Overview
ISO/TS 21357:2022 - Nanotechnologies: Evaluation of the mean size of nano-objects in liquid dispersions by static multiple light scattering (SMLS) - provides requirements and guidance to determine the mean (spherical) equivalent diameter of nano-objects (particles, droplets, bubbles) dispersed in liquids. The standard is designed for a wide range of materials and, importantly, does not require dilution of concentrated samples, enabling measurement of dispersions in their native (as‑received) state.
Key topics and technical requirements
- Measurement principle: SMLS measures transmitted and/or backscattered light after multiple elastic scattering events; outputs depend on particle size, concentration (volume fraction), optical properties (refractive index, absorption), and measurement geometry.
- Core measurands and parameters: mean equivalent particle diameter (D), mean free path (l), transport mean free path (l*), volume fraction (ϕ), asymmetry factor (g), and extinction efficiency (Qe).
- Theoretical basis: Uses Mie theory to relate measured light signals to particle diameter or volume fraction; calibration factors account for instrument geometry and detector response.
- Method applicability & limitations: Guidance on when SMLS is appropriate (concentrated vs dilute samples), and considerations for sample homogeneity, stability and optical properties.
- Practical procedure elements: apparatus specification, instrument preparation, sample handling, system settings (including procedures to verify homogeneity and to set refractive index and volume fraction), and data recording.
- Quality assurance: performance qualification, measurement uncertainty assessment, instrument qualification and interlaboratory comparison insights (annexes provide example analyses and ILC results).
Applications and users
ISO/TS 21357:2022 is particularly useful for:
- Industrial R&D and quality control teams monitoring nanoparticle dispersions (paints, coatings, inks, emulsions, suspensions).
- Laboratories needing non‑invasive size measurement without dilution to preserve aggregation/agglomeration state.
- Regulatory and compliance testing where representative, as‑received dispersion size is required.
- Instrument manufacturers and method developers implementing or validating SMLS instruments and workflows.
Practical uses include tracking mean particle size, monitoring aggregation/agglomeration or dissolution in real time, and routine QC where full size distributions are not required.
Related standards
- ISO/TS 80004 series (nanotechnology vocabulary) for consistent terms.
- Other ISO particle characterization standards (referenced within the document) for complementary methods and terminology.
Keywords: ISO/TS 21357:2022, static multiple light scattering, SMLS, mean equivalent particle diameter, nanoparticles, liquid dispersions, Mie theory, volume fraction, transport mean free path, refractive index.