Electrokinetic effect and surface free energy behavior in the adsorption process of a reactive dye onto Leacril pretreated with polyethyleneimine ion.

In a previous paper, we studied the adsorption of a polyelectrolyte, polyethyleneimine ion (PEI), onto Leacril in order to increase the amount of the reactive dye Remazol Brilliant Blue R (RBBR) taken up by these fibers. We observed that this polycation changes the fibers zeta potential sign at low concentration, ca. 0.03 g/L, and thus the RBBR adsorption onto Leacril is improved when implementing the PEI treatment. The aim of this work is to study the PEI effect related to the amount of dye adsorbed by Leacril. For this purpose, we present data on streaming potential, adsorption isotherms, and surface free energy component determination as a function of the PEI concentration used in the pretreatment, as well as a function of the RBBR concentration used in the dyeing solutions. Adsorption experimental results show that the amount of RBBR taken by the fibers increases with the PEI concentration used in the pretreatment, and this effect becomes significant at higher concentrations of RBBR solution. The zeta potential increases to positive values in the range of low concentrations of dye solution when Leacril fibers have been pretreated with the polyelectrolyte. From surface free energy component determinations it is worth noting that the electron-donor component, gamma(-), decreases with the RBBR concentration in the treatment. The results we have obtained suggest that the interaction between the amine group of the PEI previously adsorbed and the reactive beta-sulfato-ethysulfonyl group of the dye can be responsible for the improvement in dye uptake.

Effect of polyethyleneimine ion on the sorption of a reactive dye onto Leacril fabric: electrokinetic properties and surface free energy of the system.

Data are presented on the kinetics, electrokinetics, and surface free energy in the process of adsorption of polyethyleneimine (PEI) as a pretreatment of Leacril, later dyed with the reactive dye Remazol Brilliant Blue R (RBBR). The electrokinetic potential of Leacril is negative, due probably to the presence of sulfonate and sulfate end-group onto Leacril fibers. The zeta potential of Leacril decreases in absolute value as a function of NaCl concentration in solution, probably because of compression of the electrical double layer. The zeta potential of Leacril as a function of the concentration of PEI in solution increases because of the adsorption of PEI ions through chemical reaction between the sulfonate end-groups of Leacril and the amine groups of PEI. The adsorption kinetics shows that an increase in the concentration of PEI, brings about an increase in the amount of RBBR adsorbed onto the fiber. This may be an indication of the chemical reaction between the reactive groups of the polyelectrolyte and dye molecules. The behavior of the surface free energy of the systems involved confirms these conclusions.

Interpretation of colloidal dyeing of polyester fabrics pretreated with ethyl xanthogenate in terms of zeta potential and surface free energy balance.

Data are presented on the adsorption of the colloidal dye Disperse Blue 3 onto polyester fabric (Dacron 54, Stile 777), the fabric being pretreated with different amounts of the surfactant potassium ethyl xanthogenate (PEX). This study has been made by means of both the evolution of the zeta potential of the fiber/dye interface and the behaviour of the surface free energy components of the above systems. The kinetics of adsorption of the process of dyeing, using 10(-4) M of PEX in the pretreatment of the fabric, shows that increasing temperature of adsorption decrease the amount of colloidal dye adsorbed onto the fabric. This fact shows that the principal mechanism involved in this adsorption process is physical in nature. The adsorption isotherms of the colloidal dye onto polyester pretreated with different amounts of PEX, shows that the adsorption of the dye is favored with the increase in the concentration of the surfactant used in the pretreatment. This fact shows that the pretreatment with PEX is a very interesting aspect of interest in textile industry. The zeta potential of the system fabric/surfactant shows that this parameter is negative (about -25 mV) for the untreated fiber and decreases in absolute value for increasing concentration of the surfactant on the fiber, the value of the zeta potential of the system being -5 mV for 10(-2) M of PEX. This behavior can be explained for the chemical reaction nucleophilic attack between the carboxyl groups of polyester, ionized at pH 8, and the thiocarbonyl group of the xanthogenate ion. On the other hand, the zeta potential of the system polyester pretreated with PEX/Disperse Blue 3 at increasing concentrations of the surfactant and the dye shows that this parameter increases its negative value strongly with increasing concentration of the surfactant used in the treatment. This can be explained for the hydrogen bonds between the hydroxy groups of the dye and the S- ions of the thiocarbonyl group of the surfactant preadsorbed onto the fiber.

Electrokinetic and thermodynamic analysis of the adsorption process of N-cetylpyridinium chloride on polyester fabric.

An electrokinetic and thermodynamic analysis of the adsorption process of N-cetylpyridinium chloride on polyester fabric is described in the present work. The electrokinetic study was performed by means of electrophoretic mobility measurements of the polyester-surfactant system. The most significant result is the increase in electrokinetic potential, zeta, toward more positive values as the surfactant concentration in the dispersion medium is raised. Given the molecular structure of N-cetylpyridinium chloride (N-CP-Cl), which contains a pyridinium group, positively charged, it is feasible that such increase in |zeta| is due to the electrostatic attraction between the carboxyl groups of polyester, ionized at pH 8.5, and the pyridinium group of the surfactant. The uptake of N-CP-Cl by the fiber is experimentally determined at four temperatures: the strong increase in the amount of the surfactant incorporated onto the fiber as the initial concentration of N-CP-Cl is larger shows that the electrostatic attraction between the fiber and the surfactant is the main mechanism of the adsorption of the surfactant onto the fiber. The obtained data on the kinetics and thermodynamics of adsorption of N-cetylpyridinium chloride onto the polyester, standard free energy, enthalpy, and entropy related to the process of adsorption are in accordance with our hypothesis on the mechanisms of adsorption. From a different point of view, the efficient coverage of polyester by N-CP-Cl is also demonstrated by the changes experienced by the surface free energy of polyester upon treatment with N-CP-Cl.

Electrokinetic and Thermodynamic Analysis of the Dyeing Process of Polyamide Fabric with Mordant Black 17.

An electrokinetic and thermodynamic analysis of the dyeing process of polyamide 6.6 (nylon 6.6) by the dye Palatine chrome black (PCB) is described in the present work. The electrokinetic study was performed by means of electrophoretic mobility measurements on bare and dyed fiber. The most significant result is the increase in electrokinetic potential, zeta, toward more negative values as the dye concentration in the dispersion medium is raised. Given the molecular structure of PCB, which contains a sulfonate group per molecule, it is feasible that such increase in |zeta| is due to the adsorption of the negatively charged, dissociated dye entities. The uptake of PCB by the fiber is experimentally determined at two temperatures: the strong increase in the amount of dye incorporated into the fiber as the initial concentration of PCB is larger, and also the fact that higher temperatures favor the dyeing process is an indication of the existence of strong interactions between both interfaces. From a different point of view, the efficient coverage of Nylon by PCB is also demonstrated by the changes experienced by the surface free energy of Nylon upon treatment with PCB. Copyright 2001 Academic Press.

Study of the Leacril Dyeing Process by a Cationic Dye from an Emulsion System.

Adsorption studies of a cationic dye, Rhodamine B, from an emulsion phase on Leacril fabric at different temperatures were conducted. The emulsion phase consisted of n-hexadecane emulsified by isopropyl alcohol (1 M) and stabilized by tannic acid. In the alcohol solution Rhodamine B was dissolved. The kinetics of its adsorption and desorption is discussed. The changes in Leacril surface free energy components in the dyeing process were also determined. The adsorption data show that the presence of an emulsion increases the dye adsorption at room temperature (293 K) and at 313 K, while at 333 K it is smaller than that from Rhodamine solution alone. However, Rhodamine desorbs more when adsorbed from the solution. Surface free energy components differ for the Leacril samples dyed at different temperatures, and the most hydrophobic surface was obtained for the samples dyed at 333 K, where the electron-donor component is the lowest one. In general, the work of water spreading is close to zero, except for the above sample for which it is relatively highly negative. Possible mechanisms of the dye adsorption are discussed. Copyright 2001 Academic Press.

Effect of Tannic Acid on the zeta Potential, Sorption, and Surface Free Energy in the Process of Dyeing of Leacril with a Cationic Dye.

The behavior of the surface free energy in the process of dyeing Leacril pretreated with tannic acid and subsequently dyeing with the cationic dye Rhodamine B has been studied. Also the electrokinetic behavior of these systems has been analyzed by studying the zeta potential, which has been obtained by means of the streaming potential technique. Values more significative of the zeta potential of these systems have been obtained using the three models of capillaries existing in the literature. The qualitative behavior of the zeta potential is the same for the three models of capillaries tested in this paper. These models are those of Goring and Mason, Biefer and Mason, and Chang and Robertson. The zeta potential of the systems analyzed is negative in the range of concentration of the dye in the liquid phase from 10(-6) to ca. 10(-4) M of dye. In the range of low concentrations (from 10(-6) to ca. 10(-5) M of dye) the zeta potential of the system untreated Leacril/Rhodamine B increases in absolute value due to increasing hydrophobic attractions between both the hydrophobic chains of the dye and the Leacril fibers in aqueous media. In the system Leacril treated with tannic acid/Rhodamine B, this increase is also due to the presence of hydrogen bonding between the phenolic hydroxyl groups of the tannic acid and the sulfonate and sulfate end groups of Leacril fibers. For concentrations of dye between 10(-5) and 10(-4) M of dye in solution, the zeta potential decreases in absolute value due to the electrostatic attractions between the groups negatively charged in the fiber and the cation of the dye. The zeta potential changes its sign at the highest concentrations of dye used in this work. The adsorption of Rhodamine B onto both untreated Leacril and Leacril treated with tannic acid is favored by the increasing temperature of adsorption. The behavior of the components of the surface free energy obtained by the thin-layer wicking technique led us to consider that the cationic dye Rhodamine B is adsorbed on the surface of both untreated Leacril and Leacril treated with tannic acid by Lewis acid-base interactions. Copyright 1998 Academic Press.

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

Effect of N-Cetylpyridinium Chloride on the Surface Free Energy of Leacril Fabric

Changes in the Lifshitz-van der Waals, gammaLWS, electron donor, gamma-S, and electron acceptor, gamma+S, surface free energy components of leacril fabric due to the adsorption of N-cetylpyridinium chloride (N-CP-Cl) were determined by the thin-layer wicking technique. It was found that the treatment of leacril with different amounts of N-CP-Cl practically does not change the value of the gammaLWS component. The treatments reduce the gamma+S component practically to zero, and a very sharp decrease of gamma-S (from 60.5 to 35.8 mJ/m2) was observed as the leacril was treated with increasing amounts of the above surfactant. It is concluded that the adsorption of N-CP-Cl on leacril takes place by means of electrostatic attractions between the quaternary ammonium group of N-CP and both the sulfonate and the sulfate groups of leacril. These groups could impart hydrophilicity to the surface of the leacril and hence acid-base interactions between the molecules of the surfactant and the surface of the fabric could explain the interactions between the N-CP-Cl and the leacril. The decrease in the gamma-S parameter in leacril fabric at concentrations of N-CP-Cl in solution as the fabric is treated is due to the decreasing content of sulfonate and sulfate groups electron donors, in the leacril due to acid-base neutralization between the cation of the surfactant and the surface groups of the fabric. The obtained value of gamma-S, 35.8 mJ/m2, after the treatment of leacril with 10(-2) M N-CP-Cl could be due to the presence of N+-pyridinium groups, electron donors, on the leacril surface at the highest concentrations of surfactant due to the adsorption of the surfactant onto the leacril surface.