ISO/TS 21357:2022
(Main)Nanotechnologies — Evaluation of the mean size of nano-objects in liquid dispersions by static multiple light scattering (SMLS)
Nanotechnologies — Evaluation of the mean size of nano-objects in liquid dispersions by static multiple light scattering (SMLS)
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.
Nanotechnologies — Évaluation de la taille moyenne des nano-objets dans les dispersions liquides par diffusion statique multiple de la lumière (DSML)
Le présent document présente des recommandations et des exigences pour la détermination du diamètre équivalent moyen (sphérique) de nano-objets (particules, gouttelettes ou bulles) dispersés dans des liquides au moyen de la technique de diffusion statique multiple de la lumière (DSML). La technique est applicable à une large gamme de matériaux et n’exige pas la dilution des échantillons concentrés.
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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 2022
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ISO/TS 21357:2022(E)
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© ISO 2022
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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Published in Switzerland
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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
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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.
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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.
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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.]
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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
0
TEM transmission electron microscopy
CCD charge-coupled device
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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.
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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
1
2
2
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.
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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,
3
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.
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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 for dispersions of
solid particles in liquids (i.e. suspensions), liquid-in-liquid emulsions and bubble dispersions in liquids.
The SMLS technique does not allow for the analysis of particle size distributions. It yields a single
parameter based on the I or I measurement, which is converted into a mean equivalent particle
BS T
diameter (when the particle concentration and n are known). This limits the applicability of the
measurement technique to dynamic systems where at least one parameter (equivalent particle
diameter or volume fraction) remains constant during the measurement. For mean equivalent particle
diameter measurement, material n and volume fraction shall be known independently. The method has
been successfully applied to measurements of metal oxides, metals, ceramics, emulsions and ultrafine
bubble dispersions in water.
5.3.2 Sample concentration
The ability to analyse undiluted (as-received) samples that have not been modified by sample
preparation is one of the main strengths of the SMLS method. Another feature of the method is the
ability to measure mean equivalent particle diameter for a broad range of concentrations (from very
low to very high concentration). 5.1 describes how I and I relate to system parameters and the
T BS
equivalent particle diameter and concentration. Using the Mie theory, I and I can be calculated for a
BS T
given material (such as 100 nm diameter silica beads in water). Figure 3 shows these data.
Key
X φ [%] I
BS
Y intensity of light [%] I
T
Figure 3 — Variation of I and I with particle volume fraction for silica beads (n = 1,46) in
T BS
water (n = 1,33) with D = 100 nm and λ = 880 nm
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ISO/TS 21357:2022(E)
The calculated data in Figure 3 are plotted for dispersions with volume fractions varying from 0,001 %
to 40 %. The method equally applies to very low concentration. Although there is no discrete boundary
between single scattering and multiple scattering regimes, it should be noted that phenomenologically
Formulae (3) and (4) are valid in both regimes. The effect of changing concentration is demonstrated
experimentally in Annex E for TiO dispersions in water.
2
The scattering by dispersed nano-objects depends heavily on several parameters, such as a material’s
n or particle size and the optical set-up of the instrument used for the evaluation. For this reason, the
lower concentration limit is sample/instrument dependent. For the purpose of this document, the lower
−4
applicable concentration value is taken to be approximately 10 % volume fraction.
In the example given in Figure 3, the calculated data reach approximately 40 % volume fraction. Just
like for the lower concentration limit, the upper limit depends on the sample and instrument properties.
5.3.3 Mean equivalent particle diameter
Particles with diameters ranging as widely as 10 nm to 100 μm can be evaluated by SMLS. These size
limits are approximate and depend heavily on the samples. Indeed, just like for volume fraction, the
actual lower and upper size limits are determined by a number of factors, such as the particles and
continuous phase refractive indices, concentration, wavelength of light and instrument set-up.
5.3.4 Sample homogeneity and stability
SMLS is a non-destructive technique based on measurement of I and I over time to characterise
BS T
the physical evolution of a dispersion due to a destabilisation process (e.g. sedimentation, creaming,
[10]
aggregation, agglomeration or coalescence) . In all cases, the time scale of change in dispersion
parameters should be slower than the time required for a single-time-point intensity measurement in
the SMLS data sampling.
NOTE In practice a SMLS single point data acquisition interval at a given cell position is in the millisecond
range.
For the mean equivalent particle diameter measurement of nano-objects by SMLS, the sample
shall be homogeneous in terms of concentration (i.e. no sedimentation, creaming or floatation).
Spatially dependent sampling of data along the measurement cell enables one to identify these local
heterogeneities in the sample.
To identify concentration evolution due to sedimentation or creaming, the SMLS light source scans
a sample cell vertically. Repeating the scans at fixed time intervals provides information about
destabilisation kinetics (i.e. rate of change of concentration). In some systems this can be a critical
indicator of the mean equivalent particle diameter measurement quality since the local volume fraction
of measured objects in the dispersion should be uniform and stable. If local concentration change or
non-uniformity is observed, then the global volume fraction should not be used for particle sizing
measurement or homogenisation is required. In case of varying concentration with time or height, the
mean equivalent particle diameter measurement can increase its uncertainty for I and I according to
BS T
Formulae (3) and (4).
5.4 Method characteristics
Table 1 summarises the characteristics of the technique for the measurement of key dispersion
parameters.
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ISO/TS 21357:2022(E)
Table 1 — SMLS measurement characteristics
Method feature Applicability Notes
a
Sample preparation Generally not required Sample preparation procedure may not be required (see 7.2).
Concentration range Approximately from Dilution (ISO 14488) of the sample is not necessary; and most
0,000 1 % to 40 % vol- samples are measured in as-received form. Sample concentra-
ume fraction tion limits are discussed in 5.3.2.
Equivalent particle diameter Approximately from The lower and upper size limits are discussed in 5.3.3.
range 10 nm to 100 µm
Stability of suspension Sample should be sta- The size measurement as a function of aging time can be per-
ble during the time formed on the same sample. The allowed range of change of
required for the meas- the intensity is discussed in 5.3.4.
urement
Homogeneity Homogeneous over the The mean particle size and concentration can vary based on
whole sample height the position in the sample. This is due to non-uniform sample
mixing and processes such as sedimentation, creaming or
other instabilities.
Spatially dependent sampling of data along the measurement
cell enables one to identify these local heterogeneities in the
sample. The allowed range of homogeneity of suspension is
discussed in 5.3.4.
a
Sample preparation can mean any action done onto the sample including dilution, dispersion, sonication, etc. For
samples that have settled or creamed homogenisation prior to the mean equivalent particle diameter measurements is
required to have uniform concentration.
6 Apparatus
The common geometry for this kind of measurement is shown in Figure 4. Light from the source is
directed into a liquid dispersion. Two sensors (e.g. photodiodes, CCD or CMOS) allow for a simultaneous
measurement of the backscattered and transmitted light. The incident light wavelength should
be chosen in order to minimize light absorption by the dispersed particles: near-infrared light is
advantageous to utilize in the measurement of highly absorbent products. The temperature of the
sample should not vary by more than 0,5 °C during the measurement to ensure the repeatability of
the result. Temperature of the dispersion affects a number of parameters such as refractive indices,
viscosity of co
...
SPÉCIFICATION ISO/TS
TECHNIQUE 21357
Première édition
2022-01
Nanotechnologies — Évaluation de la
taille moyenne des nano-objets dans
les dispersions liquides par diffusion
statique multiple de la lumière
(DSML)
Nanotechnologies — Evaluation of the mean size of nano-objects in
liquid dispersions by static multiple light scattering (SMLS)
Numéro de référence
ISO/TS 21357:2022(F)
© ISO 2022
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ISO/TS 21357:2022(F)
DOCUMENT PROTÉGÉ PAR COPYRIGHT
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Publié en Suisse
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ISO/TS 21357:2022(F)
Sommaire Page
Avant-propos .iv
Introduction .v
1 Domaine d’application . 1
2 Références normatives .1
3 Termes et définitions . 1
4 Symboles et abréviations .2
5 Principes . 3
5.1 Théorie concernée . 3
5.2 Mesurandes principaux . 5
5.3 Applicabilité et limites de la méthode . 6
5.3.1 Généralités . 6
5.3.2 Concentration de l’échantillon . 6
5.3.3 Diamètre équivalent moyen des particules . . 7
5.3.4 Homogénéité et stabilité de l’échantillon . 8
5.4 Caractéristiques de la méthode . 8
6 Appareillage . 9
7 Mode opératoire de mesurage . .10
7.1 Préparation des instruments . 10
7.2 Manipulation des échantillons . 10
7.3 Paramètres du système . 11
7.3.1 Généralités . 11
7.3.2 Mode opératoire de vérification de l’homogénéité de l’échantillon . 11
7.3.3 Fraction volumique . 11
7.3.4 Indice de réfraction . 11
8 Qualification des performances .11
9 Enregistrement des données .12
10 Incertitude de mesure.12
Annexe A (informative) I et I versus l* et l .13
R T
Annexe B (informative) I et I en fonction de D pour des particules de dioxyde de titane et
R T
de résine mélamine .14
Annexe C (informative) Qualification de l’instrument .16
Annexe D (informative) Analyse comparative de suspensions de latex à diverses
concentrations . .17
Annexe E (informative) Analyse de suspensions de dioxyde de titane à différentes
concentrations . .18
Annexe F (informative) Résultats d’une étude de comparaison interlaboratoires .20
Bibliographie .23
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ISO/TS 21357:2022(F)
Avant-propos
L’ISO (Organisation internationale de normalisation) est une fédération mondiale d’organismes
nationaux de normalisation (comités membres de l’ISO). L’élaboration des Normes internationales est
en général confiée aux comités techniques de l’ISO. Chaque comité membre intéressé par une étude
a le droit de faire partie du comité technique créé à cet effet. Les organisations internationales,
gouvernementales et non gouvernementales, en liaison avec l’ISO participent également aux travaux.
L’ISO collabore étroitement avec la Commission électrotechnique internationale (IEC) en ce qui
concerne la normalisation électrotechnique.
Les procédures utilisées pour élaborer le présent document et celles destinées à sa mise à jour sont
décrites dans les Directives ISO/IEC, Partie 1. Il convient, en particulier de prendre note des différents
critères d’approbation requis pour les différents types de documents ISO. Le présent document
a été rédigé conformément aux règles de rédaction données dans les Directives ISO/IEC, Partie 2
(voir www.iso.org/directives).
L’attention est attirée sur le fait que certains des éléments du présent document peuvent faire l’objet de
droits de propriété intellectuelle ou de droits analogues. L’ISO ne saurait être tenue pour responsable
de ne pas avoir identifié de tels droits de propriété et averti de leur existence. Les détails concernant
les références aux droits de propriété intellectuelle ou autres droits analogues identifiés lors de
l’élaboration du document sont indiqués dans l’Introduction et/ou dans la liste des déclarations de
brevets reçues par l’ISO (voir www.iso.org/brevets).
Les appellations commerciales éventuellement mentionnées dans le présent document sont données
pour information, par souci de commodité, à l’intention des utilisateurs et ne sauraient constituer un
engagement.
Pour une explication de la nature volontaire des normes, la signification des termes et expressions
spécifiques de l’ISO liés à l’évaluation de la conformité, ou pour toute information au sujet de l’adhésion
de l’ISO aux principes de l’Organisation mondiale du commerce (OMC) concernant les obstacles
techniques au commerce (OTC), voir www.iso.org/avant-propos.
Le présent document a été élaboré par le comité technique ISO/TC 229, Nanotechnologies.
La présente version française de l'ISO/TS 21357:2022 correspond à la version anglaise publiée le 2022-
01 et corrigée le 2022-03.
Il convient que l’utilisateur adresse tout retour d’information ou toute question concernant le présent
document à l’organisme national de normalisation de son pays. Une liste exhaustive desdits organismes
se trouve à l’adresse www.iso.org/fr/members.html.
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ISO/TS 21357:2022(F)
Introduction
Les dispersions liquides de nanoparticules sont largement utilisées dans l’industrie. Les nanoparticules
dispersées dans des liquides interagissent selon diverses forces faibles ou fortes, ce qui peut entraîner
l’agrégation ou l’agglomération des objets (particules primaires, agglomérats, agrégats, etc.). Il en résulte
que l’état de dispersion et la taille moyenne des particules ainsi que la distribution granulométrique
peuvent différer de ceux qui ont été déterminés pendant la fabrication, le stockage et le traitement, en
particulier en cas d’utilisation de mesurages exigeant une dilution des échantillons ou une préparation
extensive. La préparation des échantillons peut entraîner la rupture ou la formation d’agrégats ou
d’agglomérats et peut également dans certains cas affecter la morphologie des particules primaires.
Pour des raisons de développement de produit, de contrôle qualité et de conformité règlementaire, les
industries concernées exigent des méthodes analytiques applicables aux dispersions dans leur état
natif.
Bien qu’il existe de nombreuses méthodes de caractérisation des propriétés des nanoparticules, en
particulier de leur taille et de leur distribution granulométrique, ces méthodes exigent généralement
une préparation spécifique et souvent complexe des échantillons (par exemple dilution, agitation,
cisaillement ou pompage) et par conséquent, ne fournissent pas les caractéristiques spécifiques
des dispersions en l’état. De plus, certaines expériences n’exigent pas le mesurage d’une distribution
granulométrique complète, la taille moyenne des particules étant le mesurande principal. À l’aide
du mesurage de la taille moyenne des particules, il est possible de contrôler d’autres paramètres de
dispersion du système, tels que l’état d’agglomération, d’agrégation ou de dissolution.
Les méthodes basées sur la diffusion statique multiple de la lumière (DSML) n’exigent aucune
préparation de l’échantillon, ce qui permet, dans les limites soulignées dans le présent document, un
mesurage direct du diamètre équivalent moyen des particules dans l’état de dispersion natif (en l’état).
De plus et au-delà du domaine d’application du présent document, la DSML peut dans certains cas
contrôler en temps réel l’évolution temporelle du diamètre équivalent moyen des particules due aux
processus d’agglomération ou d’agrégation.
Le présent document décrit une méthode normalisée d’évaluation du diamètre équivalent moyen des
particules dans divers types d’échantillons (dont les échantillons en l’état) présentant une large plage
de concentrations, au moyen de la méthode basée sur la DSML.
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SPÉCIFICATION TECHNIQUE ISO/TS 21357:2022(F)
Nanotechnologies — Évaluation de la taille moyenne des
nano-objets dans les dispersions liquides par diffusion
statique multiple de la lumière (DSML)
1 Domaine d’application
Le présent document présente des recommandations et des exigences pour la détermination du
diamètre équivalent moyen (sphérique) de nano-objets (particules, gouttelettes ou bulles) dispersés
dans des liquides au moyen de la technique de diffusion statique multiple de la lumière (DSML). La
technique est applicable à une large gamme de matériaux et n’exige pas la dilution des échantillons
concentrés.
2 Références normatives
Les documents suivants sont cités dans le texte de sorte qu’ils constituent, pour tout ou partie de leur
contenu, des exigences du présent document. Pour les références datées, seule l’édition citée s’applique.
Pour les références non datées, la dernière édition du document de référence s’applique (y compris les
éventuels amendements).
ISO/TS 80004-1, Nanotechnologies — Vocabulaire — Partie 1: Termes "cœur"
ISO/TS 80004-2, Nanotechnologies — Vocabulaire — Partie 2: Nano-objets
ISO/TS 80004-4, Nanotechnologies — Vocabulaire — Partie 4: Matériaux nanostructurés
ISO/TS 80004-6, Nanotechnologies — Vocabulaire — Partie 6: Caractérisation des nano-objets
3 Termes et définitions
Pour les besoins du présent document, les termes et définitions donnés dans l’ISO/TS 80004-1,
l’ISO/TS 80004-2, l’ISO/TS 80004-4, l’ISO/TS 80004-6 ainsi que les suivants s’appliquent.
L’ISO et l’IEC tiennent à jour des bases de données terminologiques destinées à être utilisées en
normalisation, consultables aux adresses suivantes:
— ISO Online browsing platform: disponible à l'adresse https:// www .iso .org/ obp
— IEC Electropedia: disponible à l'adresse https:// www .electropedia .org/
3.1
diffusion statique multiple de la lumière
DSML
technique permettant de mesurer l’intensité de la lumière transmise ou rétrodiffusée après de multiples
événements successifs de diffusion de la lumière incidente dans un milieu de diffusion aléatoire
3.2
distance moyenne de transport
distance moyenne parcourue par un photon avant que son vecteur directeur dans sa direction initiale
de déplacement soit réduit à 1/e de son amplitude initiale par diffusion élastique uniquement
[SOURCE: ISO 18115-1:2013, 4.299, modifié — «particule énergétique» a été remplacé par «photon»;
«momentum» a été remplacé par «vecteur directeur»; «valeur initiale» a été remplacé par «amplitude
initiale»; les notes à l'article ont été supprimées.]
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ISO/TS 21357:2022(F)
3.3
libre parcours moyen
distance moyenne entre des événements de diffusion de photons dans une dispersion
[SOURCE: ISO 22493:2014, 3.2.4, modifié — «électron» a été remplacé par «photon».]
3.4
fraction volumique
rapport entre le volume d’un composant spécifié et le volume total de l’échantillon
3.5
indice de réfraction
rapport entre la vitesse de la lumière (plus exactement la vitesse de phase) dans le vide et la vitesse de
cette même lumière dans un matériau
[SOURCE: ISO 18369-1:2017, 3.1.6.3, modifié — «(plus exactement la vitesse de phase)» a été ajouté; le
terme préféré alternatif «indice de réfraction» et la Note 1 à l’article ont été supprimés.]
3.6
diamètre équivalent des particules
diamètre de la sphère présentant des caractéristiques définies qui se comporte, dans des conditions
définies, exactement de la même manière que la particule décrite
[SOURCE: ISO 21501-1:2009, 2.4]
3.7
absorption
réduction de l’intensité d’un faisceau lumineux qui n’est pas due à la diffusion
[SOURCE: ISO 13320:2020, 3.1.1]
4 Symboles et abréviations
I intensité lumineuse rétrodiffusée
R
I intensité lumineuse transmise
T
l* distance moyenne de transport
l libre parcours moyen
g facteur d’asymétrie
Q efficacité d’extinction
e
φ fraction volumique
D diamètre équivalent moyen des particules
λ longueur d’onde de la lumière incidente (dans le vide)
R demi-épaisseur de l’échantillon
n indice de réfraction
T flux lumineux transmis par la phase continue
0
MET microscopie électronique à transmission
DCC dispositif à couplage de charge
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ISO/TS 21357:2022(F)
CMOS semi-conducteur à oxyde de métal complémentaire
ILC comparaison interlaboratoires
MR matériau de référence
VAMAS Versailles Project on Advanced Materials and Standards
5 Principes
5.1 Théorie concernée
La technique de DSML est basée sur le principe de la diffusion élastique de la lumière par des objets
dispersés dans un liquide. La lumière incidente est diffusée de multiples fois successivement, ce qui
entraîne une perte de corrélation de la direction de la lumière incidente. La lumière I ou I dépend de
R T
la longueur d’onde de la lumière incidente, de la concentration des particules, de la taille et de la forme
des particules, des propriétés optiques (n et absorption des deux phases continue et dispersée) et de la
géométrie de mesurage.
La propagation de la lumière dans les dispersions concentrées (Figure 1) peut être caractérisée
par deux paramètres: le libre parcours moyen (Formule (1)), l et la distance moyenne de transport,
[8],[9],[11]
l* . Le libre parcours moyen caractérise les phénomènes de diffusion au niveau microscopique,
tandis que l* décrit la diffusion multiple au niveau macroscopique, comme la profondeur de pénétration
des rayonnements dans un milieu aléatoire (c’est-à-dire qu’il n’existe pas de corrélation significative
[14]
entre les diffuseurs). Les deux paramètres l et l* sont liés par la théorie de Mie dans l’hypothèse où
[11]
l > λ :
2D
l= (1)
3ϕQ
e
où D est le diamètre équivalent moyen des particules, φ est la fraction volumique du matériau et Q est
e
l’efficacité d’extinction.
l
*
l = (2)
()1− g
NOTE 1 La diffusion anisotropique de la lumière par un objet peut être caractérisée par le facteur d’asymétrie g,
qui est la moyenne des cosinus (cos θ) des angles de diffusion pondérés par la fonction de phase ou le diagramme
de diffusion du diffuseur (par exemple g = 0 pour les diffuseurs isotropiques de Rayleigh et 0 < g < 1 pour les
[14]
diffuseurs de Mie) . Q tient compte des phénomènes de diffusion et d’absorption de la lumière.
e
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ISO/TS 21357:2022(F)
Légende
1 signal I élevé 2 signal I faible
T R
3 signal I faible 4 signal I élevé
T R
NOTE La dépendance de I à la fraction volumique est décrite.
R
Figure 1 — Représentation schématique de I , I , l et l*
R T
[8],[14]
Q et g sont tous deux décrits par la théorie de Mie et dépendent des propriétés optiques des
e
particules et du milieu, de la taille des particules et de la longueur d’onde de la lumière.
La théorie de Mie est ensuite utilisée pour déterminer soit le diamètre équivalent des particules soit
leur fraction volumique, à condition que l’autre soit connu, à partir de I ou de I . Cela est accompli par
T R
la comparaison des valeurs expérimentales de l ou l* avec les valeurs déterminées par la théorie de Mie.
Pour mesurer (par exemple) I à partir de la lumière incidente, il est possible de dériver une
R
[13]
approximation :
1
2
2
31ϕ()−gQ
α
2 e
I =+βα= +β (3)
R
*
2D
l
En raison de l’influence de la géométrie expérimentale et du détecteur optique, un étalonnage de
sortie est utilisé pour convertir les valeurs brutes de I et I (par exemple signal de tension) en
R T
unité exploitable. Le gain α et le décalage β dans la Formule (3) sont déterminés avec un ensemble
d’échantillons de fraction volumique différente avec un l* connu (calculé théoriquement par la théorie
de Mie).
[15]
Le flux lumineux transmis à travers un échantillon peut être exprimé comme suit :
3RQϕ
2R
e
− −
l D
Il,RT==eeT (4)
()
T 0 0
NOTE 2 Les variations de I et I en fonction de l* et l respectivement sont illustrées à l’Annexe A. Les
R T
variations de I et I sur le diamètre équivalent moyen des particules D pour des nanoparticules de TiO et de
R T 2
résine mélamine sont illustrées à l’Annexe B.
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ISO/TS 21357:2022(F)
5.2 Mesurandes principaux
Le mesurande utilisé dans la DSML est un diamètre équivalent (sphérique) moyen des particules. Pour
une suspension polydispersée, un l* effectif est défini qui tient compte des contributions au signal
de particules individuelles de diverses tailles (comme décrit en 5.1). Le diamètre correspondant
au l* effectif est appelé le diamètre équivalent (sphérique) moyen des particules, voir également la
Formule (2).
Il peut être démontré que pour des particules de taille inférieure à la longueur d’onde de la lumière,
le diamètre équivalent moyen des particules mesuré est linéairement corrélé au diamètre volumique
[10],[11]
moyen, D . Dans ce cas, l’intensité lumineuse rétrodiffusée est approximativement proportionnelle
3
à D , ce qui signifie que des particules «plus grosses» (mais toujours inférieures à λ) contribuent plus au
signal.
La dépendance de I et I au diamètre équivalent moyen des particules est représentée sur la Figure 2
R T
à titre d’exemple. Il s’agit de I et I calculés en fonction du diamètre équivalent moyen des particules
R T
dans une dispersion aqueuse de dioxyde de titane à 5 % de fraction volumique.
Légende
X D [nm] I
R
Y intensité de la lumière [%] I
T
Figure 2 — I et I calculés en fonction du diamètre des particules pour une dispersion aqueuse
R T
(n = 1,33) de dioxyde de titane (n = 2,50, φ = 5 %, λ = 880 nm)
Les signaux I et I dépendent des instruments et de l’échantillon. Ainsi, selon une règle empirique,
T R
l’estimation du diamètre équivalent moyen des particules est obtenue à partir du signal I à condition
T
qu’il soit non nul et du signal I lorsque I est nul.
R T
NOTE Bien que ne faisant pas partie du domaine d’application du présent document, pour les particules de
taille supérieure à λ, le diamètre équivalent moyen des particules mesuré est corrélé au diamètre de surface
[9],[10] −1
moyen D . Dans ce cas, le signal I est proportionnel à D , ce qui signifie que les particules «plus petites»
R
(mais toujours supérieures à λ) contribuent plus à l’intensité de la lumière rétrodiffusée.
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ISO/TS 21357:2022(F)
5.3 Applicabilité et limites de la méthode
5.3.1 Généralités
La technique de DSML permet de déterminer le diamètre équivalent moyen des particules de nano-objets
dans des dispersions concentrées, et de contrôler la stabilité des dispersions dans le temps sur le même
échantillon, puisqu’il s’agit d’une méthode non destructive. Il convient de noter que cette technique
peut être utilisée pour les dispersions de particules solides dans des liquides (des suspensions), des
émulsions de liquide dans du liquide et des dispersions de bulles dans des liquides.
La technique de DSML ne permet pas l’analyse des distributions granulométriques. Elle donne un
paramètre unique basé sur le mesurage de I ou de I , qui est converti en un diamètre équivalent moyen
R T
des particules (lorsque la concentration des particules et n sont connus). Cela limite l’applicabilité
de la technique de mesurage aux systèmes dynamiques dans lesquels au moins un paramètre
(diamètre équivalent des particules ou fraction volumique) reste constant pendant le mesurage. Pour
le mesurage du diamètre équivalent moyen des particules, le n et la fraction volumique du matériau
doivent être connus indépendamment. La méthode a été appliquée avec succès à des mesurages d’oxydes
métalliques, de métaux, de céramiques, d’émulsions et de dispersions de bulles ultrafines dans l’eau.
5.3.2 Concentration de l’échantillon
La capacité à analyser des échantillons non dilués (en l’état) qui n’ont pas été modifiés par une
préparation est l’un des atouts majeurs de la méthode de DSML. Une autre caractéristique de cette
méthode est la capacité à mesurer un diamètre équivalent moyen des particules pour une large plage
de concentrations (de très faible à très élevée). Le paragraphe 5.1 décrit comment I et I sont liés aux
T R
paramètres du système et au diamètre équivalent des particules et à leur concentration. À l’aide de la
théorie de Mie, I et I peuvent être calculés pour un matériau donné (par exemple des billes de silice de
R T
100 nm de diamètre dans de l’eau). La Figure 3 représente ces données.
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ISO/TS 21357:2022(F)
Légende
X φ [%] I
R
Y intensité de la lumière [%] I
T
Figure 3 — Variation de I et I en fonction de la fraction volumique des particules pour des
T R
billes de silice (n = 1,46) dans de l’eau (n = 1,33) avec D = 100 nm et λ = 880 nm
Les données calculées sur la Figure 3 sont tracées pour des dispersions présentant des fractions
volumiques allant de 0,001 % à 40 %. La méthode s’applique de la même façon à une concentration très
faible. Bien qu’il n’existe pas de limite discrète entre des régimes de diffusion simple et de diffusion
multiple, il convient de noter que de façon phénoménologique, les Formules (3) et (4) sont valides dans
les deux régimes. L’effet de la modification de la concentration est démontré de façon expérimentale à
l’Annexe E pour les dispersions de TiO dans l’eau.
2
La diffusion par des nano-objets dispersés dépend fortement de plusieurs paramètres, comme le n du
matériau ou la taille des particules et la configuration optique de l’instrument utilisé pour l’évaluation.
Pour cette raison, la limite inférieure de concentration dépend de l’échantillon ou de l’instrument. Dans
le présent document, la valeur de concentration inférieure applicable est approximativement égale à
−4
une fraction volumique de 10 %.
Dans l’exemple donné à la Figure 3, les données calculées atteignent une fraction volumique d’environ
40 %. De même que pour la limite de concentration inférieure, la limite supérieure dépend des
propriétés de l’échantillon et de l’instrument.
5.3.3 Diamètre équivalent moyen des particules
La DSML permet d’évaluer des diamètres de particules allant de 10 nm à 100 µm. Ces limites de tailles
sont approximatives et dépendent fortement des échantillons. Comme pour la fraction volumique, les
limites réelles inférieure et supérieure de taille sont en effet déterminées par un certain nombre de
facteurs, comme les indices de réfraction des particules et de la phase continue, la concentration, la
longueur d’onde de la lumière et la configuration de l’instrument.
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ISO/TS 21357:2022(F)
5.3.4 Homogénéité et stabilité de l’échantillon
La DSML est une technique non destructive basée sur le mesurage de I et de I dans le temps afin de
R T
caractériser l’évolution physique d’une dispersion due à un processus de déstabilisation (par exemple
[10]
une sédimentation, un crémage, une agrégation, une agglomération ou une coalescence) . Dans tous
les cas, il convient que l’échelle de temps du changement des paramètres de dispersion soit plus courte
que le temps nécessaire pour un point de mesurage temporel d’intensité unique dans l’échantillonnage
des données DSML.
NOTE Dans la pratique, l’intervalle d’acquisition d’une donnée unique de DSML à une position donnée de la
cellule est de l’ordre de la milliseconde.
Pour le mesurage du diamètre équivalent moyen des particules de nano-objets par DSML, l’échantillon
doit être homogène en matière de concentration (c’est-à-dire ne pas présenter de sédimentation, de
crémage ni de flottaison). L’échantillonnage spatial des données le long de la cellule de mesurage permet
d’identifier les hétérogénéités locales dans l’échantillon.
Afin d’identifier l’évolution de la concentration due à une sédimentation ou un crémage, la source de
lumière DSML balaye verticalement la cellule échantillon. La répétition des balayages à intervalles
temporels fixes donne des informations sur la cinéti
...
TECHNICAL ISO/TS
SPECIFICATION 21357
First edition
Nanotechnologies — Evaluation of the
mean size of nano-objects in liquid
dispersions by static multiple light
scattering (SMLS)
Nanotechnologies — Evaluation de la taille moyenne des nano-objets
dans les dispersions liquides par diffusion statique multiple de la
lumière (SMLS)
Member bodies are requested to consult relevant national interests in IEC/TC
113 before casting their ballot to the e-Balloting application.
PROOF/ÉPREUVE
Reference number
ISO/TS 21357:2021(E)
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ISO/TS 21357:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2021
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
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Published in Switzerland
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ISO/TS 21357:2021(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
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ISO/TS 21357:2021(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.
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.
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ISO/TS 21357:2021(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.
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TECHNICAL SPECIFICATION ISO/TS 21357:2021(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.]
1
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ISO/TS 21357:2021(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 regraction" and note 1 to enty 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
0
TEM transmission electron microscopy
CCD charge-coupled device
2
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ISO/TS 21357:2021(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.
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ISO/TS 21357:2021(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
1
2
2
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.
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ISO/TS 21357:2021(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,
3
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.
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ISO/TS 21357:2021(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 for dispersions of
solid particles in liquids (i.e. suspensions), liquid-in-liquid emulsions and bubble dispersions in liquids.
The SMLS technique does not allow for the analysis of particle size distributions. It yields a single
parameter based on the I or I measurement, which is converted into a mean equivalent particle
BS T
diameter (when the particle concentration and n are known). This limits the applicability of the
measurement technique to dynamic systems where at least one parameter (equivalent particle
diameter or volume fraction) remains constant during the measurement. For mean equivalent particle
diameter measurement, material n and volume fraction shall be known independently. The method has
been successfully applied to measurements of metal oxides, metals, ceramics, emulsions and ultrafine
bubble dispersions in water.
5.3.2 Sample concentration
The ability to analyse undiluted (as-received) samples that have not been modified by sample
preparation is one of the main strengths of the SMLS method. Another feature of the method is the
ability to measure mean equivalent particle diameter for a broad range of concentrations (from very
low to very high concentration). 5.1 describes how I and I relate to system parameters and the
T BS
equivalent particle diameter and concentration. Using the Mie theory, I and I can be calculated for a
BS T
given material (such as 100 nm diameter silica beads in water). Figure 3 shows these data.
Key
X φ [%] I
BS
Y intensity of light [%] I
T
Figure 3 — Variation of I and I with particle volume fraction for silica beads (n = 1,46) in
T BS
water (n = 1,33) with D = 100 nm and λ = 880 nm
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ISO/TS 21357:2021(E)
The calculated data in Figure 3 are plotted for dispersions with volume fractions varying from 0,001 %
to 40 %. The method equally applies to very low concentration. Although there is no discrete boundary
between single scattering and multiple scattering regimes, it should be noted that phenomenologically
Formulae (3) and (4) are valid in both regimes. The effect of changing concentration is demonstrated
experimentally in Annex E for TiO dispersions in water.
2
The scattering by dispersed nano-objects depends heavily on several parameters, such as a material’s
n or particle size and the optical set-up of the instrument used for the evaluation. For this reason, the
lower concentration limit is sample/instrument dependent. For the purpose of this document, the lower
−4
applicable concentration value is taken to be approximately 10 % volume fraction.
In the example given in Figure 3, the calculated data reach approximately 40 % volume fraction. Just
like for the lower concentration limit, the upper limit depends on the sample and instrument properties.
5.3.3 Mean equivalent particle diameter
Particles with diameters ranging as widely as 10 nm to 100 μm can be evaluated by SMLS. These size
limits are approximate and depend heavily on the samples. Indeed, just like for volume fraction, the
actual lower and upper size limits are determined by a number of factors, such as the particles and
continuous phase refractive indices, concentration, wavelength of light and instrument set-up.
5.3.4 Sample homogeneity and stability
SMLS is a non-destructive technique based on measurement of I and I over time to characterise
BS T
the physical evolution of a dispersion due to a destabilisation process (e.g. sedimentation, creaming,
[10]
aggregation, agglomeration or coalescence) . In all cases, the time scale of change in dispersion
parameters should be slower than the time required for a single-time-point intensity measurement in
the SMLS data sampling.
NOTE In practice a SMLS single point data acquisition interval at a given cell position is in the millisecond
range.
For the mean equivalent particle diameter measurement of nano-objects by SMLS, the sample
shall be homogeneous in terms of concentration (i.e. no sedimentation, creaming or floatation).
Spatially dependent sampling of data along the measurement cell enables one to identify these local
heterogeneities in the sample.
To identify concentration evolution due to sedimentation or creaming, the SMLS light source scans
a sample cell vertically. Repeating the scans at fixed time intervals provides information about
destabilisation kinetics (i.e. rate of change of concentration). In some systems this can be a critical
indicator of the mean equivalent particle diameter measurement quality since the local volume fraction
of measured objects in the dispersion should be uniform and stable. If local concentration change or
non-uniformity is observed, then the global volume fraction should not be used for particle sizing
measurement or homogenisation is required. In case of varying concentration with time or height, the
mean equivalent particle diameter measurement can increase its uncertainty for I and I according to
BS T
Formulae (3) and (4).
5.4 Method characteristics
Table 1 summarises the characteristics of the technique for the measurement of key dispersion
parameters.
Table 1 — SMLS measurement characteristics.
Method feature Applicability Notes
a
Sample preparation Generally not required Sample preparation procedure may not be required (see 7.2).
a
Sample preparation can mean any action done onto the sample including dilution, dispersion, sonication, etc. For
samples that have settled or creamed homogenisation prior to the mean equivalent particle diameter measurements is
required to have uniform concentration.
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ISO/TS 21357:2021(E)
Table 1 (continued)
Method feature Applicability Notes
Concentration range Approximately from Dilution (ISO 14488) of the sample is not necessary; and most
0,000 1 % to 40 % vol- samples are measured in as-received form. Sample concentra-
ume fraction tion limits are discussed in 5.3.2.
Equivalent particle diameter Approximately from The lower and upper size limits are discussed in 5.3.3.
range 10 nm to 100 µm
Stability of suspension Sample should be sta- The size measurement as a function of aging time can be per-
ble during the time formed on the same sample. The allowed range of change of
required for the meas- the intensity is discussed in 5.3.4.
urement
Homogeneity Homogeneous over the The mean particle size and concentration can vary based on
whole sample height the position in the sample. This is due to non-uniform sample
mixing and processes such as sedimentation, creaming or
other instabilities.
Spatially dependent sampling of data along the measurement
cell enables one to identify these local heterogeneities in the
sample. The allowed range of homogeneity of suspension is
discussed in 5.3.4.
a
Sample preparation can mean any action done onto the sample including dilution, dispersion, sonication, etc. For
samples that have settled or creamed homogenisation prior to the mean equivalent particle diameter measurements is
required to have uniform concentration.
6 Apparatus
The common geometry for this kind of measurement is shown in Figure 4. Light from the source is
directed into a liquid dispersion. Two sensors (e.g. photodiodes, CCD or CMOS) allow for a simultaneous
measurement of the backscattered and transmitted
...
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