Thermodynamic excess quantities in the adsorption of sodium alkylsulfonates at the air-solution interface

Colloid and Polymer Science - Data on the surface tension of sodium alkylsulfonate solutions at different temperatures and surfactant concentrations are presented. By applying the thermodynamic...     

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.     

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.     

Investigation of alumina/(+)-catechin system properties. Part II: ζ-potential and surface free energy changes of alumina

The effects of (+)-catechin adsorption to the alumina surface were studied by ζ-potential and surface free energy determination. The presence of catechin causes essential changes in the alumina ζ-potential, which at the concentration slightly higher than 10⁻⁵ M reverses from the positive into negative one. At constant concentration of catechin (10⁻³ M), the effect on ζ-potential of alumina as a function of pH appears in a drastic shift of the isoelectric point, from pH 8.4 to 4.6, and the equilibrium is established practically within 2 h. This is probably due to relatively low pK_a=4.6 for catechin 3′-OH group deprotonation. At high alkaline environment (pH≥10), even in the presence of catechin in the solution, the hydroxyl OH⁻ ions play principal role in the surface charge formation for the alumina. At such pH catechin molecule is double negatively charged and hence its adsorption on highly negatively charged alumina surface is rather restricted. Nevertheless, various dimeric forms of catechin, which are formed at the alkaline pH, probably adsorb on the alumina surface. This appears in small increase in apolar surface free energy component at natural and alkaline pH. On the other hand, at acidic pH 3 small increase of the electron acceptor interaction is observed. This may result from increased number of hydroxyl groups on the alumina surface originating from the adsorbed molecules of catechin, which are mostly undissociated at this pH. The interactions of catechin with alumina surface seems to be also of some specific nature, because neither changes in the ultraviolet–visible (UV–vis) absorbance (Part I) nor in the ζ-potentials had occurred in the silica suspensions in which also catechin was present.     

A Novel Method for Surface Free-Energy Determination of Powdered Solids

Interfacial solid/liquid interactions play a crucial role in wetting, spreading, and adhesion processes. In the case of a flat solid surface, contact angle measurements are commonly utilized for the determination of the solid surface free energy and its components. However, if such a surface cannot be obtained, then the contact angle can not be measured directly. Usually methods based on imbibition of probe liquids into a thin porous layer or column are applied. In this paper a novel method, also based on the capillary rise, is proposed for the solid surface free-energy components determination. Actually, it is a modification of the thin column wicking method; similar theoretical background can be applied together with that appropriate for the capillary rise method of liquid surface tension determination. The proposed theoretical approach and procedure are verified by using single glass capillaries, and then alumina and ground glass powders were used for the method testing. Thus obtained surface free-energy components for these solids, for both glass and alumina, agree well with the literature values.     

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.     

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.     

Problems of contact angle and solid surface free energy determination

The current general problems of formulation and determination of surface free energy are discussed. So far several theories and approaches have been proposed, but formulation of surface and interfacial free energy, as regards its components, is still a very debatable issue. However, as long as no method for determination of real surface free energy quantities is known, even relative values charged with many simplified assumptions are useful for better understanding of the wetting processes. In this paper special focus is concentrated on powdered solids for which direct measurement of the contact angles is not possible. For such solids the porous layer imbibition techniques are most frequently applied. Then, using the wicking results the contact angle is calculated from Washburn's equation. However, such a procedure leads to overestimated contact angle values in comparison to those measured directly on smooth surfaces of the same solid, if such surface can be obtained at all. As a consequence, the solid surface free energy components calculated via such overestimated contact angles are significantly lower than those obtained from contact angles measured directly. Methodologies to avoid this problem are also described.     

Investigation of alumina/(+)-catechin system properties. Part I: a study of the system by FTIR-UV–Vis spectroscopy

Catechin belongs to a group of flavonoids, which are present in many fruits and plants. Catechin is often employed in model investigations on antioxidant behavior of flavonoids. Recently also some anti-disease properties of flavonoids were reported. In this paper investigations were carried out on alumina/(+)-catechin solution system. FTIR spectra were taken for the catechin samples retaken from its aqueous solutions at pH 3, 5.5 (natural) and 10.5. In other series, the solutions were contacted with an alumina powder during 20 days. Also UV–Vis spectra were taken for similar solutions incubated for 1, 7, 20, 50 and 70 days with and without contact with alumina. It appeared that the alumina essentially accelerated the autooxidation processes occurring in the solutions. The results show that the processes have completed between day 20 and 50, because the UV–Vis spectra for day 50 and 70 overlapped. Moreover, it looks that this is a specific property of alumina, which behaves as a catalyst. Similar experiments with silica showed that during 50 days, this oxide affected the processes only slightly.     

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.