Experimental Design Guidelines

This appendix consolidates best practices for sample preparation, measurement protocols, and artifact avoidance across all test modes.

Sample Preparation

General Principles:

  • Temperature equilibration: 15-30 minutes before measurement

  • Loading: Avoid bubbles, ensure complete filling

  • Gap setting: Use normal force or auto-gap features

  • Pre-shear: 10-60 s at moderate rate to erase loading history

Material-Specific:

Material Type

Geometry

Special Considerations

Polymer melts

Parallel plate (25-50 mm)

Prevent oxidation (\(N_2\) purge)

Soft gels

Parallel plate (20-40 mm)

Minimize gap (<2 mm), avoid slip

Suspensions

Cone-plate, serrated

Prevent sedimentation, wall slip

Low-viscosity liquids

Double-wall couette

Minimize evaporation

Yield-stress fluids

Vane, serrated plates

Avoid wall slip

SAOS Frequency Sweep

Recommended Protocol:

  1. Strain amplitude: Verify linear regime (0.1-1% typical)

  2. Frequency range: 0.01 - 100 rad/s (3-4 decades minimum)

  3. Points per decade: 5-10 logarithmically spaced

  4. Temperature: Constant ±0.1°C

Common Artifacts:

  • Instrument inertia: \(G'\) increases at high \(\omega\) (>100 rad/s)

  • Torque limit: Erratic data at low \(\omega\) for soft materials

  • Edge fracture: Solid samples at large strain

Stress Relaxation

Recommended Protocol:

  1. Strain amplitude: 1-10% (verify linearity)

  2. Rise time: <0.01 s (instrument-dependent)

  3. Duration: 10-1000 s (3-4 decades)

  4. Sampling: Logarithmic time spacing

Common Artifacts:

  • Inertia: Oscillations at \(t < 0.1\) s

  • Sample slip: Sudden stress drop

  • Instrument compliance: Long-time artifacts

Steady Shear Flow

Recommended Protocol:

  1. Shear rate range: 0.01 - 1000 \(\text{s}^{-1}\) (for polymers)

  2. Steady-state criterion: Viscosity constant for >30 s

  3. Pre-shear: Essential to erase history

  4. Sequence: Low → high rate (reduces fracture)

Common Artifacts:

  • Wall slip: Serrated geometries, check linearity with gap

  • Edge fracture: Reduce normal stress, lower rate

  • Shear banding: Bimodal stress response

Temperature Control

Critical for:

  • Time-temperature superposition (TTS)

  • Gelation studies

  • Polymer melts

Best Practices:

  • Equilibrate 20+ minutes

  • Use heated upper geometry

  • Minimize evaporation (solvent trap, humidity chamber)

  • Verify with calibration standards

Data Quality Checklist

Before fitting models, verify:

☐ Linear regime confirmed (amplitude sweep)

☐ No instrument artifacts (inertia, compliance)

☐ Temperature stable (±0.1°C)

☐ Sufficient data range (3+ decades)

☐ Smooth data (no sudden jumps or outliers)

☐ Reproducible (repeat measurements agree)

Further Reading