The interactions between an anionic dye and two cationic surfactants were studied by conductometry. The specific conductance of dye–surfactant mixtures was measured at three different temperatures in water–ethanol mixed solvent, containing 5, 10, 15 or 20 wt.% of ethanol. The equilibrium constants and other thermodynamic functions for the process of dye–surfactant ion pair formation were calculated on the basis of two theoretical models. The results showed that the presence of ethanol decreases the tendency for ion pair formation. According to the results, long range as well as short range interactions are responsible for the formation of the ion pair. The importance of long range electrical forces is basically to bring the dye anion and the surfactant cation close enough to enable the action of short range interactions whose contribution represents the major part of the standard free enthalpy change for the formation of the anionic dye–cationic surfactant ion pair.

The formation of a dye–surfactant ion pair was studied using a conductometric method in which the conductance of aqueous solutions of C.I. Acid Orange 7 was measured in the presence of the cationic surfactants dodecylpyridinium chloride or hexadecylpyridinium chloride at four different temperatures. Two theoretical models to calculate the relevant equilibrium constants were derived. Both methods of calculation led to similar results that were in good agreement with other methods of investigation of dye–surfactant association. The results have shown that an increase in temperature lowers the tendency for ion pair formation as the equilibrium constants decrease with increasing temperature. A comparison of the behaviour of both surfactants revealed that the surfactant which contained the longer hydrophobic chain had a stronger tendency to associate with the dye and the corresponding equilibrium constants were considerably higher than those recorded for the surfactant with the shorter aliphatic chain. Such findings indicate that not only long range electrostatic forces but also short range, non-electrostatic interactions have a significant influence on dye–surfactant ion pair formation.

The formation of complexes between an anionic dye and a cationic surfactant was studied with conductometric method. The conductance of dye-surfactant mixtures in aqueous solutions and in solutions with different amount of ethanol was measured at 25°C. The results have shown that the presence of ethanol significantly decreases the formation of complexes. In the presence of 15% or 20% ethanol no interaction which would cause formation of non-conducting or less conducting species between the dye C.I. Acid Orange 7 and the surfactant N-dodecylpyridinium chloride was detected in the observed concentration range.

The association of C.I. Acid Orange 7 (D) and the surfactant cetylpyridinium chloride (S) was studied at 15, 25, 35 and 45°C in the presence of 0, 0.05 and 0.1 mol/kg NaCl, by potentiometric titration, using a surfactant cation sensitive membrane electrode. By using the association constant (K1) for the first step of the association [D−+S+ ↔(DS)°], the standard free energy change, standard enthalpy change, and standard entropy change of the association were calculated at low surfactant concentrations. The unitary entropy of association was negative, suggesting that hydrophobic interactions do not play a major role in the initial interaction between dye and surfactant. On the other hand, in the second step [S++(DS)° ↔(DS2)+], the unitary entropy change in the medium-level surfactant concentration domain was highly positive, indicating that water-structure contributions are appreciable in the stabilisation of the (DS2)+ species. It was shown that a further stepwise association is not very likely in the third domain, and that a neutral quadruple species of type (SD)2° may be present in the solution. Further increases in surfactant concentration led to a very steep increase in bound surfactant as the concentration of free surfactant ions approached the c.m.c. point. It was also shown that the addition of a simple electrolyte (e.g. NaCl) decreased K1, mainly due to interference with the interaction of dye and surfactant ions. Since long range Coulombic interactions are absent in the second association step, the increase in K2 with increasing NaCl concentration can be mainly attributed to short range hydrophobic interactions.

Interactions between the anionic dye Acid Orange 7 and two cationic surfactants N- cetylpyridinium chloride (CPC1) and cetyltrimethylammonium bromide (CTMABr) in aqueous solutions far below the CMC are studied using the method of continuous variations, also called Job's method. Light absorbance in the visible spectral range is measured. Both surfactants form stable associates with the acid dye. Job's method is suitable for determining the stoichiometric composition and equilibrium association constants of the associates studied. The molar binding ratio of both surfactant/dye associates is 1:1. The calculated equilibrium constants are high (about 10 6 ), indicating strong interactions. From the constants calculated at different temperatures ( 15, 25, and 35°C), the corresponding thermodynamic functions Δ G 0 , Δ H 0 , and Δ S 0 are ob tained. We have concluded that strong interactions between cationic surfactants and anionic dyes are the result of attractions between oppositely charged ions combined with hydrophobic and dispersive forces.

The study of the interactions between anionic azo dyes C.I. Acid Orange 7 (AO7) and C.I. Acid Red 88 (AR88), with different surfactants, i.e., the cationic surfactants dodecylpyridinium chloride (DPC) and cetylpyridinium chloride (CPC) and the anionic surfactant sodium dodecylsulphate (SDS), in submicellar concentration ranges has been researched by a potentiometric technique using a surfactant-cation-sensitive membrane electrode. The e.m.f. measurements versus surfactant concentration have been performed for the systems CPC-AO7, DPC-AO7, DPC-AR88 and SDS-AO7 in pure water at 25°C. Experimental measurements give the option to determine the concentration of free and of bound surfactant cations at a given stoichiometric concentration and calculation of the dye-surfactant complex formation constant, K, and the standard free enthalpy change, ΔG°. The results show that under the same experimental conditios the complex formation between CPC and AO7 takes place at much lower surfactant concentration than between DPC and AO7, accompanied by much higher values of K. It can be seen from the shapes of the binding isotherms that the binding of DPC to AO7 is most likely cooperative. The results indicate that in the DPC-AR88 system, where more hydrophobic dye AR88 is used, the dye-surfactant interactions are stronger compared to DPC-AO7 system. Such observations enable the conclusion, to be made that, beside the electrostatic attractive interactions, the noncoulonic interactions are also very important for the formation of the complex between the oppositely-charged dyes and surfactants. The study of the interactions between the same-charged dye AO7 and surfactant SDS shows that they do not interact with one another in the whole measured concentration range. The most logical explanation for this is that the repulsive electrostatic interactions prevent the formation of the complex between the same charged AO7 and SDS.

The critical micelle concentration (CMC) and the thermodynamic functions Delta G(mic)degrees, Delta H(mic)degrees and Delta S(mic)degrees for the micellization process of the two pyridinium cationic surfactants N-dodecylpyridinium chloride (DPC) and N-cetylpyridinium chloride (CPC) in aqueous solution were studied by a potentiometric method using surfactant cation-sensitive membrane electrodes. The e.m.f. of the galvanic cell was measured as a function of surfactant concentration at temperatures of 15, 25, 35 and 45 degrees C at different concentrations of added NaCl (0.00, 0.01, 0.05, 0.1 and 0.5 mol kg(-1)). The properties of the DPC/CPC mixture were also investigated. The results indicate that the CMC decreases as the hydrophobic character of the surfactant increases and that the addition of NaCl favours the micellization of both studied surfactants. Increase of temperature from 25 degrees C to 45 degrees C did not cause a noticeable change in the CMC of DPC, but resulted in a slight increase in the CMC of CPC. Inspection of the data for thermodynamic functions of micellization shows that the micellization of the studied surfactants is governed mainly by hydrophobic interactions between the surfactant cations, and that CPC forms micelles more readily than DPC under the same conditions.

The aggregation of a monoazo acid dye was studied with osmometry. The osmotic coefficients of the dye were measured in aqueous solution and in 0.01 M potassium chloride. The mean aggregation numbers were calculated on the basis of the spherical cell model of dye in the solution. The results showed that the aggregation process is more distinctive in the presence of a simple electrolyte, probably because of the screening effect of the salt ions.

The thermodynamic aspects of the self-association of three monoazo dyes, viz. C.I. Acid Red 88, C.I. Acid Orange 7 and C.I. Acid Orange 8, in aqueous solution have been studied by means of a potentiometric method. An ion-selective membrane electrode, selective to a dye anion, has been constructed. This electrode permits a direct determination of the dye monomer concentration.Measurements of e.m.f: versus dye concentration were carried out and the results show that the e.m.f response is not linear over the whole measured concentration range. Because of dye association at higher concentrations the measured e.m.f values start to deviate from the theoretical linear relationship. From these deviations the dye monomer concentration at a given total dye concentration was determined. Using an appropriate stepwise association model the dimerization constants and concentrations of the dimers and highs multimers were calculated. It is concluded that C.I. Acid Red 88 aggregates more readily than C.I. Acid Orange 7. C.I. Acid Orange 8, the structure of which includes a charged sulphonic acid group in the central part of the molecule, does not aggregate in the measured concentration range. The effects of temperature and added salt on the association of C.I. Acid Red 88 have also been investigated. From the results, it can be seen that the association of C.I. Acid Red 88 decreases with increasing temperature, and strongly increases with increasing salt concentration. Thermodynamic functions of dimerization of C.I. Acid Red 88 in aqueous solutions at different temperatures were also determined. It appears that the dimerization of C.I. Acid Red 88 in aqueous solution is governed mainly by dispersive interactions between the dye molecules.

An ion-selective membrane electrode selective to the Acid Red 88 (C.I. 15620) dye anion has been constructed. This electrode, with the Acid Red 88 dye anion-cetylpyridinium cation carrier complex incorporated within a poly(vinyl chloride) gel membrane, permits direct determination of the dye monomer concentration. In this work its fabrication, general performance and selectivity are described. The selectivities have been obtained by a mixed solution method for the Acid Orange 7 (C.I. 15510), Acid Red 13 (C.I. 16045) and Acid Blue 25 (C.I. 62055) interfering onions. The selectivity coefficients suggest that the dye electrode is not sensitive to interfering dye anions of similar structure and different charge or size.

Die Makromolekulare Chemie, Rapid CommunicationsVolume 4, Issue 11 p. 697-701 Article Electrical transport in poly(styrenesulfonate) solutions with divalent counterions Dušan Bratko, Corresponding Author Dušan Bratko Laboratory of Physical Chemistry, Edvard Kardelj University, Ljubljana, Murnikova 6, YugoslaviaLaboratory of Physical Chemistry, Edvard Kardelj University, Ljubljana, Murnikova 6, YugoslaviaSearch for more papers by this authorDavorin Dolar, Davorin Dolar Laboratory of Physical Chemistry, Edvard Kardelj University, Ljubljana, Murnikova 6, YugoslaviaSearch for more papers by this authorAndrej Godec, Andrej Godec Laboratory of Physical Chemistry, Edvard Kardelj University, Ljubljana, Murnikova 6, YugoslaviaSearch for more papers by this authorJož Špan, Jož Špan Laboratory of Physical Chemistry, Edvard Kardelj University, Ljubljana, Murnikova 6, YugoslaviaSearch for more papers by this author Dušan Bratko, Corresponding Author Dušan Bratko Laboratory of Physical Chemistry, Edvard Kardelj University, Ljubljana, Murnikova 6, YugoslaviaLaboratory of Physical Chemistry, Edvard Kardelj University, Ljubljana, Murnikova 6, YugoslaviaSearch for more papers by this authorDavorin Dolar, Davorin Dolar Laboratory of Physical Chemistry, Edvard Kardelj University, Ljubljana, Murnikova 6, YugoslaviaSearch for more papers by this authorAndrej Godec, Andrej Godec Laboratory of Physical Chemistry, Edvard Kardelj University, Ljubljana, Murnikova 6, YugoslaviaSearch for more papers by this authorJož Špan, Jož Špan Laboratory of Physical Chemistry, Edvard Kardelj University, Ljubljana, Murnikova 6, YugoslaviaSearch for more papers by this author First published: November 1983 https://doi.org/10.1002/marc.1983.030041101Citations: 11AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume4, Issue11November 1983Pages 697-701 RelatedInformation

Die Makromolekulare Chemie, Rapid CommunicationsVolume 4, Issue 12 p. 783-788 Article Conductivity of polyelectrolyte solutions containing mono-and divalent counterions† Dušan Bratko, Corresponding Author Dušan Bratko Department of Chemistry, Edvard Kardelj University, 61000 Ljubljana, YugoslaviaDepartment of Chemistry, Edvard Kardelj University, 61000 Ljubljana, YugoslaviaSearch for more papers by this authorNada Celija, Nada Celija Department of Chemistry, Edvard Kardelj University, 61000 Ljubljana, YugoslaviaSearch for more papers by this authorDavorin Dolar, Davorin Dolar Department of Chemistry, Edvard Kardelj University, 61000 Ljubljana, YugoslaviaSearch for more papers by this authorJože Špan, Jože Špan Department of Chemistry, Edvard Kardelj University, 61000 Ljubljana, YugoslaviaSearch for more papers by this authorLibuše Trnkova, Libuše Trnkova Department of Chemistry, Edvard Kardelj University, 61000 Ljubljana, Yugoslavia Faculty of Natural Sciences, University of Brno, 61137 Brno, Czechoslovakia.Search for more papers by this authorVojko Vlachy, Vojko Vlachy Department of Chemistry, Edvard Kardelj University, 61000 Ljubljana, YugoslaviaSearch for more papers by this author Dušan Bratko, Corresponding Author Dušan Bratko Department of Chemistry, Edvard Kardelj University, 61000 Ljubljana, YugoslaviaDepartment of Chemistry, Edvard Kardelj University, 61000 Ljubljana, YugoslaviaSearch for more papers by this authorNada Celija, Nada Celija Department of Chemistry, Edvard Kardelj University, 61000 Ljubljana, YugoslaviaSearch for more papers by this authorDavorin Dolar, Davorin Dolar Department of Chemistry, Edvard Kardelj University, 61000 Ljubljana, YugoslaviaSearch for more papers by this authorJože Špan, Jože Špan Department of Chemistry, Edvard Kardelj University, 61000 Ljubljana, YugoslaviaSearch for more papers by this authorLibuše Trnkova, Libuše Trnkova Department of Chemistry, Edvard Kardelj University, 61000 Ljubljana, Yugoslavia Faculty of Natural Sciences, University of Brno, 61137 Brno, Czechoslovakia.Search for more papers by this authorVojko Vlachy, Vojko Vlachy Department of Chemistry, Edvard Kardelj University, 61000 Ljubljana, YugoslaviaSearch for more papers by this author First published: December 1983 https://doi.org/10.1002/marc.1983.030041206Citations: 13 † Presented at the 27th International Symposium on Macromolecules, Strasbourg 1981. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume4, Issue12December 1983Pages 783-788 RelatedInformation

Most dyes constitute a class of electrolytes display ing peculiar properties in their relationship with water. There is a great deal of evidence that dye ions aggregate in aqueous solutions.15 Several methods have been proposed for the study of this phenomenon. Although very promising, vapour pressure osmometry has been almost completely neglected. Milicevic and Eigenmann6 reported the values of activity coefficients of two simple acid dyes obtained by this method. Supposing that there is no specific counterion binding and using the Debye-Huckel limiting law, they have shown that Orange II, in contrast to its isomer Orange VIII, is not appreciably dimerized. In our work, the method was applied for the determination of the extent of aggregation in solutions of two direct and two acid dyes, where higher aggregates were also expected. Using the spherical cell model of collo·id solutions,110 we were able to estimate the mean aggregation numbers of the four dyes studied.

AbstractThe electromotive force of the concentration cell with transference consisting of two identical cadmium amalgam electrodes and two solutions of cadmium polystyrenesulfonate with different concentrations, was measured for concentrations from 0,002 to 0,1 molal in monomer units. In the same concentration range transference and conductance measurements were performed in order to obtain the polyion transference number and the fraction of free counterions as functions of concentration. The logarithm of the mean activity coefficient derived from electromotive force and transference number is found to be a linear function of the logarithm of concentration. The experimental results are compared with the predictions of the cylindrical cell model and infinite line charge model. Satisfactory agreement between theory and experiment indicates that these models better represent the experimental results than the cube‐root relation which would follow from the ionic lattic structure of solution.

The preferential interaction of the solvent components with lysozyme and β-lactoglobulin was determined in aqueous guanidine·HCl solutions by means of equilibrium dialysis and differential refractometry. It has been found that on the molal scale at all concentrations studied the denaturant was preferentially bound.

The results of transference and conductance measurements on solutions of sodium polystyrenesulpnonate, in the concentration range from 0.0025 to 0.075 monomolar, are presented. The fraction of free Counterions calculated from experimental data is found to he independent of molecular weight of the polyelectrolyte within the range of degree of polymerization from 200 to 2400. The experimental data, combined with the cell model, are used to calculate the electrostatic potential at a cylindrical surface Which surrounds the polyion and divides the counterions into bound and free. The same value for this potential is found for the whole concentration range investigated, which lends support to the assumption of cylindrical distribution of counterions in polyelectrolyte solutions.

The preferential interaction of the solvent components with β-lactoglobulin and chymotrypsinogen A, respectively, was determined in aqueous urea solutions by means of equilibrium dialysis and differential refractometry. It has been found that at all concentration studied urea was preferentially bound.

Series of experiments were performed to show the influence of the concentration and flow rate of solution on the self-diffusion of the iodide ion into the ion-exchange resin Dowex 1 × 8. Using a model based on the concept of an effective diffusion layer with the nonlinear concentration profile, rate curves were calculated and compared with experimental results. Good fitting in the whole concentration and flow range is observed. Using the same model, concentration profiles in both solid and liquid phases for three different thicknesses of the diffusion layer were calculated.