THE SURFACE FREE-ENERGY AND FREE-ENERGY OF ADSORPTION OF CETYLTRIMETHYLAMMONIUM BROMIDE

The surface tension of cetyltrimethylammonium bromide (CTAB) solutions (y) has been measured as a function of their concentration (C). The r esults obtained were used for determination of the amount of CTAB adso rbed at the water/air interface, the area occupied by the CTAB molecul e at this interface and the standard free energy of adsorption. The st andard free energy of adsorption was also calculated from interfacial hydrocarbon-water and hydrocarbon-air tension data. It was found that the value of the standard free energy of adsorption calculated from th e Rosen and Aronson equation is twice as low as that determined from t he modified Langmuir equation, but is close to that obtained on the ba sis of interfacial tension data. From analysis of the equation of stat e it was found that the limiting value for the product of pi A is 2 kT irrespective of whether the Gibbs or Frumkin equation of adsorption w as used for A determination.