Standard Rheometer Research Articles

High-frequency ultrasonic imaging: A spatio-temporal approach of rheology

We describe how high-frequency ultrasound can be used to measure and follow velocity profiles in complex fluids sheared in the Couette geometry with a 0.5–1 mm gap. The technique provides a spatial resolution of 40 μ m and velocity profiles can be recorded every second typically. Such ultrasonic velocimetry is coupled to a standard rheometer. The resulting “ultrasonic rheo-velocimeter” is tested on various complex fluids that display both inhomogeneous velocity profiles and temporal fluctuations close to a shear-induced transition: a lamellar phase, a triblock copolymer, a concentrated emulsion, and an organogel.

Modification of Bending Beam Rheometer Specimen for Low-Temperature Evaluation of Bituminous Crack Sealants

It is difficult to evaluate effectively the low-temperature stiffness of bituminous hot-poured crack sealants with existing test methods. The standard bending beam rheometer (BBR) was found to be inappropriate for testing soft bituminous-based hot-poured crack sealant, even at a temperature of-40°C. To address this issue, the moment of inertia of the tested beam was increased by doubling its thickness (from 6.35 mm to 12.7 mm). For the new beam dimensions, only 4% of the beam center deflection is due to shear, a value deemed acceptable for sealant evaluation and comparison. On this basis, the BBR stiffness of hot-poured sealants was obtained at several discrete temperatures between-10°C and -40°C to assess the repeatability of the method for the evaluation of the low-temperature stiffness of bituminous sealants. Ten different sealants were tested at -40°C; three of these 10 were further tested at –35°C, –30°C, –28°C, –25°C, and –20°C; and the three “hard” sealants were tested at –10°C. A minimum of three replicates were used. The coefficient of variation on the measured stiffness after 60 s of loading was always lower than 18%, with almost 75% of the measurements having a coefficient of variation less than 10%. A pairwise comparison showed that the modified BBR could be used to classify sealant products according to their measured stiffness. As to the effect of temperature, it was found that the stiffness varies exponentially with temperature in the range of –40°C to –20°C. A statistical analysis of the results indicated that the modified BBR method could be used to classify sealants based on low-temperature stiffness.

Part 4: Crack Sealants and LTPP Results: Modification of Bending Beam Rheometer Specimen for Low-Temperature Evaluation of Bituminous Crack Sealants

It is difficult to evaluate effectively the low-temperature stiffness of bituminous hot-poured crack sealants with existing test methods. The standard bending beam rheometer (BBR) was found to be inappropriate for testing soft bituminous-based hot-poured crack sealant, even at a temperature of-40°C. To address this issue, the moment of inertia of the tested beam was increased by doubling its thickness (from 6.35 mm to 12.7 mm). For the new beam dimensions, only 4% of the beam center deflection is due to shear, a value deemed acceptable for sealant evaluation and comparison. On this basis, the BBR stiffness of hot-poured sealants was obtained at several discrete temperatures between-10°C and -40°C to assess the repeatability of the method for the evaluation of the low-temperature stiffness of bituminous sealants. Ten different sealants were tested at -40°C; three of these 10 were further tested at –35°C, –30°C, –28°C, –25°C, and –20°C; and the three “hard” sealants were tested at –10°C. A minimum of three replicates were used. The coefficient of variation on the measured stiffness after 60 s of loading was always lower than 18%, with almost 75% of the measurements having a coefficient of variation less than 10%. A pairwise comparison showed that the modified BBR could be used to classify sealant products according to their measured stiffness. As to the effect of temperature, it was found that the stiffness varies exponentially with temperature in the range of –40°C to –20°C. A statistical analysis of the results indicated that the modified BBR method could be used to classify sealants based on low-temperature stiffness.

Monolithic rheometer plate fabricated using silicon micromachining technology and containing miniature pressure sensors for N1 and N2 measurements

An attachment suitable for any standard torsional rheometer is described; it extends the capability of the rheometer, thereby enabling simultaneous measurement of the first (N1) and second (N2) normal stress differences. The attachment is a monolithic rheometer plate 25 mm in diameter that contains eight miniature capacitive pressure sensors, each with a pressure-sensing area less than or equal to 1 mm2. It is found that when the sensor plate is adapted to an ARES rheometer, highly accurate values of N1 and N2 can be measured at room temperature for a standard elastic polymer solution (SRM-1490 from the National Institute of Standards and Technology). Compared to standard measurement methods for N1, use of novel sensor plates of this type should reduce the axial compliance and allow smaller sample sizes to be studied, since no spring-type normal force transducers are required. In addition, a rheometer adapted with the sensor plate, unlike a conventional rheometer, can be used to measure N1 and N2 with a single sample.

Viscoelastic properties of pig kidney in shear, experimental results and modelling

In this paper, the results from a series of rheological tests of fresh pig kidney have been reported. Using a standard strain-controlled rheometer, the oscillation strain sweep experiment showed a linear viscoelastic strain limit of the order of 0.2% strain. To determine the components of dynamic moduli in terms of frequency, shear oscillation tests were done at strain 0.2% using a stress-controlled rheometer. Shear stress relaxation tests were carried out with a fixed strain of 0.2% and 0.02 s rise time. The model we have developed uses a multi-mode upper convected Maxwell (UCM) model with variable viscosities and time constants, to which we have added a Mooney hyper-elastic response, both multiplied by a damping function. Different forms of damping functions that control the non-linearity of strain-stress profile have been tested. The model was fitted to our experimental data, and matched the entire test data reasonably well with a single set of parameters.

Measurement of Elastic Properties of Kamaboko and Other Food Gels by a New Simplified Rheometer

A simplified rheometer was manufactured to measure the elastic properties of kamaboko and other food gels. Mechanical force applied to the gel through the penetration of a plunger was recorded using a potentiometric recorder. The gel quality of laboratory made surimi products and that of kamaboko and meat products in the market was also measured using this rheometer. The data obtained maintained a strong correlation with those from corresponding folding and sensory tests. A high correlation (p < 0.001) was observed between the textural parameters obtained using the simplified rheometer and a standard rheometer generally used in Japanese laboratories.

Viscosity measurement in a pipe flow using a numeric recursion approach for in-line quality control

The use of a pipe as a sensor for measuring viscosity and shear rate would require a separated flow rate instrument and would result in a more complicated mechanism for in-line quality control. In this study, a method of applying numeric recursion to the pipe pressure drop to directly calculate the viscosity and the shear rate is proposed. This viscosity sensor was verified by using it to measure the viscosity and shear rate for low-density polyethylene. The viscosity and shear rate obtained by this approach differ little from those obtained by using a standard off-line capillary rheometer. Therefore, this viscosity measurement method is applicable for in-line quality control.

A rheological study of shear induced crystallization

The isothermal crystallization of three isotactic polypropylene (iPP) types, with different molar mass (distributions), was studied after a well defined shear treatment of the melt at an elevated temperature and a subsequent quench to the crystallization temperature. For these experiments a standard rheometer of the cone and plate configuration was used. The development of the crystallization was monitored by dynamic oscillatory measurements. Shearing in the melt was shown to enhance subsequent crystallization at lower temperatures. Not only the total shear at constant rate is of importance, but also the chosen combination of rate and shearing time. Moreover, a pronounced influence of molar mass was detected. The exploration of the melting temperatures and times which are necessary for an erasion of the memory effects showed that the effect of shearing could not completely be erased, possibly as a consequence of mechanical degradation.

On the significance of pressure relaxations in capillary or slit flow

It is occasionally proposed by Leblanc (1976) and GOttfert (1994) that information about the viscoelasticity of molten polymers can be obtained by recording the pressure as a function of time when the piston driving a capillary or slit rheometer is suddenly stopped. In the cited reference by G6ttfert (1994), a single exponential is fitted to the pressure decay curve in order to estimate a measure of the melt's relaxation time, while in the other work cited by Leblanc (1976) a "relaxation spectrum" is inferred from the pressure data. The purpose of this note is to demonstrate that the pressure decay depends primarily on the viscosity and compressibility of the melt and that the contribution of melt elasticity is too small to be measured using a standard capillary rheometer. Hatzikiriakos and Dealy (1992, 1994) have modelled the pressure transients in a capillary rheometer, and it will be convenient to build on their analysis. For purposes of the present demonstration, I consider the case of a fluid with constant viscosity, as this makes it possible to obtain an analytical solution. As an initial condition, we consider that the piston speed, Vp, the reservoir pressure, P, and the flow rate, Q, are at steady state. At t = 0, the piston is suddenly stopped, and we wish to calculate P ( t ) and see how it is related to the properties of the fluid. We make the following simplifying assumptions:

A device to measure the dynamic shear properties of small samples

An attachment for a standard torsional rheometer based on the sliding plate geometry is described which can measure the dynamic shear rheological properties of small samples with total volume on the order of 5–25 μl. The overall error is found to be 1.86% in measuring the dynamic viscosity and 4.04% in the storage modulus when compared to data collected with standard geometries for three fluids: a Brookfield oil, a high density polyethylene melt, and a paint base. It is found that there is an optimum gap between the sliding plates and surface tension can influence the results particularly for the lower viscosity Brookfield oil. This attachment is most useful for fluids which can degrade with repeated moulding, as must be done when preparing samples for the standard attachments, and may be used to determine various shear properties of suspensions including: large amplitude true dynamic shear properties, yield stress, and time‐dependent viscosity.