Effect of a cationic dye on the surface free energy of Leacril fabric

Changes in Leacril fabric surface free energy components (Lifshitz-van der Waals gamma(s)(LW), electron donor gamma(s)(-), and electron acceptor gamma(s)(+)) due to absorption of the cationic dye Crystal Violet (CV) were determined by means of the thin-layer wicking technique. It was found that the treatment of Leacril with different amounts of CV produced practically no changes in the value of the gamma(S)(LW) component. However, the above treatment reduces the gamma(s)(+) component practically to zero. In contrast, the gamma(s)(-) component increases from 60 mJ m(-2) for untreated Leacril up to 79 mJ m(-2) for Leacril treated with 10(-4) M CV, with a very sharp decrease of gamma(s)(-) to 67 mJ m(-2) for increasing concentrations of CV Cup to 10(-2) M). The initial increase in gamma(s)(-) with 10(-4) M CV could be due to the presence of three disubstituted aromatic amine groups in the molecule CV. These groups are strong electron donors and their presence increases the value of the gamma(s)(-) component of the Leacril. The initial value of 60 mJ m(-2) of the gamma(s)(-) component for the untreated Leacril could be due to the presence of a large amount of both sulphonate and sulphate end-groups on untreated Leacril. These groups are also donors of electrons. For increasing concentrations of CV in the treatment of Leacril, the electrostatic interactions between the cation of the dye and both the sulphonate and sulphate end-groups of the Leacril produce a blockade of these groups on the fabric and a decrease of the gamma(s)(-) component to a value of 67 mi m(-2) for a concentration of 10(-2) M CV. The amount of CV uptake by Leacril increases with the concentration of the cationic dye in solution and with the temperature of absorption. It is concluded that the absorption of CV on Leacril takes place by means of electrostatic attractions between the disubstituted aromatic amine groups of the cationic dye used and both the sulphonate and sulphate end-groups of Leacril. These groups could impart hydrophilicity to the surface of the Leacril and hence acid-base interactions between the molecules of the cationic dye and the surface of the fabric could explain the interactions between the CV and the Leacril. The value of 67 mi m(-2) obtained for gamma(s)(-) after the treatment of Leacril with 10(-2) M CV could be due to the final presence of the three (electron donor) disubstituted aromatic amine groups per molecule of the cationic dye on the Leacril surface due to the absorption process of the dye on the Leacril fabric. (C) 1998 Elsevier Science B.V.