Rheology Testing Services Performs Viscosity & Viscoelasticity Assays & More!​​​​​​
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"I wished we reached out to you much earlier in the R&D process to better rheologically understand our product and the impact of manufacturing conditions, especially before locking down specifications." Comments like this have been mentioned by RTS clients more than a few times. Performing either a single assay to address a specific technical need or an array of assays to generate a comprehensive rheological profile, is often a very small investment with a potentially large return.
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RTS provides a broad range of rheological assay options with flexibility, no bureaucracy and rapid turnaround for clients ranging from academics, start-ups to international conglomerates. In contrast to many large "all-in-one" Contract Research Organizations (CRO) and Contract Development and Manufacturing Organizations (CDMO), RTS is focused on rheology. RTS clients particularly appreciate the very responsive and personalized interactions along with real-time flexibility and technical experience that RTS consistently provides, especially for the "Houston we have a problem" situations (see "Testimonials" below).
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Not sure what assays and parameters would be most appropriate to address the question you seek to answer?
No problem - RTS will provide guidance.
OFTEN REQUESTED ASSAYS
Additional assays listed under "Assays" tab (page top)
Viscosity with Shear Rate Ramp
Viscosity (resistance to flow) is one component of a detailed rheological profile to support product development.
Viscosity can be quantified with several methodologies. A frequently requested assay is the rotational shear rate ramp applied across a wide range of conditions. For example: Honey being a Newtonian fluid does not appreciably shear thin with increasing shear rate; whereas, mayonnaise (non-Newtonian) does.
Typically, these assays are helpful to generate shear thinning or flow curves that efficiently model processes and applications. ​
Yield Stress with Shear Stress Ramp
Yield stress is often determined by a shear stress ramp assay to quantify the rheological "breakpoint" that leads to flow.
For example: While on a flat surface, a spoonful of yogurt spreads (flows) over a relatively short time has a much lower yield stress & yield viscosity than peanut butter, which takes much longer to spread.
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Yield stress determinations are helpful to model pumpability, spreading, delivery, sedimentation potential (Stokes' Law) and feel.
LVER with Amplitude Sweep
An amplitude sweep is an oscillatory assay during which amplitude (energy input as either strain or stress) increases over time and frequency is held constant.
During this assay, the sample is increasingly deformed during back & forth oscillation to determine its rheological breakpoint (LVER; Linear Viscoelastic Region) which correlates with rheological stability. As described in the next panel, knowing the LVER is important to determine the experimental strain or stress input for frequency-modulated assays.
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An analogy for amplitude sweep is when molded gelatin is wiggled beyond its LVER, it falls apart.
Viscoelasticity with
Frequency Sweep
A frequency sweep is another oscillatory assay during which amplitude (either strain or stress) is held constant and frequency changes over time. This assay is often used to quantify viscoelastic properties for materials that are not amenable to rotational assays. The typical measurables for frequency sweep assay is stiffness (G*; complex modulus), solid nature (G'; elastic or storage modulus), liquid nature (G"; viscous or loss modulus), degree of fluidity (phase angle), complex viscosity, and tan delta (G"/G').
To properly perform this assay, it is important to use a strain or stress input within its LVER determined from amplitude sweep. This ensures the sample's rheological integrity is maintained during the assay and hence validity of the results.
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Silly Putty is an excellent example of changing viscoelastic properties with frequency. When near at rest (low frequency), it slowly spreads like a liquid (G">G'). However, when rolled into a ball and dropped on a table (high frequency), it bounces like a solid (G'>G"). Check out "Learn More" below to see actual plot.