CEN ISO/TS 21357:2023

SLOVENSKI STANDARD
01-maj-2023
Nanotehnologije - Vrednotenje srednje velikosti nanoobjektov v tekočih
disperzijah s statičnim večkratnim sipanjem svetlobe (SMLS) (ISO/TS 21357:2022)
Nanotechnologies - Evaluation of the mean size of nano-objects in liquid dispersions by
static multiple light scattering (SMLS) (ISO/TS 21357:2022)
Nanotechnologies - Évaluation de la taille moyenne des nano-objets dans les
dispersions liquides par diffusion statique multiple de la lumière (DSML) (ISO/TS
21357:2022)
Ta slovenski standard je istoveten z: CEN ISO/TS 21357:2023
ICS:
07.120 Nanotehnologije Nanotechnologies
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

CEN ISO/TS 21357
TECHNICAL SPECIFICATION
SPÉCIFICATION TECHNIQUE
March 2023
TECHNISCHE SPEZIFIKATION
ICS 07.120
English Version
Nanotechnologies - Evaluation of the mean size of nano-
objects in liquid dispersions by static multiple light
scattering (SMLS) (ISO/TS 21357:2022)
Nanotechnologies - Évaluation de la taille moyenne des
nano-objets dans les dispersions liquides par diffusion
statique multiple de la lumière (DSML) (ISO/TS
21357:2022)
This Technical Specification (CEN/TS) was approved by CEN on 17 March 2023 for provisional application.

The period of validity of this CEN/TS is limited initially to three years. After two years the members of CEN will be requested to
submit their comments, particularly on the question whether the CEN/TS can be converted into a European Standard.

CEN members are required to announce the existence of this CEN/TS in the same way as for an EN and to make the CEN/TS
available promptly at national level in an appropriate form. It is permissible to keep conflicting national standards in force (in
parallel to the CEN/TS) until the final decision about the possible conversion of the CEN/TS into an EN is reached.

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United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2023 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN ISO/TS 21357:2023 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
The text of ISO/TS 21357:2022 has been prepared by Technical Committee ISO/TC 229
"Nanotechnologies” of the International Organization for Standardization (ISO) and has been taken over
as CEN ISO/TS 21357:2023 by Technical Committee CEN/TC 352 “Nanotechnologies” the secretariat of
which is held by AFNOR.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
Any feedback and questions on this document should be directed to the users’ national standards body.
A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and the
United Kingdom.
Endorsement notice
The text of ISO/TS 21357:2022 has been approved by CEN as CEN ISO/TS 21357:2023 without any
modification.
TECHNICAL ISO/TS
SPECIFICATION 21357
First edition
2022-01
Corrected version
2022-03
Nanotechnologies — Evaluation of the
mean size of nano-objects in liquid
dispersions by static multiple light
scattering (SMLS)
Nanotechnologies — Évaluation de la taille moyenne des nano-objets
dans les dispersions liquides par diffusion statique multiple de la
lumière (DSML)
Reference number
ISO/TS 21357:2022(E)
ISO/TS 21357:2022(E)
© ISO 2022
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
ISO/TS 21357:2022(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms.2
5 Principles . 3
5.1 Relevant theory . 3
5.2 Key measurands . 5
5.3 Method applicability and limitations . 6
5.3.1 General . 6
5.3.2 Sample concentration . 6
5.3.3 Mean equivalent particle diameter . 7
5.3.4 Sample homogeneity and stability . 7
5.4 Method characteristics . 7
6 Apparatus . 8
7 Measurement procedure . 9
7.1 Instrument preparation . 9
7.2 Sample handling . 9
7.3 System settings . 10
7.3.1 General . 10
7.3.2 Procedure to verify sample homogeneity . 10
7.3.3 Volume fraction . 10
7.3.4 Refractive index . 10
8 Performance qualification .11
9 Data record .11
10 Measurement uncertainty .11
Annex A (informative) I and I versus l* and l .13
BS T
Annex B (informative) I and I as a function of D for titanium dioxide and melamine resin
BS T
particles . . .14
Annex C (informative) Instrument qualification .16
Annex D (informative) Comparative analysis of Latex suspensions at various concentrations .17
Annex E (informative) Analysis of titanium dioxide suspensions at different concentrations .18
Annex F (informative) Results of an interlaboratory comparison study .20
Bibliography .23
iii
ISO/TS 21357:2022(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 229, Nanotechnologies.
This corrected version of ISO/TS 21357:2022 incorporates the following correction:
— the IEC logo has been removed from the cover page.
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.
iv
ISO/TS 21357:2022(E)
Introduction
Dispersions of nanoparticles in liquids are widely used in industry. Nanoparticles dispersed in liquids
interact via a variety of weak and strong forces, which can lead to aggregation or agglomeration of
objects (primary particles, agglomerates, aggregates, etc.). As a result, the dispersion state and the
apparent mean particle size and size distribution can differ from those determined during product
manufacturing, storage, and processing, particularly when using measurements requiring sample
dilution or extensive preparation. Sample preparation can result in breaking or formation of aggregates
or agglomerates and in some cases can also affect morphology of primary particles. Industrial
stakeholders require analytical methods that are applicable to dispersions in their native state for
reasons of product development, quality control and regulatory compliance.
While many methods exist for characterization of nanoparticle properties, in particular their size and
size distribution, these methods typically require a specific and frequently complex sample preparation
(e.g. dilution, stirring, shearing or pumping) and, therefore, do not yield characteristics specific to as-
received dispersions. In addition, some experiments do not require measurement of a full particle
size distribution with the mean particle size being the main measurand. Using the mean particle size
measurement, it is possible to monitor other dispersion parameters of the system such as the state of
agglomeration, aggregation or dissolution.
Static multiple light scattering (SMLS) based methods do not require sample preparation allowing,
within limitations outlined in this document, direct measurement of the mean equivalent particle
diameter in the native (as-received) state of dispersion. In addition, and beyond the scope of this
document, SMLS is capable in some cases of monitoring in real time the temporal evolution of mean
equivalent particle diameter due to agglomeration or aggregation processes.
This document describes a standardized method for evaluating the mean equivalent particle diameter
in various sample types (including as-received samples) having a wide range of concentrations using
the SMLS based method.
v
TECHNICAL SPECIFICATION ISO/TS 21357:2022(E)
Nanotechnologies — Evaluation of the mean size of nano-
objects in liquid dispersions by static multiple light
scattering (SMLS)
1 Scope
This document provides guidance and requirements for the determination of the mean (spherical)
equivalent diameter of nano-objects (i.e. particles, droplets or bubbles) dispersed in liquids using
the static multiple light scattering (SMLS) technique. The technique is applicable to a wide range of
materials and does not require dilution of concentrated samples.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO/TS 80004-1, Nanotechnologies — Vocabulary — Part 1: Core terms
ISO/TS 80004-2, Nanotechnologies — Vocabulary — Part 2: Nano-objects
ISO/TS 80004-4, Nanotechnologies — Vocabulary — Part 4: Nanostructured materials
ISO/TS 80004-6, Nanotechnologies — Vocabulary — Part 6: Nano-object characterization
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO/TS 80004-1, ISO/TS 80004-2,
ISO/TS 80004-4, ISO/TS 80004-6 and the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
static multiple light scattering
SMLS
technique in which transmitted or backscattered light intensity is measured after multiple successive
scattering events of incident light in a random scattering medium
3.2
transport mean free path
average distance that a photon travels before its direction vector in its initial direction of motion is
reduced to 1/e of its initial magnitude by elastic scattering alone
[SOURCE: ISO 18115-1:2013, 4.299, modified — "an energetic particle" has been changed to "a photon";
"momentum" has been changed to "direction vector"; "initial value" has been changed to "initial
magnitude"; notes to entry have been deleted.]
ISO/TS 21357:2022(E)
3.3
mean free path
mean distance between photon scattering events in a dispersion
[SOURCE: ISO 22493:2014, 3.2.4, modified — "electron" has been changed to "photon".]
3.4
volume fraction
quotient of the volume of a specified component and the total sample volume
3.5
refractive index
ratio of the speed of light (more exactly, the phase velocity) in a vacuum to the speed of that same light
in a material
[SOURCE: ISO 18369-1:2017, 3.1.6.3, modified — “(more exactly, the phase velocity)” has been added;
the alternative preferred term "index of refraction" and note 1 to entry have been deleted.]
3.6
equivalent particle diameter
diameter of the sphere with defined characteristics which behaves under defined conditions in exactly
the same way as the particle being described
[SOURCE: ISO 21501-1:2009, 2.4]
3.7
absorption
reduction of intensity of a light beam not due to scattering
[SOURCE: ISO 13320:2020, 3.1.1]
4 Symbols and abbreviated terms
I backscattered light intensity
BS
I transmitted light intensity
T
*
transport mean free path
l
l
mean free path
g
asymmetry factor
Q extinction efficiency factor
e
ϕ
volume fraction
D
mean equivalent particle diameter
λ
wavelength of the incident light (in vacuum)
R sample half thickness
n refractive index
T light flux transmitted by the continuous phase
TEM transmission electron microscopy
CCD charge-coupled device
ISO/TS 21357:2022(E)
CMOS complementary metal–oxide–semiconductor
ILC interlaboratory comparison
RM reference material
VAMAS Versailles Project on Advanced Materials and Standards
5 Principles
5.1 Relevant theory
The SMLS technique is based on the principle of elastic light scattering from dispersed objects in a
liquid. Incident light is scattered multiple times successively, which results in a loss of correlation
of the incident light direction. The I or I light depends on the incident light wavelength, particle
BS T
concentration, particle size and shape, optical properties (n and absorption of both the continuous and
dispersed phases), and the measurement geometry.
Light propagation in concentrated dispersions (Figure 1) can be characterised by two parameters: the
*
[8],[9],[11]
mean free path (Formula (1)), l , and the transport mean free path, l . The mean free path
*
characterizes scattering phenomena at the microscopic level, while l describes multiple scattering at a
macroscopic level as the penetration depth of radiation in a random medium (i.e. no significant
*
[14]
correlation between scattering objects). Both parameters l and l are related by the Mie theory
[11]
under the hypothesis where l>λ :
2D
l= (1)
3ϕQ
e
where D is the mean equivalent particle diameter, ϕ is the volume fraction of the material and Q is the
e
extinction efficiency factor.
l
*
l = (2)
1− g
()
NOTE 1 The anisotropic scattering of light by an object can be characterized by the asymmetry factor g, which
is the average cosine (cos θ) of the scattering angles weighted by the phase function or scattering diagram of the
[14]
scatterer (e.g. g = 0 for isotropic Rayleigh scatterers and 0 < g < 1 for Mie scatterers) . Q takes into account
e
scattering efficiency and light absorption phenomena.
ISO/TS 21357:2022(E)
Key
1 high I signal 2 low I signal
T BS
3 low I signal 4 high I signal
T BS
NOTE The I dependence on the volume fraction is depicted.
BS
*
Figure 1 — Schematic representation of the I , I , l and l
BS T
[8],[14]
Both Q and g are described by the Mie theory and depend on optical properties of the particles
e
and the medium, particle size and wavelength of light.
The Mie theory is then used to determine either equivalent particle diameter or volume fraction,
provided that the other is known, from I or I . This is accomplished by comparing the experimental
T BS
*
values of l or l with the values determined from the Mie theory.
[13]
For measuring (for instance) I from the incident light, it is possible to derive an approximate :
BS
31ϕ()−gQ
α  
2 e
I =+βα= +β (3)
BS
 
*
2D
l  
Due to the influence of experimental geometry and the optical detector, an output calibration to convert
the raw I and the raw I (e.g. voltage signal) into an exploitable unit is used. The gain α and offset β
BS T
*
in Formula (3) are determined with a set of samples of different volume fraction with known l
(calculated theoretically with the Mie theory).
[15]
The light-flux transmitted through a sample can be expressed as :
3RQϕ
2R
 
  e
−
−
 
 
D
l
   
Il(),RT==eeT (4)
T 0 0
*
NOTE 2 Variations of I and I as a function of l and l respectively are illustrated in Annex A. Variations of
BS T
I and I on mean equivalent particle diameter D for TiO and melamine resin nanoparticles are illustrated in
BS T 2
Annex B.
ISO/TS 21357:2022(E)
5.2 Key measurands
The measurand used in SMLS is a volume weighted mean equivalent (spherical) particle diameter. For a
*
polydisperse suspension case, an effective l is defined that takes into account contributions to the
signal from individual particles of various sizes (as described in 5.1). The diameter corresponding to
*
the effective l is called the mean equivalent (spherical) particle diameter, also see Formula (2).
It can be shown that for particles smaller than the wavelength of light, the measured mean equivalent
[10],[11]
particle diameter linearly correlates with the mean volume diameter, D . In this case,
backscattered light intensity scales approximately as D , meaning that “larger” (but still smaller than
λ ) particles contribute more to the signal.
The dependence of I and I on the mean equivalent particle diameter is shown in Figure 2 by way
BS T
of example. It is the calculated I and I as a function of mean equivalent particle diameter in a 5 %
BS T
volume fraction titanium dioxide aqueous dispersion.
Key
X D [nm] I
BS
Y intensity of light [%] I
T
Figure 2 — Calculated I and I as a function of particle diameter for an aqueous dispersion
BS T
(n = 1,33) of titanium dioxide (n = 2,50, φ = 5 %, λ = 880 nm)
The I and I signals are instrument and sample dependent. Thus, as a rule of thumb, mean equivalent
T BS
particle diameter estimation is obtained from I signal provided that it is not null and I signal when
T BS
I is null.
T
NOTE Although outside the scope of the document, for particles larger than λ , the measured mean
[9],[10]
equivalent particle diameter correlates with the mean surface diameter D . In this case, the I signal scales
BS
−1
as D , meaning that “smaller” (but still larger than λ ) particles contribute more to the backscattered intensity.
ISO/TS 21357:2022(E)
5.3 Method applicability and limitations
5.3.1 General
The SMLS technique can determine the mean equivalent particle diameter of nano-objects in
concentrated dispersions as well as monitor stability of dispersions over time on the very same sample
as it is a non-destructive method. It should be noted that this technique may be used
...