RELATIONSHIP BETWEEN WETTING OF TEFLON BY CETYLTRIMETHYLAMMONIUM BROMIDE SOLUTION AND ADSORPTION

Contact angles for cetyltrimethylammonium bromide (CTAB) solution (the ta) and for series of n-alkanes from n-hexane to n-hexadecane on a Tef lon surface were measured. In addition, contact angle measurements for water and diiodomethane on Teflon surface covered with CTAB layer wer e 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 sol ution, the standard free energy of adsorption and the standard free en ergy of micellization. From an adhesion tension plot of gamma(L) cos t heta vs gamma(L) and application of the Gibbs and Young equations it a ppears that the amount adsorbed to the Teflon/water interface at a hig h equilibrium concentration of CTAB is close to that adsorbed at the w ater/air interface, whereas in the range of low concentrations there a re considerable differences between adsorption at Teflon/water and wat er/air interfaces. This is confirmed by data obtained from the plot of Teflon/solution interface free energy against CTAB solution concentra tion. It is found that the standard free energy of adsorption at the T eflon/water interface can be determined approximately from the interfa cial tail of surfactant-water, tail-tail and tail-Teflon tension data. A good agreement between the standard free energy of micellization an d free energy of interactions of CTAB ions through water is found. The free energy of interactions between CTAB ions through water is determ ined on the basis of the surface free energy of CTAB and the psi poten tial. (C) 1997 Elsevier Science Ltd.