Rheology Testing Services Performs Viscosity & Viscoelasticity Assays & More!​​​​​​
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Rheology Applications​
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​Prove/Disprove Equivalence for Regulatory & IP (Q3)
"We should have reached out to RTS 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 highly responsive and personalized interactions along with real-time flexibility and technical experience for methodical investigations, especially for the "not sure what's going on with our sample" and "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 just one component of a detailed rheological profile to understand material response to various conditions.
Viscosity can be quantified with several methods. A frequently requested assay is the rotational shear rate ramp applied across a wide range of conditions. The figure below shows honey, a Newtonian fluid does not appreciably shear thin with increasing shear rate; whereas, mayonnaise (non-Newtonian) does shear thin.
Typically, these assays are helpful to generate flow curves, often with shear thinning 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, yogurt will spread (flow) 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 & Stability with
Amplitude Sweep
An amplitude sweep is an oscillatory assay during which amplitude (deformation 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 oscillations to determine its rheological breakpoint (LVER; Linear Viscoelastic Region) that correlates with rheological stability (i.e gelatin wiggled beyond its LVER fall apart). As described in the next panel, knowing the temperature dependent LVER is important to determine the experimental strain or stress input for often subsequent frequency-modulated assays.
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​The figure below shows typical amplitude sweep output as G' (elastic modulus) with increasing % strain to determine LVER for 3 very different gels containing hyaluronic acid. Among similar samples, larger LVER values correlate with increasing physical stability. As shown below, liquids tend to have higher LVER with lower G’ (less rheological integrity to lose).
Viscoelasticity with
Frequency Sweep
A frequency sweep is another routine oscillatory assay during which amplitude (either strain or stress) is held constant and frequency changes over time. In addition to many applications, this assay is helpful to quantify viscoelastic properties for semisolids 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 frequency sweep, 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.
