Partial molar volume and isentropic compressibility of symmetrical and asymmetrical quaternary ammonium bromides in aqueous solution

Values of apparent molar volume and isentropic compressibility of symmetric and asymmetric isomers of tetrabutylammonium bromide, namely tetra-n-butylammonium bromide, tetra-iso-butylammonium bromide, tetra-sec-butylammonium bromide, di-n-butyl-di-iso-butylammonium bromide and di-n-butyl-di-sec-butylammonium bromide, in aqueous solution were determined from density and speed of sound measurements. These properties were obtained as a function of molal concentration within the range of 0.01 < m/mol · kg⁻¹ < 0.1 covering temperatures from 278.15 ⩽ T/K ⩽ 293.15. The partial molar volumes and the apparent isentropic molar compressibility at infinite dilution were calculated and their dependence on temperature examined. The results show that cations with sec-butyl chains have larger structural volumes compared to those with iso-butyl chains. In addition, cations with sec-butyl chains induce smaller structural changes in their hydration shell than the others.     

Partial molar volume of dodecyltrimethylammonium hydroxide in water and NaOH aqueous solutions

 The partial molar volume of dodecyltrimethylammonium hydroxide in water and aqueous NaOH solutions was measured. The addition of NaOH did not affect either the micellized or the unmicellized molecules. The expansion on micellization is much larger than in dodecyltrimethylammonium bromide systems, which reflects the stronger ionization of the hydroxide surfactant micelles, when compared with that of the bromide amphiphile. Received: 27 October 1997 Accepted: 4 March 1998     

Partial molar volumes of tetraalkylammonium hydroxides in aqueous solution at 25°C

The densities of aqueous solutions of tetramethylammonium, tetraethylammonium, tetra-n-propylammonium and tetra-n-butylammonium hydroxide have been measured at 25°C in the concentration range 0.1–1.0 mol-kg^-1 . The apparent and partial molar volumes are calculated from the density measurements. The apparent molar volumes of the solutes show considerable deviation from the Debye-Hülckel limiting law, even at high dilution. The relation for the concentration dependence of the apparent molar volume is given in an analytical form. The limiting apparent molar volumes of the solutes are split into their ionic components by an extrathermodynamic approach and are discussed in terms of ion-solvent interactions. In this way, the limiting partial molar ionic volume for the hydroxide ion is found to be 2 cm³-mol^-1.     

Electrical conductivity of cationic polyelectrolytes in aqueous solution

Four different fluoride, chloride, bromide, and nitrate cationic polyelectrolytes were prepared. Their electrolytic conductivity in aqueous dilute solution was investigated. The results show a remarkable increase, with dilution being practically constant down to limiting concentration. The limiting equivalent conductivity Λ° follows the order The distances between neighboring charges calculated from experimental data are in good agreement with those calculated geometrically according to Manning's definition. The results are mainly dependent on the assumption that Br^? and NO₃^? interact in a similar manner with the cationic charges on the polyion. This phenomenon also has been observed in cationic micelles.     

Interaction of cationic surfactant and anionic polyelectrolytes in mixed aqueous solutions

Surfactant–polymer interactions in aqueous solutions have been studied using dynamic surface tension, polyelectrolyte titration, nephelometric turbidity, and dynamic light scattering. For the preparation of complexes, a technical cationic surfactant was used in combination with two poly(maleic acid-co-polymers) of similar structure but different hydrophobicity. The dynamic surface tensions of mixed solutions as functions of surfactant concentration at constant polyelectrolyte content, as well as changes in the surface activity due to the influence of polyanion at constant surfactant concentration are discussed in terms of a complex or aggregate formation in the bulk phase. The interaction of the surfactant with poly(maleic acid-alt-propene) (P-MS-P) and poly(maleic acid-alt--methylstyrene) (P-MS-MeSty), respectively, is strong in both cases and results in the formation of nanoparticles with properties depending on the composition of the corresponding mixture.     

Gel permeation chromatography on polyelectrolytes in aqueous solution

Gel permeation chromatography of water-soluble polymers, with special attention to polyelectrolytes, has been studied. A three-detector system (refractometry, conductimetry, viscometry) is used to characterize the polymers. A single curve is obtained for the calibration of the set of columns taking into account the hydrodynamic volume of the solutes and using a 0.1 N salt solution as the eluent to screen electrostatic forces. The role of the low adsorption of dextran on silica gel is pointed out. The dependence of elution volume on polymer concentration is demonstrated and interpreted in terms of the screening length of the molecules.     

Interaction between oppositely charged polyelectrolytes in aqueous solution

Oppositely charged polyelectrolytes interact in solution, forming polyelectrolyte complexes, which often appear as gel-like precipitates. This kind of complex formation was studied by means of calorimetric and rheological measurements. The enthalpy effects, though being fairly small, give some information about the binding strength of counterions to the macroion. We studied the system poly(p-styrene sulfonate)/poly(trimethylammonium-2-ethyl methacrylate) (PSS-PTMA), varying systematically the low molar mass counterions of PSS. In every case, the maximum of enthalpy was found around a 1:1 (mol:mol monomer units) composition of the complexes, with the shape of enthalpy versus composition-curve indicating a stoichiometric interaction. The maximum enthalpy decreased with increasing atomic mass of the counterion when the alkaline metal salts of PSS were used and no change was made on the side of the cationic polyelectrolyte. The salts of the alkaline earth metals gave a distinctly higher enthalpy. On the contrary, viscosity measurements showed a very broad minimum as a function of composition, indicating that the formation of non-stoichiometric complexes is also occurring. The conclusion of these observations is that the complex formation is stoichiometric with respect to the monomeric units, but not necessarily stoichiometric with respect to the entire macromolecules.     

Counterion binding to cationic polyelectrolytes in aqueous solution

The mean ion activity coefficient, (γ_±)_px/(γ_±)_salt for different high-linear charge density cationic polyelectrolyte fluoride, bromide, chloride and nitrate has been determined. The order found is: F^? > CI^? ≧ Br^? > NO. The results obtained with added nitrate were compared with those predicted by Iwasa, Guéron, and Weisbuch and Manning's models. The latter presents the best agreement for polyion chloride and bromide. It was possible to establish the most probable microconfiguration for the polyions studied here. Manning's theory gives a moderate agreement for polyion fluoride values compatible with a lower charge density than for polyelectrolyte chloride and bromide.     

The limiting partial molar volume and apparent molar volume of glycylglycine in aqueous KCl solution at 298.15 and 308.15 K

Apparent molar volumes V_Φ of glycylglycine in aqueous KCl solutions have been obtained from densities at 298.15 and 308.15 K measured with a vibrating-tube densimeter. These data have been used to deduce partial molar volumes of transfer from water to different KCl–water mixtures. values are positive. This result arises from the interaction of KCl with the charged centers of glycylglycine. The results show that depends less on temperature. Hydration numbers are calculated from data and are interpreted in terms of various interactions.     

Group contributions to the partial molar volume of ionic organic solutes in aqueous solution

Partial molar volumes at infinite dilution in water at 25°C for more than 400 organic electrolytes (carboxylic acid and amine salts, sulfates, sulfonates, selected polyelectrolyes, aminoacids and derivatives) are described through a simple additivity scheme already adopted for non-electrolytes. Twenty-five charged groups are assigned a contribution and the partial molar volumes of more than 150 monofunctional organic ions are reproduced with a standard deviation of 0.8 cm³-mol^–1. The different volumetric behavior of hydrophobic and hydrophilic centers, either charged or uncharged, is discussed. Deviations from additivity for mono-and polyfunctional ions are analyzed in terms of (i) extension of the hydration cosphere of different polar centres; (ii) intramolecular interactions and their dependence on the nature, number and mutual separation of interacting groups.     

Thermodynamic properties of peptide solutions 3. Partial molar volumes and partial molar heat capacities of some tripeptides in aqueous solution

Partial molar volumes, V ₂ ^o , and partial molar heat capacities, C _p,2 ^o , of the tripeptides glycylglycylglycine, glycylglycylalanine, glycylalanylglycine and alanylglycylglycine have been determined in aqueous solution at 25°C. For the three alanyl-containing tripeptides, the data indicate that the tripeptide-water interaction is influenced by the side chain position within the molecule. The results have been rationalized in terms of likely solutesolvent interactions. The V ₂ ^o and C _p.2 ^o data have also been used to calculate the contribution to these properties of a-CH₃ side chain.     

Partial molar volume of small molecules in glassy polymers

The sorption of atoms or molecules in glassy polymers is assumed to occur within a variety of sites belonging to the intermolecular volume and providing different space for the dissolved molecules. If the size of the small molecule is larger than the size of the site, the glassy polymer is elastically distorted during sorption of the solute molecules. Minimizing the total free energy yields the result that large sites are occupied first, giving rise to small volume changes only. By increasing the solute concentration, smaller sites have to be occupied as well and the corresponding volume changes are larger. Thus the molecules can be considered to act as probes for the intermolecular space. A quantitative analysis and comparison with experimental results provides information on the intermolecular space in a glassy polymer. Compared to the dual-sorption model, the model of this study is able to explain the nonlinear relationship between volume change of the polymer and the partial pressure of the solute. At large solute concentrations, swelling of the glassy polymer or its transformation into the rubbery state occurs, which gives rise to structural changes after desorption. © 1993 John Wiley & Sons, Inc.     

Interactions between hairy rod anionic conjugated polyelectrolytes and nonionic alkyloxyethylene surfactants in aqueous solution: observations from cloud point behaviour

The effect of three anionic, hairy-rod fluorene based conjugated polyelectrolytes on the cloud points of the alkyloxyethylene surfactants C10E3, C12E4, C12E5, and C12E6 has been studied in aqueous solution. Although the association behaviour of these rigid polymers with surfactants is different from that of more flexible polyelectrolytes, both types of polymers are seen to increase the cloud points, probably as a consequence of associative interactions. The possible importance of Coulombic interactions is suggested by the decrease in cloud points with these systems in the presence of NaCl. With the conjugated polyelectrolytes, the effect appears to be most pronounced with poly[9,9-bis(4-phenoxybutylsulfonate)fluorene-co-2,5-thienylene], which may result from specific interactions between oxyethylene groups and the thiophene ring. The value of cloud point behaviour in designing water based formulations for preparation of devices of these conjugated polyelectrolytes is discussed.     

Threadlike micelle formation of anionic surfactants in aqueous solution

We have investigated the formation of threadlike micelles consisting of anionic surfactants and certain additives in aqueous solution. Threadlike micelles long enough to be entangled with each other were formed in a clear aqueous solution of two anionic surfactants, sodium hexadecyl sulfate and sodium tetradecyl sulfate. These solutions also contained pentylammonium bromides or p-toluidine halides and exhibited remarkable viscoelasticity. Because the molar ratio of surfactants to cationic additives in these micelles seemed close to unity, they formed 1:1 stoichiometric complexes between surfactant anions and additive cations, as previously found in systems of cationic surfactants such as hexadecyltrimethylammonium bromide and sodium salicylate. The viscoelastic behavior of these anionic threadlike micellar systems was adequately described by a simple Maxwell element with a single relaxation time and strength, as in many similar cationic systems.     

Relative partial molar enthalpies and apparent molar volumes of dipeptides in aqueous solution

Enthalpies of dilution at 25°C of aqueous solutions of the dipeptides glycylglycine, glycylalanine and alanylalanine have been determined and used to calculate the partial molar enthalpies of the solvent water in the solutions. The partial molar volumes of these dipeptides are also reported. The results are discussed in terms of the likely solute-solvent interactions.     

Self-assembly of mixed anionic and nonionic surfactants in aqueous solution

We present the phase diagram and the microstructure of the binary surfactant mixture of AOT and C(12)E(4) in D(2)O as characterized by surface tension and small angle neutron scattering. The micellar region is considerably extended in composition and concentration compared to that observed for the pure surfactant systems, and two types of aggregates are formed. Spherical micelles are present for AOT-rich composition, whereas cylindrical micelles with a mean length between 80 and 300 ? are present in the nonionic-rich region. The size of the micelles depends on both concentration and molar ratio of the surfactant mixtures. At higher concentration, a swollen lamellar phase is formed, where electrostatic repulsions dominate over the Helfrich interaction in the mixed bilayers. At intermediate concentrations, a mixed micellar/lamellar phase exists.     

Changes in partial molar volume and isentropic partial molar compressibility of self-association of purine and caffeine in aqueous solution at 1–1600 bar

Ultrasound measurements of purine and caffeine in aqueous solution as function of pressure are reported at 25°C and used to calculate the changes in their partial molar volumes and partial molar compressibilities due to self-association. The effect of pressure is to increase the association. The volume changes are negative for the self-association process, becoming less negative with increasing pressure. This is caused by the monomer in the associated state. The partial molar volume of the monomer in the associated state increases with pressure, contrary to what is expected for nonelectrolytes in water. Hydration of the associated monomer must be a key to this increase. The result suggest that dipole-induced dipole interactions is a possible mechanism for the association process and not hydrophobic interactions. The change in the partial molar compressibility of the association is positive, decreasing with increasing pressure.     

Thermodynamic properties of peptide solutions: 7. Partial molar isentropic pressure coefficients of some dipeptides in aqueous solution

The partial molar isentropic pressure coefficients at infinite dilution, K _S,2 ^o , have been determined for a number of dipeptides in aqueous solution at 25°C. For a series of dipeptides of sequence gly-X, where X is an amino acid with a neutral side chain, the K _S,2 ^o values are all more negative than that for diglycine. The results are discussed in terms of the hydration of the side chains. There are significant differences in the K _S,2 ^o values for sequence isomeric dipeptides. These differences can be rationalized in terms of the mutual interactions between the side chain and the ionic end groups in the dipeptides. Possible relationships between K _S,2 ^o and V ₂ ^o , the partial molar volume at infinite dilution, were investigated. For the dipeptides of sequence gly-X there is an interesting linear relationship between K _S,2 ^o /V ₂ ^o and V ₂ ^o .     

Emission behavior of 1-methylaminopyrene in aqueous solution of anionic surfactants

A new fluorescent probe, methylamino derivative of pyrene, has been considered to characterize the concentration dependent emission behavior of an aqueous solution of anionic surfactants, viz., SDS, DSS, and SDBS. It was found that the emission of the probe is uniquely sensitive to the changes in surfactant (anionic) concentration due to the functional group effect of the probe over the parent moiety, pyrene. Here, 1-methylaminopyrene (MAP) showed significant quenching of emission well below the critical micellar concentration (cmc) of the surfactant. Excimer emission of the probe due to the formation of premicellar aggregates of the surfactant solutions at a concentration close to but below the cmc and again an enhanced emission of the probe above the cmc were observed as a consequence of definite MAP-surfactant interactions. These observations assisted the possible quantification ofsurfactant concentrations and their chain length dependent premicellar aggregate formations. Significant monomer emission in relation to probe distribution in micelle was analytically authenticated. Dynamic light scattering (DLS) studies revealed the incorporation of the probe molecules in the micellar core. The fluorophore emission showed nonlinear behavior when the surfactant concentration was far above the cmc. Abrupt changes in the emission characteristics in relation to the micellar concentration led to the determination of the cmc of the surfactants.