Strukturviskosität von verdünnten Lösungen von Biopolymeren

The importance of the rheological behaviour of solutions of macromolecules is briefly evaluated. The viscosity of the solutions depends on concentration, shear rate and time of shear, this relation being determined by the structure of the dissolved molecules. In dilute solutions shear dependence of viscosity is very frequently caused by the preferential orientation of anisotropic molecules. In such a case the particle dimensions can be calculated from the true limiting viscosity number, an anisotropy factor, the rotational diffusion constant and the effective particle density. These numbers can be derived from the flow curve, which has been extrapolated to zero concentration. It is necessary to measure the flow curve at shear gradients, which are sufficiently low to allow for an extrapolation to vanishing shear rate. By comparing the experimental flow curve with a choice of theoretical ones, the rotational diffusion constant and the anisotropy factor (axial ratio) can be found. From the limiting viscosity number and the axial ratio, the particle density can be calculated.     

Structural evolution of colloidal crystals with increasing ionic strength

We have directly observed the structural evolution of colloidal crystals as a function of increasing ionic strength using confocal scanning laser microscopy. Silica colloids were sedimented onto a glass substrate in deionized water to create large, single domain crystals. The solution ionic strength was then increased by one of three methods of controlled electrolyte addition: (1) direct injection of electrolyte solutions, (2) single step diffusion of electrolyte solutions through a dialysis membrane, and (3) multiple step diffusion of electrolyte solutions of increasing ionic strength through a dialysis membrane. During direct injection of electrolyte solutions, initially large, single domain colloidal crystals were shear melted and then evolved into polycrystalline structures at low ionic strengths and gels at higher ionic strengths. Diffusion of electrolyte solutions though dialysis membranes in a single step produced gradient-driven transport that also melted initial single domain crystals to yield polycrystalline and gel structures similar to the injection approach. Interestingly, the multistep diffusion of several electrolyte solutions through dialysis membranes facilitated retention of large, single domain crystals even as particles came into adhesive contact. This was achieved by reducing the contraction rate of the crystalline lattice to allow sufficient time for diffusion-limited configurational rearrangements to occur within the evolving structure. These mechanically robust, single domain colloidal crystals may find important applications as templates for photonic materials and sensors.     

Intradiffusion coefficients for iron and water and shear viscosities in aqueous iron(II) perchlorate solutions at 25°C

Intradiffusion coefficients of iron(II) and water were determined in acidified solutions of iron(II) perchlorate for an iron concentration range of 0 to 2.5 mol-dm^–3 at 25°C. In addition ancillary shear viscosity and density data were measured for each solution. Results were compared with existing diffusion data for iron(III) perchlorate solutions and highlighted the differences in the solvent dynamics around the two metal ions. By use of a simple model the effective hydration of the iron(II) ion was estimated to be 12, comparable to that of other divalent, uncomplexed metal cations; the same model indicates an effective hydration of 19 for iron(III).     

Gaussian approximation for Hookean dumbbells with hydrodynamic interaction: Translational diffusivity

The recently developed Gaussian approximation for the hydrodynamic interaction is used to discuss the translational diffusivity of polymers in dilute solutions undergoing homogeneous flows. For the Hookean dumbbell model, we derive the diffusion tensors associated with (i) the average polymer velocity caused by external forces; (ii) the mean-square displacement of a single polymer caused by the Brownian forces; and (iii) the polymer mass flux caused by concentration gradients. We discuss the model predictions for these diffusion tensors for steady shear flow in detail.This paper was presented at the Frühjahrstagung des Fachausschusses Polymerphysik der Deutschen Physikalischen Gesellschaft in Hamburg (West Germany), March 14–16,1988.     

Effective concentration difference model to study the effect of various factors on the effective diffusion coefficient in the dialysis membrane

Cellulose acetate dialysis membrane (CDM) has been used in the diffusive gradients in thin films (DGT) technique, where accurate diffusion coefficients are essential for the assessment of the concentrations of labile metal in solution. Effective concentration difference model (ECDM), based on the assumption that the effective diffusion coefficient of metal ion in the dialysis membrane is determined by the effective concentration difference (ΔC(e)) across the dialysis membrane, is proposed and applied to study the effect of ionic strength, binding agent, ligands and Donnan potential on the effective diffusion coefficient. The effective diffusion coefficients of Cd(2+) through the dialysis membrane immersed in receptor solutions with binding agent were almost the same as those in receptor solutions without binding agent at higher ionic strengths (0.01-1 M) but much higher than those at lower ionic strengths (0.001-0.0001 M). The effective diffusion coefficients of Cd(2+) through the dialysis membrane immersed in deionized water receptor solutions with binding agent were not significantly different from those in synthetic receptor solutions (receptor solutions with various ionic strengths) with binding agent. The DGT-labile fractions were measured in synthetic solutions and natural waters, which indicated that the effective diffusion coefficients, through the dialysis membrane immersed in the deionized water solution with binding agent as receptor solution and in the spiked natural water as source solution, were more suitable for DGT application.     

Nonlinear rheology of CTAB/NaSal aqueous solutions: finite extensibility of a network of wormlike micelles

The nonlinear rheology of aqueous solutions of cetyltrimethylammonium bromide (CTAB) and sodium salicylate (NaSal) was investigated. The concentration of CTAB was fixed at 0.1 mol L(-1), and the concentration of NaSal was varied from 0.07 to 0.4 mol L(-1). For all test solutions, dynamic moduli were described with the Maxwell model having a single relaxation time, tau. Time evolutions of the shear stress, sigma, and the first normal stress difference, N(1), after inception of the steady shear flow were measured. For solutions having low NaSal concentrations, strain-hardening was observed and sigma and N(1) diverged at a certain strain when the shear rate, , exceeded tau(-1). For solutions with high NaSal concentrations, stress overshoot similar to that of ordinary entangled polymer solutions was observed at between tau(-1) and a certain critical rate, (C), while the strain-hardening was observed at > (C). A simple relationship for elastic solids, N(1)/sigma = gamma with gamma being the strain imposed by shear flow, held for all the solutions in the strain-hardening regime. The strain-hardening was attributable to the strain-dependent shear modulus and well described with the network theory considering the finite extensibility of network strands. The segment size of network strands was successfully determined. Thus, the stress-strain relationship obtained after the inception of fast flows is useful for characterizing the network properties.     

The effect of pressure and temperature of self-diffusion coefficients in several concentrated deuterium oxide diamagnetic electrolyte solutions

The pressure dependences of the self-diffusion coefficients of deuterium oxide in 4.5m solutions of LiCl–D₂O and CsCl–D₂O (also 7m) and 3.06m CaCl₂–D₂O have been measured by the NMR spin-echo method at 30°C, 60°C, and 90°C. Shear viscosities and densities of these solutions have also been determined over the same range of experimental conditions. The experimental data show that the diffusion constantD decreases with the increasing structure-making ability of the electrolyte cation Ca⁺²>Li⁺. In contrast, the diffusion coefficient for D₂O in the 4.5 and 7m CsCl solutions is equal to that for pure D₂O at 30°C but lower at 60°C and 90°C. It has been found that the Stokes-Einstein equation relates well the diffusion coefficients to shear viscosity in these concentrated electrolyte solutions.     

Intrinsic viscosity of solutions of rigid particles at high shear rates

The results of a numerical calculation which extends Scheraga's calculation on the non-Newtonian behavior of the viscosity factor v of rigid ellipsoid solutions are given here and compared to experimental data obtained on different poly(γ-benzyl L -glutamate) samples in helical configuration, over a wide range of molecular weight, up to 980,000. Relations for the axial ratio p, the rotary diffusion constant D, and a test of the deformability of the polymer under shear, are given as functions of the shear-rate dependence of the intrinsic viscosity. The experimental behavior under shear shows that PBLG becomes somewhat flexible in dichloroethane, but not in m-cresol. The dimensions calculated from the viscometric results suggest discrete changes in the length per monomeric unit of the helix at different well defined molecular weights.     

Microviscosity of dilute latex + gelatin dispersions determined by dynamic light-scattering

The microviscosity of dilute latex + gelatin dispersions has been studied by dynamic light-scattering at gelatin concentrations up to 1.0 wt % and temperatures in the range 8–45 °C. The change in mean particle diffusion coefficient following a rapid quench correlates strongly with the change in bulk shear viscosity of the gelatin solution. Slow thermal studies of latex + gelatin exhibit hysteresis effects which are mirrored by bulk viscometry data for gelatin solutions at the same concentration.     

Rheology of concentrated solutions of helical polypeptides

Rheological studies were carried out on concentrated m-cresol solutions of two helical synthetic polypeptides; poly-γ-benzyl-L -glutamate (PBLG; molecular weight, 150,000) and poly-?-carbobenzyloxy-L -lysine (PCBZL; molecular weight, 200,000). Steady shear measurements were made over a range of 0.01–16,000 sec^?1 to obtain steady shear viscosity and first normal stress difference. Dynamic viscosity and dynamic storage modulus were measured both by oscillatory shear between cone and plate and also by an eccentric rotating disk device over frequency ranges of 0.1–400 and 0.1–63 rad/sec, respectively. The concentration ranges were such that both liquid crystalline and isotropic solutions were investigated. The previously reported observations of an apparent negative first normal stress difference within a defined range of shear rate for liquid crystalline solutions were confirmed for the PBLG and PCBZL solutions. At high shear rates the peaks in plots of steady shear viscosity against concentration were profoundly suppressed but peaks in first normal stress difference versus concentration were not. The observation of liquid crystalline order in PCBZL/m-cresol solutions at room temperature constitutes evidence that the inverse coil-helix transition temperature is lower in concentrated solutions than in dilute solutions. The critical concentration for formation of the liquid crystalline phase was higher for PCBZL than for PBLG, despite a higher axial ratio, due to helix flexibility.     

Shear and extensional rheology of solutions of mixtures of poly(ethylene oxide) and anionic surfactants in ionic environments

Interactions between a high molecular weight poly(ethylene oxide) (PEO) and the anionic surfactant sodium dodecyl benzene sulfonate (SDBS) in aqueous solutions were investigated by shear and extensional rheometry. Results for mixtures between PEO and sodium dodecyl sulfate (SDS) are also presented for comparison purposes. Addition of anionic surfactants to PEO solutions above the critical aggregation concentration (CAC), at which micellar aggregates attach to the polymer chain, results in an increase in shear viscosity due to PEO coil expansion, and a strengthening of interchain interactions. In extensional flows, these interactions result in a decrease of the critical shear rate for the onset of the characteristic extension thickening of the PEO solutions that is due to transient entanglements of polymer molecules. The relaxation times associated with these transient entanglements are not directly proportional to the shear viscosity of the solutions, but rather vary more rapidly with surfactant concentration. In the presence of an electrolyte, coil contraction results in lower shear viscosities and a decrease in the extension thickening effects at surfactant concentrations just beyond the CAC. The relaxation times associated with transient entanglement reach a minimum at the same surfactant concentration as the shear viscosity, which indicates that coil contraction is responsible for the observed effects in both types of flow. However, the increase in extensional-flow entanglement relaxation times is much more abrupt than the decrease in shear viscosity. All these results point to a greater sensitivity of extensional flows on the molecular conformation of PEO/surfactant complexes.     

Orientation and relaxation of polymer–clay solutions studied by rheology and small-angle neutron scattering

The influence of shear on viscoelastic solutions of poly(ethylene oxide) (PEO) and clay [montmorillonite, i.e., Cloisite NA+ (CNA)] was investigated with rheology and small-angle neutron scattering (SANS). The steady-state viscosity and SANS were used to measure the shear-induced orientation and relaxation of the polymer and clay platelets. Anisotropic scattering patterns developed at much lower shear rates than in pure clay solutions. The scattering anisotropy saturated at low shear rates, and the CNA clay platelets aligned with the flow, with the surface normal parallel to the gradient direction. The cessation of shear led to partial and slow randomization of the CNA platelets, whereas extremely fast relaxation was observed for laponite (LRD) platelets. These PEO–CNA networklike solutions were compared with previously reported PEO–LRD networks, and the differences and similarities, with respect to the shear orientation, relaxation, and polymer–clay interactions, were examined. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3102–3112, 2004     

Rheologic Properties of a Water-Soluble Terpolymer with Vinyl Biphenyl

A water-soluble acrylamide-modified terpolymer (PAAP) with sodium 2-acrylamido-2-methylpropane sulfonate and vinyl biphenyl as the hydrophobic monomer was synthesized to obtain a polymeric thickening agent applied in middle- and low-permeability oil reservoirs. The polymer is expected to possess a low molecular weight and high solution viscosity. The steady-state consecutive shear cycles of PAAP in aqueous and brine solutions were measured, and the viscoelastic properties of PAAP solutions were investigated as a function of polymer, NaCl and sodium dodecylbenzene sulfonate (SDBS) concentrations. The aqueous PAAP solutions exhibits pseudoplastic and thixotropic behavior over the range of shear rate and shear thickening behavior at very low shear rate. The steady-state shear results show that some disrupted associating aggregates at high shear rate can be reformed during the shear reversion process and the suitable shear rate is favorable to the formation of hydrophobically associative structures in the brine solutions. Above 0.05 g⋅dL⁻¹ PAAP, aqueous PAAP solutions have predominantly elastic character over the range of angular frequency that is strengthened with increasing polymer concentration. The PAAP brine solutions exhibit predominantly elastic behavior only above 3 rad⋅s⁻¹ and a salt-thickening effect. By addition of an optimum amount of SDBS (0.5–0.8 mmol⋅L⁻¹), the complex viscosities become much higher than the dynamic viscosities, although the loss tangent values increase owing to the formation of loose associative structures.     

Electrospinning of composite nanofibers based on chitosan,poly(ethylene oxide), and chitin nanofibrils

Composite chitosan nanofibers containing 20 wt % chitin nanofibrils and 10 wt % PEO are obtained via the electrospinning method. Additions of 0.5–20.0 wt % chitin nanofibrils into chitosan solutions with concentrations of 3–7 wt % in acetic acid (70 vol %) insignificantly increase the electrical conductivity, surface-tension coefficient, and viscosity of these mixed solutions. Decreases in the viscosities of chitosan solutions containing chitin nanofibrils with increases in shear rate provide evidence for the structuring of solutions and the orientation of chitosan macromolecules and chitin nanofibrils in the shear flow. The effects of shear stress and a high-voltage electric field on chitosan solutions containing chitin nanofibrils and PEO result in a decrease in the imperfection of composite nanofibers. The introduction of chitin nanofibrils allows the content of PEO in the composite nanofibers to be reduced.     

Momentum and stress relaxation in fluids illustrating caging

The self diffusion coefficient, shear viscosity, and velocity time correlation function are calculated for a hard sphere fluid under a severe assumption, namely, the friction arises from uncorrelated binary collisions and from correlated backscattering (caging) collisions as represented in the memory function. Relaxation of the memory function from its zerotime caging value is described as a diffusion process. Derived diffusion coefficients and the shear viscosities, relative to their Enskog values decrease and increase with density, respectively, in a monotonic and gradual fashion in contrast with simulation values that show a precipitous change near the fluid-solid transition. In the present pair diffusion model, the velocity time correlation function vanishes at the proper time but its tail is overly damped relative to the simulation data. A weak breakdown of the Stokes-Einstein relation is also predicted.     

Quantum diffusion in liquid para-hydrogen from ring-polymer molecular dynamics

We have used the ring-polymer molecular dynamics method to calculate approximate Kubo-transformed velocity autocorrelation functions and self-diffusion coefficients for low-pressure liquid para-hydrogen at temperatures of 25 and 14 K. The resulting diffusion coefficients are shown to be consistent with experimental shear viscosities and the established finite-size relation D(L) approximately = D(infinity)-2.837k(B)T6pietaL, where k(B) is the Boltzmann constant, T the absolute temperature, eta the shear viscosity, and L the length of the (cubic) simulation cell. The diffusion coefficients D(L) obtained in simulations with finite system sizes are therefore too small. However, the extrapolation to infinite system size corrects this deficiency and leads to excellent agreement with experimental results. This both demonstrates the influence of system-size effects on quantum mechanical diffusion coefficients and provides further evidence that ring-polymer molecular dynamics is an accurate as well as practical way of including quantum effects in condensed phase molecular dynamics.     

Ternary diffusion coefficients of diethanolamine and N-methyldiethanolamine in aqueous solutions containing diethanolamine and N-methyldiethanolamine

Ternary diffusion coefficients of diethanolamine (DEA) and N-methyldiethanolamine (MDEA) in aqueous solutions containing DEA and MDEA using the Taylor dispersion technique have been measured for temperatures (303.2, 313.2, and 323.2 K). The systems studied were aqueous solutions containing total amine concentrations of 2.5 and 4.0 kmol m⁻³, each having four different amine molar ratios. The density and viscosity of the blended amine solutions were also measured. The mutual diffusion coefficients of aqueous DEA and aqueous MDEA solutions were also reported. The main diffusion coefficients (D₁₁ and D₂₂) and the cross-diffusion coefficients (D₁₂ and D₂₁) were reported as function of temperature and concentration of alkanolamines. The limiting conditions for the main diffusion coefficients and the cross-diffusion coefficients were discussed at first, and a comparison between the ratios of the cross-diffusion coefficients to the main diffusion coefficients for DEA and MDEA was made. The dependence of the main diffusion coefficients on the viscosity of solutions was also investigated.     

Intradiffusion and viscosity measurements in acidified iron(III) chloride solutions at 25°C

Intradiffusion of species in acidified (using eithe hydrochloric or perchloric acid) iron(III) chloride solutions has been studied using labeled iron(III), chloride and water. Comparison with data for iron(III) perchlorate has enabled the influence of complexed species upon the diffusion to be ascertained. The chloro-iron species formed have larger diffusion coefficients than the free iron(III) ion as would be expected from their lower net charge. Simple diffusion models have been employed to enable estimates of the diffusion of the complexed species and of the free chloride diffusion coefficients to be obtained. These are discussed in relation to literature data for similar systems. In addition esitmates of the effective hydration of the iron(III) species in solutions have been obtained from the diffusion data. These are discussed in relation to two other trivalent metal salt systems, chromium chloride and lanthanum chloride; the overall hydration of the three cations is virtually identical.     

Shear‐Induced Diffusion in Dilute Suspensions of Charged Colloids

We propose a model for the nonequilibrium enhancement of colloidal self‐diffusion in an externally imposed shear flow in charged systems. The diffusion enhancement is calculated in terms of electrostatic, two‐body interactions between the particles in shear flow. In the high‐shear rate, low‐volume fraction limit in which the model is valid, we compare these calculations to the experiments of Qiu et al. [PRL 61, 2554 (1988)] and simulations of Chakrabarti et al. [PRE 50, R3326 (1994)] and find good agreement on scaling and magnitude to within experimental uncertainty of the electrostatic parameters.     

Photochemical degradation of hyaluronic acid by singlet oxygen

Changes of the rheological properties of hyaluronic acid (sodium-magnesium salt) solutions after exposure to UV radiation indicate a vigorous decrease in their viscosity, but its still strong shear rate dependence. Whereas the presence of the singlet oxygen sensitizer (anthracene-1-sulphonic acid) brings about a loss of shear dependence; the studied solutions show newtonian behavior.