Relationship between wetting of teflon by cetyltrimethylammonium bromide solution and adsorption

Contact angles for cetyltrimethylammonium bromide (CTAB) solution (theta) and for series of n-alkanes from n-hexane to n-hexadecane on a Teflon surface were measured. In addition, contact angle measurements for water and diiodomethane on Teflon surface covered with CTAB layer were carried out. The results obtained are used for the determination of the amount of CTAB adsorbed at the Teflon/water interface, the surface free energy of Teflon, the interfacial free energy of Teflon/CTAB solution, the standard free energy of adsorption and the standard free energy of micellization. From an adhesion tension plot of gamma(L) cos theta vs gamma(L) and application of the Gibbs and Young equations it appears that the amount adsorbed to the Teflon/water interface at a high equilibrium concentration of CTAB is close to that adsorbed at the water/air interface, whereas in the range of low concentrations there are considerable differences between adsorption at Teflon/water and water/air interfaces. This is confirmed by data obtained from the plot of Teflon/solution interface free energy against CTAB solution concentration. It is found that the standard free energy of adsorption at the Teflon/water interface can be determined approximately from the interfacial tail of surfactant-water, tail-tail and tail-Teflon tension data. A good agreement between the standard free energy of micellization and free energy of interactions of CTAB ions through water is found. The free energy of interactions between CTAB ions through water is determined on the basis of the surface free energy of CTAB and the psi potential. (C) 1997 Elsevier Science Ltd.