Effect of supersaturation on the viscosity of solutions

Ohne Zusammenfassung     

Effect of solutes on the viscosity of supercritical solutions

This study shows that solutes can impart significant structure to supercritical solutions, resulting in unexpectedly high solution viscosity at pressures close to the critical value. The viscosity passes through a minimum as the pressure is increased, and this is accounted for by a solvation of the solutes leading to a decrease in solute-solute interactions. At high pressure, the solution viscosity is similar to that of the pure solvent as solvent-solvent interactions dominate. The increase in relative viscosity is modeled using a modified Dole-Jones equation, and it is shown that the change in relative viscosity is related to the volume fraction occupied by the solute. A general model is presented for simple solutes whereby the viscosity of a supercritical solution can be calculated from the molecular volume of the solute and the viscosity of the pure fluid. The higher than expected viscosity observed at low pressures is used to explain the variation of reaction rate constant with pressure.     

Dynamic viscosity of polymer solutions

The dynamic viscosity of different long chain polymers in Aroclor permits an easy extrapolation to zero concentration only in the limiting cases of Newtonian, i. e., constant viscosity at low and high frequency, respectively. The first intrinsic viscosity []₀ is independent of any concept of the internal viscosity. In the case of polystyrene it is proportional toM ^0,65 which shows that Aroclor is a good solvent for this polymer. The second intrinsic viscosity [] turns out to be independent ofM. It is best reproduced by the model where the internal viscosity resists only the deformation rate of the single link. The displacement rate of more distant beads is affected by the internal viscosity only in the case that it involves the deformation rate of the links. The angles between successive links may be changed at any rate.In the intermediate range of frequencies the extrapolation of the observed dynamic viscosity to the intrinsic value was never made. The experimental data are so much affected by the concentration, i. e., by the interaction of adjacent molecules, that no conclusion may be derived from them about the properties of the isolated macromolecule. A master curve independent ofM andc is obtained by plotting of (G- )K/c over ₁. This means that the deformation mode in the whole molecular weight and concentration range investigated is the same. But this mode is different from that of the independent macromolecule in infinite dilution. The master curve may be described by the excess intrinsic viscosity of the Rouse model with the internal viscosity acting either between the beads on the same link only or between any distinct beads. As a consequence of the concentration effects, however, no conclusions about the properties of the single molecule can be derived from such an agreement.Dedicated to Prof. Dr. F. H. Müller.     

Studies on the viscosity behavior of polymer solutions at low concentrations

Viscosity measurements had been made on poly(vinyl alcohol) (PVA), poly(N-vinyl-2-pyrrolidone) (PVP) and poly(ethylene oxide) (PEO) solutions down to low concentrations. It was found that defined as the flow time of the pure solvent in ideal conditions and obtained practically by extrapolating the flow time of polymer solution t to zero concentration, was not equal to the flow time of the pure solvent t₀ measured. The reduced viscosity η_sp/C determined by (t/t₀-1)/C exhibited either a drastic increase or a significant decrease with dilution, depending upon the polymer solution investigated. On the other hand, η_sp/C determined by was proportional to C even at low concentrations. The anomalous viscosity behavior of neutral polymer solutions at low concentrations, therefore, was due to the incorrect method by which η_sp/C was determined. The detailed experiments indicated that the effective diameter of the viscometer capillary, the surface property of the capillary wall and the additional pressure corresponding to the measurement of t and t₀ for PVA, PVP and PEO solutions were not the same. Taking into account the contact anger and the surface tension of the liquid, together with the geometric parameter of the viscometer, the influence of the additional pressure upon the flow time measurement could be studied quantitatively. The calculation was in a good agreement with the experimental result. According to the method presented in this paper, the thickness of the adsorbed polymer layers on the capillary walls could be determined. It was noted that the thickness of the adsorbed polymer layers on the capillary walls was closely related to the solvent in which the polymer molecules were dissolved. The polymer molecular weight, however, had little or no effect on the thickness of the adsorbed polymer layers on the walls of the viscometer capillary.     

Investigation of the viscosity of solutions of graft copolymers

Living polystyrene was grafted on fractions of poly(methyl methacrylate) by an anionic grafting reaction. Unreacted polystyrene was separated by fractional precipitation. The composition of copolymer, i.e., the molecular weight of main chains and side chains, was determined. The influence of molecular weight and structure of graft copolymers on the intrinsic viscosity of solutions was examined. This may be expressed in the form [η] = KM^agⁿ. The dependence between a and n in this equation was established.     

Molecular mechanism of the viscosity of aqueous glucose solutions

Experimental relations are obtained for the viscosity of aqueous glucose solutions in the temperature range of 10–80°C and concentration range 0.01–2.5%. It is found that the concentration dependence of fluidity is linear when the concentration is higher than a certain value and varies at different temperatures. The existence of such a dependence indicates that the mobilities of solvent and solute molecules are independent of the concentration of solutions. This assumption is used to construct a theoretical model, in which the structure of an aqueous glucose solution is presented as a combination of two weakly interacting networks formed by hydrogen bonds between water molecules and between glucose molecules. Theoretical relations are obtained using this model of network solution structure for the concentration and temperature dependence of solution viscosity. Experimental data are used to calculate the activation energies for water (U _w = 3.0 × 10^–20 J) and glucose molecules (U _g = 2.8 × 10^–20 J). It is shown that the viscosity of a solution in such a network structure is governed by the Brownian motion of solitons along the chains of hydrogen bonds. The weak interaction between networks results in the contributions to solution fluidity made by the motion of solitons in both of them being almost independent.     

Relative viscosity and the solvation number in solutions

It has been shown that part of the free volume of a solvent attaching to the solvation shell must be excluded from the total free volume in the Bachinskii equation. This determines the increase of viscosities of solutions with positive solvation. An equation has been obtained for the inverse relative viscosity of solutions ₀/ = 1-zN₂/(1-N₂), where no and are the dynamic viscosities respectively of the solvent and the solution; z is the solvation number, N₂ is the mole fraction of dissolved material. A method is proposed for determining the solvation number (hydration) from solution viscosity data. Solvation numbers obtained by this method are in good agreement with values of z obtained from the literature and determined by other methods.Translated from Teoreticheskaya i Experimental'naya Khimiya, Vol. 21, No. 5, pp. 627–631, September–October, 1985.The author wish to express their gratitude to professors Yu. Ya. Fialkov and M. A. kvadrigin for fruitful discussions of the result of the current work.     

Intrinsic viscosity of polyelectrolytes in salt solutions

The dependence of the intrinsic viscosity of polyelectrolytes on the concentration of added salt is given satisfactorily by a formula obtained recently. A new viscosity—molecular weight relation gives satisfactory agreement with experiments.     

Temperature dependence of the non-Newtonian viscosity of elongated micellar solutions

We report in this work new results of the study on the non-Newtonian viscosity of aqueous micellar solutions of cetyltrimethylammonium bromide (CTAB) in the presence of potassium bromide (KBr), in the concentration range where the elongated micelles overlap. The experiments have been performed as a function of the surfactant concentration, temperature and shear rate by use of a Couette-viscosimeter.In the non-Newtonian range, at relatively low surfactant concentration (0.25 M/l), our results show that the flow curves obtained at different temperatures converge to a single liner curve with a characteristic slope varying with the surfactant concentration. These same data can be superposed on a master curve when appropriate reduced variables are used. The shape of the flow curves obtained at different temperatures for a sufficiently high surfactant concentration is similar to that obtained for monodisperse polymer solutions at different molecular weights. The slope obtained of about –1 is also predicted by Graessley's model in the theory of microviscoelasticity based on the concept of entanglement for polymer solutions. However, at surfactant concentration higher than 0.25 M/l our results show an unusual behavior. Above some critical shear rate it is possible to obtain an increase of the apparent viscosity with temperature. One possible explanation of this effect can be found in the increase of the entanglement with concentration coupled with the temperature and direct now effects on scission and recombination rate of the micelles.     

Effect of metal ions on the viscosity of polyacrylamide solution and the mechanism of viscosity degradation

聚丙烯酰胺( HPAM)是油田常用的驱油聚合物,用油田污水配制HPAM溶液易导致其黏度明显降低,影响驱油效果.依据埕东油田污水实测的各种金属阳离子含量来配制HPAM溶液,测得各金属阳离子对其黏度影响由大到小的顺序为:Na+ ＞Fe2+ ＞Ca2+ ＞K+＞ Mg2+;通过红外光谱和扫描电镜分析金属阳离子导致HPAM溶液降黏的机理,Na+、K+、Ca2+、Mg2+主要是通过与HPAM链上的羧酸根阴离子静电引力相互作用,降低HPAM分子表面原有的电荷密度,造成分子链卷曲,同时减弱了极性基团的溶剂化能力,释放大量的“束缚水”,从而使黏度显著降低;Fe2+离子主要是与水中溶解氧共同作用,引发自由基反应,导致HPAM骨架水解断裂,致使黏度显著降低.     

金属阳离子对聚丙烯酰胺溶液黏度的影响及其降黏机理研究

聚丙烯酰胺(HPAM)是油田常用的驱油聚合物,用油田污水配制HPAM溶液易导致其黏度明显降低,影响驱油效果。依据埕东油田污水实测的各种金属阳离子含量来配制HPAM溶液,测得各金属阳离子对其黏度影响由大到小的顺序为:Na⁺>Fe²⁺>Ca²⁺>K⁺>Mg²⁺;通过红外光谱和扫描电镜分析金属阳离子导致HPAM溶液降黏的机理,Na⁺、K⁺、Ca²⁺、Mg²⁺主要是通过与HPAM链上的羧酸根阴离子静电引力相互作用,降低HPAM分子表面原有的电荷密度,造成分子链卷曲,同时减弱了极性基团的溶剂化能力,释放大量的"束缚水",从而使黏度显著降低;Fe²⁺离子主要是与水中溶解氧共同作用,引发自由基反应,导致HPAM骨架水解断裂,致使黏度显著降低。     

The viscosity of aqueous electrolyte solutions and the TTG model

An equation covering the dynamic viscosity from zero to high concentrations has been derived on the basis of the TTG model. The equation is compatible with the Eyring andNMR theories and has a similar form to the Othmer-rule equation. A component of the limiting viscosity slope is shown to be proportional to the Falkenhagen slope. The TTG equation was tested for 20 electrolytes of diverse charge type and found to fit the data within the experimental errors. The equation is simply extended to cover pressure, temperature, and component changes. The viscosities of three multicomponent systems are predicted to within the experimental errors. The derived parameters of the equation were found to be simply related to the TTG volume of the solute.     

Self-consistent mode-coupling theory for the viscosity of rodlike polyelectrolyte solutions

A self-consistent mode-coupling theory is presented for the viscosity of solutions of charged rodlike polymers. The static structure factor used in the theory is obtained from polymer integral equation theory; the Debye-Huckel approximation is inadequate even at low concentrations. The theory predicts a nonmonotonic dependence of the reduced excess viscosity eta(R) on concentration from the behavior of the static structure factor in polyelectrolyte solutions. The theory predicts that the peak in eta(R) occurs at concentrations slightly lower than the overlap threshold concentration, c*. The peak height increases dramatically with increasing molecular weight and decreases with increased concentrations of added salt. The position of the peak, as a function of concentration divided by c*, is independent of salt concentration or molecular weight. The predictions can be tested experimentally.     

Time dependence of viscosity of dilute polyisobutylene solutions

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

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

     

Effect of surface viscosity on the vibration of microcantilevers

Using the theory of beam bending and the theory of surface rheology, the equation describing the effect of a surface viscous film on the vibration of an elastic microcantilever is derived. A generalized solution for the vibration of the microcantilever is obtained, which depends on the boundary conditions and the surface viscosity. There is a phase lag between the externally harmonic excitation and the microcantilever response due to the energy loss from surface flow. For small energy dissipation with negligible surface energy, the maximum energy loss occurs approximately at the natural frequencies of the microcantilever.