Rheological analysis can provide many benefits for soft material development, processing, and quality control through the versatile test methods. But is rheology the best tool for your current project? Read below to see which criteria apply to your circumstances.
Rheology is a good fit if:
Your samples are primarily fluids or soft solids.
Rheology is the study of materials with both liquid-like and solid-like characteristics;
therefore, the samples to be analyzed have to be either soft solids (gels, pastes), liquids, films, coatings, soft foams, or fibers. From watery solutions to a piece of rubber, there is an appropriate rheometer set-up for each of these sample types.
You want to know the mechanical properties under low strains for processing, storage, and application.
Mechanical properties are physical properties, which include qualities such as stiffness, strength, and physical stability over time. Rheometry data indicates changes in physical structure in response to applied forces and strains, such as those undertaken during pumping, pouring, mixing, spreading, spraying, and settling. Experiments focused on sample change over time are especially suited for rheometry due to the high sensitivity to low strain conditions that come close to measuring the sample at rest. However, high strain settings are less obtainable with a shear rheometer. Studies focusing on ripping apart films or solids or applying ballistic force to the sample are better off with tensile testing – a characterization technique designed for high force testing - rather than rheometry.
You are interested in how the sample changes in response to temperature.
Rheometry experiments can be conducted at a constant temperature or with an increasing or decreasing temperature, which enables a wide assortment of tests for quantifying temperature-induced changes in the sample. Such precision is possible due to advancements in temperature control technology. With rheological properties being highly dependent on temperature, a rheometer is a trusty instrument for examining how your sample responds to temperature extremes or ages over time.
Rheology is not advised if:
Your main focus is the mechanical behavior of completely solid components.
Any substance that can flow or deform is theoretically included in the study of rheology, but the practical limitations of rheometers prevent measurement of samples that are too solid, such as metals and hard plastics. The exceptions to this are softening or melting studies that seek to examine the properties of molten metals or polymer melts. Rheometry experiments can work for examining materials that start off as liquids or gels that solidify into a solid, but once the substance is completely solid (such as a hardened epoxy), it cannot be measured by a conventional rheometer unless it is softened.
Your samples are always low concentrations of chemical in a solvent.
For solutions with low concentrations, simple viscometry can be utilized instead of rheometry. Viscometers apply different mechanisms to measure Newtonian fluids (substances without dynamic rheological behavior) than rheometers. This enables some viscometers to work with sample volumes as low as 50 μL, which is especially useful for pharmaceutical development.
You want to figure out the chemical properties of the substance rather than learn about the physical characteristics.
If investigating the chemical structure is far more pertinent to the project than evaluating the physical structure, then rheology is not where you want to start. Although rheometry can give insights to physio-chemical aspects such as the presence of crosslinking, sample stability, and how chemistries impact physical properties, it cannot directly identify the chemical composition. After defining the chemical structure through chemical analysis (GPC, spectrometry, and others), if physical properties are of interest then consider probing the nano- and microstructure with rheometry and microscopy.
Click here to access our free “Is Rheology a Good Fit?” checklist.
Have questions about the suitability of rheology for your project? Contact us to receive a free consultation.