ISO/PRF TS 22107

Dispersibility of solid particles into a liquid

Dispersibilité de particules solides dans un liquide

General Information

• Status: Published
• ICS: 19.120 - Particle size analysis. Sieving
• Technical Committee: ISO/TC 24/SC 4 - Particle characterization
• Drafting Committee: ISO/TC 24/SC 4/WG 16 - Characterisation of particle dispersion in liquids
• Current Stage: 0000 - Proposal for new project received
• Start Date: 27-Oct-2016

Standards Content (sample)

TECHNICAL ISO/TS
SPECIFICATION 22107
First edition
Dispersibility of solid particles into a
liquid
Dispersibilité de particules solides dans un liquide
PROOF/ÉPREUVE
Reference number
ISO/TS 22107:2021(E)
ISO 2021
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ISO/TS 22107:2021(E)
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ISO/TS 22107:2021(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Basic aspects of dispersion process ................................................................................................................................................. 4

5 Definition of dispersibility ......................................................................................................................................................................... 6

5.1 Dispersibility definitions in existing standards .......................................................................................................... 6

5.2 Generic definition of dispersibility ........................................................................................................................................ 7

6 Methods to characterize dispersibility of solid particles into a liquid ........................................................8

Annex A (informative) A compilation of national and international standards .....................................................9

Bibliography .............................................................................................................................................................................................................................20

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ISO/TS 22107:2021(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 24, Particle characterization including

sieving, Subcommittee SC 4, Particle characterization.

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 22107:2021(E)
Introduction

Dispersing particles is crucial for many end-use product properties such as colour, sensorial quality,

polishing, film homogeneity, conductivity, therapeutic efficacy, opacity of paints and inks, as well as

UV protection in cosmetics. Dispersions are evaluated over the life-cycle of a product, beginning in the

design stage, through production and for the end product. Additionally, some type of dispersion process

is a prerequisite for many routine particle characterization methods. Finally, the state of dispersion is an

[37]

important issue for risk evaluation of fine particles and for classification of nano-enabled products .

However, the ease with which a particulate material is dispersed in a liquid phase to meet established

or desired criteria, commonly referred to as dispersibility, is not well defined; and its common usage

varies widely across different fields and applications. Most existing definitions are application or

product specific. Therefore, the need exists for a document that summarizes the common practice, and

which also clearly defines dispersibility in a generic manner that is not application dependent. This

document addresses that stated need.

The definition for dispersibility is established based on a survey of existing standards of national and

international organisations as well as standardized procedures of industry in different application

fields. With respect to the final product in different applications, the state of dispersion can be

characterized according to the uniformity of the dispersed phase over the entire volume and according

to the mean particle size or size distribution with respect to application specific criteria.

This document does not address intermediate- or long-term alterations including aging of a suspension

following processing, nor does it address secondary destabilization phenomena. Stability and shelf life

are considered in specific standards such as ISO/TR 13097 and ISO/TR 18811.
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TECHNICAL SPECIFICATION ISO/TS 22107:2021(E)
Dispersibility of solid particles into a liquid
1 Scope

This document establishes a generally applicable (i.e. not application specific) definition for

dispersibility. It identifies significant characteristics for evaluating dispersibility and lists examples of

methods used to characterize dispersibility in various applications.

This document applies to processes that disperse powders into a liquid continuous phase while reducing

the size of agglomerates or flocs down to the intended level, that homogenize an existing dispersed

solid phase of a suspension or the mixture of two suspensions, or that exchange the original continuous

phase in a suspension for another. Specific methods to disperse particles and to characterize the state

of dispersion and/or homogeneity are only referenced, if necessary, for context.

This document is applicable to nano- and micro-sized particles across a range of product applications.

2 Normative references
There are no normative references.
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:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
agglomerate

loosely coherent assembly of particles (3.12) and/or aggregates (3.2) held together by weak physical

interactions, with a total surface area virtually equal to the sum of the surface areas of the constituent

particles (3.13)

Note 1 to entry: The transitive verb “agglomerate” means “to gather into a cluster”, and the process by which the

cluster or assembly is formed is generally called “agglomeration”.
Note 2 to entry: Agglomeration can be a reversible process.
3.2
aggregate
assemblage of particles (3.12) into rigidly joined structures
Note 1 to entry: Formation of aggregates is usually an irreversible process.

Note 2 to entry: The forces holding an aggregate together are strong, for example covalent bonds or those

resulting from sintering or complex physical entanglement.

Note 3 to entry: In common use, the terms aggregate and agglomerate (also aggregation and agglomeration) are

sometimes applied interchangeably, but this practice is deprecated since the terms are not synonymous.

Note 4 to entry: The transitive verb “aggregate” means “to gather into a mass or whole”, and the process by which

the structure is formed is generally called “aggregation”.
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[SOURCE: ISO/TR 13097:2013, 2.2, modified — The term has been changed from "aggregation" to

"aggregate"; notes 1 and 3 to entry has been updated; note 4 to entry has been added.]

3.3
comminution

operation of reducing particle (3.12) size by crushing, grinding or pulverisation

[SOURCE: ISO 12743:2021, 3.14]
3.4
dispersing agent
dispersant
substance capable of promoting the formation of a dispersion (3.7)

[SOURCE: ISO 862:1984, 82, modified — The admitted term "dispersant" has been added.]

3.5
disperse

distribute particles (3.12) homogeneously throughout a continuous phase, often by means of reducing

the size of agglomerates (3.1)
3.6
dispersibility

qualitative or quantitative characteristic or property of a particulate source material assessing the

ease with which said material can be dispersed (3.5) within a continuous phase

Note 1 to entry: Spatially uniform distribution (homogeneity (3.11)) of the dispersed phase is considered an

integral part of the desired end point.

Note 2 to entry: Particle (3.12) size or particle size distribution is often used as an end point relative to defined

criteria specific to the application.

Note 3 to entry: Dispersibility refers to a specific dispersion (3.7) process and specific process time.

Note 4 to entry: Dispersion stability (3.8), though a related phenomenon, should not be confused with dispersibility.

3.7
dispersion

multi-phase system in which discontinuities of any state (solid, liquid or gas) are homogeneously

distributed in a continuous phase of a different composition or state

Note 1 to entry: If solid particles (3.12) are dispersed (3.5) in a liquid, the dispersion is referred to as a suspension.

If the dispersion consists of two or more immiscible liquid phases, it is termed an emulsion.

Note 2 to entry: This term can also refer to the act or process of producing a dispersion, but in this context the

term “dispersion process” shall be used.

[SOURCE: ISO/TR 13097: 2013, 2.5, modified — The words "in general, microscopic" have been

removed from the begining of the definition; "discontinous phase" has been remove from the within the

parentheses; "dispersed" has been replaced by "homogeneously distributed"; note 1 to entry has been

updated; note 2 to entry has been added.]
3.8
dispersion stability

ability to resist change or variation in the initial properties (state) of a dispersion (3.7) over time, in

other words, the quality of a dispersion in being free from alterations over a given time scale

Note 1 to entry: In this context, for instance agglomeration or segregation represents a loss of dispersion stability.

[SOURCE: ISO/TR 13097:2013, 2.6, modified — In note 1 to entry, "creaming" has been replaced by

"segregation".]
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3.9
energy density
amount of energy per unit volume of sample applied to a material
3.10
floc

ensemble of particles (3.12) that form a loosely coherent structure with high void fraction

Note 1 to entry: Flocs are held together by weak particle-particle attraction or by the osmotic pressure of a

continuous phase containing polymers not adsorbing to dispersed (3.5) particles (loss of configurational entropy

of polymers, depletion flocculation).

Note 2 to entry: The term floc may be used to denote an agglomerate (3.1) produced by addition of a flocculating

agent (e.g., a polyelectrolyte), but flocs can also form spontaneously.
3.11
homogeneity

degree to which a property or a constituent is uniformly distributed throughout a quantity of material

[38]
[SOURCE: IUPAC Gold Book ]
3.12
particle
minute piece of matter with defined physical boundaries
Note 1 to entry: A physical boundary can also be described as an interface.
Note 2 to entry: A particle can move as a unit.

[SOURCE: ISO 14644-5:2004, 3.1.7, modified — The original note to entry has been replaced by 2 new

notes to entry.]
3.13
constituent particle
identifiable, integral component of a larger particle (3.12)
[SOURCE: ISO/TS 80004-2:2015, 3.3, modified — Note 1 to entry has been removed.]
3.14
primary particle

original source particle (3.12) of agglomerates (3.1) or aggregates (3.2) or mixtures of the two

Note 1 to entry: Although a primary particle is often a constituent particle (3.13), a constituent particle is not

necessarily a primary particle.

[SOURCE: ISO 26824:2013, 1.4, modified — The 2 original notes to entry have been replaced by a new

note to entry.]
3.15
sedimentation

settling (separation) of the dispersed (3.5) phase due to the higher density of the dispersed particles

(3.12) compared to the continuous phase

Note 1 to entry: The accumulation of the dispersed phase at the bottom of the container is evidence that

sedimentation has taken place.

Note 2 to entry: Particles with a lower density compared to the continuous phase float rather than sink.

Note 3 to entry: Sedimentation leads to a loss of homogeneity (3.11).

[SOURCE: ISO/TR 13097:2013, 2.13, modified — The second sentence in the definition has been moved

to note 1 to entry; the original note 1 to entry has been removed; notes 2 and 3 to entry have been

added.]
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3.16
surfactant

substance that lowers the interfacial energy of a material in contact with a liquid

Note 1 to entry: This term is a contraction of surface-active agent.

[SOURCE: ISO 18115-1:2013, 4.464, modified — The words "or the surface energy of that liquid" have

been removed at the end of the definition; the 2 original notes to entry have been replaced by a new

note to entry.]
4 Basic aspects of dispersion process

Dispersing particulate matter into a liquid continuous phase in the context of processing is a common

method to produce suspension-based products in many industrial fields and to prepare samples

for analysis (e.g. particle size analysis). In this document, the term “dispersion process” is used in

the context of processing (dispersing a material) . A dispersion process may start from dry source

material or a pre-existing suspension. Dispersions can be created by mixing particles into a liquid to

achieve a uniform distribution throughout the entire volume, and additionally tailoring the size or

size distribution by mechanical or chemical means. Comminution, the size reduction of aggregates or

primary particles by milling, for example, is not considered here. Furthermore, the dispersion process

results in a multiphase system and not a solution.

The performance of a dispersion process, and therefore the quality/state of the final suspension,

depends on the source materials, the liquid continuous phase, the type and conditions of processing,

and is application-dependent and often quantified by reference specifications or criteria.

There are numerous textbooks, scientific papers, national and international standards, etc., dealing

with different aspects of dispersing particles and characterization of achieved results(see ISO 8780-1,

ISO 14887, ISO/TS 27687 and Reference [40]). Relevant ISO documents are included in the Bibliography

and Annex A.

Various terms are introduced to compare or to quantify the success of the dispersion process, such as

“dispersibility”, “level of dispersion”, “ease of dispersion”, “dispersibility index”, “degree of dispersity”,

“re-dispersibility”, focussing often on a specific, mostly application driven aspect. These broad views

and discussions reflect the practical need to characterize the suspension with regard to different

sample preparation or manufacturing processes, as well as the supplied raw materials of different

suppliers or batches from the same supplier. On the other hand, comparison or evaluation of the

outcome is difficult due to the use of different terms and definitions. To arrive at a generic definition

for material “dispersibility”, it is appropriate to define the starting point of a (liquid-based) dispersion

process.

To disperse powder, the process starts with powder consisting of particles, aggregates and/or

agglomerates and has the following objectives (see ISO 14887):
— wet the powder (source material) with the liquid (continuous phase);

— obtain a uniform distribution of mass throughout the liquid volume (primarily for mixing, not size

reduction);

— decrease (reduce) the size of agglomerates of the source material to the application specific criteria

for size or size distribution, or down to constituent particles or primary particles if desired.

In practice, these procedures are often combined intentionally with additional appropriate measures

to prevent the occurrence of spatial inhomogeneities in volume concentration (e.g. due to separation

or sedimentation) and any re-association of dispersed particles impacting the specified size or size

distribution, respectively. These latter phenomena concern the stability of the dispersion state

1) In literature the term “dispersion” and its derivatives (disperse, dispersed, dispersing) can be used both as an

active verb (as in “to disperse” something) and in reference to the material itself (as in “a colloidal dispersion”).

2) Withdrawn.
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(ISO/TR 13097 and ISO/TR 18811) with respect to time, which is beyond the scope of this document.

ISO/TR 13097 provides guidelines to characterize dispersion stability.

To disperse pre-existing suspensions, the process starts with a liquid suspension of the source material

that has degraded over time due to destabilization phenomena or requires, for its ultimate purpose,

an exchange or alteration of the continuous phase or further processing to achieve product-specific

criteria. In this case the objective may be one or more of the following:

— re-disperse agglomerated particles and sediments of a destabilized (e.g. aged) suspension;

— disperse the particles into a different liquid matrix or formulation (e.g. exchange of solvents);

— disperse two or more different types of source material to form a single suspension;

— reduce the size of agglomerated particles to the required size or size distribution for a specific

application or end-use.

According to the above description, dispersion processes may be theoretically divided into distributive

and disruptive processes. These processes often occur in parallel.

Distributive processing involves the mixing of particles throughout the continuous phase volume, often

called homogenisation, to obtain uniformly distributed particles throughout the entire suspension

volume. This process may not involve size reduction, if the energy input is insufficient to break apart

existing agglomerates. In this case, the cohesive forces between particles are stronger than the applied

disruptive forces.

Disruptive processing involves the reduction in size of the source material (such as agglomerates, flocs)

and is often called dispersive processing, deagglomeration or simply dispersion. Success is attained

when the disruptive forces necessary to separate an agglomerate’s constituent particles overcome

the attractive forces between them. It should be noted that achievement of product specified fineness

(endpoint of disruptive processing) does not necessarily correspond with attainment of constituent

particles, nor does it necessarily mean that a uniform spatial distribution has been achieved.

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Key
X level of disruptive process
Y level of distributive process
[40]
Figure 1 — Schematic illustration of distributive and disruptive processes

Three independent factors influence the success of the distributive or disruptive process:

a) the inherent chemical and physical properties of the source materials, for example, dry or wet,

particle size and size distribution, shape, brittleness or state of agglomeration;

b) the interaction between the particle surface and the continuous phase; this factor depends, for

instance, on wettability, electrostatic interactions, depletion forces, van der Waals forces, polarity

interaction, and hydrogen bonding;

c) the dispersion process itself; time, energy, intensity and mechanism (mechanical principle) have an

influence on the success of the distributive or disruptive process.

Therefore, to describe dispersibility all three factors shall be considered (multidimensional approach).

Each of these independent factors can be characterized by a number of different attributes and

quantified by suitable metrics.
5 Definition of dispersibility
5.1 Dispersibility definitions in existing standards

The concept of dispersibility has been used across a wide range of applications and industries for a

substantial period of time; however, its interpretation and usage vary widely even among existing

international and national standards. Therefore, a survey of existing standards and published

references was conducted in order to identify commonalities and differences.

Annex A consists of an annotated listing of relevant standards. According to those standards,

dispersibility can refer to the ease with which one can incorporate a powder into a suspension or

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achieve deagglomeration (breaking or peptization of agglomerates or flocs into constituent particles).

The process of dispersion frequently results in both outcomes, as in the use of ultrasonication. In

ISO/TR 13329 (pertaining to nanotechnology), dispersibility is defined as the level of dispersion when

it has become constant under defined conditions, a definition adapted from ISO 8780-1. In the latter

context, the “level of dispersion” is understood as the extent to which particles have been separated

and stabilized by milling in a binder system under defined conditions (taken from ISO 8780-1).

As described in brief above (for details refer to Annex A), there is a broad variety of descriptions that

are often very specific, but, on the other hand, also connected with general product behaviour (quality).

Summing up the existing definitions and common usage, dispersibility is related to:

— ease of the dispersion process, e.g. energy input, process time, necessary equipment;

— quality of the dispersed end-product, e.g. stability, tinting strength, gloss development, rheological

behaviour, opacity/appearance;

— geometrical particle characteristics, e.g. fineness or coarseness, target particle size, target size

distribution, specific surface area, particle shape;
[46],[47]

— assessment of characteristics of processing outcome, dispersion hardness filtering, sieving,

amount of dry matter that can be dispersed, suspension viscosity

Stability of the processed suspension or end product, strictly speaking, shall be distinguished from

“dispersibility”, despite the fact that they are interconnected in practice. Dispersibility is related to the

dispersion process, while stability is the capacity for such a suspension to maintain its state over a

specified period of time. Although beyond the scope of the present document, it can be necessary to

apply additional process steps or stabilizing agents (dispersing agents, surfactants) to ensure long term

stability of the suspension state (e.g. against agglomeration, flocculation) or to prevent loss of spatial

uniformity (e.g. sediment formation by particle sedimentation) of the dispersed phase over time.

5.2 Generic definition of dispersibility

Based on literature sources and other considerations discussed above, dispersibility is defined

generically as stated in 3.6.

Dispersibility of a specific source material in a specific liquid application therefore depends upon:

— mass or volume ratio of particulate material to continuous phase;
— density of the particle(s);
— wettability of dry powders;
— primary or constituent particle size and initial state of agglomeration;
— surface/interfacial properties of the dispersed material;
— properties of the continuous phase in which the material is dispersed;

— specified product fineness to be achieved (i.e., the “endpoint” of deagglomeration, which does not

necessarily correspond to the primary particle size);

— type and conditions of the dispersion process (e.g. ultrasonication, high pressure or rotor-stator-

equipment, pH, temperature);
— energy density applied to the material.
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6 Methods to characterize dispersibility of solid particles into a liquid

There are different points of departure for a dispersion process and correspondingly distinctive

meanings of dispersibility. Specific topics of characterization methods are dealt with in numerous

standards and, in more detail, listed in Annex A.

When the raw particulate material is a powder, "dispersibility" is often used to indicate the ease of

bringing a powder into a dispersion by achieving uniform spatial particle distribution and, if aimed,

"deagglomeration”. In this context, dispersibility can be quantified as the “percentage by mass of the

dry matter of the sample that can be dispersed in water”, determined by the procedure specified”

(ISO/TS 17758). It is also common in this case to characterize dispersibility based on the capacity to

achieve a specified particle size or size distribution via deagglomeration of the powder.

On the other hand, if the raw material is already in suspension, the task consists of transferring the

dispersed particles into another continuous phase or matrix, of reducing the particle size or achieving

a necessary size distribution, of mixing one type of dispersed material with a different type, or of re-

dispersing separated or re-associated particles (e.g. in an aged dispersion). In this context, dispersibility

is characterized primarily by the degree of uniformity and/or the particle size that can be achieved in

the suspension.

Homogeneity (uniformity) can be assessed using methods based on imaging the entire sample or

optical scanning, for instance. Metrics based on particle size can utilize a wide range of sizing methods.

Indirectly, suspension viscosity, opacity, or other property measurands that relate to the degree to

which size has been reduced can also be used as proxies for dispersibility.

Alternatively, some standards focus on the assessment of product quality to define dispersibility. For

example, ISO 105-Z04 states that dispersibility is the degree to which particles can be broken down to

some minimum size such that they will pass through the interstices of a reference filter media. A similar

definition is given for instant dried milk relating dispersibility of a powder in water to its ability to

break down into particles passing through a 150 µm sieve. Dispersion hardness is another description

[24]
to characterize the amount of work required to achieve the tinting stre
...