Foreword

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This document was prepared by Technical Committee ISO/TC 24, Particle characterization including sieving, Subcommittee SC 4, Particle characterization.

This third edition cancels and replaces the second edition (ISO 22412:2017), which has been technically revised.

The main changes are as follows:

inclusion of multi-angle dynamic light scattering (MADLS);
inclusion of imaging dynamic light scattering (DLS);
addition of Clause A.5 on polarisation-separated backscatter photon cross-correlation spectroscopy;
extension of Annex B on online measurements;
incorporation of the content from ISO TR 22814 into Annexes C and D.

Any feedback or questions on this document should be directed to the user’s national standards body. A complete listing of these bodies can be found at www.iso.org/members.html.

Introduction

Particle size analysis in the sub micrometre size range is performed on a routine basis using the dynamic light scattering (DLS) technique, which probes the hydrodynamic mobility of the particles. The technique is successful because it provides estimates of the average particle size and size distribution within a few minutes, and because user-friendly commercial instruments are available. Nevertheless, proper use of the instrument and interpretation of the result involve certain precautions.

The principle of DLS for a concentrated suspension is the same as for a dilute suspension. However, specific requirements for the instrument setup and specification of test sample preparation are specified for concentrated suspensions. At high concentrations, particle-particle interactions and multiple light scattering can become dominant and can result in apparent particle sizes that differ between concentrated and dilute suspensions.

DLS is also referred to as “quasi-elastic light scattering (QELS)” and “photon correlation spectroscopy (PCS),” although PCS is actually one of the measurement methods.

Several methods have been developed for DLS. These methods can be classified in several ways:

by the difference in raw data acquisition (autocorrelation, cross-correlation and frequency analysis, spatial correlation);
by the difference in optical setup (homodyne mode versus heterodyne mode);
by the angle of observation.

In addition, instruments show differences with respect to the type of laser source and often allow application of different data analysis algorithms, e.g. cumulants, non-negative least squares (NNLS), CONTIN, etc.

1 Scope

This document specifies the application of dynamic light scattering (DLS) to the following:

measurement of average hydrodynamic particle size;
measurement of the size distribution of mainly sub micrometre-sized particles, emulsions or fine bubbles dispersed in liquids.

This document is applicable to the measurement of a broad range of dilute and concentrated suspensions.

2 Normative references

3 Terms and definitions

4 Symbols and units

5 Principle

6 Apparatus

6.1

6.2

6.3

6.4

6.5

6.6

6.7

7 Test sample preparation

7.1 General

7.2 Concentration limits

7.3 Checks for concentration suitability

8 Measurement procedure

9 Evaluation of results

9.1 General

9.2 Correlation analysis

9.3 Frequency analysis

9.4 Multi angle dynamic light scattering (MADLS)

9.5 Imaging dynamic light scattering (DLS)

10 System qualification and quality control

10.1 System qualification

10.2 Quality control of measurement results

10.3 Method precision and measurement uncertainty

11 Test report

Bibliography