Bijan Das

Conductance of Selected Alkali Metal Salts in Aqueous Binary Mixtures of 2-Methoxyethanol at 25°C

Precise conductance measurements have been performed for lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, sodium perchlorate, and sodium tetraphenylborate in 2-methoxyethanol–water mixtures at four different mole fractions, i.e., 0.056, 0.136, 0.262, and 0.486 of 2-methoxyethanol (69.73 ≥ D ≥26.55) at 25°C in the concentration range 0.0004–0.0642 mol-dm−3. The limiting molar conductivity Λ°, the association constant KA, and the association distance R for the solvent mixtures have been evaluated from the conductance concentration data using the 1978 Fuoss conductance equation. The single-ion conductances have been estimated using the “reference electrolyte” tetrabutylam-monium tetraphynylborate(Bu4NBPh4). The analysis of the data indicates that for most salts ion association is appreciable in the solvent mixtures with a mole fraction of the cosolvent of 0.262 or higher. The results have been interpreted in terms of ion-solvent interactions and structural changes in the mixed solvent media.

Conductance of Some 1:1 Electrolytes in N,N-Dimethylacetamide at 25°C

Precise conductance measurements of solutions of lithium chloride, lithium bromide, lithium iodide, lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, tetrabutylammonium bromide, and tetrabutylammonium tetraphenylborate in N,N-dimethylacetamide are reported at 25°C in the concentration range 0.005–0.015 mol-dm−3. The conductance data have been analyzed by the 1978 Fuoss conductance equation in terms of the limiting molar conductance (Λ0), the association constant (Ka), and the association diameter (R). The limiting ionic conductances have been estimated from an appropriate division of the limiting molar conductivity of the “reference electrolyte” Bu4NBPh4. Slight ionic association was found for all these salts in this solvent medium. The results further indicate significant solvation of Li+ion, while the other ions are found to be unsolvated in N,N-dimethylacetamide.

Electrical conductances and viscosities of tetrabutylammonium thiocyanate in acetonitrile in the temperature range 25-45 °C

Abstract The electrical conductances and viscosities of the solutions of tetrabutylammonium thiocyanate (Bu4NCNS) in acetonitrile have been reported at 25, 30, 35, 40 and 45 °C. The conductance data have been analyzed by the 1978 Fuoss conductance-concentration equation in terms of the limiting molar conductance (Λ0), the association constant (KΛ) and the association diameter (R). The viscosity data have been analyzed by the Jones–Dole equation for the associated electrolytes to evaluate the viscosity B-coefficients of the electrolyte. These data have also been analyzed by the transition-state treatment to obtain the contribution of the solutes to the free energy of activation for viscous flow of the solution. The ionic contributions to the limiting molar conductance (Λ0), the viscosity B-coefficient and the free energy of activation for viscous flow have been estimated using the “reference electrolyte” tetrabutylammonium tetraphenylborate (Bu4NBPh4). Slight ionic association was always found for this salt in this solvent medium. The tetrabutylammonium ion is found to be unsolvated whereas the thiocyanate ion undergoes solvation in acetonitrile in the temperature range investigated here.

The osmotic coefficient of spherical polyelectrolyte brushes in aqueous salt-free solution

A study on the osmotic coefficient of polyelectrolyte brushes in aqueous solution is reported. The systems studied here consist of a solid polystyrene core with chemically grafted linear poly(sodium styrenesulfonate) chains. The osmotic pressure of the counterions of these spherical polyelectrolyte brushes in aqueous solution without added salt has been investigated in the dilute regime (0.05-0.50 gl-1). The osmotic coefficient, φ, as a function of particle concentration was deduced from the measured osmotic pressure. The range of φ is a few percent, which demonstrates that nearly all the counterions are confined within the charged corona of the spherical polyelectrolyte brushes. It is also observed that the greater the contour length of the grafted polyelectrolyte chains, the lower is the number of osmotically active counterions in these spherical polyelectrolyte brushes. A comparison with φ measured for free polyelectrolyte chains demonstrates that φ is much lower in the case of the polyelectrolyte brushes. This demonstrates directly the trapping of counterions in an osmotic brush predicted by theory.

Electrical Conductance of Some Symmetrical Tetraalkylammonium and Alkali Salts in N,N-Dimethylacetamide at 25°C

Precise measurements of electrical conductances of solutions of tetraethylammonium bromide, tetrapropylammonium bromide, tetrapentylammonium bromide, tetrahexylammonium bromide, tetraheptylammonium bromide, tetraocytylammonium bromide, sodium tetraphenylborate, and potassium tetraphenylborate in N′,N-dimethylacetamide at 25°C are reported for the concentration range 0.005-0.015 mol-dm−3. The conductance data have been analyzed by the 1978 Fuoss conductance-concentration equation in terms of the limiting molar conductance, the association constant, and the association diameter. The limiting ionic conductances have been estimated from the appropriate division of the limiting molar conductivity value of the “reference electrolyte” Bu4NBPh4. Slight ionic association was found for all these salts in this solvent medium. Tetraalkylammonium ions are found to be unsolvated in N,N-dimethylacetamide, whereas significant solvation has been noticed for sodium and potassium ions.

Electrical Conductances of Tetrabutylammonium Bromide, Sodium Tetraphenylborate and Sodium Bromide in 2-Ethoxyethanol in the Temperature Range 35–50°C

Abstract The electrical conductances of the solutions of tetrabutylammonium bromide (Bu4NBr), sodium tetraphenylborate (NaPh4B) and sodium bromide (NaBr) in 2-ethoxyethanol have been reported at 35, 40, 45 and 50°C. The conductance data have been analyzed by the 1978 Fuoss conductance–concentration equation in terms of the limiting molar conductance (Λ0), the association constant (KΛ) and the association diameter (R). The ionic contributions to the limiting molar conductances (Λ0) have been estimated using the “reference electrolyte” tetrabutylammonium tetraphenylborate (Bu4NPh4B). Appreciable ionic association was observed for all of these electrolytes which were found to exist in the form of solvent-separated ion-pairs in 2-ethoxyethanol. The tetrabutylammonium and tetraphenylborate ions are found to remain scarcely solvated whereas the sodium and bromide ions undergo substantial solvation in 2-ethoxyethanol medium in the temperature range investigated here.

Electrical conductances of some alkali-metal salts in N, N-dimethylacetamide-water mixture at 25°C

Abstract Precise measurements on electrical conductances of the solutions of lithium chloride (LiCl), lithium bromide (LiBr), lithium iodide (LiI), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), sodium bromide (NaBr), sodium tetraphenylborate (NaBPh4), potassium bromide (KBr), rubidium bromide (RbBr), cesium bromide (CsBr) and tetrabutylammonium bromide (Bu4NBr) in N,N-dimethylacetamide + water (50 v/v) mixture have been reported at 25 °C in the concentration range 0.02–0.05 mol dm−3. The conductance data have been analyzed by the 1978 Fuoss conductance–concentration equation in terms of the limiting molar conductance (Λ0), the association constant (KA) and the association diameter (R). The limiting ionic conductances (λ0±) have been estimated from the appropriate division of the limiting molar conductivity value of the “reference electrolyte” tetrabutylammonium tetraphenylborate (Bu4NBPh4). The electrolytes investigated here are found to be significantly dissociated in this solvent medium and all ions remain unsolvated in N,N-dimethylacetamide + water (50 v/v) mixed solvent system with exception of the lithium ion where significant solvation has been noticed. The results have been interpreted in terms of the specific constitutional and structural factors of the solvent and of the solute ions.

Viscosities of Some Tetraalkylammonium and Alkali-Metal Salts in N, N-Dimethylacetamide at 25 - C

The viscosities of solutions of tetrapropylammonium bromide (Pr4NBr), tetrabutylammonium bromide (Bu4NBr), tetrapentylammonium bromide (Pen4NBr), tetrahexylammonium bromide (Hex4NBr), tetraheptylammonium bromide (Hep4NBr), tetraoctylammonium bromide (Oct4NBr), tetrabutylammonium tetraphenylborate (Bu4NBPh4), sodium tetraphenylborate (NaBPh4), and potassium tetraphenylborate (KBPh4) in N,N-dimethylacetamide are reported at 25°C. The viscosity data havebeen analyzed by the Jones-Dole equation for associated electrolytes to evaluate the viscosity B coefficients of the electrolytes. These data have also been analyzed by the transition-state theory to obtain the contribution of the solutes to the free energy of activation for viscous flow of the solution. The ionic contribution to the viscosity B coefficient and the free energy of activation for viscous flow have been estimated using of the “reference electrolyte” Bu4NBPh4. The bromide, tetraphenylborate, and tetraalkylammonium ions are found to be weakly solvated in N,N-dimethylacetamide, whereas significant solvation has been detected for sodium and potassium ions. The viscosity of the solvent is greatly modified by the presence of all the ions investigated here with the exception of the bromide ion.

Physicochemistry of mixed micellization: Binary and ternary mixtures of cationic surfactants in aqueous medium

The importance of studying mixed micellization lies in tuning the performance of an amphiphile to bend through variation of stoichiometry of the blend. In this study, the binary and ternary mixed systems of cetylpyridinium chloride (CPC), tetradecyltrimethylammonium bromide, and dodecylpyridinium chloride (DPC) have been studied at 30°C using tensiometry and conductometry. In most cases, the cmc observed from either method is in close proximity whereas in CPC/DPC mixtures, tensometric cmc precedes conductometric cmc which may arise from a lowering in degree of counterion binding on micellar interface in the mixed system with lower stoichiometric mole fraction of CPC. Various existing theories have been used and the results were compared with the experimental observations.

Influence of sodium carboxymethylcellulose on the aggregation behavior of aqueous 1-hexadecyl-3-methylimidazolium chloride solutions.

The influence of sodium carboxymethylcellulose (NaCMC) on the aggregation phenomena of a surface active ionic liquid 1-hexadecyl-3-methylimidazolium chloride (C16MeImCl) was studied in aqueous solutions using electrical conductivity and surface tension measurements. The counterion condensation behavior of NaCMC (aq) and the premicellar ion-association behavior of C16MeImCl (aq) were also investigated. Two characteristic concentrations, namely the critical aggregation concentration and polymer saturation concentration, before free C16MeImCl micelles appear in C16MeImCl-NaCMC solutions have been identified. Effects of temperature, NaCMC concentration, and the charge density parameter of NaCMC on the self-aggregation of the C16MeImCl have been discussed to elucidate C16MeImCl-NaCMC interactions. The thermodynamic parameters for micellization of C16MeImCl were estimated both in absence and in the presence of NaCMC. The observed enthalpy-entropy compensation effect in C16MeImCl and C16MeImCl-NaCMC systems provided important insight as to how micellization processes are governed by the bulk structural property of the solution with respect to that of the water.