Oscillatory Rheometer Research Articles

Measurements of interfacial shear viscoelasticity with an oscillatory torsional viscometer

The stress-deformation behavior of a non-Newtonian surface subject to an oscillatory shearing flow was theoretically as well as experimentally investigated. The rheological properties of such an interface were interpreted using the complex viscosity surface fluid model. The measurements of surface shear viscoelasticity of an air-liquid surface were performed with the in-house built oscillatory torsional interfacial viscometer. The behavior of the liquid-liquid interface was described based on the exact solution obtained from the analysis of the interfacial rheometer, assuming a non-Newtonian surface and Newtonian bulk phases. The interfacial angular velocity distributions are illustrated as functions of surface viscous and elastic components described by the complex viscosity surface fluid model. An extensive experimental investigation of the surfactant concentration and temperature dependence of the surface viscoelasticity of aqueous gelatin solutions was carried out. The surface rheological behavior encompasses both shear thickening and shear thinning, below and above a characteristic frequency, respectively. The characteristic frequency is independent of temperature, except at 35°C. The surface shear elasticity attains maximum values at a characteristic frequency which is independent of surfactant concentration and temperature, except at 40°C. The temperature dependence of the surface shear viscoelasticity and the origin of the characteristic frequency are explained in terms of the two conformations of gelatin molecules, namely, the α-conformation at 40 and 45°C, and the β-conformation at 35°C. In general, it was found that the temperature and surfactant concentration dependence of the surface shear elasticity was more complex than the corresponding dependence of the surface shear viscosity. Moreover, the experimental results proved the appropriateness of the complex viscosity surface fluid model and the viability of the oscillatory torsional interfacial rheometer.

OSCILLATORY PROBE RHEOMETRY AS A TOOL FOR DETERMINING THE RHEOLOGICAL PROPERTIES OF STARCH‐WATER SYSTEMS 1

An oscillatory probe rheometer was effective at measuring the viscosity of starch pastes and the viscoelastic properties of starch gels. Because low shear strains were applied, the integrity of the gel was not disrupted during the testing. As the starch concentration of the systems increased, the complex modulus (G*) and storage modulus (G′) increased. At 20°C, the strength of the resulting gels, as measured by log G′, was a linear function of starch concentration. Loss tangent values (G″/G′) could be used to determine the approximate temperature at which the sol became a gel. As the starch concentration of the systems increased, the temperature of the sol to gel transformation increased from approximately 35°C (5% starch) to 60°C (10% starch).

On the influence of fluid inertia in oscillatory rheometry

It is known that evaluating oscillatory rheological shear experiments in the usual way may lead to complete misinterpretation of the experimental data, especially for low viscosity fluids in the high frequency range. We used a modern type of oscillatory rheometer with a stiff transducer. When measuring Newtonian liquids artificial, second‐order fluid‐like data for the complex shear modulus were found. In order to explain those findings, it is essential to take into account the influence of fluid inertia. Accordingly a method, based on theoretical considerations, is suggested for the correction of experimental data for slightly elastic fluids in order to obtain the true viscoelastic material functions.

Measurement of blood coagulation by a damped oscillation rheometer

Measurement of blood coagulation by a damped oscillation rheometer

Viscoelasticity of fibrinogen solution and of blood during coagulation studied by a new damped oscillation rheometer.

The behavior of a newly developed damped oscillation type rheometer was analyzed for fibrinogen solution and blood during coagulation. This rheometer consists of a cylindrical tube suspended from a torsion wire, that is filled with liquid to be tested. The logarithmic damping factor (LDF) during coagulation for blood and fibrinogen solution was obtained by this rheometer, which was closely related to the changes of viscosity and/or viscoelasticity of the blood sample. The slight increase of LDF prior to the rapid decrease was observed for blood. The increase of LDF would be reflected in the formation of the aggregation structure of red blood cells (rouleaux network) prior to the formation of fibrin network. The value of LDF for fibrinogen solution sharply increased and then decreased through a maximum value with the progress of coagulation, although the change of LDF was remarkably dependent on the fibrinogen concentration. The initial increase in LDF for fibrinogen solution was considered to be due to the formation of small clots in the solution. The decrease in LDF after attaining a maximum value is ascribed to the formation of fully developed fibrin network. The maximum value of LDF during coagulation for fibrinogen solution is higher than that for blood. The behavior was compared with that for non-biological fluids such as viscosity standard liquids and polyvinyl alcohol solution. From those data, it was concluded that the higher value of LDF than that for Newtonian liquids was due to the formation of aggregation structure or inhomogeneous fine clots in the liquid, which was accompanied with the appearance of the elasticity.

Studies of cyclic and linear poly(dimethylsiloxanes): 23. Low temperature behaviour as studied by dynamic oscillatory shear viscometry and differential scanning calorimetry

Fractions of cyclic and linear poly(dimethylsiloxanes) have been investigated by using a differential scanning calorimeter (d.s.c.) and an oscillatory shear rheometer. Different heating and cooling rates were found to have a significant effect on the crystallization behaviour of the materials. The d.s.c. results are compared with those from an earlier study as well as with data from dynamic oscillatory shear viscometry. Cyclics in the range 24< n n<63 and linears in the range 10< n n<17 (where n n is the number average number of bonds) were found to show no propensity to crystallize, whether heated or cooled at slow or fast rates. By contrast, all the siloxane materials outside these ranges have been shown to crystallize readily.

A Newly Developed Damped Oscillation Type Rheometer

A new type of damped oscillation rheometer was developed for the study of biorheology. The rheometer consists of the cylindrical tube suspended from a torsion wire and filled with test liquid. The cylindrical tube may be made of various materials. The tube is excited in torsional oscillation and the subsequent damped oscillation is observed. The apparatus can sensitively follow the change of fluidity of liquid sample. Changes of logarithmic damping factor for blood and fibrinogen solution during coagulation were measured. The change of logarithmic damping factor for blood during coagulation remarkably depended on tube material, suggesting that the present method is probably available for in vitro evaluation of anticoagulability of artificial materials as well as for analysis of coagulation mechanism of blood.

A Newly Developed Damped Oscillation Type Rheometer

Theoretical basis for a newly developed damped oscillation rheometer is presented for a Newtonian fluid. This rheometer essentially consists of a cylindrical tube suspended by a torsion wire and filled with fluid to be tested. The damped oscillation of the cylinder is observed. Based on some assumptions, the equations of motion for a Newtonian fluid in the tube are solved. The numerical solution and some approximate solutions valid for certain ranges of parameters are obtained. From these solutions the logarithmic damping factor and the period of oscillation are obtained as functions of fluid viscosity.

Application of nonlinear viscoelastic analysis by the oscillation method to some pharmaceutical ointments in the Japanese pharmacopeia.

Several kinds of ointments in the Japanese pharmacopeia were tested in an oscillation rheometer and the results were analyzed by the nonlinear method proposed by Onogi. The stress (σ) curve obtained by application of sinusoidal strain (γ=γ0sinωt) was approximated by a Fourier series, and the first order function (σ1st) was regarded as the linear part. A nonlinearity parameter Dnl was defined as the difference between observed σ and σ1st. Dnl showed different ω dependency for each ointment, and seemed to be related to the pattern of the rheogram. Ordinal viscoelastic parameters such as storage modulus (G'), loss modulus (G"), loss tangent (tan δ), and so on were calculated from the 1st function. The ω dependencies of these parameters were also different for each ointment. The influence of the weight fraction of solid (f8) or liquid component (1-f8) on these parameters was examined for simple ointment and macrogol ointment. A bending point was observed on the log G' vs. f8 plot, which might correspond to the occurrence of stiff bridge structures in the vehicles. Tan δ of the simple ointment was found to increase, in spite of the increase of solid component. This was presumed to be due to a greater increase of G" than of G'. This example shows that the increase of fs does not always result in a relative increase of rheological elasticity. Continuous shear measurement was performed with a Ferranti-Shirley viscometer and several parameters were compared with those obtained by the oscillation method. The correlation seemed to be closer when the shear rate was smaller.

Colloid Chemical Studies of Starching Materials. V. Rheological Properties of Concentrated Polyvinyl Alcohol Solutions

Abstract The dynamic viscosity, dynamic rigidity and steady-flow viscosity at 30°C have been measured for 11∼12% solutions of four specimens of polyvinyl alcohol, GH-17, GH-23, NH-17 and HN-26, 20, 60 and 110 hr. after the preparation of the solutions. In the dynamic measurement by a top-drive coaxial oscillation rheometer, the relations of η and G vs. ω did not depend on time and have all been explained by Rouse’s theory except for NH-26, the latter showing time and ω dependencies of the structure. In the steady-flow measurement by a coaxial rotation viscometer, the viscosity of all the polymers showed both time and velocity gradient dependencies.

G-Actin: Preparation by gel filtration and evidence for a double stranded structure

This study investigates possible sources for the variance of more than two orders of magnitude in the published values for the shear moduli of purified actin filaments. Two types of forced oscillatory rheometers used in some of our previous work agree within a factor of three for identical samples. Polymers assembled in EGTA and Mg2+ from fresh, gel-filtered ATP-actin at 1 mg/ml typically have an elastic storage modulus (G′) of ∼1 Pa at a deformation frequency of 0.1–1 Hz. G′ is slightly higher when actin is polymerized in KCl with Ca2+ and Mg2+. Gel filtration removes minor contaminants from actin but has little effect on G′ for most preparations of actin from acetone powder. Storage of actin monomers without frequent changes of buffer containing fresh ATP and dithiothreitol can result in changes that increase the G′ of filaments by more than a factor of 10. Frozen storage can preserve the properties of monomeric actin, but care is necessary to prevent protein denaturation or aggregation due to freezing or thawing.

Visco-elastic Behaviors of Aluminum Soap-Hydrocarbon Systems. I. Aluminum Stearate in Nujol

Abstract Dynamic visco-elastic behaviors of the aluminum stearate nujol system were studied, using a concentric cylinder type forced oscillation rheometer. The system behaves always as a typical visco-elastic body in a wide range of concentrations and temperatures, and manifests conspicuous amplitude and frequency dependence, which indicates non-linear visco-elastic properties. Wedge type relaxation spectra of the system were obtained, and it was found that the system is thermo-rheologically simple in a confined region of temperatures. The time effect of the specimen and temperature dependence of dynamic properties were examined, and the rheological structures in the system under various conditions were discussed.

Visco-elastic Behaviors of Aluminum Soap-Hydrocarbon Systems. II. Aluminum Soaps in Nujol

Abstract Dynamic visco-elastic behaviors of aluminum soaps from various fatty acids and aluminum stearates of different compositions in nujol were studied, using a forced oscillation rheometer. The systems behave always as typical visco-elastic bodies in a wide range of concentrations and temperatures. Aluminum palmitate, myristate, and laurate show properties similar to stearate, whereas caprate and caprylate show less effects on rheological properties. Optimum composition of aluminum stearate as thickener was obtained. Rheological structures in the systems were discussed and comparison of the results by static and dynamic measurements was made.