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Rotational Rheology / Rotational Rheometry / Dynamic Mechanical Analysis (DMA) Testing of Materials

Significance and Purpose

Rotational Rheology / Rotational Rheometry Testing by Dynamic Mechanical Analysis (DMA) is a versatile technique for characterizing the viscoelastic properties of materials over a range of shear rates, frequencies, and deformation conditions. By using a dynamic mechanical analyzer equipped with cone-and-plate or parallel plate geometries, this technique can provide detailed insights into elasticity, viscosity, relaxation behavior, cure kinetics, and equibiaxial elongational viscosity of complex materials such as polymers, composites, and soft solids. Below is a comprehensive summary of DMA for rotational rheology with references to ASTM D4440, ISO 6721-10, ASTM D4473, and other relevant standards.

The DMA technique in rotational rheometry is essential for studying material behavior under shear and extensional deformations. Its purpose includes:

  • Material Characterization: Evaluating viscoelastic properties such as storage modulus (G′), loss modulus (G″), and complex viscosity (η∗) for polymers, elastomers, and composites.
  • Thermal Transitions: Identifying glass transition temperature (Tg) and other transitions critical for performance.
  • Process Optimization: Simulating processing conditions such as extrusion, molding, or curing to optimize formulations.
  • Cure Kinetics: Monitoring the curing behavior of thermosetting polymers and adhesives to assess reaction rates and final properties.
  • Flow and Elastic Behavior: Investigating steady-state shear properties (e.g. viscosity, first normal stress difference) and extensional properties (e.g. equibiaxial elongational viscosity).
  • Failure Analysis: Understanding deformation and relaxation behavior under complex loading conditions.

Relevant ASTM and ISO Standards

The following standards govern DMA for rotational rheology:

  • ASTM D4440: Standard Test Method for Rheological Measurements of Polymer Melts Using Dynamic Mechanical Properties.
  • ISO 6721-10: Plastics — Determination of dynamic mechanical properties — Part 10: Complex shear modulus using a parallel-plate or cone-and-plate device.
  • ASTM D4473: Standard Test Method for Cure Behavior of Thermosetting Resins Using Rheometers: Standard for cure kinetics.
  • ASTM D575: Standard Test Methods for Rubber Properties in Compression
  • ASTM D695 and ISO 604: Standards for compression testing of plastics, relevant for equibiaxial elongational viscosity measurements.

These standards provide detailed methodologies for conducting dynamic, transient, and steady-state rheological measurements across different material classes.

DatapointLabs Tests for Rotational Rheology / Rotational Rheometry by DMA

Tests in the DatapointLabs test catalog that reference rotational rheology testing / rotational rheometry testing by dynamic mechanical analysis (DMA) are as follows:

General Rotational Rheology / Rotational Rheometry Testing (inquire regarding material suitability)

Test Test Description Standards
R-020 DMA Cone and Plate Dynamic Rheology (1 Temperature) ASTM D4440 / ISO 6721-10
R-021 DMA Cone and Plate Steady Shear Rheology (1 Temperature) ASTM D4440 / ISO 6721-10
R-022 DMA Parallel Plate Dynamic Rheology (3 Temperatures) ASTM D4440 / ISO 6721-10
R-023 First Normal Stress Difference by DMA (1 Temperature) ASTM D4440 / ISO 6721-10
R-024 Characteristic Relaxation Time by DMA (5 Temperatures) ASTM D4440
R-025 Thermal Stability by Cone and Plate DMA ASTM D4440
R-026 Transition Temperature by DMA ASTM D4440
R-027 Cure Kinetics by DMA-isothermal ASTM D4473
R-028 Cure Kinetics by DMA -non isothermal ASTM D4473
R-040 Equibiaxial Elongational Viscosity (1 Temperature, 1 Strain Rates) ASTM D575 / ASTM D695 / ISO 604

Principle of Operation

DMA in rotational rheometry measures the viscoelastic response of a material when subjected to oscillatory, steady, or transient shear deformation. Key principles include:

  1. Shear Deformation and Stress Response:
    • A sample is placed between two plates (parallel plate) or a cone and a plate.
    • One plate oscillates (dynamic mode) or rotates (steady mode) while the other remains stationary.
    • The material’s response (stress or strain) is measured.
  2. Viscoelastic Characterization:
    • The storage modulus (G′) measures elastic energy storage.
    • The loss modulus (G″) measures viscous energy dissipation.
    • The complex viscosity (η∗) reflects overall flow resistance.
    • By the Cox-Merz Rule, the rotational shear viscosity as a function of shear rate is equivalent to the oscillatory complex viscosity as a function of angular frequency.
  3. Geometries:
    • Cone-and-Plate: Ideal for uniform shear stress but limited to low-viscosity materials.
    • Parallel Plate: Suitable for a wider range of viscosities and large-particle suspensions.
  4. Shear vs. Extensional Behavior:
    • Shear flow (using standard geometries) captures in-plane deformation.
    • Equibiaxial elongational viscosity is assessed using specialized fixtures and tests under compressive deformation.

Typical Procedure

  1. Sample Preparation:
    • Prepare a small, representative sample (e.g. solid disc or molten polymer).
    • Ensure the sample is free of air bubbles or defects.
  2. Instrument Calibration:
    • Calibrate the torque, normal force, and temperature sensors.
    • Zero the gap height to ensure accurate sample placement.
  3. Test Setup:
    • Load the sample between the cone-and-plate or parallel plates.
    • Set the gap height (typically micrometers for cone-and-plate).
  4. Testing Conditions:
    • Define the test mode:
      • Dynamic Oscillation: Frequency sweeps to measure G′, G″, and η∗.
      • Steady Shear: Shear rate sweeps for viscosity and first normal stress difference.
      • Time-Temperature Superposition: For creating master curves of relaxation behavior.
      • Cure Kinetics: Isothermal or non-isothermal ramps to monitor curing.
  5. Data Collection and Analysis:
    • Measure torque, strain, normal force, and temperature.
    • Analyze results to determine viscoelastic properties, cure behavior, and elongational viscosity.

Specimen Types

Specimens used by DatapointLabs in various types of rotational rheology testing / rotational rheometry testing by dynamic mechanical analysis (DMA) are as follows:

Specimen Type DatapointLabs Test IDs
Pellets [Details] R-020, R-021, R-022, R-023, R-024, R-025, R-026
Plate Rheology Discs [Details] R-040
Contact Us [Details] R-027, R-028

Characterization Measurements

Storage and Loss Modulus (G′ and G″) Curves

  • G′ (Storage Modulus): Measures the elastic (solid-like) response.
  • G″ (Loss Modulus): Measures the viscous (liquid-like) response.
  • Crossover Point: The frequency where G′ = G″, indicating the material’s transition from viscous-dominant to elastic-dominant behavior.

Complex Viscosity (η∗) vs. Frequency

  • Reflects the material’s resistance to deformation under oscillatory conditions.
  • Shear thinning behavior is observed with increasing frequency.

Complex Viscosity (η∗) vs. Time

  • Reflects changes in a material’s resistance to flow over time.

Strain Sweep

  • Identifies the linear viscoelastic region (LVR) by measuring G′ and G″ at increasing strain amplitudes.

First Normal Stress Difference (N1) vs. Shear Rate

  • N1: The difference between the normal stress acting in the flow direction and the normal stress acting perpendicular to the flow direction under shear deformation.
  • Provides insights into elastic recovery and material anisotropy.

Shear Viscosity vs. Shear Rate

  • Measured in steady shear mode to assess shear thinning or thickening behavior.

Time-Temperature Superposition (aT) and Relaxation Master Curves

  • Shifts data from different temperatures to create a single master curve of relaxation behavior.
  • Characterizes long-term performance and stability.

Cure Kinetics

  • Complex Viscosity vs. Time: Monitors viscosity increase during polymerization.
  • Shear Modulus vs. Time: Tracks modulus changes as curing progresses.
  • Used to determine gelation time, onset of cure, and final material properties.

Equibiaxial Elongational Viscosity

  • Compressive Modulus: Measures resistance to equibiaxial deformation.
  • Monitors melt elasticity and extensional behavior critical for film blowing and fiber spinning.

Typical Data Reported (see test descriptions for exact details)

  • G′, G″, and η∗: Storage modulus, loss modulus and complex viscosity as functions of frequency or temperature.
  • Crossover Point: Of G′ and G″ curves, marking transition from viscous to elastic dominant behavior.
  • Relaxation Master Curve: Characterization of long-term relaxation behavior.
  • Cure Kinetics: Complex viscosity, shear modulus and derived properties as a function of time.
  • First Normal Stress Difference: Difference normal stresses in the in-flow and orthogonal-flow directions, respectively.

Suitable Material Types

  • Polymers: Thermoplastics, thermosets, elastomers.
  • Composites: Fiber-reinforced materials.
  • Adhesives: Curing behavior and viscoelastic performance.
  • Biomaterials: Hydrogels, tissue scaffolds.
  • Food Products: Doughs, gels, and other viscoelastic materials.

Suitable Applications

  • Material Development: Optimizing formulations for desired flow and elastic properties.
  • Material Modeling: Informing viscoelastic models for extrusion and blow molding simulation.
  • Process Optimization: Extrusion, molding, and film blowing.
  • Quality Control: Ensuring batch-to-batch consistency.
  • Failure Analysis: Diagnosing flow instabilities or defects.
  • Curing Applications: Monitoring thermoset and adhesive cure behavior.

Conclusion

Rotational rheology / rotational rheometry testing by dynamic mechanical analysis (DMA), as standardized by ASTM D4440, ISO 6721-10, ASTM D4473, and other relevant standards, is an invaluable tool for characterizing the viscoelastic, thermal, and processing behavior of materials. It provides detailed insights into loss, storage and compressive moduli, viscosity, cure kinetics, and elongational properties, enabling optimized material design and processing across diverse industries, including polymers, adhesives, composites, and food products.

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