Adsorption of acrylic and polyacrylic acids on the mercury electrode/sodium chloride solution interface (original) (raw)
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Adsorption of polyacrylic acid on hydrophobic and hydrophilic surfaces
Colloid & Polymer Science, 1996
In this paper the adsorption of polyacrylic acid (MW = 5000) on the hydrophobic mercury surface and on the hydrophilic 7-AlzO3 surface at pH = 3-4 in 0.55 M sodium chloride solution was investigated. Measurements of change of the double layer capacitance by phase selective a.c. voltammetry were used for determination of the adsorption of polyacrylic acid on the mercury electrode. The same method was used for the determination of the polyacrylic acid remaining in the solution after the adsorption on hydrophilic particles (~-A1203 particles). The results obtained for adsorption of polyacrylic acid were compared to the results of the adsorption of humic substance of similar molecular weight under similar experimental conditions. The study has shown that polyacrylic acid in acidic solution is strongly adsorbed on the mercury surface, which is comparable to the adsorption of humic substance on the mercury surface. At the same time, the adsorption/deposition of polyacrylic acid on the 7-A1203 surface is weaker compared to humic acid, indicating at a smaller degree of interaction of polyacrylic acid with aluminium ions and with hydrophilic surface.
Electroanalysis, 1996
In this article we explore the kinetics of adsorption of octanoic acid at the mercury-water interface using phase sensitive AC voltammetry. These measurements were performed before and after stepwise purification of the octanoic acid solution, in order to distinguish between the adsorption behavior of the octanoic acid and its impurities. The adsorption of both octanoic acid and the surface active impurities decrease the capacitance with time. Removing the latter during the purification procedure results in a faster achievement of the equilibrium state and in higher capacitance values. The adsorption was also studied at the air-water interface using dynamic surface tension measurements. Comparable results are obtained for both interfaces.
On the Adsorption of Octanoic Acid at the Mercury/Electrolyte and Air/Water Interfaces
Journal of Colloid and Interface Science, 1997
dynamics are usually considerably changed by coadsorption The adsorption of a purified solution of octanoic acid at the (6, 7). As already reported in it is indispensable to use mercury/solution and air/water interfaces was studied. The equisurfactant solutions with a sufficient grade of purity, called librium capacitance values were obtained by phase sensitive ac ''surface-chemically purity,'' by means of which interfering voltametry. From the concentration dependence of the capacitance effects of trace impurities at the air/solution interface.
The adsorption of sodium oleate from electrolyte solutions on a polarized mercury electrode can be studied by monitoring the differential capacitance of the electrode double layer. Its variation with potential and time can provide qualitative information on the state of the oleate adsorbate. A new experimental methodology, three-dimensional phase-sensitive ac voltammetry, is used to provide safer information on the equilibrium transition characteristics and also to follow the time evolution of the phenomenon. The steady-state differential capacitance vs electrode potential curve is interpreted by means of recently developed thermodynamic criteria for phase transitions of surfactants at charged interfaces. At concentrations below the bulk critical micelle concentration monolayer adsorption takes place at moderate and negative polarizations, whereas there is some evidence of multilayer adsorption at more positive potentials. At higher concentrations, multilayer adsorption occurs throughout the potential range studied. In both cases, the formation of a close-packed structure is likely to be restricted to the first layer and the phase transitions of the latter to be realized via aggregates formed by its interaction with the outer layers. In addition, a close-packed polylayer is also observed at extreme positive potentials for high bulk oleate concentrations. Analysis of the capacitance transients based on simple diffusion, adsorption, or Avrami formalisms cannot describe successfully the time dependence of oleate adsorption on mercury, indicating that the latter is under mixed control or/and a complex process.
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 1994
In order to study the influence of the adsorption of fulvic compounds on voltammetric signals and to understand better the adsorption of these compounds on hydrophobic natural water interfaces, adsorption studies of macromolecules such as poly(ethylene glycol) (HO(CH,CH,O),) with molecular weight of 8000 were done on the mercury/water interface by a.c. voltammetry at the potential of zero charge. The maximum surface concentration, adsorption equilibrium constant and adsorption rate constant have been determined from the global adsorption mechanism, controlled by two determining steps: diffusion and kinetics of adsorption at the interface.
Journal of Colloid and Interface Science, 2000
The adsorption and the changes in the interfacial composition of octanoic acid at the mercury/electrolyte interface was studied by measuring the differential capacitance at different concentrations of the supporting electrolyte, at various supporting electrolyte systems and at various temperatures. The adsorption was followed by means of capacity-potential curves in the short-term region and capacity-time transients in the long-term region at selected potentials, in all the potential ranges. A decrease of the capacitance with time was observed in most cases, followed either by a constant capacitance value or by its increase. In the short-term region, anion-surfactant complexes are formed, where the anions act as bridges between the perpendicularly oriented surfactant molecules. The larger is the negative charge of the anion, the more negative will be the charge of the anion-surfactant complex leading to a shift of the potential of maximal adsorption to more positive values. The formation of metastable condensed films is best when the hydration of the anion and its size are not too large. In the long-term region the observed increase of the capacity with time can be explained as an exchange of the metastable condensed film by a hemimicellar surface state. Here, the anions act as cores of the hemimicelles, and the hydrophilic acid groups of the amphiphiles contact the solution. Two contrary effects determine the formation of the hemimicelles. The greater is the specific adsorption of the anions, the larger is the formation of hemimicelles and the increase of the capacity. With an increase in the ability of the anions to break the water structure (lyotropic or Hofmeister series), the formation of hemimicelles will be decreased. C 2000 Academic Press Key Words: octanoic acid; mercury electrode; differential capacitance; electrolyte effect on adsorption; supporting electrolyte concentration effect on adsorption. 398
Journal of Colloid and Interface Science, 1999
The adsorption of hydrophobically modified polyacrylic acid (HM-PAAc) has been compared to the adsorption of unmodified polymers by means of reflectometry. The polymers were adsorbed onto a noncharged hydrophobic polystyrene surface. The adsorption kinetics of both types of polymer is the same until a certain surface coverage. Then the unmodified sample shows a saturation while the hydrophobically modified polyacrylic acid continues to adsorb. The adsorption behavior of the polyelectrolyte can be controlled by the pH and the ionic strength of the solution. For ionic strengths of 0.001 M NaCl the hydrophobically modified polymer shows a larger adsorbed amount at pH 3 to 4 compared to the unmodified polymer. At pH higher than 4 the differences are less significant. At higher ionic strength the amount of adsorbed material increases for both polymers. While doing adsorption-desorption cycles a hysteresis-effect was detected. At the same pH the hydrophobically modified polymer sticks to the surface while the unmodified polymer is already desorbing completely. The hysteresis vanishes when the ionic strength of the solution is increased.
Adsorption of acrylonitrile and its electrohydrodimerization on mercury from aqueous solutions
Journal of Electroanalytical Chemistry and Interfacial Electrochemistry, 1991
aqueous solutions of 1.5 M lithium citrate containing 10m3 M dodecylethyldimethylammonium (DE-. DMA) bromide. Under these conditions, AN adsorptivity was shown to increase progressively towards more negative charge densities on the metal, due to co-adsorption with DEDMA bromide. Upon relating the adsorption isotherm of AN with its EHD rate, it was shown that AN EHD takes place through a rate-determining radical-substrate coupling step in the adsorbed state. 0022-0728/91/$03.50 0 1991 -Elsevier Sequoia S.A. All rights reserved
Adsorption of some mixtures of surface active substances at the mercury electrode
Journal of Electroanalytical Chemistry and Interfacial Electrochemistry, 1980
Adsorption behaviour at the mercury electrode of some mixtures of surface-active substances, relevant and important for natural and polluted seawater, has been studied on the basis of capacity current measurements using the polarographic method of discontinuously changing potential known as the Kalousek commutator technique. The total adsorption effects of different mixtures of selected surface-active substances (albumin, lecithin, oleic acid, Triton-X-100, sodium dodecyl sulphate) were determined in the seawater as a supporting electrolyte and compared with the values calculated from the individual isotherms.
Journal of Electroanalytical Chemistry, 1992
Ak%ra&-The interfacial behaviour of two phosphonium cations, tetraphenylphosphonium chloride (TPPCl) and cetyltributylphosphonium bromide (CTBPBr), is studied in the polarized mercury electrode/ aqueous electrolyte solution interface by means of diierential capacitance measurements. Both phosphonium cations are extremely surface active compounds and in a concentration as low as 5 x 10-6mol/l their adsorption is controlled only by diffusion. CTBPBr molecules, which are. known to form micelles in bulk, are also associated into surface aggregates at the Q/electrolyte solution charged interface. This is extract4 from the shape of the dilTerential capacitance (C) vs. applied potential (E) curves. The application of a new methodology, known as three-dimensional phase sensitive ac voltammetry, based on the reconstruction of C vs. E curve from isochronous C data, sampled after many chronocapacitometric experiments, gives the opportunity to produce a picture of the transition curves that cannot be. obtained by the classic ac voltamme&y. This methodology provides the equilibrium C vs. E curves for long time pe.riods and also gives information about the time evolution of adsorption phenomena Key words: three-dimensional phase sensitive voltammetry, adsorption on mercury, phosphonium cations, phase transitions.