Overview
ISO 18747-2:2019 - Determination of particle density by sedimentation methods, Part 2: Multi-velocity approach - defines an in situ method to determine the density of solid particles or liquid droplets dispersed in a liquid continuous phase. The method relies on direct experimental measurement of particle migration velocity (sedimentation or creaming/flotation) in gravitational or centrifugal fields and uses Stokes law to calculate particle density, taking into account the dynamic viscosities and densities of the continuous media. The procedure does not require prior knowledge of particle size distribution but assumes particle-relevant characteristics (volume, shape, agglomeration state) remain unchanged during measurement. Polydispersity in particle density is not considered.
Key technical topics and requirements
- Measurement principle: Determine terminal velocities of particles in different liquids/media and convert velocities to density using Stokes‑law–based relationships.
- Required input data: Known densities and dynamic viscosities of the continuous phase liquids, measured migration velocities, and experimental conditions (gravity or centrifugal acceleration).
- Assumptions & limitations:
- Particle size distribution is not required, but particle shape/volume/agglomeration must remain constant across measurements.
- All particles are assumed to share the same material composition (no density polydispersity).
- Surface “corona” and wettability effects can affect apparent volume and introduce uncertainty, especially for nanoparticles.
- Sample preparation and measurement: Includes guidance on preparing continuous phase liquids, dispersing procedures, and techniques to determine sedimentation or creaming/flotation velocities.
- Data analysis & uncertainty: Procedures for analyzing velocity distributions, calculating densities, and estimating measurement uncertainty are included, plus informative annexes with examples (emulsions, monodisperse spheres, non‑spherical particles).
- Reference materials and uncertainty propagation approaches are addressed.
Practical applications
- Characterizing dispersed systems in research and industry where knowing particle density is critical, including:
- Formulation and stability testing of emulsions (food, cosmetics, coatings)
- Pharmaceutical particle and capsule characterization
- Environmental and toxicology studies (nanoparticle sedimentation and dosimetry)
- Quality control in materials production (polymers, fillers, pigment dispersions)
- Supporting sedimentation‑based particle size or mass transfer calculations
Who should use this standard
- Particle characterization laboratories, QA/QC teams, formulation scientists, nanotoxicology researchers, and instrument manufacturers developing sedimentation or centrifugation methods. Standards bodies and test labs can adopt ISO 18747-2:2019 to harmonize in situ density determination protocols.
Related standards
- ISO 18747-1 (other parts of the series covering complementary approaches)
- ISO 14887 (sample preparation - dispersing procedures for powders in liquids)
- ISO/TC 24/SC 4 (technical committee responsible for particle characterization)
Keywords: ISO 18747-2:2019, particle density, sedimentation methods, multi-velocity approach, Stokes law, dynamic viscosity, centrifugation, migration velocity, in situ density determination.
Open preview (PDF)Determination of particle density by sedimentation methods — Part 2: Multi-velocity approach
