properties of these materials. Investigations of dye adsorp-The effects of tannic acid and Rhodamine B on the zeta potention on the materials and the electrical and thermodynamic tials and surface free energy components of polyester fabric (Daproperties of the fiber/solution interface are fundamental for cron 54, Style 777) were studied. Knowledge of these parameters understanding the dyeing mechanism and the finishing of may be helpful in improving the dyeing process of the polyester textile materials (1, 2). Results of the investigation of surfabric. It was found that the zeta potential of the fabric in tannic face free energy can be correlated with some important techacid solutions (10 06 -10 02 M) was negative and its absolute value nical properties of the textile (3-6). The polyester fibers decreased with increasing concentration of the acid. It was conare highly crystalline and markedly hydrophobic and usually cluded that H / ions from the tannic acid adsorbed on the polyester do not contain basic or strongly acidic groups. Therefore, surface caused a decrease in the negative zeta potential. The adsorption of tannic acid probably occurs via hydrogen bonding be-generally they do not dye easily with anionic or cationic tween the hydroxyl phenolic groups of the acid and the carboxyl dyestuffs (3, 4). Hence, the presence of surfactants during end-groups of the polyester, which hydrolyze in the acidic medium. the dyeing process, in some cases, favors the uptake of dyes The free energy components determined show that the untreated by the fibers. However, for polyester fibers little work has polyester surface is practically monopolar basic with the electron been done (4, 5), and practically no papers have been redonor component, g 0 s , equal to 56.7 mJ/m 2 . This relatively high ported in the literature in which the application of tannic value probably results from the presence of highly polar carboxyl acid as a dyeing assistant was studied.
end-groups. The adsorbed tannic acid causes an increase in the
The purpose of this paper is to investigate the changes g 0 s component to 66.4 mJ/m 2 due to the presence of more polar in surface free energy of polyester fiber, which are due to groups on the fabric surface. The subsequent dyeing of the surface adsorption of tannic acid and of a cationic dye on surfaces with Rhodamine B causes a further increase of this interaction to
with preadsorbed tannic acid, and the electrokinetic potential g 0 s Å 70.6 mJ/m 2 . Rhodamine B contains two amine groups and one carboxyl group which can strongly interact with the polyester of the polyester fabric. Results of this study may be helpful surface as well as with the adsorbed tannic acid molecules. Because in improving the dyeing properties of polyester. To deterof the cationic character of Rhodamine B molecules, the electromine the changes the thin-layer wicking method was used. static interaction with the negatively charged polyester surface The method was originally applied by Giese et al. (7) and plays an essential role. The thin-layer method for determining the later modified by Chibowski and Holysz (8, 9). This method surface free energy components of the fabric appeared to be very seems especially suitable for investigation of the surface useful, especially because the contact angle method cannot be apfree energy of textiles in the process of surfactant and dye plied here.