Thixotropic Index Calculator

Formula Used

This calculator uses the common viscosity-ratio definition of the thixotropic index:

TI = η_low / η_high

• η_low is the apparent viscosity at a lower shear condition.
• η_high is the apparent viscosity at a higher shear condition.
• Values greater than 1 usually indicate stronger structure breakdown under shear.

How to Use This Calculator

1. Measure viscosity at a low shear condition and at a higher shear condition.
2. Enter both viscosities and select the unit used by your instrument.
3. Optionally record the shear rates and temperature for documentation.
4. Press Calculate to show results above the form.
5. Use Download CSV or Download PDF for reporting.

Example Data Table

Article

1) What the thixotropic index represents

The thixotropic index (TI) is a practical ratio that compares apparent viscosity under two shear conditions. It summarizes how strongly a material’s internal structure resists motion at low shear and how much it breaks down at higher shear. Higher TI values typically indicate stronger structure breakdown under shear, followed by recovery when shear decreases.

2) Why two-point viscosity data is useful

In routine quality control, two viscosity readings are faster than full flow curves and still capture meaningful behavior. The low-shear reading reflects leveling, sag resistance, and storage stability. The high-shear reading reflects application behavior such as pumping, mixing, spraying, rolling, or dispensing. TI converts these readings into a single comparison-ready number.

3) Typical measurement ranges and units

Many coatings, gels, slurries, and polymer solutions are reported in mPa·s (or cP), while high-viscosity pastes may be recorded in Pa·s. Because TI is a ratio, units cancel as long as both viscosities use the same unit. This calculator accepts common viscosity units and displays results in your preferred output unit for documentation.

4) Role of shear rate and test protocol

Two-point TI depends on the shear rates, dwell times, and pre-conditioning used during testing. For example, comparing 1 s⁻¹ to 100 s⁻¹ can produce a different TI than comparing 0.5 s⁻¹ to 50 s⁻¹. Record shear rate values when available and keep instrument geometry and timing consistent to make comparisons valid across batches.

5) Temperature sensitivity and repeatability

Apparent viscosity often changes strongly with temperature, so TI can drift if test temperature is not controlled. A difference of only a few degrees can noticeably shift the low-shear viscosity in structured fluids. Logging temperature alongside TI helps identify whether a change is formulation-related or a measurement condition change.

6) Interpreting TI values in practice

As a working rule, TI close to 1 suggests near-constant viscosity across the selected shear conditions. Values around 1.2–2 often indicate mild structure breakdown. Values near 2–4 suggest moderate thixotropic behavior that can improve sag control while still allowing application flow. Very high values can indicate strong shear-thinning and recovery, which may require tuning to avoid poor leveling.

7) When a ratio is not enough

TI is not a full thixotropy test, because thixotropy is time-dependent and can involve hysteresis and recovery kinetics. If you must quantify structure rebuild time, use step-shear recovery tests or up-down flow sweeps and evaluate loop area. Still, TI remains a fast screening metric for day-to-day comparisons.

8) Using exports for reporting and audits

For traceability, the export tools capture TI, percent change, and optional test context such as sample name, temperature, and notes. CSV files work well for spreadsheets and trend charts, while the PDF report is useful for batch records and customer documentation. Consistent reporting improves troubleshooting and reduces variability in production decisions.

FAQs

1) Is TI dimensionless?

Yes. TI is a ratio of two viscosities, so units cancel when both readings are taken in the same viscosity unit.

2) What if my low-shear viscosity is smaller than my high-shear value?

That usually indicates unusual input data or swapped readings. Recheck the shear conditions, units, and instrument settings before drawing conclusions.

3) Which shear rates should I use?

Use the two shear conditions that match your process or application. Keep them fixed across samples so TI comparisons remain meaningful.

4) Does TI measure recovery time?

No. TI compares two shear points and does not capture time-dependent rebuild. Use recovery tests or hysteresis sweeps when kinetics matter.

5) Why include temperature in the inputs?

Temperature affects viscosity and can change TI indirectly. Recording temperature helps you separate formulation changes from test-condition differences.

6) Can I compare TI across different instruments?

Only with caution. Geometry, calibration, and timing can shift viscosity readings. For best comparability, use the same instrument and protocol.

7) What is a good TI value?

There is no universal target. “Good” depends on the product: high TI may improve sag control, while lower TI can improve leveling and ease of application.