Limit Of Infinite Dilution Research Articles

Luminescent methacrylic copolymers with side-chain cyclometalated iridium(III) complexes

A series of eight copolymers made of a poly (methyl methacrylate) backbone with a luminescent iridium(III)-based pendant is presented. These materials are obtained by radical copolymerization of different ratios of methyl methacrylate (MMA) with the reactive Ir-based MMA monomer [Ir(ppy)2(ptmma)]Cl (Hppy = 2-phenylpyridine, ptmma = 11-(4-pyridin-2-yltriazol-1-yl)undecyl 2-methylprop-2-enoate). The products are characterized by NMR, IR and DSC methods. The specific ratio among the two monomers, dictates the concentration of the emissive iridium-based centers along the polymer backbone, which affects the overall luminescence behavior of the material. The position of the absorption and emission maxima of the iridium-based monomer and of the related polymeric compounds are virtually identical, pinpointing the optically innocent character of the polymer matrix. Photophysical investigations show that the emission quantum yields (PLQYs) of the iridium-based emitters improve upon increasing the fraction of the inert MMA co-monomer, due to a progressive decrease in self-absorption and self-quenching, approaching the infinite-dilution limit at the relatively low [MMA]:[Ir] molar ratio of 500, with PLQY = 0.51 ± 0.05.The concentration-quenching rate process follows a power-law proportional to R–(2.6±0.9), where R is the calculated average distance between the emitting units of the copolymers. Such a deviation from the expected dipole-dipole interaction (i.e., R−6 dependence) suggests the partial formation of aggregates leading to the occurrence of static self-quenching in the solid matrix, as the concentration of the iridium centers increases. These results offer valuable hints for the formulation of strongly emitting hybrid materials in which a high concentration of triplet luminophores is embedded in organic polymers solely serving as solid transparent scaffolds.

Communication: Potentials of mean force study of ionic liquid ion pair aggregation in polar covalent molecule solvents.

Molecular dynamics (MD) simulations were conducted for 1-ethyl-3-methylimidazolium methylsulfate [EMIM][MeSO4] dissolved in six polar covalent molecules [acetic acid, acetone, chloroform, dimethyl sulfoxide (DMSO), isopropyl alcohol, and methanol] to understand the free energies of ionic liquid (IL) ion pairing/aggregation in the limit of infinite dilution. Free energy landscapes or potentials of mean force (PMF) were computed using umbrella sampling and the weighted histogram analysis method. The PMF studies showed the strongest IL ion pairing in chloroform, and the strength of IL ion pairing decreases in the order of chloroform, acetone, propanol, acetic acid, DMSO, and methanol. In the limit of infinite dilution, the free energy curves for IL ion aggregation in co-solvents were characterized by two distinct minima [global (∼3.6 Å) and local (∼5.7 Å)], while free energy values at these minima differed significantly for IL in each co-solvent. The PMF studies were extended for determining the free energy of IL ion aggregation as a function of concentration of methanol. Studies showed that as the concentration of methanol increased, the free energy of ion aggregation decreased, suggesting greater ion pair stability, in agreement with previously reported MD clustering and radial distribution function data.

Correction of Kovalenko-Hirata closure in Ornstein-Zernike integral equation theory for Lennard-Jones fluids

We have studied the accuracy of Ornstein-Zernike (OZ) integral equation theory in terms of the solvation free energy (SFE) for a two-component Lennard-Jones system at the infinite dilution limit. We have employed the hypernetted chain (HNC), Kovalenko-Hirata (KH), Kobryn-Gusarov-Kovalenko (KGK), and Percus-Yevick (PY) closure equations. Further, we have extended the Verlet-modified (VM) closure to the two-component system to examine the accuracy of this method in terms of the SFE. Molecular dynamics simulations were employed to compare the results with the above mentioned OZ theories. The HNC and KH approximations significantly overestimate the SFE, whereas the PY approximation tends to underestimate it. The overestimation of the SFE by the KGK approximation becomes significant when the solvent density is relatively high. In contrast, the VM approximation is found to be rather accurate at all studied conditions. An analysis of the integrand for the SFE reveals that, to improve the SFE, the first rising (FR) region in the radial distribution function (RDF) must be corrected. We have also tested the sigma-enlarging-bridge (SEB) function that we proposed previously [T. Miyata and Y. Ebato, J. Mol. Liq. 217 (2016) 75] for the correction of the FR region of the RDF. In this study, we applied the SEB function to both HNC-type and KH-type closures and found that these combinations (SEB-HNC and SEB-KH) improve the SFE significantly.

A Novel Technique To Predict the Solubility of Planar Molecules

We present a new computational technique to quantify the solubility of planar molecules in a solvent. Solubility is calculated as the critical concentration at which solute molecules cease to stack as columns, but rather aggregate in all directions. An explicit expression for the solubility is obtained, which involves the potential of mean force between two solute molecules as a function of their center-of-mass distance in the limit of infinite dilution. This function can be easily obtained from molecular dynamics simulations involving a pair of solute molecules in a solvent using the umbrella-sampling method. As a validation of our approach, we use a generic coarse-grained molecular model to represent the molecular interactions of polycyclic-aromatic-hydrocarbon. Within that coarse-grained model, the solubility of pyrene and acenaphthene in heptane is estimated through large molecular dynamics simulations and compared to the experimental results. The umbrella-sampling method, applied to single pairs of t...

Dielectric relaxation of nitromethane and its mixtures with ethylammonium nitrate: Evidence for strong ion association induced by hydrogen bonding

Binary mixtures of the aprotic protophobic solvent nitromethane (NM) and the protic room-temperature ionic liquid ethylammonium nitrate (EAN) were studied with dielectric relaxation spectroscopy in the two single-phase regions, 0 < xEAN ≤ 0.013 and 0.4 ≤ xEAN < 1, of the binary mixtures at 25 °C. All spectra were well described by a superposition of two relaxation processes whose origins were of composite nature. At low xEAN the solutions behave as a strongly associated electrolyte, displaying moderate ion solvation by nitromethane at the infinite-dilution limit. At high xEAN far from the miscibility gap, the observed dynamics represents the typically observed behaviour of a lubricated ionic liquid smoothly reaching the properties of pure EAN. Additionally, neat NM was investigated in the temperature range of 5 to 65 °C to explore its potential as a calibration standard in dielectric spectroscopy. The obtained 0.05 to 89 GHz spectra were well fitted by a single Debye equation. The dynamics of this medium-permittivity dipolar liquid is governed by rotational diffusion of NM dipoles close to slip boundary conditions with only weak dipole-dipole correlations. Unfortunately, difficulties in obtaining samples of reproducible purity discredit NM as a calibration standard for dielectric measurements.

Pitfalls in Simulating the Diffusion Potential of Li-Ion Cells

Variations of liquid-phase composition in electrochemical devices induce overpotentials referred to as ‘diffusion potential’ or ‘concentration potential’, which can have large effects for high current operation. Recently, an apparent discrepancy was observed in the electrochemical modelling literature when accounting for the effect of liquid-phase concentration on electrochemical devices’ voltage drop [1]. Liquid-phase potential is modelled using a modified form of the Ohm’s law known as the ‘MacInnes equation’ that accounts for the diffusion potential. The diffusion potential term in this equation presents a pre-factor involving the cation transference number t+ . The pre-factor 2(1-t+) is mostly used [2–5] but sometimes (1-2t+) is found in the literature [1, 6–8]. We argue that this apparent disagreement arises from the use of distinct albeit confusing formalisms when deriving the MacInnes equation [9]. The pre-factor (1-2t+) emerges when the Nernst–Planck theory (dilute solution) is used to derive the MacInnes equation, whereas the pre-factor 2(1-t+) appears when using the Onstager–Stefan–Maxwell theory (concentrated solution). However, we show that the definition of liquid-phase electric potential differs in these theories. In the concentrated solution theory, a voltage measured by a cation-reversible reference electrode is used providing an unambiguous connection to a measurement process. We show that the apparent discrepancy is resolved when relating Nernst–Planck voltage to a properly referenced voltage and demonstrate that both theories agree when considering the Onstager–Stefan–Maxwell theory in the limit of infinite dilution. Finally, we present a case study for lithium-ion batteries that shows the impact on simulation results of using the Nernst–Planck voltage instead of a measurable voltage. Although the battery terminal voltage remains relatively unaffected, this has a significant impact on the predicted heat generated by the battery (see Figure 1). Acknowledgements This work was funded by the Joint Center for Energy Storage Research, an energy storage hub supported by the United States Department of Energy. A.M. Bizeray was supported by Samsung Electronics Co. Ltd. through a Global Research Outreach program in collaboration with the Samsung Advanced Institute of Technology.

Dynamics and rheology of Janus drops in a steady shear flow

The behavior and rheology of a dispersion of Janus drops (or Janus emulsion) under a steady shear flow are explored in the infinite dilution limit. To achieve analytical progress, the Janus drops are assumed to consist of a pair of fluids bounded to hemispherical domains of equal radii. At ‘freely’ suspended conditions the Janus drops undergo periodic orbits in a shear flow that are intermediate to that of a solid sphere and a disk that depend on the viscosities of the internal fluids. Non-Newtonian behavior is found for this system on account of the anisotropic hydrodynamics of the Janus drops. The viscosity of the Janus emulsion that corresponds to the minimum energy of dissipation is analogous to that derived by Taylor (1932) for a dispersion of simple drops. It is also found that an external force can induce the Janus drops to adopt a preferential orientation in a shear flow. Interestingly, a neutrally buoyant Janus drop with a displaced center of gravity can migrate lateral to the undisturbed shear flow; it is inferred that this phenomenon can lead to spatial-dependent rheology in pressure-driven flows.

Flexible magnetic filaments under the influence of external magnetic fields in the limit of infinite dilution.

In the present work we use Langevin dynamics computer simulations to understand how the presence of a constant external magnetic field modifies the conformational phase diagram of magnetic filaments in the limit of infinite dilution. We have considered the filaments immersed in either a good (non-sticky filaments) or a poor (Stockmayer polymers) solvent. It has been found that in the presence of an applied field, filaments turn out to be much more susceptible to parameters such as temperature and solvent conditions. Filaments owe this increased susceptibility to the fact that the external magnetic field tends to level the free energy landscape as compared to the zero-field case. The field induces equalization in the free energy of competing conformational states that were separated by large energy differences in the zero-field limit. In this new scenario multistability arises, and manifests itself in the existence of broad regions in the phase diagram where two or more equilibrium configurations coexist. The existence of multistability greatly enhances the possibility of tuning the properties of the filament.

An effective medium approach for the elongational viscosity of non-colloidal and non-Brownian hard-sphere suspensions

An effective-medium fluid mechanics model based on the original idea first presented by Brinkman [“A calculation of the viscous force exerted by a flowing fluid on a dense swarm of particles,” Appl. Sci. Res. 1, 27-34 (1949)] for the viscous force exerted by a flowing fluid on a dense swarm of fixed spherical particles is utilized for the prediction of the elongational viscosity of a non-colloidal, non-Brownian hard-sphere suspension in an incompressible Newtonian matrix fluid. The same model was explored by Housiadas and Tanner [“A model for the shear viscosity of non-colloidal suspensions with Newtonian matrix fluids,” Rheol. Acta 53, 831-841 (2014)] for the derivation of an analytical formula for the bulk shear viscosity of the suspension as a function of the volume fraction of the solid phase, a formula which is in very good agreement with widely used semi-empirical relationships and available experimental data from the literature. In the present paper, it is assumed that a spherical particle is subject, in an average sense, to a far-field uniform uniaxial elongational flow and a suitable pressure gradient. Under steady, isothermal, creeping conditions, and imposing no-slip and no-penetration conditions at the surface of a particle in a stagnation point of the fluid and the far-field velocity and pressure profiles, the solution of the three-dimensional Brinkman equations is found analytically. The solution shows a faster decay of the velocity disturbances around a reference particle than the single-particle case. A volume average of the total stress tensor gives an analytical formula for the bulk elongational viscosity of the complex system as a function of the particle concentration. A significant increase of the elongation viscosity with increasing the particle concentration is predicted. The increase is larger than the corresponding increase of the shear viscosity, in qualitative accordance with the theoretical formula of Batchelor and Green [“The determination of the bulk stress in a suspension of spherical particles to order c2” J. Fluid Mech. 56(3), 401-427 (1972)]. The new formula reduces to Einstein’s expression in the infinite dilution limit and agrees well with other theoretical formulas in the semi-dilute regime. Moreover, the agreement of the new formula with recently developed semi-empirical formulas over the whole concentration regime is remarkable. Finally, the model predictions perform very well, and better than other formulas, when compared with a few experimental data for extensional measurements of hard-particle suspensions from the literature.

Gaseous absorption of fluorinated ethanes by ionic liquids

Solubilities of 1,1-difluoroethane (R152a), pentafluoroethane (R125), fluoroethane (R161), 1,1,1-trifluoroethane (R143a) and 1,1,1,2-tetrafluoroethane (R134a) in trihexyltetradecylphosphonium bis(2,4,4-trimethylpentyl) phosphinate ([P(14) 666][TMPP]) from 302.2K to 343.6K and up to 1.14MPa are presented in this work. Effects of fluorine atoms of fluorinated ethanes, the cations and anions of ionic liquids on the solubility behaviors are investigated by comparing the solubilities of fluorinated ethanes and ethane in different ionic liquids. Moreover, the partial molar enthalpies and partial molar entropies of solutions at infinite dilution limit for R161, R143a, R125, R134a and R152a in [P(14) 666][TMPP] are obtained. The experimental results are successfully correlated with a modified Krichevsky–Kasarnovsky equation.

Solid + Liquid Equilibria for the Systems CsBr + ErBr3 + H2O and CsBr + ErBr3 + HBr (∼12.3%) + H2O at 298.15 K and Atmospheric Pressure and Thermodynamic and Fluorescent Properties of the New Solid-Phase Compound

The phase equilibria of the ternary system CsBr + ErBr3 + H2O and the quaternary system CsBr + ErBr3 + HBr (∼12.3 %) + H2O at 298.15 K were determined experimentally with the isothermal solubility method. Based on the measured solubility data, the corresponding phase diagrams were plotted. In the ternary system, three crystallization regions corresponding to CsBr, 3CsBr·2ErBr3·16H2O, and ErBr3·9H2O were found. Similarly, there were three crystallization regions corresponding to CsBr, 3CsBr·2ErBr3·16H2O, and ErBr3·7H2O in the quaternary system. The phase diagrams of the ternary and quaternary systems were compared, and it showed that (1) a new double salt 3CsBr·2ErBr3·16H2O was formed which was incongruently soluble in the two systems; (2) the area of the crystallization region of 3CsBr·2ErBr3·16H2O increased with the increasing concentration of HBr in the equilibrium liquid phase, and (3) ErBr3·9H2O transformed into ErBr3·7H2O when the HBr reached a certain amount. The new solid-phase compound 3CsBr·2ErBr3·16H2O was characterized by chemical analysis, XRD, and TG-DTG techniques. The standard molar enthalpy of solution of 3CsBr·2ErBr3·16H2O in water was confirmed to be −(6.69 ± 0.29) kJ·mol–1 by microcalorimetry in the limit of infinite dilution and its standard molar enthalpy of formation was determined to be −(7846.1 ± 1.2) kJ·mol–1. The fluorescence excitation and emission spectra of 3CsBr·2ErBr3·16H2O were measured. The results indicated that up-conversion spectra of the new solid phase compound exhibit at 470 nm and are excited at 710 nm.

Solutes at the liquid:liquid phase boundary--Solubility and solvent conformational response alter interfacial microsolvation.

A detailed understanding of solvent structure and dynamics at liquid:liquid interfaces is a necessary precursor for control and manipulation of these phase boundaries. Experimentally, amphiphilic solutes are often used to alter transport properties across water:organic interfaces; however, a fundamental model for the mechanism of this action has not been determined. This work compares the solvation profiles of ampiphilic solutes that traverse the phase boundary in binary water:n-hexane, and the individual microsolvation processes for interfacial water and hexane molecules therein. Microsolvation is defined as the rare event where one solvent molecule temporarily penetrates the co-solvent phases and is fully solvated therein. The solutes tri-butyl phosphate (TBP), hydrogen di-butyl phosphate, and di-hydrogen mono-butyl phosphate have been examined as they exhibit a systematic increase in aqueous solubility and selectively partition to the interfacial region at the infinite dilution limit. The relationship between adopted configurations of the solute, orientation of the solvent, and the ability of the solute to enhance microsolvation, specifically the ability of n-hexane to penetrate the aqueous phase, is demonstrated within a 20 Å radius of TBP.

Studying the concentration dependence of the aggregation number of a micellar model system by SANS.

We present a small-angle neutron scattering (SANS) structural characterization of n-alkyl-PEO polymer micelles in aqueous solution with special focus on the dependence of the micellar aggregation number on increasing concentration. The single micellar properties in the dilute region up to the overlap concentration ϕ* are determined by exploiting the well characterized unimer exchange kinetics of the model system in a freezing and diluting experiment. The micellar solutions are brought to thermodynamic equilibrium at high temperatures, where unimer exchange is fast, and are then cooled to low temperatures and diluted to concentrations in the limit of infinite dilution. At low temperatures the kinetics, and therefore the key mechanism for micellar rearrangement, is frozen on the experimental time scale, thus preserving the micellar structure in the dilution process. Information about the single micellar structure in the semidilute and concentrated region are extracted from structure factor analysis at high concentrations where the micelles order into fcc and bcc close packed lattices and the aggregation number can be calculated by geometrical arguments. This approach enables us to investigate the aggregation behavior in a wide concentration regime from dilute to 6·ϕ*, showing a constant aggregation number with concentration over a large concentration regime up to a critical concentration about three times ϕ*. When exceeding this critical concentration, the aggregation number was found to increase with increasing concentration. This behavior is compared to scaling theories for star-like polymer micelles.

Charge density stabilised local electron spin pair states in insulating polymers

A model is presented that addresses the energy stability of localized electron states in insulating polymers with respect to delocalized free electron-like states at variable charge densities. The model was derived using an effective Hamiltonian for the total energy of electrons trapped in large polarons and spin-paired bipolarons, which includes the electrostatic interaction between charges that occurs when the charge density exceeds the infinite dilution limit. The phase diagram of the various electronic states with respect to the charge density is derived using parameters determined from experimental data for polyethylene, and it is found that a phase transition from excess charge in the form of stable polarons to a stable state of bipolarons with charge = 2 and spin number S = 0 is predicted for a charge density between 0.2 C/m3 and ∼2 C/m3. This transition is consistent with a change from low mobility charge transport to charge transport in the form of pulses with a mobility orders of magnitude higher that has been observed in several insulating polymers.

Shell Model for Atomistic Simulation of Lithium Diffusion in Mixed Mn/Ti Oxides

Mixed Mn/Ti oxides present attractive physicochemical properties such as their ability to accommodate Li for application in Li-ion batteries. In this work, atomic parameters for Mn were developed to extend an existing shell model of the Li–Ti–O system and allow simulations of pure and lithiated Mn and mixed Mn/Ti oxide polymorphs. The shell model yielded good agreement with experimentally derived structures (i.e., lattice parameters and interatomic distances) and represented an improvement over existing potential models. The shell model was employed in molecular dynamics (MD) simulations of Li diffusion in the 1 × 1 c-direction channels of LixMn1–yTiyO2 with the rutile structure, where 0 ≤ x ≤ 0.25 and 0 ≤ y ≤ 1. In the infinite dilution limit, the arrangement of Mn and Ti ions in the lattice was found to have a significant effect on the activation energy for Li diffusion in the c channels due to the destabilization of half of the interstitial octahedral sites. Anomalous diffusion was demonstrated for Li ...

Depletion force in the infinite-dilution limit in a solvent of nonadditive hard spheres.

The mutual entropic depletion force felt by two solute "big" hard spheres immersed in a binary mixture solvent of nonadditive "small" hard spheres is calculated as a function of the surface-to-surface distance by means of canonical Monte Carlo simulations and through a recently proposed rational-function approximation [R. Fantoni and A. Santos, Phys. Rev. E 84, 041201 (2011)]. Four representative scenarios are investigated: symmetric solute particles and the limit where one of the two solute spheres becomes a planar hard wall, in both cases with symmetric and asymmetric solvents. In all cases, the influence on the depletion force due to the nonadditivity in the solvent is determined in the mixed state. Comparison between results from the theoretical approximation and from the simulation shows a good agreement for surface-to-surface distances greater than the smallest solvent diameter.

Structural and electronic properties of aqueous NaCl solutions from ab initio molecular dynamics simulations with hybrid density functionals

We present a study of a dilute solution (1M) of NaCl in water, carried out using ab initio molecular dynamics with semilocal and hybrid functionals. We showed that the structural and electronic properties of the solute and the solvent are the same as those obtained in the infinite dilution limit, i.e. for aqueous ions in the presence of a uniform compensating background. Compared to semilocal functionals, simulations with hybrid functionals yield a less structured solution with a smaller number of hydrogen bonds and a larger coordination number for the Cl− anion. In addition, hybrid functionals predict qualitatively correct positions of the energy levels of the ions with respect to the valence band of water.

Flows and torques in Brownian ferrofluids subjected to rotating uniform magnetic fields in a cylindrical and annular geometry

Ferrofluid flow in cylindrical and annular geometries under the influence of a uniform rotating magnetic field was studied experimentally using aqueous ferrofluids consisting of low concentrations (&amp;lt;0.01 v/v) of cobalt ferrite nanoparticles with Brownian relaxation to test the ferrohydrodynamic equations, elucidate the existence of couple stresses, and determine the value of the spin viscosity in these fluids. An ultrasound technique was used to measure bulk velocity profiles in the spin-up (cylindrical) and annular geometries, varying the intensity and frequency of the rotating magnetic field generated by a two pole stator winding. Additionally, torque measurements in the cylindrical geometry were made. Results show rigid-body like velocity profiles in the bulk, and no dependence on the axial direction. Experimental velocity profiles were in quantitative agreement with the predictions of the spin diffusion theory, with a value of the spin viscosity of ∼10−8 kg m/s, two orders of magnitude larger than the value estimated earlier for iron oxide based ferrofluids, and 12 orders of magnitude larger than estimated using dimensional arguments valid in the infinite dilution limit. These results provide further evidence of the existence of couple stresses in ferrofluids and their role in driving the spin-up flow phenomenon.

Variation and decomposition of the partial molar volume of small gas molecules in different organic solvents derived from molecular dynamics simulations

The partial molar volumes, V(i), of the gas solutes H2, CO, and CO2, solvated in acetone, methanol, heptane, and diethylether are determined computationally in the limit of infinite dilution and standard conditions. Solutions are described with molecular dynamics simulations in combination with the OPLS-aa force field for solvents and customized force field for solutes. V(i) is determined with the direct method, while the composition of V(i) is studied with Kirkwood-Buff integrals (KBIs). Subsequently, the amount of unoccupied space and size of pre-formed cavities in pure solvents is determined. Additionally, the shape of individual solvent cages is analyzed. Calculated V(i) deviate only 3.4 cm(3) mol(-1) (7.1%) from experimental literature values. Experimental V(i) variations across solutions are reproduced qualitatively and also quantitatively in most cases. The KBI analysis identifies differences in solute induced solvent reorganization in the immediate vicinity of H2 (<0.7 nm) and solvent reorganization up to the third solvation shell of CO and CO2 (<1.6 nm) as the origin of V(i) variations. In all solutions, larger V(i) are found in solvents that exhibit weak internal interactions, low cohesive energy density and large compressibility. Weak internal interactions facilitate solvent displacement by thermal solute movement, which enhances the size of solvent cages and thus V(i). Additionally, attractive electrostatic interactions of CO2 and the solvents, which do not depend on internal solvent interactions only, partially reversed the V(i) trends observed in H2 and CO solutions where electrostatic interactions with the solvents are absent. More empty space and larger pre-formed cavities are found in solvents with weak internal interactions, however, no evidence is found that solutes in any considered solvent are accommodated in pre-formed cavities. Individual solvent cages are found to be elongated in the negative direction of solute movement. This wake behind the moving solute is more pronounced in case of mobile H2 and in solvents with weaker internal interactions. However, deviations from a spherical solvent cage shape do not influence solute-solvent radial distribution functions after averaging over all solvent cage orientations and hence do not change V(i). Overall, the applied methodology reproduces V(i) and its variations reliably and the used V(i) decompositions identify the underlying reasons behind observed V(i) variations.

Intrinsic viscosities of polyelectrolytes: specific salt effects and viscometric master curves

Dilute solutions of the sodium salt of polystyrene sulfonic acid (PSS-Na) were measured viscometrically as a function of composition in aqueous solvents of different salinity, where the extra salt was either NaCl or CaCl2. Such experiments yield {η}, the generalized intrinsic viscosities (hydrodynamic specific volume) of the polyelectrolyte for arbitrary polymer concentrations, c. In the limit of infinite dilution {η} becomes identical to the intrinsic viscosity [η]. For NaCl {η} decreases monotonously with rising c, whereas maxima are passed in the case of CaCl2. Condensing c and the concentration of extra salt in the mixed solvent into a single variable enables the establishment of predictive master curves. The viscometrically observed changes in the spatial extension of the individual polymer coils are discussed in light of the corresponding thermodynamic information.