Multiple-Use, High-Performance Rotational Viscometers for Research and Quality Control

Simple viscosity measurements can be a daunting task for many companies. Most measurements are performed using a rotational rheometer to determine the flow characteristics of processed materials and/or flowing systems. Rotational rheometers can be quite expensive and complicated to use, often requiring an operator who has an advanced degree to accurately set up test methods and run the instrument. Achieving these requirements can push the cost of acquiring simple viscometric data out of the reach of many users and applications. The BLACK PEARL Viscometer (Figure 1) (ATS RheoSystems, Bordentown, NJ) was developed to address these issues. The instrument is a cost-effective, simple-to-operate, multiple-use rotational viscometer that provides data similar to a more expensive rotational rheometer at a fraction of the cost. It is capable of performing routine, QC-type rheological tests as well as complete rheological analysis of materials and products. The BLACK PEARL Viscometer allows quick, single-point viscosity checks, along with complete flow profile determinations and yield stress measurements. This is done without complicated test method setup and extensive laboratory facilities such as compressed air and/or water. The viscometer is fully self-contained and is provided with a full suite of DIN standard measuring systems including cup and bob, parallel plate, and cone and plate.

Figure 1 - BLACK PEARL Viscometer.

Viscometer types and applications

Applications of the BLACK PEARL Viscometer include the mixing, stirring, and pumping behaviors of coatings, emulsions, and dispersions. Conventional flow and viscosity profile experiments are another important function. The design incorporates a built-in Peltier temperature control system that permits isothermal, step, and/or ramp temperature profiles in the range –10 to 120 °C. The DIN standard sample measuring systems of cone and plate, parallel plate, and bob and cup, coupled with a wide shear rate (angular velocity 0.01–200 rad/sec), torque (0.005–20 mNm), and temperature range provide a measurable viscosity range from 1 to 1E08 cP. Additional measuring systems allow for a wider range of product investigation and experimentation. These include bladed “vane” tools and narrow gap couette systems. The narrow gap couette system utilizes a smaller annular gap (1.25 mm for the DIN standard vs 0.5 mm for the narrow gap system) to optimize testing of low-viscosity samples.

Figure 2 - Fungilab Viscolead Pro Series Viscometer.

In addition to the BLACK PEARL Viscometer, the Fungilab Viscometer Series (ATS RheoSystems) (Figure 2) are an economical, efficient, and simple-to-use range of rotational viscometers applicable for many types of investigation and experimentation. They are available from easy-to-use, single-point viscometry tests to multistep and linear ramping shear rate tests. Several different models are designed to fit the budget and testing requirements for any application. Materials like biochemicals, petrochemicals, surfactants, molten polymers, polymer solutions, pharmaceuticals, foods, cosmetics, paints, coatings, inks, asphalt, adhesives, and sealants can be effectively tested using the Black Pearl Viscometer and Fungilab Viscometer Series.

Multiple-use BLACK PEARL Viscometer

A nominal 1000-cP silicone oil was evaluated at 25 °C using each of the three standard measuring systems—1) 30-mm diam parallel plate, 2) 30-mm/5° cone and plate, and 3) 25-mm-diam bob and cup. The 5° cone and plate has a 0.150- mm truncation, and the parallel plate experiment was performed with a 0.5-mm gap. Experiments of high to low shear rate were performed using the Windows-based MICRA user interface software.


Figure 3 - Comparison of viscosity measurement for 1000-cP oil at 25 °C using cone and plate, 30 mm; parallel plate, 30 mm; and bob and cup, 25 mm.

Figure 3 shows a plot of the resulting steady-state viscosity (Pa s) versus torque (mNm); to normalize the data for the experiments, torque is plotted on the abscissa rather than the shear rate (s–1). The three measuring systems demonstrate similar data. The instrument is able to handle a greater range of materials and sample sizes/amounts as a result of the various sample geometries. Low-viscosity materials and/or low shear rate measurements benefit from use of the bob and cup system because it provides more sample contact surface area, and therefore more measured torque signal.


Figure 4 - Comparison of different viscosity standards run consecutively on the BLACK PEARL Viscometer. All tests were performed with a DIN cup and bob geometry at 25 °C.

The BLACK PEARL Viscometer allows the user to test a wide range of samples using the same measuring system. For example, the 25-mm bob and cup geometry was used to test multiple viscosity standard samples—nominal 1000, 500, 100, and 10 cP (see Figure 4). The results for each sample are within acceptable accuracy levels for the viscometer. The instrument allows for multiple viscosity applications with high precision and accuracy throughout the measurement range.

Measurement of low-viscosity liquids


Figure 5 - Time sweep data on a 5-cP standard oil and distilled water using a narrow gap cup. Note the accuracy and precision of the results using the narrow gap cup.

Some materials require special measurement systems to attain accurate and precise results. For these samples, special measurement systems are utilized for the BLACK PEARL Viscometer. One example is low-viscosity liquids. Low-viscosity samples require a smaller annular gap, cup and bob measuring system to determine accurate results. The viscometer has an optional narrow gap cup that can be used in place of the standard cup for these samples. The narrow gap cup has an annular gap of 0.5 mm, and enables the user to routinely test low-viscosity samples. Figure 5 shows results on a nominal 5-cP oil along with bottled, pure water (~1 cP). The results with the narrow gap cup and bob are accurate for both samples.


Figure 6 - Comparison of sticky point measurements of two samples using the vane tool via temperature ramps. The sticky point is where the sample viscosity spikes dramatically.

As with more expensive rheometers, the BLACK PEARL Viscometer can accommodate different types of samples and experiments. It can be used to determine the “sticky point” of a powdered product. The sticky point is the temperature where a sample would change structure and transition from a flowable powder to a cohesive solid at a specific temperature. The viscometer can determine the sticky point of a sample using the vane tool. Utilizing the built-in Peltier temperature control, the instrument can test for the sticky point over the temperature range –10 to 120 °C. Figure 6 shows an example of a sticky point on two similar samples using the vane tool. The sudden increase in viscosity indicates the sticky point temperature.


Figure 7 - A PDMS sample subjected to a shear rate sweep using a 15-mm parallel plate measuring system. The sample was tested on both the BLACK PEARL Viscometer and the NOVA Rheometer. Note the high viscosity achieved using the parallel plate system.

The BLACK PEARL Viscometer can be used on a wide variety of products—from low-viscosity fluids, to paints and coatings, powder samples and gels, all the way to high-viscosity polymer melts and thick pastes. Due to the broad measurement range and variety of measuring systems, it can even measure very high-viscosity products using a parallel plate measuring system. Figure 7 shows the results of a silicone gum sample (PDMS) tested with a 15-mm parallel plate system. Data from a NOVA Research Rheometer (ATS RheoSystems) are included for comparison. Note the excellent agreement between the BLACK PEARL Viscometer and the NOVA Rheometer, priced at more than five times the BLACK PEARL.

Although the BLACK PEARL Viscometer has the ability to perform certain experiments equivalent to a high-priced, complex rheometer, its cost is significantly lower. The instrument can measure simple, one-point viscosity tests, to yield stress points, to complex flow curve analysis. It can be utilized as a simple quality control unit through a research instrument, yet is simple to use and cost effective.

Fungilab Viscometer Series

The Fungilab Viscometer Series are easy-to-use, economical, high-quality rotational viscometers available in a wide range of units well equipped to handle specific rheological needs. From a premium-level viscometer with Microsoft Windows-based software, through an entry-level, manual model for basic testing applications, each instrument offers a wide variety of options that differentiate it from other low-cost viscometers.

The Fungilab Viscometer Series can perform a wide range of test parameters including single point, ramping shear rates, and shear rate steps. Each model offers different features to better accommodate specific testing needs and budgets. Individual features include temperature recognition, time to torque, and time to stop. Time to torque allows the user to set a predetermined target torque for which the data will be collected during the experiment. With time to stop, the user can set a target time at which data will be collected.

The Fungilab Viscometer Series software can be loaded onto a computer, and the results of the experiment can be viewed, stored, and printed. Once a test is completed, the data can be loaded through the software to be further analyzed. This type of feature is not offered on other low-cost viscometers; most require that the data be analyzed by hand once the experiment is complete.

A wide selection of accessories allows users to customize the instrument. Each system is supplied with an assortment of measuring system geometries to choose from, which permit testing of a wide range of viscosities. Additional accessories include small-sample and low-viscosity attachments as well as an accessory for helicoidal movement adapters.

Conclusion

As demonstrated in this article, single-point viscosity and complete flow curve data can be generated precisely using the BLACK PEARL Viscometer. Its multiuse measurement systems allow for examination of broad range of products. Built-in Peltier temperature control enables accurate and routine measurement of the flow properties of a wide range of samples under a variety of temperatures.

The Fungilab Viscometer Series are simple to operate and customizable for a wide variety of applications, and provide an economical and effective alternative to larger, more costly rheometers.

Robert W. Nixon is Associate Staff Engineer, and Dr. Jeshwanth K. Rameshwaram is Staff Engineer, ATS RheoSystems, 231 Crosswicks Rd., Bordentown, NJ 08505, U.S.A.; tel.: 609-298-2522; e-mail: info@atsrheosystems.comwww.atsrheosystems.com . Nick Roye is Western Region Manager, ATS RheoSystems, Valley Village, CA, U.S.A.

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