ISO/TR 13097:2013

TECHNICAL ISO/TR
REPORT 13097
First edition
2013-06-15
Guidelines for the characterization of
dispersion stability
Lignes directrices pour la caractérisation de la stabilité des dispersions
Reference number
©
ISO 2013
© ISO 2013
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ii © ISO 2013 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Terms and definitions . 1
3 Basics of stability . 3
3.1 Stability — Summary . 3
3.2 Characteristic features with regard to dispersion stability . 4
3.3 Alteration of the state of a dispersion . 4
4 Characterizing the change of the state of a dispersion . 6
4.1 General comments . 6
4.2 Direct methods . 7
4.3 Correlative methods . 8
4.4 Procedures to accelerate the evaluation of long-term stability . 8
5 Prediction of the shelf life of a dispersion .10
5.1 General comments .10
5.2 Comparative analysis .10
5.3 Predictive analysis .10
Annex A (informative) A compilation of relevant international and national standards .12
Bibliography .14
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
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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. www.iso.org/directives
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The committee responsible for this document is ISO/TC 24, Particle characterization including sieving,
Subcommittee SC 4, Particle characterization.
iv © ISO 2013 – All rights reserved

Introduction
Stability with respect to changes in relevant product specifications and product performance is
important in industry and for end users.
Various terminologies are used to reflect different phenomena as well as different user perspectives.
In the literature and in practice, one frequently finds terms such as dispersion, suspension or emulsion
stability, demixing or separation stability, sedimentation or creaming stability, physical stability,
colloidal stability, and kinetic stability.
This Technical Report focuses on instability driven by thermodynamics and does not include phenomena
1)
that are due too, e.g., radiation, chemical or enzymatic reactions or are related to the growth/metabolism
of biological organisms like bacteria. These phenomena are often described as photo, UV or irradiation
stability, thermal or chemical stability of one or the other constituent, enzymatic or microbial stability, etc.
The Technical Report concerns general aspects of stability test methods, acceleration procedures and
data evaluation. In addition, recommendations of instrument manufacturer, information from the
scientific or user community as well as from regulatory bodies are intended to be taken into account.
1) Chemical and physical properties are often interrelated.
TECHNICAL REPORT ISO/TR 13097:2013(E)
Guidelines for the characterization of dispersion stability
1 Scope
This Technical Report addresses the stability characterization of liquid dispersions (suspensions,
emulsions, foams and mixtures thereof) for applications, such as new product design, optimization
of existing products, quality control during processing and during usage of the product. The stability
of a dispersion in the sense of this Technical Report is defined in terms of the change in one or more
physical properties over a given time period. Stability can be either monitored (determined) in real time
or predicted on the basis of physical quantities related to stability. In the case of very stable dispersions,
procedures that accelerate the changes under consideration or accelerated aging tests administered
over a shorter time scale can be appropriate. Shelf life can be estimated based on the observed rate of
the change in the physical property and the user-required specifications for the product. Guidelines
are given for choosing relevant measurements that can be used for the ranking, identification and
quantification of instability.
2 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
2.1
agglomeration
assembly of particles in a dispersed system into loosely coherent structures that are held together by
weak physical interactions
Note 1 to entry: Agglomeration is a reversible process.
Note 2 to entry: Synonymous with coagulation and flocculation.
1 2
[SOURCE: ISO 14887:2000, 3.1, modified — text altered; IUPAC Gold Book, modified]
2.2
aggregation
assembly of particles into rigidly joined structures
Note 1 to entry: Aggregation is 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 aggregation and agglomeration are often applied interchangeably.
1 3
[SOURCE: ISO 14887:2000, 3.2, modified — text has been altered; ISO 26824 ]
2.3
coalescence
disappearance of the boundary between two particles (usually droplets or bubbles) in contact, or between
one of these and a bulk phase followed by changes of shape leading to a reduction of the total surface area
Note 1 to entry: The flocculation of an emulsion, namely the formation of aggregates, may be followed by coalescence.
[SOURCE: IUPAC Gold Book ]
2.4
creaming
rise (separation) of the dispersed phase in an emulsion due to the lower density of the dispersed phase
(droplets) compared to the continuous phase
Note 1 to entry: Creaming velocity has a negative sign as particle movement is opposite to the acting force.
2.5
dispersion
in general, microscopic multi-phase system in which discontinuities of any state (solid, liquid or gas:
discontinuous phase) are dispersed in a continuous phase of a different composition or state
Note 1 to entry: If solid particles are dispersed in a liquid, the dispersion is referred to as a suspension. If the
dispersion consists of two or more liquid phases, it is termed an emulsion. A suspoemulsion consists of both solid
and liquid phases dispersed in a continuous liquid phase.
4 2
[SOURCE: Hackley et al. ; IUPAC Gold Book, modified]
2.6
dispersion stability
ability to resist change or variation in the initial properties (state) of a dispersion 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 creaming represents a loss of dispersion stability.
[SOURCE: IUPAC Gold Book ]
2.7
flocculation
assembly of particles in a dispersed system into loosely coherent structures that are held together by
weak physical interactions
Note 1 to entry: The term flocculation is used frequently to denote agglomeration facilitated by the addition of a
flocculating agent (e.g. a polyelectrolyte).
Note 2 to entry: See 2.1.
2.8
flotation
migration of a dispersed solid phase to the top of a liquid continuous phase, when the effective particle
density is lower relative to the continuous phase density
Note 1 to entry: It may be facilitated by adhering gas bubbles, for example dissolved air flotation, or the application
of lipophilic surfactants (e.g. in ore processing).
2.9
particle
minute piece of matter with defined physical boundaries
Note 1 to entry: A physical boundary may also be described as an interface.
Note 2 to entry: A particle may move as a unit.
[SOURCE: ISO 14644-5:2004, 3.1.7, modified — Note 1 is different and Note 2 has been added;
ISO/TS 27687:2008, modified — Notes 1 and 2 have been altered and Note 3 has been deleted.]
2.10
Ostwald ripening
dissolution of small particles and the redeposition of the dissolved species on the surfaces of larger particles
Note 1 to entry: The process occurs because smaller particles have a higher surface energy, hence higher total
Gibbs energy, than larger particles, giving rise to an apparent higher solubility.
2 © ISO 2013 – All rights reserved

[SOURCE: IUPAC Gold Book ]
2.11
phase inversion
phenomenon whereby the phases of a liquid-liquid dispersion (emulsion) interchange such that the
dispersed phase spontaneously inverts to become the continuous phase and vice versa, under conditions
determined by the system properties, volume ratio and energy input
[SOURCE: Yeo et al. ]
2.12
phase separation
process by which a macroscopically homogeneous suspension, emulsion or foam separates into two or
more new phases
[SOURCE: Yeo et al. ]
2.13
sedimentation
settling (separation) of the dispersed phase due to the higher density of the dispersed particles compared
to the continuous phase. The accumulation of the dispersed phase at the bottom of the container is
evidence that sedimentation has taken place
Note 1 to entry: In the case of a dispersed liquid (emulsion), droplets can sediment if their density is higher than
that of the continuous liquid phase (e.g. water in oil emulsion).
[SOURCE: IUPAC Gold Book ]
2.14
shelf life
recommended time period during which a product (dispersion) can be stored, throughout which the
defined quality of a specified property of the product remains acceptable under expected (or specified)
conditions of distribution, storage, display and usage
[SOURCE: Gyeszly ]
3 Basics of stability
3.1 Stability — Summary
Stability is the capacity of a dispersion to remain unchanged with respect to predefined stability criteria
over a given time under stated or reasonably expected conditions of storage and use. It depends therefore
on the application. For instance a cosmetic emulsion may be considered stable if no o
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