Shear Viscosity Of Solutions Research Articles

Rheology, stability, and physicochemical properties of NaOH-tannic acid solvent for β-chitin dissolution

The applicability of chitin in food systems is limited by its poor solubility in ordinary solvents. This study explores a novel solvent system composed of sodium hydroxide and tannic acid (NaOH/TA) in combination with a repeated freeze-thaw process for dissolving chitin. The highest chitin solubility in 8% NaOH/0.3% TA and 10% NaOH/0.3% TA was 2.1% and 2.3% (w/v), respectively. The lower NaOH and excessive tannic acid content may lead to reduction of chitin solubility. We also observed a unique rheological property of the chitin/NaOH/TA system. A higher concentration of TA reduced the chitin solution's shear viscosity, storage modulus, loss modulus, and gelling temperature. Its shear viscosity decreases with increasing shear rate, showing a shear thinning behavior. When the chitin/NaOH/TA solution system was stored at 30oC, the crystalline degree of chitin decreased, and the diffraction peak shifted, suggesting the formation of different intermolecular forces. The TA contents show no significant effect on the crystallinity of chitin. With increased storage time, the molecular weight of chitin decreased, and the degree of deacetylation (DD) increased. These results underscore the potential applications of the chitin/NaOH/TA system in the food industry.

Extensional flow affecting shear viscosity: Experimental evidence and comparison to models

The effect of extensional flow on apparent shear viscosity has never previously been directly measured nor is it often considered. Here, for the first time, through using a novel flow configuration (two-phase shear response under extensional flow), we have directly measured the effect extensional flow has on the apparent shear viscosity of a viscoelastic polymer solution in a controlled and kinematically mixed manner. We show, via a control transient shear experiment, that the apparent shear viscosity of the solution under mixed deformation depends not only on the shear rate but also on the extension rate and their relative direction: shear thinning being enhanced by parallel and reduced by perpendicular extensional flow, respectively. A 62% reduction in apparent viscosity with parallel extension was seen in this work. We then test the ability of the commonly used Giesekus and Carreau–Yasuda (incorporating generalized shear rate) models to predict the effect of extension rate on apparent shear viscosity against our data. The Giesekus model was found to predict the correct qualitative behavior under both parallel and perpendicular extensional flow, and depending on the fitting parameters, also provided a loosely quantitative agreement. Conversely, the generalized shear rate description does not capture the qualitative behavior, with the most significant errors occurring for perpendicular extension (i.e., expansion) flows. This work emphasizes the rarely noted shortcomings of the latter approach when used for experimental analysis and engineering design when extensional flows are additionally present.

Bulk viscosity of hydrocarbon solutions at extreme state parameters. I. Linear alkane solutions ([formula omitted

The paper presents the results of studies of the bulk viscosity of binary solutions of linear alkanes. The bulk viscosity coefficients of the C6H14-C16H34 system were obtained in the pressure range up to 98.0 MPa and the temperature range 293–393 K (concentrations of 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0 mol fractions). The bulk viscosity coefficients were determined with an accuracy of 7–12% from the experimental data on the speed and absorption coefficient of ultrasound. A number of equations that approximate the concentration dependence of the bulk viscosity coefficients are analyzed. An approach that requires a minimum of input information, which is based on approximating the ratio of the coefficients of the bulk and shear viscosities of solutions by the geometric mean of the components, is proposed. This approach allows to predict the bulk viscosity coefficients of linear alkane solutions with an average accuracy of 15%. The advantage of this approximation method is the possibility of its obvious generalization to multicomponent systems.

Analyzing the Size of Albumin Macromolecules in Aqueous Solutions

Changes in the structure and size of macromolecules of human and bovine serum albumin in aqueous solutions are considered, depending on temperature, concentration, and acid–base equilibrium. It is found that a change in the hydrodynamic radius of the macromolecule is an indicator of the structural phase transformations of globular proteins. Ways of determining the radii of macromolecules from data on the shear viscosity of solutions and the self-diffusion of macromolecules in them are discussed. The hydrodynamic radii of albumin macromolecules found by these means are compared. It is shown that conclusions can be drawn about the nature of bonding between water molecules and protein macromolecules using the obtained data.

Controlling the elongational flow behavior of complex shear-thinning fluids without affecting shear viscosity

Complex flow fields including high elongational deformation occur in numerous industrial processes such as spraying, coating, fiber spinning, and screen or inkjet printing. Fully exploiting the potential of these technologies suffers from a lack of knowledge regarding how elongational flow properties of the processed fluids affect the results of these operations. Here, we present two strategies that allow for varying the elongational flow behavior independent of shear rheology. First, two acrylic thickener solutions that differ with respect to the fraction of hydrophobic co-monomers and hence with respect to their degree of inter- and intramolecular hydrophobic association were mixed to vary the elongational relaxation time, as determined using capillary breakup elongational rheometry (CaBER), by almost two orders of magnitude without affecting shear viscosity of these solutions in a wide, processing-relevant shear rate range. Second, a substantial increase in the elongational flow resistance was achieved by adding a small amount of plate-like particles without affecting the shear viscosity of these thickener solutions. A fourfold increase of the elongational relaxation time was observed upon the addition of 3.5 vol.% of glass flakes to such a highly shear-thinning system. A similar effect was also observed for an industrial waterborne automotive basecoat due to added aluminum flakes. This work may be useful for product development since the control of extensional viscosity can improve technological applications, and the introduced model systems may therefore be used for systematic, goal-oriented investigations of the relevance of elongational flow properties in the technological processes mentioned above.

High-frequency shear viscosity and ionic mobility of solutions of polyethylene glycol in ionic liquids

The frequency-dependent complex shear viscosity of the solutions of polyethylene glycol (PEG) in various ionic liquids is measured in the frequency range of 5–205 MHz, and the ionic mobility of the corresponding solutions was also determined. The plateau viscosity in the MHz regime increases on the addition of PEG, and the relaxation in the 100 MHz regime is retarded simultaneously. The amount of the increase in the plateau viscosity correlates with that in the relaxation time, suggesting that the retardation of the relaxation is a reason for the increase in the plateau viscosity. Although the increase in the plateau viscosity is far smaller than that in the zero-frequency viscosity, these two values are correlated with each other, which can be explained as the consequence of the strength of the same kind of the solute-solvent attractive interaction. The decrease in the molar ionic conductivity also correlates with the increase in the plateau viscosity, suggesting that the plateau viscosity can be regarded as the local viscosity of ionic liquids related to the ion conduction. Based on the correlation with the Kamlet-Taft α parameter, the hydrogen bond between the ionic liquid and the oxygen atoms of PEG is suggested to be a possible origin of the increase in the plateau viscosity.

Physicochemical Properties of LiFSI Solutions II: LiFSI with Water, MTBE, and Anisole

This article is the second in a series in which the thermodynamic properties of solutions of lithium bis(fluorosulfonylimide (LiFSI) are investigated. The solvents that are considered here are methyl tert-butyl ether (MTBE) and water (H2O), which are good solvents for LiFSI, and anisole, which is an antisolvent for LiFSI. The solubility of LiFSI in MTBE, as well as in the binary solvent mixture MTBE-anisole, was measured at temperatures of between 283 and 303 K and concentrations of LiFSI of up to 0.47 mol mol–1. Furthermore, the liquid–liquid equilibrium of the system LiFSI-MTBE-H2O was studied at 293 K and ambient pressure. Moreover, the density and shear viscosity of solutions of LiFSI in MTBE were studied at temperatures between 273 and 308 K and concentrations of LiFSI up to 0.4 mol mol–1.

Viscosity-temperature dependence and activation energy of cellulose solutions

The dependence of cellulose solution shear viscosity as a function of temperature and measurements of solution activation energy are reviewed based on results obtained in our laboratory and elsewhere. Cellulose is not easy to solubilize. Solutions are often forming aggregates and are not stable in time and with temperature variations. This can be highlighted by the calculation of the activation energy of the shear viscosity, a parameter which is very sensitive to any change in the state of the solution during the shear experiments. Changes in the organization of the solution like gelation or cellulose or solvent degradation are phenomena which are strongly influencing the values of activation energy. Cellulose solutions in three classes of solvent, ionic liquids, N-methylmorpholine-N-oxide-monohydrate and (7-9)% NaOH-water with and without additives, were analyzed. Cellulose was of various molecular weights. The plot of the reduced activation energy versus cellulose concentration shows that most points fall within a narrow range of values, with a low downward curved shape, not in agreement of the predictions developed for flexible chains in semi-dilute regime.

Effect of association on rheological behaviors in the non-aqueous solutions of semi-flexible cellulose derivatives

The rheology of cellulose derivatives dissolved in highly viscous solvent was studied. Results demonstrated that a concentration-dependent transition occurred at ca. 10 vol% for ethyl cellulose, and at ca. 2.0 vol% for hydroxypropyl cellulose. Below the transition point, steady shear viscosity of solutions showed weak concentration dependency. The exponent of the power law model was about 3.7. Above the transition, the viscosity was strongly dependent on the concentration. Further studies showed that such a transition strongly depended on the association between chains. Above the transition point, their long-time dynamics were dominated by the hydrogen bonds acting as the transient cross-links between chains. While below this point, long-time dynamics were governed by the percolation statistics. As a result, their viscosities indicated different concentration dependence relationships. Our studies showed that the entanglement and association behaviors were different, for the flexible and semi-flexible chains.

Effect of ultrasound on the aqueous viscosity of several water-soluble polymers

The effect of ultrasound (US) on the shear viscosity of water-soluble polymers, polyvinyl alcohol, polyethylene glycol and polyacrylic acid, was studied in aqueous solutions with US exposure of 23, 43, 96 and 141 kHz for an 8.5–9 W US. The US exposure significantly decreased the shear viscosity of the solutions in this order: 43>23>96>141 kHz. When US exposure was stopped, the shear viscosities of the aqueous polymer solutions reverted to their original values. US stimulation during the decrease in viscosity was supported by the ultrasonic power transmitted through the aqueous polymer solution. In addition, Fourier-transform infrared spectra obtained during US exposure showed that hydrogen bonds in the aqueous polymer solution could be broken, especially at 43 kHz. We concluded that US exposure influenced hydrogen-bond interactions between the OH groups of the polymer and water molecules in the aqueous medium. This finding was supported by US absorption of the aqueous polymer solution in the transmittance model, which shows the US absorptivity, ɛUS, for each polymer system. The effect of US on the shear viscosity of water-soluble polymer solutions was studied. The 43 kHz US significantly decreased the shear viscosity of the solutions. FT-IR spectra obtained during the US exposure showed that hydrogen bonds in the aqueous polymer solution could be broken. US absorption model was proposed to explain US absorption and the breakage in the hydrogen bonds. US effect influenced the condition of water solvation to the water-soluble polymers.

Viscosity and diffusion: crowding and salt effects in protein solutions

We report on a joint experimental-theoretical study of collective diffusion in, and static shear viscosity of solutions of bovine serum albumin (BSA) proteins, focusing on the dependence on protein and salt concentration. Data obtained from dynamic light scattering and rheometric measurements are compared to theoretical calculations based on an analytically treatable spheroid model of BSA with isotropic screened Coulomb plus hard-sphere interactions. The only input to the dynamics calculations is the static structure factor obtained from a consistent theoretical fit to a concentration series of small-angle X-ray scattering (SAXS) data. This fit is based on an integral equation scheme that combines high accuracy with low computational cost. All experimentally probed dynamic and static properties are reproduced theoretically with an at least semi-quantitative accuracy. For lower protein concentration and low salinity, both theory and experiment show a maximum in the reduced viscosity, caused by the electrostatic repulsion of proteins. The validity range of a generalized Stokes-Einstein (GSE) relation connecting viscosity, collective diffusion coefficient, and osmotic compressibility, proposed by Kholodenko and Douglas [PRE 51, 1081 (1995)] is examined. Significant violation of the GSE relation is found, both in experimental data and in theoretical models, in semi-dilute systems at physiological salinity, and under low-salt conditions for arbitrary protein concentrations.

Ultrasound stimuli on viscometric change of aqueous copolymers having acrylic acid and N-isopropyl acrylamide for thermo-sensitive segments

Ultrasound (US) was used to change the shear viscosity of an aqueous solution of copolymers having acrylic acid (AA) and N-isopropylacrylamide (NIPAM) segments. The US effect on the shear viscosity of the copolymers containing 10, 50 and 90 mol% of the NIPAM group having thermo-responsible property was examined when the US was exposed to the aqueous solution at different temperatures. The shear viscosity of the solution had a significant change at about 30–35 °C when the viscosity was measured in the range of 0–60 °C. While, the viscosity decreased with the increase of the temperature, the US operated at 28, 45 and 100 kHz also induced significant reduction of the shear viscosity. Evidence of the US effect on the shear viscosity reduction was observed by measurement of FT-IR spectra of the copolymer solution when the US was exposed. It was noted that considerable change of the spectra at the 28 kHz US was observed relative to that of the 45 and 100 kHz US. The tendency of the change in the shear viscosity and IR spectra was almost similar. Furthermore, the shear viscosity and IR spectra changed gradually to recover its original value as the US was stopped. This was due to the breaking and reformation of the hydrogen bonding between NIPAM and AA segments when the US was exposed and stopped, respectively.

Structure–function relationships for corn bran arabinoxylans

Fiber incorporation in foods has, to date, been approached largely in an empirical manner, with emphasis on modifying process conditions and formulation and fiber characteristics to obtain an acceptable product. There is a lack of fundamental studies relating fiber functionality during processing with its structural characteristics. In this study, we have investigated the rheological properties; such as solution shear viscosity and extensional viscosity, and some structural features of four corn bran arabinoxylan preparations. The solution shear viscosity of the fibers was influenced by the molecular weight and size of the molecules. The extensional viscosity of doughs containing the fibers was affected by the degree of branching, and differences in extensional viscosity have been explained on the basis of differences in branching as observed using multi-angle laser light scattering. Clear relationships between solution viscosity and molecular weight, and extensional viscosity and degree of branching were established for the fibers. Fundamental studies such as this one will aid in building a strong science-based approach to fiber incorporation in food by improving understanding of how structure of fiber molecules affects their functionality in food systems and how the structure can be modified to improve functionality.

Transport and diffusion processes in trehalose–water solutions: Theory and experiments

In the present work the attention is focused on the nature of the diffusion and transport processes in trehalose–water solutions investigated by using both theoretical and experimental approaches. For this purpose hydrodynamic methods and cell approach for determining the shear viscosity of solution are applied. The dependence of the average and effective shear viscosities, as well as the diffusion and self-diffusion coefficients, on the volume fraction of admixture molecules are investigated. Finally, the role of hydration effects is discussed.

Neutral polymer slow mode and its rheological correlate

AbstractQuasi‐elastic light scattering spectroscopy intensity–intensity autocorrelation functions [S(k,t)] and static light scattering intensities of 1 MDa hydroxypropylcellulose in aqueous solutions were measured. With increasing polymer concentration, over a narrow concentration range, S(k,t) gained a slow relaxation. The transition concentration for the appearance of the slow mode (ct) was also the transition concentration for the solution‐like/melt‐like rheological transition (c+) at which the solution shear viscosity [ηp(c)] passed over from a stretched exponential to a power‐law concentration dependence. To a good approximation, we found ct[η] ≈ c+[η] ≈ 4, [η] being the intrinsic viscosity. The appearance of the slow mode did not change the light scattering intensity (I): from a concentration lower than ct to a concentration greater than ct, I/c fell uniformly with increasing concentration. The slow mode thus did not arise from the formation of compact aggregates of polymer chains. If the polymer slow mode arose from long‐lived structures that were not concentration fluctuations, the structures involved much of the dissolved polymer. At 25 °C, the mean relaxation rate of the slow mode approximately matched the relaxation rate for the diffusion of 0.2‐μm‐diameter optical probes observed with the same scattering vector. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 323–333, 2005

Free convection and surface kinetics in crystal growth from solution

As a crystal grows from solution, there is ordinarily a boundary layer depleted in solute, which forms at the crystal–solution interface. When the normal to the growing crystal surface is oriented in any direction other than parallel to gravity, the boundary layer is set into motion by the force of buoyancy. Using a similarity transformation and a boundary layer approximation, we have solved the Navier–Stokes equation and the equation for convective diffusion for a crystal in the form of a flat plate growing with normal perpendicular to gravity. Parameters in the theory include solute concentration, c0, and diffusion coefficient, D; solution shear viscosity, μ, mass density, ρ, and logarithmic density derivative with respect to concentration, α; crystal solubility, cs, height, h, and linear growth rate, kG; the specific rate, k (sticking coefficient), of the reaction which transfers molecules from the solution to the crystal and the kinetic order, n, of this reaction; and the acceleration due to gravity, g. We find these parameters to be related by the equation log[1−Sh/a (Sc) 1/4(Gr) 1/4φ s1/4]=(1/n) log[a(5/4) n(D/hkc 0n−1)(Sc) 1/4(Gr) 1/4]+[(5/4−n)/n]log φs, where a=0.9, Sh=kGh/D, Sc=μ/ρD, Gr=gαh3ρ2/4μ2, and φs=(c0−cs)/c0. Given a knowledge of the solution physical properties, if Sh is measured as a function of φs and the results plotted in accord with the above equation, both n and k can be determined.

Effects of dynamic spatial disorder on ionic transport properties in polymer electrolytes based on poly(propylene glycol)(4000)

The equivalent ionic dc conductivity (Λ) generally exhibits a dramatic concentration dependence in electrolytic systems based on the host polymer poly(propylene glycol) of molecular weight 4000 (PPG4000). In particular, Λ typically increases rapidly with increasing salt concentration passing through a temperature dependent maximum at high concentration. Prompted by recent reports on a microscopic phase separation occurring in these electrolytes, we here report vibrational spectroscopic, ionic conductivity, and restricted diffusion data for ion-conductors based on PPG4000 complexed with the lithium salts LiCF3SO3 and LiN(CF3SO2)2, in an attempt to resolve seemingly contradictory results concerning ionic transport phenomena in these complexes. We find that the differential salt diffusion coefficient Ds, describing bulk salt motion over long time scales, exhibits a qualitatively similar concentration dependence as Λ. This is contrary to recent F19 pfg-NMR diffusion results for the PPG4000-LiCF3SO3 system which show that the anionic diffusion coefficient decreases monotonically with increasing salt concentration and is inversely proportional to solution shear viscosity. As determined from analyses of characteristic vibrational modes of the [CF3SO3]− and [(CF3SO2)2N]− anions, respectively, the spectroscopic data show very small changes in the distribution of anionic species over the range of electrolyte compositions corresponding to a sharp enhancement of Λ. The results are interpreted in terms of slowly fluctuating salt-rich electrolyte microdomains in equilibrium with salt-depleted polymer regions.

Living poly(α-methylstyrene) near the polymerization line: Shear viscosity in tetrahydrofuran

We have measured the shear viscosity of solutions of living poly(α-methylstyrene) in tetrahydrofuran, initiated by sodium naphthalide, as a function of temperature, mole fraction of initial monomer in solvent, and concentration of the initiator species. For these “living” polymers, the average molecular weight and the volume fraction of polymer change when the temperature changes. We plot the logarithm of the viscosity as a function of the logarithm of the degree of polymerization, which we obtain from the dilute n → 0 vector magnet model, as applied to such living polymers by Wheeler and Pfeuty[Phys. Rev. Lett. 71 1653 (1993)]. Our study has produced more questions than answers. We see reversibility on heating and cooling over short times and small temperature steps, but we see hysteresis over longer ranges of time and temperature. Our data suggest a distinct difference between the average molecular weight at which the living polymers begin to overlap, and the average molecular weight at which the living polymers are entangled; the ratio of the two molecular weights seems to be about twice the ratio observed in terminated, nearly monodisperse polymers at constant concentration. Better understanding of these systems will require measurements over a larger range of temperature in order to observe a larger range of average molecular weight.

Relationship between solution shear viscosity and density at the saturation point

Properties of supersaturated solutions such as the density, viscosity, and solute diffusivity are dependent on the solute concentration. The diffusion-boundary-layer equations are derived and solved for the natural convection case with the viscosity and density dependent on the solute concentration. The solution obtained demonstrates that, at the vicinity of the saturation concentration cs, there is a non-trivial dependence of the solution viscosity η on its density ρ:η(cs) = η(ρs)αρ12s, where ρs = ρ(cs). This result has been verified in experiments with aqueous solutions of inorganic and organic salts.

Effective viscosities in thin ionic micellar liquid films

AbstractThin liquid films stabilized by surfactants above the critical micelle concentration exhibit stratification or stepwise dynamic thinning. A continuum hydrodynamic model is outlined for stepwise film thinning that incorporates equilibrium micellar structuring through self‐consistent oscillatory disjoining pressures and effective viscosities. Effective viscosities as functions of thickness are evaluated with an extension of the local average density model, considering dilute colloidal suspension shear viscosities and solvent effects. To establish local shear viscosities, structured DFT micellar profiles, coarse‐grained densities, and disjoining pressure are used. Ionic micelles and other colloidal systems with repulsive interactions show structured effective viscosities that are generally less than the corresponding homogeneous solution shear viscosity, bounded by the pure solvent viscosity and that of the bulk micellar solution. For 0.1 and 0.2‐M sodium dodecylsulfate micellar solutions, the effective viscosities are less than 5 and 10%, respectively, below the homogeneous fluid viscosity, except at small thicknesses, indicating that the micellar film thins faster than a pure water film of the same thickness.Calculated thinning curves closely resemble experimental observations in the stepwise thinning behavior, displaying decreasing slopes and increased step durations at later times. Despite the micellar structuring within the film, the ionic micelles do not contribute appreciably to the viscous resistance of the thinning film. Rather, Reynolds' film thinning is obeyed, with the equilibrium oscillatory disjoining pressures driving the stepwise dynamics. The shear viscosity of the ionic micellar film is well approximated by that of the bulk solution.