Prediction of activity coefficients of electrolytes in aqueous mixed electrolyte solutions

A method is proposed for calculating the activity coefficient of constituent electrolytes in aqueous mixed electrolyte solutions. The equations derived from the knowledge of Λ^*, the overall reduced ionic activity coefficient in a mixture, are found to predict activity coefficients accurately up to an ionic strength of 12 mol kg⁻¹ and a temperature of 473 K.     

Calculations of the frequency dependences of viscosity coefficients and elastic moduli for solutions of electrolytes over broad ranges of thermodynamic parameter variations

The dynamic equations obtained earlier for the coefficients of bulk η_V(ω) and shear η_S(ω) viscosities and bulk K(ω) and shear μ(ω) elastic moduli were used to calculate these values for a certain model of solution structure in the approximation of the theory of osmotic solution properties. The interparticle interaction potential was written as the sum of the potential of hard spheres and Coulomb attraction. The corresponding thermodynamic parameter values for the density ρ, temperature, concentration C, and adiabatic bulk modulus K _S were taken from experimental works. The results of numerical calculations of the viscoelastic properties of solutions over broad ranges of thermodynamic parameter and frequency variations were plotted and tabulated. The calculation results are compared with the available experimental data. The theoretical viscoelastic properties of solutions of electrolytes were in satisfactory agreement with the published experimental data and the results of numerical experiments for classic liquids.     

Dependence of the frequency dispersion of the bulk viscosity coefficient of solutions of electrolytes on the nature of the decay of relaxing fluxes

The region of the frequency dispersion of the bulk viscosity coefficient η_V(ω) of solutions of electrolytes is studied as a function of the nature of the decay of the stress tensor in the momentum and configuration space, the analytical expressions of which are derived by means of kinetic equations. Numerical calculations of η_V(ω) for a water solution of NaCl are performed over a wide range of frequencies, temperatures, and densities using a selection of the potentials of intermolecular interaction Φ{in{itab}}(|\(\vec r\)|) and radial distribution function {itg}{in{itab}}(|\(\vec r\)|). It is shown that the region of frequency dispersion η_V(ω) based on the power law of the decay of the stress tensor is wide (~10⁵ Hz), while the region based on the exponential law is narrow (~10² Hz).     

Liquid crystal-forming aqueous hydroxypropyl cellulose solutions: Effects of surfactants on the turbidity and shear viscosity

The effects of type and concentration of surfactant on the turbidity and viscometric behavior for dilute and concentrated aqueous hydroxypropyl cellulose (HPC) solutions were examined. Two anionic surfactants, sodium dodecyl benzene sulfonate (SDBS) and sodium dodecyl sulfate (SDS), caused the cloud point of the dilute system to increase, but a nonionic and two cationic surfactants did not do so markedly. The transmittance for the dilute system increased with surfactant. The transmittance and viscometric behavior for the concentrated system were strongly dependent on the phase of the system: In the single-phase (isotropic and anisotropic), the transmittance and viscosity increased with SDBS, but, in the biphasic region, the behaviors were not as simple. An attempt was made to explain the transmittance and viscometric behavior in the single-phase on the basis of the change in apparent molecular weight and in order of HPC molecules. The phase transformation appeared to become less sensitive to temperature with SDBS. © 1993 John Wiley & Sons, Inc.     

Frequency dispersion of the viscoelastic properties of solutions of electrolytes

Analytical expressions obtained earlier are used to numerically calculate the dynamic coefficients of the bulk η_ν(ω) and shear η _s (ω) viscosity and the corresponding modules of their bulk K(ω) and shear μ(ω) elasticity at a certain choice of the model of solution structure in an approximation of the osmotic solution theory. The potential energy of the interaction between ions Φ _ab (r) was taken as the sum of the Lennard-Jones potential and the generalized Debye potential, taking into account the configuration and size of ions. In this approximation, the viscoelastic properties of the NaCl water solution were numerically calculated over a wide interval of change in the thermodynamic parameters and frequency ranges. Satisfactory agreement with the literature experimental data was obtained.     

Molecular mechanism of the viscosity of aqueous glucose solutions

Experimental relations are obtained for the viscosity of aqueous glucose solutions in the temperature range of 10–80°C and concentration range 0.01–2.5%. It is found that the concentration dependence of fluidity is linear when the concentration is higher than a certain value and varies at different temperatures. The existence of such a dependence indicates that the mobilities of solvent and solute molecules are independent of the concentration of solutions. This assumption is used to construct a theoretical model, in which the structure of an aqueous glucose solution is presented as a combination of two weakly interacting networks formed by hydrogen bonds between water molecules and between glucose molecules. Theoretical relations are obtained using this model of network solution structure for the concentration and temperature dependence of solution viscosity. Experimental data are used to calculate the activation energies for water (U _w = 3.0 × 10^–20 J) and glucose molecules (U _g = 2.8 × 10^–20 J). It is shown that the viscosity of a solution in such a network structure is governed by the Brownian motion of solitons along the chains of hydrogen bonds. The weak interaction between networks results in the contributions to solution fluidity made by the motion of solitons in both of them being almost independent.     

Relative viscosity and viscosity coefficients of aqueous azoniaspiroalkane bromides at 25°C

The relative viscosities η_r of dilute aqueous solutions of azoniaspiroalkane bromides, (CH₂) _n N⁺ (CH₂) _n Br^? (wheren=4, 5, and 6), have been measured at 25°C. The viscosityB _η andD _η coefficients were determined using the extended Jones-Dole equation $$\eta _r = 1 + A_\eta c^{1/2} + B_\eta c + D_\eta c^2$$ TheB _η coefficients obtained for the bicyclic azoniaspiroalkane bromides were compared with those of the corresponding homologous tetra-n-alkylammonium bromides. Based on the obtained sign and magnitude of (B _n ?0.0025ø _v ^° ) for the salts and for the bicyclic ions, the structural effects of cation geometry and alkyl group flexibility on water are discussed. The results indicate that the hydrophobic (clathrate hydrate-like) character of the larger tetra-n-alkylammonium ions is reduced significantly when cyclic groups are formed from the alkyl chains in symmetrical quaternary ammonium ions.     

Ionic association in aqueous solutions of strong electrolytes

A more accurate calculation of relaxation effects obtained with the standard Debye-Hückel-Onsager model has been presented recently and is here applied to several aqueous 1:1 electrolytes. The variation of the standard deviation between calculated and observed equivalent conductivities withK _A leads to an ill-defined minimum; but, where data over a wide concentration range are available, the minimum corresponds to values of the contact distancea which approximate to estimates from ionic dimensions. It is therefore proposed that, although preciseK _A values from conductance cannot be determined, the most probable values are those associated with realistic estimates ofa. When data cover a limited concentration range, minimum standard deviations are often indeterminate or vary greatly for duplicate runs. It is shown that reasonable values ofK _A can be obtained from such data if comparison is made at estimated values ofa.Notation The symbols not defined in the text are the following b e ²/kTa for 1:1 electrolytes - e electronic charge - k Boltzmann gas constant - T absolute temperature - dielectric constant of solvent - –(3/2y)(_e0/₀)     

Diffusion coefficients of paracetamol in aqueous solutions

Binary mutual diffusion coefficients measured by the Taylor dispersion method, for aqueous solutions of paracetamol (PA) at concentrations from (0.001 to 0.050) mol·dm⁻³ at T = 298.15 K, are reported. From the Nernst–Hartley equation and our experimental results, the limiting diffusion coefficient of this drug and its thermodynamic factors are estimated, thereby contributing in this way to a better understanding of the structure of such systems and of their thermodynamic behaviour in aqueous solution at different concentrations.     

The viscosity of aqueous electrolyte solutions and the TTG model

An equation covering the dynamic viscosity from zero to high concentrations has been derived on the basis of the TTG model. The equation is compatible with the Eyring andNMR theories and has a similar form to the Othmer-rule equation. A component of the limiting viscosity slope is shown to be proportional to the Falkenhagen slope. The TTG equation was tested for 20 electrolytes of diverse charge type and found to fit the data within the experimental errors. The equation is simply extended to cover pressure, temperature, and component changes. The viscosities of three multicomponent systems are predicted to within the experimental errors. The derived parameters of the equation were found to be simply related to the TTG volume of the solute.     

On the origin of frequency dispersion at the interface between mercury electrode and aqueous solutions of alkali halides

The origin of frequency dispersion of electrochemical impedance is investigated at the interface of mercury and aqueous solutions of single alkali halides. It is found that in the presence of each one of KI, CsI, CsF and CsBr salts, the interface presents certain potential regions where frequency dispersion effects are detected and others where the ideal capacitor behavior is closely approximated. Frequency dispersion effects are contributed by interfacial processes such as anion and cation adsorption, mercury halide film formation and dissolution and charge transfer reactions. The discrimination between frequency dispersion due to charge transfer processes occurring at the Hg/solution interface and that due to reactant adsorption itself is generally difficult and depends on the reaction mechanism, provided that a discrete adsorption step is anticipated.     

Prediction of the non-Newtonian viscosity and shear stability of polymer solutions

The structure-property relationships derived here permit the prediction of both the zero-shear viscosity ₀, as well as the shear rate dependent viscosity . Using this molecular modeling it is now possible to predict over the whole concentration range, independently of the molecular weight, polymer concentration and imposed shear rate. However, the widely accepted concept: dilute — concentrated, is insufficient. Moreover it is necessary to take five distinct states of solution into account if the viscous behavior of polymeric liquids is to be described satisfactorily. For non-homogeneous, semi-dilute (moderately concentrated) solutions the slope in the linear region of the flow curve (= must be standardized against the overlap parameterc · []. As with the ₀-M-c-relationship, a-M -c- relationship can now be formulated for the complete range of concentration and molecular weight. Furthermore, it is possible to predict the onset of shear induced degradation of polymeric liquids subjected to a laminar velocity field on the basis of molecular modeling. These theoretically obtained results lead to the previously made ad hoc conclusion (Kulicke, Porter [32]) that, experimentally, it is not possible to detect the second Newtonian region.Roman and Italian symbols a exponent of the Mark-Houwink relationship - b exponent of the third term of the ₀-M -c relationship - c concentration /g · cm^–3 - E number of entanglements per molecule - F(r) connector tension - f function - G _i ^A shear modulus; A indicates that it /Pa has been evaluated by a transient shear flow experiment; i is the shear rate to whichG ^A refers to - G storage modulus /Pa - G _p plateau modulus /Pa - H() relaxation spectrum /Pa - h shift factor (₀/_r) - K _H Huggins constant - K _b third constant of the ₀-M -c relationship - K constant of the Mark-Houwink relationship - M molecular weight /g · mol^–1 - M _e molecular weight between two /g · mol^–1 entanglement couplings - N number of segments per molecule - n slope in the power-law region of the flow curve - p p-th mode of the relaxation time spectrum - R gas constant /8.314 J·K^–1·mol^–1 - r direction vector - T temperature /K Greek symbols ß reduced shear rate - shear rate /s^–1 - shear viscosity /Pa·s - _s solvent viscosity /Pa·s - _sp specific viscosity - ₀ zero-shear viscosity /Pa·s - apparent viscosity at shear rate - reduced viscosity - viscosity of polymeric liquid in /Pa·s the second Newtonian region - [] intrinsic viscosity/cm³·g^–1 - screening length/m - /g·cm ^–3 density - relaxation time/s - ₀ experimentally derived relaxation time/s - angular frequency of oscillation Indices conc concentrated - corr slope corrected - cr critical - deg degradation - e entanglement - exp experimental - mod moderately concentrated/semi-dilute - n number average - p polymer - R Rouse - rep reptation - s solvent - sp specific - theo theoretical - weight average - relaxation time - o experimental or steady state - * critical - ** transition moderately conc. — conc. - + transition dilute — moderately cone. Paper presented at the 2nd bilateral U.S.-West German Polymer Symposium, Yountville, the 7th–11th September 1987.