Overview of Rheometer Geometries and Selection Criteria
📌 Selecting the right measuring system is crucial for reliable and reproducible rheological results.
📐 Standard geometries include cone and plate, parallel plates, various coaxial cylinders (Dean/ISO, double gap, Mooney-EVE), and vane/spindle types.
⚙️ The choice depends on three main factors: rheometer performance (torque/speed range, bearing type), sample properties (viscosity, particle size), and the intended test (absolute vs. relative data, temperature control, oscillation/rotation mode).

Influence of Rheometer Performance and Sample Properties
💨 Rheometers with air bearings offer a much wider theoretical measuring range than those with mechanical bearings, allowing testing of most liquid/semi-solid samples with a standard setup (e.g., 35 mm 1° cone and plate).
📈 For highly viscous samples (e.g., polymer melts), small diameter parallel plate or cone and plate geometries are ideal, while double gap geometries suit very low viscous liquids (like water at 1 mPa·s).
📏 When testing samples with particles, the measuring gap should generally be ten times larger than the maximum particle size; vane rotors are necessary for particles $\geq 500 \mu\text{m}$ but yield only relative data.
💧 To minimize sample slippage (which yields incorrect results), use geometries with profiled surfaces instead of smooth ones on parallel plates and coaxial cylinders.

Detailed Geometry Characteristics
🌟 Cone and Plate: Offers constant shear rate across the radius; excellent for low-risk to high-viscous liquids and determining the first normal stress difference (elasticity measure).
➕ Parallel Plates: Feature an adjustable gap, but shear rate varies (highest at the rim), leading to accurate results only for Newtonian samples or within the LVE range for non-Newtonian ones.
♨️ Coaxial Cylinders (e.g., Dean/ISO): Suitable for pourable, low to medium viscous liquids; certain types (recessed end) are highly accurate but unsuitable for temperature ramp tests due to air bubble expansion.
📊 Vane Rotors: Provide relative viscosity data only; best for samples with particles too large for narrow gaps or those whose structure would be irreversibly destroyed by small gaps.

Specialized and Advanced Setups
🧊 Solids Clamping Tool: Enables dynamic mechanical thermal analysis (DMTA) on solid specimens to determine phase transitions like glass transition ($T_g$).
↔️ Extensional Rheometer Tool: Clamps a polymer film on drums to measure resistance against stretching (extensional testing).
🔬 Bicone Setup: Used for interfacial rheology to measure properties of thin layers, often surfactants, formed at liquid interfaces.

Key Points & Insights
➡️ The Range Calculator tool in rheometer software can display the theoretical measuring range for any geometry/rheometer combination, including specific reference samples.
➡️ For shear thinning materials, the difference in results between cone and plate and parallel plates increases as the degree of shear thinning becomes greater.
➡️ Heavy rotors in oscillation mode (like large diameter coaxial cylinders) should be avoided to minimize negative effects of instrument inertia on test results.
➡️ For oscillatory tests on low viscous materials, choose a geometry with a small measuring gap (e.g., small gap parallel plates or small angle cone/plate) to reduce sample inertia influence.

📸 Video summarized with SummaryTube.com on Jan 12, 2026, 11:18 UTC