Surface Energetics of the Adsorption Process of a Cationic Dye on Leacril Fabrics.

In this paper are presented data on the zeta potential, adsorption processes, and energy of interaction between Leacril and a cationic dye, crystal violet (CV) in the process of dyeing of Leacril. The method for obtaining the values of zeta potential of the system is the streaming potential technique. Previous models of bundles of capillaries have been tested by comparison with precise values of the zeta potential of the system. The model that presents a higher confidence level is the Goring and Mason model. The zeta potential results reveal that the uptake of crystal violet on Leacril fibers takes place by means of electrostatic attraction between the cation of the dye and both the sulfonate and the sulfate end-groups of the Leacril. Given the hydrophobic character of the Leacril and the amphiphilic nature of the dye molecules, hydrophobic attractions between the fiber and the hydrophobic part of the crystal violet might account for the adsorption of the cationic dye onto the fibers even when hindered by electrostatic repulsion. The data for the adsorption of the dye on the fibers indicate that the adsorption is favored by increasing the temperature of the process. This could be due to increased ionization of the sulfonate and sulfate end-groups of the Leacril, with increasing temperature of adsorption. The behavior of the components of the interaction energy, between the Leacril and the dye, is analyzed in the present paper in light of van Oss's theory. Using both the thin layer wicking and contact angle techniques, we have determined the values of the components of the surface-free energy of Leacril fabrics and of the crystal violet, respectively. The total interaction energy between the Leacril and the cationic dye has been obtained by means of sum of three components, the electrical, DeltaGEL, acid-base, DeltaGAB, and Lifshitz-van der Waals, DeltaGLW, respectively. Estimation of the electrical component makes use of the zeta potential of the system Leacril/cationic dye obtained by means of the streaming potential technique. Two approaches were followed in order to estimate the interfacial (excluding electrostatic) free energy of interaction DeltaGIF between Leacril fibers and CV: (i) the determination of the interactions between the fiber and dye solutions of different concentrations and (ii) estimations of DeltaGIF between fiber and dye molecules in the presence of water. These combined methods are in agreement with the experimental results obtained in this work. These methods explain qualitatively the adsorption of the cationic dye on Leacril in the entire range of concentrations of dye used in the present work. Based on the study of the interfacial interactions carried out in the present work the adsorption of crystal violet onto Leacril is favorable from a thermodynamic point of view. Copyright 1997 Academic Press. Copyright 1997Academic Press