, is complicated by a limited inherent expansion of the surface and by convection. The latter should be excludable by proper apparatus design, the effect of the former can be roughly estimated. © 1990.