EFFECT OF ORGANIC-MATTER ON BUBBLE SURFACE-TENSION

Bubble surface tension (BST) is measured by spinning single bubbles in a rotating cell and relating the resulting bubble deformation to the Centrifugal number Ce. Using this method bubbles in ''clean'' fresh wa ter (distilled, deionized, passed through activated charcoal and filte red at 0.2 mu m) are found to have a BST similar to that reported for the ''clean'' air-water interface (72.4 mN/m), whereas adsorption of o rganic films are observed to decrease the BST, with the effect increas ing as the bubbles are aged. In natural coastal sea water (North West Arm, Halifax Harbour (10 m)) the BST decreases to 70.5 mN/m and in phy toplankton culture (Nirzschia pungens) decreases to 67 mN/m. Saturated stearic acid solution shows a BST of 57 mN/m. Coalescence of two bubb les with equilibrium surface film is accompanied by a rapid decrease i n the surface tension, a decrease that we attribute to compression of the merging surface films at the newly created smaller interface. The decrease is most pronounced in water rich in organic surfactants.