ISO 18747-2:2019
(Main)Determination of particle density by sedimentation methods — Part 2: Multi-velocity approach
Determination of particle density by sedimentation methods — Part 2: Multi-velocity approach
This document specifies an in situ method for the determination of the density of solid particles or liquid droplets (herein referred to as "particle") dispersed in liquid continuous phase. The method is based on direct experimental determination of particle velocity in these liquids or media in gravitational or centrifugal fields based on Stokes law. The particle density is calculated from experimentally determined particle velocities in different liquids or media, taking into account their dynamic viscosities and densities, respectively. The approach does not require the knowledge of particle size distribution but assumes that sedimentation relevant characteristics (e.g. volume, shape, agglomeration state) do not change. This document does not consider polydispersity with regard to particle density, i.e. all particles are assumed to be of the same material composition.
Détermination de la densité de particules par méthodes de sédimentation — Partie 2: Approche à multi vitesses
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INTERNATIONAL ISO
STANDARD 18747-2
First edition
2019-06
Determination of particle density by
sedimentation methods —
Part 2:
Multi-velocity approach
Détermination de la densité de particules par méthodes de
sédimentation —
Partie 2: Approche à multi vitesses
Reference number
©
ISO 2019
© ISO 2019
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
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2019 – All rights reserved
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols . 2
5 Basic principle of the method . 2
6 Measuring techniques to determine sedimentation and creaming/flotation velocity
of dispersed particles . 4
7 Preparation of samples. 5
7.1 Continuous phase liquids . 5
7.2 Dispersing procedure . 6
8 Measurements and data analysis . 6
9 Reference materials and measurement uncertainty . 7
9.1 Reference materials . 7
9.2 Measurement uncertainty . 8
Annex A (informative) Isopycnic density gradient (buoyant density) centrifugation .10
Annex B (informative) Examples of measurements and data analysis to determine particle
density by multi-velocity approach .11
Annex C (informative) Uncertainty derivation of particle density based on uncertainty
propagation rules .15
Bibliography .18
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 24, Particle characterization including
sieving, Subcommittee SC 4, Particle characterization.
A list of all parts in the ISO 18747 series can be found on the ISO website.
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 2019 – All rights reserved
Introduction
Dispersions are widely used in industry and everyday life. There is a need to understand the density
of dispersed particles or droplets, e.g. for physico-chemical calculations such as kinematic viscosity
[1] [2][3]
of dispersions , determination of particle size distribution by sedimentation or acoustic
[4] [5]
techniques , particle characterization by field-flow approaches , optimization of dispersion long-
[6]
term stability by density matching as well as, more generally, characterization of particles (e.g.
composition, internal phase content of double emulsions or homogeneity of hollow capsules) in manifold
academic and industrial areas. Nowadays there is an increasing interest in using particle density to
estimate the mass transfer of nanoparticles atop cell layers by sedimentation (dosage calculation for in
[7][8][9]
vitro nanotoxicity assessment ).
The density of a body is defined as its mass divided by its volume. This calculation is straightforward
for a large uniform body or particle. However, determination of the volume of a macroscopic body is
difficult. The geometrical volume (defined by length, width and thickness) and the volume relevant for
the determination of density may differ due to surface irregularities, fractures, fissures and pores or
the measuring techniques employed.
Density determination of micro-particles, especially nanoparticles dispersed in a liquid, is difficult not
only due to the determination of mass and volume for small particles, but also due to the fuzzy boundary
[10]
between the liquid and the particle, which is often described in terms of a corona . Liquid and solute
molecules in the continuous phase are partially immobilized at the surface. Physico-chemical properties
(e.g. viscosity, ion composition, solute concentration) in the fuzzy coat differ from the bulk. This effect
is especially important for small microparticles and nanoparticles that are dispersed in a polymer or
[11]
biological media . The so-called corona may be interpreted as an integral part of the particle and
increases the effective/apparent volume compared to the space occupied by the dry particle. The
thickness of this layer ranges between a few to tens of nanometres. The effective/apparent volume
deviates increasingly from the “geometrical” volume of dry particles as the particles become smaller.
Correspondingly, density determination by traditional methods is affected. These concerns hold also
for particle size, which may refer to different geometrical and physical properties. In the context of this
document, the Stokes diameter and diameter of the enveloping sphere/hull are particularly relevant.
INTERNATIONAL STANDARD ISO 18747-2:2019(E)
Determination of particle density by sedimentation
methods —
Part 2:
Multi-velocity approach
1 Scope
This document specifies an in situ method for the determination of the density of solid particles or liquid
droplets (herein referred to as “particle”) dispersed in liquid continuous phase. The method is based
on direct experimental determination of particle velocity in these liquids or media in gravitational
or centrifugal fields based on Stokes law. The particle density is calculated from experimentally
determined particle velocities in different liquids or media, taking into account their dynamic viscosities
and densities, respectively. The approach does not require the knowledge of particle size distribution
but assumes that sedimentation relevant characteristics (e.g. volume, shape, agglomeration state) do
not change. This document does not consider polydispersity with regard to particle density, i.e. all
particles are assumed to be of the same material composition.
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 14887, Sample preparation — Dispersing procedures for powders in liquids
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http: //www .electropedia .org/
— ISO Online browsing platform: available at https: //www .iso .org/obp
3.1
buoyant density
ratio of particle mass to particle volume including filled or closed pores as well as adjacent layers of
liquid or other coating materials
3.2
dynamic viscosity
measure of the resistance of a fluid which is being deformed by shear stress
Note 1 to entry: Dynamic viscosity is calculated by shear stress divided by shear rate and determines the
dynamics of an incompressible Newtonian fluid.
3.3
migration
directed particle movement (sedimentation or creaming/flotation) due to acting gravitational or
centrifugal fields
Note 1 to entry: Sedimentation occurs when the density of droplets/particles is larger than that of the liquid.
Creaming/flotation occurs when the density of droplets/particles is smaller than that of the liquid. In these two
processes, particles move in opposite directions.
3.4
migration velocity
absolute value of sedimentation or creaming/flotation terminal velocity
Note 1 to entry: Velocity of creaming/flotation is indicated by a negative sign.
3.5
shape factor
ratio of the sedimentation velocity of a non-spherical particle to the one of a spherical particle of the
same volume and density
4 Symbols
Quantity Symbol Unit Derivative unit
Acceleration a m/s
Angular velocity ω rad/s
Coverage factor k —
Dynamic viscosity η Pa·s mPa·s
Expanded uncertainty for density U kg/m
Liquid density ρ kg/m
L
Maximum density ρ kg/m
max
Minimum density ρ kg/m
min
Particle density ρ kg/m
P
Radius r m mm
Relative centrifugal acceleration RCA —
Standard acceleration due to gravity g m/s
Temperature ϑ °C
Time t s
Velocity v m/s
Wavelength λ m nm
5 Basic principle of the method
Density is the mass of a body divided by its volume. In case of fine particles, microscopic surface and
internal structure have to be taken into account to define the true particle volume of a dry particle.
The true volume can be defined as the volume of the particle envelope minus the volume of external
and internal voids as depicted in Figure 1 a) and Figure 1 b). Voids may also be pores [see Figure 1 d)].
The measured “volume” depends on the applied determination technique (ideally 3D) and conditions
of measurement. When determining the envelope volume, adequate resolution is crucial for detecting
external voids due to surface irregularities, small fractures, fissures etc. Often the only information
[13][14]
available is from image analysis , and the volume is extrapolated based on geometric assumptions.
True particle density
...
© ISO 2019 – All rights reserved
INTERNATIONAL STANDARD
Deleted: /FDIS
2019-06
ISO TC 24/SC 4
Secretariat: BSI
Determination of particle density by sedimentation methods — Part 2: Multi-
velocity approach
Détermination de la densité de particules par méthodes de sédimentation — Partie 2:
Approche à multi vitesses
© ISO 2019, Published in Switzerland
All rights reserved. Unless otherwise specified, 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
Ch. de Blandonnet 8 • CP 401
CH‐1214 Vernier, Geneva, Switzerland
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
copyright@iso.org
www.iso.org Deleted: www.iso.org¶
ii © ISO 2019 – All rights reserved
Contents
Foreword . 5
Introduction. 6
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols . 2
5 Basic principle of the method . 2
Figure 1 — Schematic structures of particles (cross section) with regard to the measurand
particle density . 3
6 Measuring techniques to determine sedimentation and creaming/flotation velocity
of dispersed particles . 4
7 Preparation of samples . 5
7.1 Continuous phase liquids . 5
7.2 Dispersing procedure . 5
8 Measurements and data analysis . 6
Table 1 — Stock emulsion diluted with mixtures of H O and D O of different fractions,
2 2
density and dynamic viscosity of continuous phase (tuned by normal and heavy
water mixtures) and harmonic mean separation velocity of dispersed oil droplets
calculated from velocity distributions (see Figure B.1) . 6
Figure 2 — Experimental determined droplet density of polydimethylsiloxane emulsion . 7
9 Reference materials and measurement uncertainty . 7
9.1 Reference materials . 7
9.2 Measurement uncertainty . 8
Annex A (informative) Isopycnic density gradient (buoyant density) centrifugation . 9
Annex B (informative) Examples of measurements and data analysis to determine particle
density by multi-velocity approach . 10
B.1 Density determination of liquid particles (droplets) of polydimethylsiloxane
emulsion . 10
Figure B.1 — Creaming of dispersed phase (oil droplets) during centrifugation . 10
B.2 Density determination of spherical monodisperse polystyrene (PS) particles . 11
Figure B.2 — Cumulative velocity distributions and densities of monodisperse polystyrene
particles (x = 1,1 µm) dispersed in water and in five different concentrated sucrose
solutions . 12
B.3 Density determination of non-spherical reference particles produced from pine
pollen . 12
Figure B.3 — Cumulative velocity distributions of solid non-spherical microparticles
produced from pine pollen and pairwise calculated particle density according to
Formula (3) for three different percentiles . 13
© ISO 2019 – All rights reserved iii
Annex C (informative) Uncertainty derivation of particle density based on uncertainty
propagation rules . 14
Bibliography . 17
iv © ISO 2019 – All rights reserved
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
Deleted: www.iso.org/directives
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). Deleted: 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. Deleted: www.iso.org/iso/foreword.ht
ml
This document was prepared by Technical Committee ISO/TC 24, Particle characterization including
sieving, Subcommittee SC 4, Particle characterization.
A list of all parts in the ISO 18747 series can be found on the ISO website.
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. Deleted: www.iso.org/members.html
© ISO 2019 – All rights reserved v
Introduction
Dispersions are widely used in industry and everyday life. There is a need to understand the density of
dispersed particles or droplets, e.g. for physico‐chemical calculations such as kinematic viscosity of
[1] [2][3] [4]
dispersions , determination of particle size distribution by sedimentation or acoustic techniques ,
[5]
particle characterization by field‐flow approaches , optimization of dispersion long‐term stability by
[6]
density matching as well as, more generally, characterization of particles (e.g. composition, internal
phase content of double emulsions or homogeneity of hollow capsules) in manifold academic and
industrial areas. Nowadays there is an increasing interest in using particle density to estimate the mass
transfer of nanoparticles atop cell layers by sedimentation (dosage calculation for in vitro nanotoxicity
[7][8][9]
assessment ).
The density of a body is defined as its mass divided by its volume. This calculation is straightforward for
a large uniform body or particle. However, determination of the volume of a macroscopic body is
difficult. The geometrical volume (defined by length, width and thickness) and the volume relevant for
the determination of density may differ due to surface irregularities, fractures, fissures and pores or the
measuring techniques employed.
Density determination of micro‐particles, especially nanoparticles dispersed in a liquid, is difficult not
only due to the determination of mass and volume for small particles, but also due to the fuzzy
[10]
boundary between the liquid and the particle, which is often described in terms of a corona . Liquid
and solute molecules in the continuous phase are partially immobilized at the surface. Physico‐chemical
properties (e.g. viscosity, ion composition, solute concentration) in the fuzzy coat differ from the bulk.
This effect is especially important for small microparticles and nanoparticles that are dispersed in a
[11]
polymer or biological media . The so‐called corona may be interpreted as an integral part of the
particle and increases the effective/apparent volume compared to the space occupied by the dry
particle. The thickness of this layer ranges between a few to tens of nanometres. The effective/apparent
volume deviates increasingly from the “geometrical” volume of dry particles as the particles become
smaller. Correspondingly, density determination by traditional methods is affected. These concerns
hold also for particle size, which may refer to different geometrical and physical properties. In the
context of this document, the Stokes diameter and diameter of the enveloping sphere/hull are
particularly relevant.
vi © ISO 2019 – All rights reserved
Determination of particle density by sedimentation methods —
Part 2: Multi-velocity approach
1 Scope
This document specifies an in situ method for the determination of the density of solid particles or
liquid droplets (herein referred to as “particle”) dispersed in liquid continuous phase. The method is
based on direct experimental determination of particle velocity in these liquids or media in
gravitational or centrifugal fields based on Stokes law. The particle density is calculated from
experimentally determined particle velocities in different liquids or media, taking into account their
dynamic viscosities and densities, respectively. The approach does not require the knowledge of
particle size distribution but assumes that sedimentation relevant characteristics (e.g. volume, shape,
agglomeration state) do not change. This document does not consider polydispersity with regard to
particle density, i.e. all particles are assumed to be of the same material composition.
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 14887, Sample preparation — Dispersing procedures for powders in liquids
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http://www.electropedia.org/ Deleted: http://www.electropedia.or
g/
— ISO Online browsing platform: available at https://www.iso.org/obp Deleted: https://www.iso.org/obp
3.1
buoyant density
ratio of particle mass to particle volume including filled or closed pores as well as adjacent layers of
liquid or other coating materials
3.2
dynamic viscosity
measure of the resistance of a fluid which is being deformed by shear stress
Note 1 to entry: Dynamic viscosity is calculated by shear stress divided by shear rate and determines the
dynamics of an incompressible Newtonian fluid.
3.3
migration
directed particle movement (sedimentation or creaming/flotation) due to acting gravitational or
centrifugal fields
Note 1 to entry: Sedimentation occurs when the density of droplets/particles is larger than that of the liquid.
Creaming/flotation occurs when the density of droplets/particles is smaller than that of the liquid. In these two
processes, particles move in opposite directions.
© ISO 2019 – All rights reserved 1
ISO 18747-
...
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