Concentration dependence of the first cumulant for partially labeled chains in dilute solutions

We use Zimm's single-contact approximation to investigate the concentration dependence of the first cumulant for partially labeled chains in dilute solutions. This approximation allows us to express interchain properties (such as the interference part of the generalized mobility) in terms of static structure factors, which are then modeled using a Gaussian chain model. We present numerical results for three specific labeling sequences.     

Ionic strength dependence in dilute common-ion electrolyte mixtures

The relation between the coefficients of the Harned's rule behavior and the mixing coefficients in the expression for the total excess free energy of a common-ion mixture is elucidated. The results are used to see if the strong ionic-strength dependence of theg ₁ coefficient is reflected in certain modified Harned's coefficients. This is the case for the system studied; moreover, in this case the experimental data are in agreement with the theoretical model calculation made previously.Contribution in memory of Prof. R. A. Robinson.     

Evaluation of the concentration dependence of transference numbers for dilute electrolyte solutions at various temperatures

At various temperatures the concentration dependence of transference numbers of electrolytes in methanol, ethanol, 1-propanol, acetonitrile, propylene carbonate, and water is investigated with the help of equations which take into account non-coulombic effects. A general rule for predicting the sign and magnitude of the concentration dependence of transference numbers is established. Literature data are reevaluated with the help of these equations and consistency of experimental data with the prediction is examined. Reference data for ion limiting conductances from experimental investigations are proposed which may be used for the judgment as to the reliability of empirical reference electrolyte methods.Dedicated to Professor Viktor Gutmann on the occasion of his 65th birthday.     

Time dependence of viscosity of dilute polyisobutylene solutions

Summary Shearing at constant gradient of polyisobutylene (PIB) solutions in viscous polybutene oils results in time dependent changes of their viscosities. Two PIB fractions (M=8·10⁶ and 3.8·10⁶) have been studied in a variety of solvents, covering the viscosity range from 5 to 0.5·10⁻² poise. The overall phenomenon is similar to that already observed for polymethylmethacrylate, polystyrene, and polyethylene oxide solutions in Aroclor. Results have been discussed in terms of polymer molecular weight and concentration, solvent viscosity and gradient. The systems investigated are free from strong polar interactions and tendency toward molecular aggregation; time dependent changes of viscosity are therefore observable also for true molecularly dispersed solutions.

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Zusammenfassung Scherung mit konstantem Geschwindigkeitsgradienten von Polyisobutylen (PIB)-L?sungen in viskosen Polybuten-?len ergibt zeitabh?ngige ?nderungen ihrer Viskosit?ten. Zwei PIB-Fraktionen (M=8·10⁶ und 3,8·10⁶) wurden in einer Vielzahl von L?sungsmitteln untersucht, die den Viskosit?tsbereich von 5 bis 0,5·10⁻² Poise überdeckten. Das ph?nomenologische Erscheinungsbild ist ?hnlich dem schon beobachteten für Polymethylmethacrylat, Polystyrol und Poly?thylenoxid-L?sungen in Aroclor. Die Ergebnisse wurden hinsichtlich des Polymer-Molekulargewichts und der Konzentration, der L?sungsmittelviskosit?t und des Gradienten diskutiert. Die untersuchten Systeme sind frei von starken polaren Wechselwirkungen und von Tendenzen in Richtung auf molekulare Aggregation. Zeitabh?ngige ?nderungen der Viskosit?t sind deshalb auch für wahre molekulardisperse L?sungen beobachtbar.

     

Statistical model of the localized electron in dilute ionic solutions

A theoretical model of the localized excess electron in dilute ionic solutions is presented. The model is based on the ion-pair theory of ionic solutions. The giant quasi-dipoles built of separated cation-anion pairs have been considered as electron traps. The statistical distribution of the depth of the electron traps and the optical absorption spectrum of the localized electron have been calculated. The trap distribution results from the statistical distribution of the distances separating two ionic partners of opposite charge and depends on the solvation degree of the ions. Numerical calculations of the electron absorption spectra have been performed for dilute NaX and LiX solutions (X stands for single-charged anion) in tetrahydrofuran at room temperature.     

An organic ionic plastic crystal electrolyte based on the triflate anion exhibiting high proton transport

A novel organic ionic plastic crystal (OIPC) electrolyte based on a quaternary ammonium cation and the triflate anion has been synthesized, which shows fast proton transport and high thermal stability in the solid state when doped with triflic acid.     

Instantaneous dissolution of cellulose in organic electrolyte solutions

Herein a novel class of solvent systems for cellulose is introduced. Surprisingly, organic electrolyte solutions, which contain just a small molar fraction of ionic liquid, dissolve instantaneously large amounts of cellulose. The solvation properties of the solvent systems, required for dissolving the polymer, are discussed here.     

Thermodynamics of dilute aqueous solutions of imidazolium based ionic liquids

Experimental measurements of density ρ, speed of sound u, and viscosity η of aqueous solutions of various 1-alkyl-3-methylimidazolium based ionic liquid (IL) solutions have been performed in dilute concentration regime at 298.15 K to get insight into hydration behaviour of ILs. The investigated ILs are based on 1-alkyl-3-methylimidazolium cation, [C_nmim] having $[{\text{BF}}_4{]}^{-}$, [Cl]^?, $[{\text{C}}_1{\text{OSO}}_3{]}^{-}$, and $[{\text{C}}_8{\text{OSO}}_3{]}^{-}$ as anions where n = 4 or 8. Several thermodynamic parameters like apparent molar volume φ_V, isentropic compressibility β_s, and viscosity B-coefficients have been derived from experimental data. Limiting value of apparent molar volume has been discussed in terms of intrinsic molar volume (V_int) molar electrostriction volume (V_elec), molar disordered (V_dis), and cage volume (V_cage). Viscosity B-coefficients have been used to quantify the kosmotropic or chaotropic nature of ILs. Hydration number of ILs obtained using elctrostriction volume, isentropic compressibility, viscosity, and differential scanning calorimetry have been found to be comparative within the experimental error. The hydrophobic hydration has found to play an important role in hydration of ILs as compared to hydration due to hydrogen bonding and electrostriction. Limiting molar properties, hydration numbers, and B-coefficients have been discussed in terms of alkyl chain length of cation or nature of anion.     

Concentration dependence of the diffusion coefficient of polydisperse polystyrene in dilute solution

The concentration dependence of the diffusion coefficients (D) of two different polystyrenes in toluene was measured. The concentration dependence of D of a standard monodisperse sample (M = 498,000) for concentrations up to 1 · 25 g/dl is not linear. The dependence is adequately described by the theory of dilute polymer solutions up to about 0·7 g/dl and the second virial coefficients of the osmotic pressure can be evaluated. For a polystyrene sample having a broad molecular weight distribution, the concentration dependence of four different average diffusion coefficients was determined so indirectly characterizing the molecular weight distribution. These dependences are not linear and differ from each other owing to the different sensitivity of the individual averages to high-molecular and low-molecular weight fractions. The apparent distribution of the diffusion coefficients becomes narrower with increasing concentration. When evaluating polydispersity from the free diffusion data obtained in good solvents, it is necessary to determine directly the differential diffusion coefficients; an extrapolation of the integral diffusion coefficients can be misleading.     

Electroviscous effects on pressure-driven flow of dilute electrolyte solutions in small microchannels

A fundamental understanding of the flow characteristics of electrolyte solutions in microchannels is critical to the design and control of microfluidic devices. Experimental studies have shown that the electroviscous effect is appreciable for a dilute solution in a small microchannel. However, the experimentally observed electroviscous effects cannot be predicted by the traditional theoretical model, which involves the use of the Boltzmann distribution for the ionic concentration field. It has been found that the Boltzmann distribution is not applicable to systems with dilute electrolyte solutions in small microchannels because it violates the ion number conservation condition. A new theoretical model is developed in this paper using the Nernst equation and the ion number conservation, instead of the Boltzmann distribution, to obtain the ionic concentration field. The ionic concentration field, electrical potential field, and flow field in small microchannels are studied using the model developed here. In order to verify this model, the model-predicted dP/dx (applied pressure gradient) Re (Reynolds number) relationship is compared with the experimentally determined dP/dx approximately Re relationship. Strong agreement between the model predictions and the experimental results supports this model.     

Pressure dependence of the viscosity of dilute polystyrene solutions in toluene

The effect of pressure on the viscosity of dilute solutions of anionically polymerized polystyrene (M?_w = 209,000; M_w/M_n = 1.12) in toluene has been studied at different temperatures and concentrations using a falling-body viscometer. Measurements were performed in the concentration range from 0.0025 to 0.02 g/mL and at temperatures from 25 to 45°C under pressure up to 1057 bars. The viscosity coefficient η increases exponentially with pressure at a given temperature and concentration, while the apparent volume of activation V^? decreases with increasing temperature. The hypothesis that the pressure dependence of η is given by the pressure dependence of the activation energy holds true under the prevailing thermodynamic conditions. Log η increases linearly with increasing concentration at a given pressure. Intrinsic viscosity increases with increasing pressure, whereas the Huggins constant decreases.     

Adsorption of guar gum onto quartz from dilute mixed electrolyte solutions

The effect of potassium, sodium, calcium, magnesium, and hydrogen cations on adsorption of guar gum onto quartz was investigated at natural pH. The role of the background ions was analyzed in terms of their water-structure making or breaking capabilities. In dilute solutions (0.01 mol/L) of structure-makers (NaCl, HCl, CaCl2, and MgCl2), the guar gum adsorption density did not change compared to the adsorption densities obtained in distilled water. Potassium, the only structure-breaking ion (chaotrope) among the tested cations, significantly enhanced guar gum adsorption. The results obtained in mixed electrolytes demonstrate that the strong structure-breaking properties of K+ overcome any contributions from weak structure making ions (kosmotropes), and guar gum adsorption remains at the levels observed in KCl alone. Only when strongly hydrated Mg2+ ions are mixed with KCl, the overall effect becomes additive and the influence of potassium is proportionally reduced by increasing concentrations of magnesium cations. In this approach, guar gum adsorption on quartz is viewed as a competition between polysaccharide and water molecules for silanol surface sites. The hydration of the quartz surface inhibits the adsorption process but the competition equilibrium, and hence polysaccharide adsorption, can be affected by the presence of chaotropes or kosmotropes.     

Temperature dependence of excited-state proton transfer in water electrolyte solutions and water-methanol solutions

The reversible proton dissociation and geminate recombination of a photoacid is studied as a function of temperature in water electrolyte solutions and binary water-methanol mixtures, containing 0.1 and 0.2 mole fractions of methanol. 8-Hydroxypyrene-1,3,6-trisulfonate trisodium salt (HPTS) is used as the photoacid. The experimental data are analyzed by the reversible geminate recombination model. We found that the slope of the logarithm of the proton-transfer rate constant as a function of the inverse of temperature (Arrhenius plot) in the liquid phase of these samples are temperature-dependent, while in the solid phase, the slope is nearly constant. The slope of the Arrhenius plot in frozen electrolyte solution is larger than that of the water-methanol mixtures, which is about the same as in pure water. Careful examination of the time-resolved emission in ice samples shows that the fit quality using the geminate recombination model is rather poor at relatively short times. We were able to get a better fit using an inhomogeneous kinetics model assuming the proton-transfer rate consists of a distribution of rates. The model is consistent with an inhomogeneous frozen water distribution next to the photoacid.     

Macrokinetics of electrolysis of dilute solutions in systems with a solid polymer electrolyte

A model of contact between an electrode and a MF-4SK membrane in sulfuric acid solutions is studied by the impedance method. It is shown that a layer of higher electrolyte concentration forms near the free electrode surface in heavily diluted solutions. The layer ensures participation of this surface in the electrode process. Electrical fields in the region of contact between the membrane and a current collector are calculated     

A kinematic approach to ionic transport in aqueous electrolyte solutions and structural theory of hydration of alkali metal ions

While considering the self-diffusion processes in aqueous electrolyte solutions, transport of ions, not only by jumps of single ions, but also by jumps of their solvation shells, are to be taken into account. Samoilov estimated the relative number of the two kinds of ionic jumps from experimental data on diffusion assuming an approximately uniform value for the α factor. In the present paper entirely different theory of the α factor based on the structural hydration model of one of the authors (S.V.T.) for alkali metal ions is given and its ion-wise values are calculated at different temperatures. The theory not only dispenses with the approximate fixation of α but also throws light on the structure of water, formation of clusters and their population variation with temperature.     

On the theoretical calculation of the dielectric constant of dilute electrolyte solutions

In dilute ionic solutions, the solute-dependent dielectric constant varies as a linear function of concentration. In this note we consider alternative theoretical routes to the limiting slope, and compare numerical results for ions in dipolar hard-sphere and water-like solvents.     

The ionic product of water in highly concentrated aqueous electrolyte solutions

Summary The ionic product of water, , has been determined in aqueous NaCl (0.5–5.0M), KCl (3.0M), NaNO₃ (3.0 and 5.0M), and KNO₃ (2.5M) at 25 °C from high-precision potentiometric titrations carried out in cells with liquid junction using either glass or hydrogen electrodes. Measurements ofK _w provide a set of self-consistent data that can be used in the estimation of activity coefficient changes and liquid junction potentials in the study of extremely concentrated electrolyte solutions. Where comparison is possible, results obtained by hydrogen electrode measurements are in excellent agreement (ca ± 0.005 inpK _w) with other reliable experimental values and the predictions of thePitzer activity-coefficient model. The glass electrode results are, as expected, routinely lower (by 0.03–0.05pK _w units), owing to interference by Na⁺ ions. This effect virtually disappears in solutions of potassium salts. Comparison of the experimental results with thePitzer predictions shows that knowledge of the ternary interaction parameters is essential to account for specific ionic effects in the concentration dependence ofpK _w.On leave from the Abteilung für Physikalische Chemie und Theoretische Hüttenkunde, Montanuniversität Leoben, A-8700 Leoben, Austria     

Pressure dependence of the second virial coefficient of dilute polystyrene solutions

The pressure derivatives of the second virial coefficients [dA₂/dP; 0.1 ≤ P (MPa) ≤ 35.0] for dilute polystyrene (PS) solutions in good, θ, and poor solvents were measured with static light scattering. The solvent quality improved (dA₂/dP > 0) in the good and poor solvents that we investigated (toluene, chloroform; and methylcyclohexane) but deteriorated (dA₂/dP < 0) in θ solvents (cyclohexane and 50‐50 cis,trans‐decalin). The effects of temperature [22 < T (°C) < 45] and molecular weight [25 × 10³ < weight‐average molecular weight (amu mol^?1) < 900 × 10³] on dA₂/dP for PS/cyclohexane solutions were examined. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3070–3076, 2003