The number Σ of polymer molecules that flow together in a cluster at the crossover concentration (separating the solvent-dominated from the polymer-dominated regime) is for a given mass of the solutes in the case of polyelectrolytes by two to three orders of magnitude smaller than for uncharged polymers. According to the present analysis, this difference is attributed to the ability of polyelectrolytes to form ordered structures even at very small concentrations. The cluster size at the crossover concentration varies in large limits from system to system. This observation can be rationalized by the fact that the crossover concentration is primarily given by static properties of the polymers in contrast to the cluster size, for which interactions are decisive. At sufficiently high dilution, the number of macromolecules flowing together as a function of their concentration c (mass/volume) obeys the following relationship: Σ = Ksystem + log c, where the constant characterizes the system.

Rheological behavior of brea gum in aqueous solutions results from two particularities of this polysaccharide: (i) its ability to assume two different structures in solution: coils or self-assembled structures (probably helices) and (ii) the very dissimilar contribution of these conformations to the viscosity. The fraction of coils existing at given values of polymer concentration (c) and pressure increases with temperature and shear rate, where the transformation is taking place within a comparatively small temperature interval (approximately 20 C-degrees) shifting towards higher temperatures as c rises. The observation that coils dissipate considerably more energy than helices is interpreted in terms of microphase equilibria leading to volume elements with reduced flow-through of the solvent. The bimodal flow curves of the present system reflect the presence of two different processes, the disentanglement of coils in the range of lower shear rates and the destruction of helical structures at higher ones.

This paper calculates for liquid mixtures of high and low molecular weight components, how many solute molecules flow on the average conjointly. The application of the approach to solutions of poly(dimethyl siloxane) in its pentamer, to suspensions of gibbsite (Al(OH)3) in dimethyl sulfoxide, and to human blood testifies that the approach is applicable without restrictions regarding the chemical nature of the high molecular weight compound. The shear thinning of the systems under investigation can be understood in terms of a reduction of the shear-overlap parameter Σ, where the generalized intrinsic viscosity {η} constitutes the central property governing the composition and shear rate dependence of the viscosities. Furthermore, the present analysis demonstrates that intrinsic viscosities can be determined for all solutes and that they decrease with rising shear rates according to a Boltzmann sigmoid for the systems DMS5/PDMS and blood. The comparison of the hydrodynamic specific volumes of the solutes (i.e., of [η]) with the corresponding specific volumes in the pure state leads to the conclusion that solutes that cannot interpenetrate carry a considerable amount of solvent piggyback with them when flowing. In addition to the pure description of the observations, the approach was able to point to new phenomena, e.g., the solidification of the gibbsite suspensions beyond a characteristic solute concentration, which shifts to higher values with increasing shear rates. Because of its general nature, the present approach should become helpful, above all in the areas of technology (reactions in flowing systems) and health (rheology of blood).

Solution viscosities were measured for an uncharged polymer [poly(ethylene oxide): PEO], for a polyelectrolyte [poly(sodium 4-styrenesulfonate): PSS-Na] and for the blends of these components in water of variable salinities. The evaluation of these data with respect to the intrinsic viscosities revealed the following: for NaCl as extra salt, the intrinsic viscosities of the blends are always less than predicted by additivity; moreover the [eta] values of PEO increase with rising salinity of the solvent, in contrast to that of PSS-Na which decrease. This situation leads to an inversion point of the salt effects at the salinity of approximately 2.9 mol/L. This finding becomes comprehensible by treating the salt solutions as mixed solvents. Replacing NaCl by the CaCl2 (divalent cation) as extra salt leads to the [eta] values for the blends, which are larger than additive. Based on phenomenological thermo-dynamic consideration this behavior is attributed to an entropy driven formation of interpolymer complexes and explained in molecular terms.

Information on the miscibility of different polymers A and B on a molecular level is important in many ways. However, along the traditional lines this knowledge is difficult and time consuming to achieve. The current study presents a simple alternative, based on the determination of the intrinsic viscosities (specific hydrodynamic volume of isolated coils) for blend solutions in a common solvent. In the case of incompatible polymers, isolated coils contain one macromolecule only, either A or B. In contrast, compatible polymers form mixed isolated coils, because of favorable interactions. The present investigation was carried out for the system water/poly(ethylene oxide)/poly(sodium 4-polystyrenesulfonate), for which the reason of compatibility lies in the formation Na+ bridges between the sulfonate groups of the polyelectrolyte and the OH groups of the poly(ethylene oxide). Zero shear viscosities were measured as a function of polymer concentration for blends of different compositions and modeled quantitatively by means of relations yielding the excess intrinsic viscosities ε (zero in the case of incompatibility) and viscometric interaction parameters. Particular attention is being paid to the role the molar masses of the polymers play for the resulting ε values.

Experimental information on the viscosities, eta, of polymer solutions and of polymer melts as a function of shear rate is modeled by means of an approach that describes the diminution of ln eta as a function of shear stress, tau, in terms of an exponential decay. The approach uses the following three adjustable parameters: the zero-shear viscosity of the system, a characteristic shear stress, quantifying its susceptibility toward shear thinning, and a dimensionless parameter stating the magnitude of the effect. This procedure gives access to the Newtonian behavior also in cases where direct measurements are impractical or impossible; it discloses two phenomena not reported so far: a qualitative change in the efficacy of tau at a characteristic concentration and indicates the occurrence of two different disentanglement mechanisms in thermodynamically unfavorable solvents.

Polymer solutions are inhomogeneous on mesoscopic scales as a result of chemical bonds linking their monomeric units. This situation leads to polymer clusters within which the polymer concentration ccluster is only a small fraction of the overall concentration c. The ratio c/ ccluster (overlap parameters Ω) quantifies the number of clusters that need to overlap to yield c. Equilibrium clusters (minimization of Gibbs energy) and shear clusters (minimization of entropy production) differ fundamentally where Ωequil ≥ Ωshear. Only in the vicinity of the glass transition temperature and at high concentration the opposite is the case. Experimental information on Ωequil as a function of φ, the volume fraction of polymer, yields coil-overlap and cross-over concentrations in agreement with the results of scattering studies; analogous information on Ωshear (φ) gives access to cross-over concentrations under shear. Theoretical aspects and questions of practical interest arising from the observed differences between equilibrium and shear clusters are being discussed.

The viscometric behaviour of kappa-carrageenan in aqueous solutions and in the presence of monovalent salts was investigated at 25 degrees C. Coil, helix or double helix conformations were induced by cooling hot kappa-carrageenan solutions under appropriate ionic conditions. A new viscometric approach was used for modeling the behaviour of kappa-carrageenan solutions. The intrinsic viscosity, [eta], is markedly changed by the presence of different monovalent salts (NaCl, NaI and CsI). In pure water, the intrinsic viscosity amounts to 48 dL.g(-1). In 0.1 M NaCl solutions (single helix state) [eta] is 6.2 whereas in 0.1 M NaI (double helix conformation) it is approximately twice as large. In 0.1 M CsI (dissimilar cation and counter-ion) the intrinsic viscosity is three times larger, suggesting the formation of the associated kappa-carrageenan helices. Stepwise association of kappa-carrageenan helices was followed in presence of NaI/CsI mixtures of different compositions. The value of Smidsred-Haug stiffness parameter (B) measured for kappa-carrageenan in NaCl solutions is 4.47 x 10(-2), higher than that of DNA (5.5 x 10(-3)), but lower than those reported for carboxymethyl cellulose (6.3 x 10(-2)), indicating that the chain conformation is moderately rigid. (C) 2019 Elsevier B.V. All rights reserved.

The capabilities of an alternative definition of intrinsic viscosities [eta] published some years ago is being studied by means of comprehensive viscometric data reported in the early days of polymer science. It introduces the generalized intrinsic viscosity {eta} as the specific hydrodynamic volume at arbitrary polymer concentration c. {eta} quantifies the size of the flow unit and decreases monotonously for T >> T-g (glass transition temperature) as a function of c but passes a pronounced minimum as T approaches T-g. In the limit of the pure polymer melt, {eta} becomes [eta]; this newly introduced property is termed intrinsic bulkiness, by analogy to the intrinsic viscosity, and provides noncalorimetric experimental access to T-g; it also allows estimates of entanglement molecular weights based on the Newtonian flow behavior. Moreover, the molecular weight dependence of [eta] provides information on the contributions of endgroups to the flow behavior.

Joint solutions of oppositely charged weak polyelectrolytes are considerably less studied than their strong counterparts; as a result, their thermodynamic understanding is still unsatisfactory. This shortcoming hampers the development of a general picture about the physical properties of these mixtures, which further hampers their use to design new materials. To close this gap, we investigate the ternary system ethanol/polyacid/polybase (polyacid: methacrylic acid containing copolymer; polybase: N,N-dimethylaminoethyl methacrylate containing terpolyrner) with respect to its demixing and viscometric behavior. Complete homogeneity can only be reached if the total polymer concentration remains below 0.005 g dL(-1). The locations of the fie lines in the phase diagram reveal that the interpolymer contacts are favorable at low polymer concentrations but unfavorable at high concentrations; viscosity measurements corroborate these findings. Adding either acid or base to the solvent extends the region of homogeneity, where low concentrations of HCl split the two-phase region into two separate parts. This phenomenon is rationalized in terms of concentration-dependent changes in the degree of ionization of the polybase.

The intrinsic viscosity of polymer blends in a common solvent may deviate markedly from additivity. Such behavior testifies favorable interactions between the two types of macromolecules. Under these conditions, isolated polymer coils contain one macromolecule of each species and represent the simplest possible case of self-organization. The particular thermodynamic situation required for the occurrence of that phenomenon is being analyzed in terms of microphase equilibria by means of an approach, which subdivides the dilution process into two steps. The first step quantifies the opening of intersegmental contacts at constant conformations of the components and the second step the conformational relaxation required to attain equilibrium. The intrinsic viscosities resulting for the mixed isolated coils are normally smaller than calculated from additivity. However, the opposite behavior can also occur under special conditions. The possibilities to gain quantitative information on polymer/polymer interaction parameters from the intrinsic viscosities of polymer blends are being discussed.

We use plasmon rulers made from two connected gold nanoparticles to monitor the conformation and stiffness of single PEG molecules and their response to cations. By observing equilibrium fluctuations of the interparticle distance, we obtain the spring constants or stiffness of the connecting single-molecule tether with pico-Newton sensitivity. We observe a transition of the PEG molecules' extension and stiffness above about 1.2 mM K+ ion concentration which is specific to potassium ions. Molecular dynamics simulations reveal the formation of crown-like structures as the most likely molecular mechanism responsible for this specific effect.

The intrinsic viscosities, [a], of the 3-arm star polyelectrolyte in pure water are for a given molar mass considerably lower than for the linear product because of the higher monomer concentration and charge density in isolated coils. These effects are much more pronounced than in the case of uncharged macromolecules. Extra salt (NaCI, NaI, CaCl2) reduces the solution viscosities of the 3-arm star polymer less than of the linear product. The transition of [eta] from the value in pure water to the minimum saturation value at high salt concentrations follows a Boltzmann sigmoid. In saline solvents the changes of the viscosities with rising polymer concentration depend strongly on the chemical nature of the salt and on the molecular architecture of the solute. The present findings demonstrate the necessity to account for thermodynamic interactions between all components of the mixture, in addition to the usual electrostatic considerations. These considerations should turn out helpful for a better understanding of salt induced topological transitions of charged biopolymers.

Copolymers of ethylene oxide (EO) and N,N-dimethyl aminoethyl methacrylate (R) or [2(methacryloyloxy)ethyl] trimethylammonium iodide (R+) were studied in dilute solution: P(EOp -b -R-n)(I), P(Rn(1-f) - ran - R-n(+) (f) ).(II), and P(EOP - b - R-n(+))(III); n and p give the numbers of monomers and f is the degree of charging. For II (variable)) and III (variable n) the effects of charging on the intrinsic viscosities [n] are well described by Boltzmann sigmoids. The deviation of [n] from [n](add) (calculated from the corresponding homopolymer data, assuming additivity of the individual contributions) are quantified by sigma =[n]/[n](add) -1 measuring the segregation (sigma > 0) or clustering (sigma < 0) of dissimilar monomers in isolated coils. For II, changes from negative at low f to positive at high) I and III pass maxima as n becomes larger, where a is positive at low and negative at high n for I, but always larger than zero for III. The investigation of salt effects using NaCl, CaCl2 and Nal corroborates the observations for the homopolymers. (C) 2016 Elsevier Ltd. All rights reserved.

Macromolecular co-assemblies built up in aqueous solutions, by using a linear polypeptide, poly(aspartic acid) (PAS), and a globular protein, bovine serum albumin (BSA), have been studied. The main interest was to identify the optimum conditions for an interpenetrated complex formation in order to design materials suitable for biomedical applications, such as drug delivery systems. BSA surface possesses several amino- and carboxylic groups available for covalent modification, and/or bioactive substances attachment. In the present study, mixtures between PAS and BSA were investigated at 37°C in dilute aqueous solution by viscometry, dynamic light scattering and zeta potential determination, as well as in solid state by AFM microscopy and dielectric spectroscopy. The experimental data have shown that the interpolymer complex formation occurs for a PAS/BSA molar ratio around 0.541.

Viscosities of casein solutions were measured within the dilute range in ammoniacal water and in saline solvents containing different amounts and different kinds of salt. All these data are modeled quantitatively by means of an approach accounting for the polyelectrolyte character of casein micelles. Two parameters are required: The intrinsic viscosity [η ] and a viscometric interaction parameter β. The behavior of casein is compared with that of chain-like polyelectrolytes. For both polymers one observes a pronounced reduction of [η ] with increasing salt concentration. However, for casein the decline of [η ] is less pronounced by more than an order of magnitude and depends on the chemical nature of the salt. In the case of low solvent salinities, the β values are in both cases positive (less than exponential increase of the viscosity with rising solute concentration). However, for casein β changes from positive to negative (more than exponential increase) with rising salt concentration. Reasons for the dissimilarities between the two types of polyelectrolytes are discussed.

Intrinsic viscosities, generalized intrinsic viscosities and viscometric interaction parameters were measured for aqueous solutions of poly(ethylene oxide) [PEO poly(N,Ndimethyl aminoethyl methacrylate) [PR] (uncharged) and for poly{[2-(methacryloyloxy)e thyl] trimethylammonium iodide} [PR+] (charged) within a wide range of molar masses. In this manner it was possible to establish the information required for the study of non-additivity effects upon the formation of binary copolymers from the monomers specified above. The following additional items were of particular interest: The effects of charging PR to PR+. and the composition dependence of the coil overlap in the case of saline (NaCI, CaCl2 and Nal) solvents. NaCI turned out to be much less efficient in shielding the electrostatic interactions than the other salts due to its large tendency to form ion pairs in solution. (C) 2016 Elsevier Ltd. All rights reserved.

Generalized intrinsic viscosity {η} of sodium polystyrene sulfonate as a function of polymer concentration in pure water and in saline solvents.