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Surface free energy components, apolar Lifshitz-van der Waals, γs LW , and polar electron acceptor, γs + , and electron donor, γs -, were determined for leacril (a copolymer of 90% acrylonitryle and 9% vinyl acetate) fibers with preadsorbed tannic acid solutions (10 -5 -10 -2 M). A thin layer wicking method was applied for this purpose. The components were calculated considering van Oss et al.'s (J. Chem. Rev. 1988, 88, 927) polar components of surface tension of probe liquids (formamide and water, γw -) γw + ) 25.5 mJ/m 2 for water) as well as those suggested very recently by Lee (Langmuir 1996(Langmuir , 12, 1681, who considered for water γw -) 19 mJ/m 2 and γw + ) 34.2 mJ/m 2 . The trend of changes of the calculated components is the same, except for the surface treated with 10 -2 M tannic acid. However, the electron donor components of the leacril calculated with Lee's data are somewhat lower. From the calculated work of spreading of water, results indicate that the bare leacril surface is slightly hydrophobic, the surface treated with 10 -5 M tannic acid becomes low hydrophilic, and in the range of concentrations 10 -4 -10 -3 M becomes increasingly hydrophobic. When equilibrated with 10 -2 M it is again hydrophilic. The changes can be explained by reorientation of the tannic acid molecules on the leacril surface and micelle formation above cmc, which was determined to be at ca. 3 × 10 -4 M. Adsorption measurements show that the process is very fast and physical in nature. The rate constants and empirical diffusion coefficients were evaluated at 275, 283, 293, and 303 K. Also thermodynamic functions for the adsorption process were calculated from the adsorption isotherms. It was concluded that hydrogen bonding and Lifshitz-van der Waals interactions are responsible for the adsorption, while electrostatic interactions play a rather second-order role. The leacril shows small negative zeta potentials which drop almost to zero at concentrations higher than 10 -4 M.

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Data are presented on the kinetics and thermodynamics of absorption of N-cetylpyridinium chloride (N-CP-Cl) by Leacril fibers at different temperatures. The increased temperature of the system increases the surfactant content of the fibers. The experimental time-sorption isotherms are represented by the exponential kinetic equation, M, = M,,( l -e-kf), where M, and M,, refer to the amounts of surfactant taken up by Leacril at time t and equilibrium, respectively, and k refers to the rate constant. The empirical rate constant decreases with temperature. Values of half-absorption time at different temperatures are presented. Sorption equilibria of N-CP-Cl by Leacril are described by a Freundlich isotherm equation. Changes of enthalpy and entropy related to the process of absorption are calculated from the Clausius-Clapeyron equation. Isosteric heats of absorption are positive, between 20 and 120 kllmol. The global change of entropy is positive, between 126 and 500 Jim01 K. The best thermodynamic conditions for surfactant uptake by Leacril appear at the highest temperatures, when the standard free energy of absorption takes the most negative values. From the results, we find that the absorption of N-CP-Cl by Leacril in the temperature interval investigated takes place with establishment of chemical bonds, although physical contributions of an electrostatic nature between the cation of the surfactant and the sulphonate and sulfate end-groups of Leacril are the most important.

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