ISO/TR 23015:2020

TECHNICAL ISO/TR
REPORT 23015
First edition
Fine bubble technology —
Measurement technique matrix for
the characterization of fine bubbles
Technologie des fines bulles — Matrice de méthodes de mesure pour
la caractérisation des fines bulles
PROOF/ÉPREUVE
Reference number
ISO/TR 23015:2020(E)
©
ISO 2020

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ISO/TR 23015:2020(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2020
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Published in Switzerland
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ISO/TR 23015:2020(E)

Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Abbreviated terms . 1
5 Fine bubble characterization . 1
5.1 General . 1
5.2 Comparison of size and concentration indices from different sources . 2
6 Characterization techniques . 3
6.1 Dynamic light scattering . 3
6.1.1 General. 3
6.1.2 Reference standard . 3
6.1.3 Size . 3
6.1.4 Size distribution . 4
6.1.5 Concentration . 4
6.1.6 Measurement time . 4
6.2 Methods for Zeta potential determination (electrophoretic mobility) . 4
6.2.1 General. 4
6.2.2 Reference standard . 4
6.2.3 Charge . 4
6.2.4 Zeta distribution . 4
6.2.5 Concentration . 4
6.2.6 Measurement time . 4
6.3 Particle tracking analysis method . 5
6.3.1 General. 5
6.3.2 Reference standards . 5
6.3.3 Size . 5
6.3.4 Size distribution . 5
6.3.5 Concentration . 5
6.3.6 Measurement time . 6
6.4 Laser diffraction methods . 6
6.4.1 General. 6
6.4.2 Reference standard . 6
6.4.3 Size . 6
6.4.4 Concentration . 6
6.4.5 Measurement time . 6
6.5 Resonant mass measurement . 6
6.5.1 General. 6
6.5.2 Reference standard . 7
6.5.3 Size . 7
6.5.4 Size distribution . 7
6.5.5 Concentration . 7
6.5.6 Measurement time . 7
6.6 Electrical sensing zone method . 7
6.6.1 General. 7
6.6.2 Reference standard . 7
6.6.3 Size . 7
6.6.4 Size distribution . 7
6.6.5 Concentration . 8
6.6.6 Measurement time . 8
6.7 Ultrasonic attenuation spectroscopy . 8
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ISO/TR 23015:2020(E)

6.7.1 General. 8
6.7.2 Reference standard . 8
6.7.3 Size . 8
6.7.4 Size distribution . 8
6.7.5 Concentration . 8
6.7.6 Measurement time . 8
6.8 Single particle light interaction methods . 8
6.8.1 General. 8
6.8.2 Reference standards . 9
6.8.3 Size . 9
6.8.4 Size distribution . 9
6.8.5 Concentration . 9
6.8.6 Measurement time . 9
6.9 Static image analysis method . 9
6.9.1 General. 9
6.9.2 Reference standard . 9
6.9.3 Size . 9
6.9.4 Size distribution . 9
6.9.5 Concentration .10
6.9.6 Measurement time .10
6.10 Dynamic image analysis methods .10
6.10.1 Reference standard .10
6.10.2 Size .10
6.10.3 Size distribution .10
6.10.4 Concentration .10
6.10.5 Measurement time .10
6.11 Static multiple light scattering (SMLS).10
6.11.1 General.10
6.11.2 Reference standard .11
6.11.3 Size .11
6.11.4 Size distribution .11
6.11.5 Concentration .11
6.11.6 Measurement time .11
Bibliography .12
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ISO/TR 23015:2020(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 281, Fine bubble technology.
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/TR 23015:2020(E)

Introduction
Fine bubble technology has numerous applications across industries such as cleaning, transport,
maintenance, agriculture, aquaculture, food and drink, cosmetics as well as biomedical. The detection,
characterization and quantification of properties of fine bubble mixtures are central to the development
of this horizontal general purpose technology.
A number of techniques used for particle detection and characterization may be applicable to the
characterization of fine bubble mixtures in liquids. Some techniques may have a number of special
sample handling, sample preparation or equipment settings to yield quantifiable and reliable results.
This document lists a number of techniques and discusses their applicability for the characterization
of fine bubble mixtures as well as their limitations. Fine bubbles are able to exist in opaque liquids
or liquids of high viscosity. Some fine bubble samples are turbid due to a large number of bubbles. All
fine bubble samples are dynamic in nature and their properties change with time. For this reason, the
acquisition time of each technique is of great relevance. Most fine bubble samples contain particles as
well as fine bubbles. Distinguishing particles and bubbles and then additionally characterizing them by
size and number or vice-versa may not be possible with all particle characterization equipment.
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TECHNICAL REPORT ISO/TR 23015:2020(E)
Fine bubble technology — Measurement technique matrix
for the characterization of fine bubbles
1 Scope
This document focuses on listing most commonly used preparation and characterization techniques for
fine bubbles and their interpretation. The merits and limitations of each of the techniques are outlined.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
No terms and definitions are listed in this document.
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/
4 Abbreviated terms
CCD Charge coupled device
DLS Dynamic light scattering
EZ Electrical sensing zone method
LD Laser diffraction methods
PSD Particle size distribution
PTA Particle tracking analysis method
RMM Resonance mass measurement
SPOS Single particle light interaction methods
SMLS Static multiple light scattering
USS Ultrasonic attenuation spectroscopy
ZP Methods for Zeta-potential determination
5 Fine bubble characterization
5.1 General
A number of general particle counting and sizing techniques are available commercially. Some of them
are applicable for the characterization of fine bubble dispersions and ultrafine bubble dispersions. Such
dispersions may be in liquid of any kind. Some liquids may not be transparent (e.g. printer ink) or stable
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ISO/TR 23015:2020(E)

(e.g. flammable fuel). This document refers to a selection of commercially available techniques and
evaluates their applicability and their limitations.
The following are the parameters of interest.
— Fine bubble size – This usually refers to the equivalent hydrodynamic diameter but could be different
depending on the techniques.
— Fine bubble size distribution – For the purpose of this document, this is the number-size (or
equivalent) distribution.
— Number concentration – The total number (or equivalent) of bubbles per unit volume.
— Measurement time – The time to complete data acquisition.
5.2 Comparison of size and concentration indices from different sources
Consideration should be given when different techniques are being compared, that each technique
measures a different physical property of the sample. In deriving size and/or concentration indices
from different techniques, it should be anticipated that results will demonstrate differences in value
but they will likely show trend and/or correlate.
Care should be taken when comparing size and concentration indices. Even if the same technique is used,
the method from example two laser diffraction machines will need to be checked to verify parameters
such as measurement time, analysis models and pump rate. Table 1 provides a quick reference for the
typical size and concentration indices of different techniques in the measurement of bubbles.
Table 1 — Quick-use-matrix
Bubble measurands
Number
International
Size concentra- Measure-
Techniques
Standard
Size distribu- tion ment
tion (bubbles time
per ml)
5 nm - Intensity- Typical
9
Dynamic light scattering DLS ISO 22412 > 10
10 μm based 5 min
Methods for Zeta-potential
ZP ISO 13099-2 < 5 min
determination
50 nm – Number-
b 7 9
Particle tracking analysis method PTA ISO 19430 10 - 10 ~5 min
1 000 nm based
100 nm – Volume-
Laser diffraction methods LD ISO 13320 0,000 1 % ms - 10 s
3 mm based
7 9
10 - 10
micro-
a
sensor :
120 nm – Number- 0,2 nl/s
a 6
Resonance mass measurement RMM Not available 9 × 10
1 000 nm based ~15 min
nano-
a
sensor :
8
2 × 10
50 nm- Number-
8
Electrical sensing zone method EZ ISO 13319 1 × 10 10 min
8 000 nm based
6
> 1 × 10
For
Ultrasonic attenuation 100 nm – Volume-
USS ISO 20998-1 5 min
ultra-
spectroscopy 1 mm based
fine
8
> 1 × 10
a
Technique may require a special procedure or detector for obtaining appropriate results.
b
Nanoparticle tracking analysis (NTA) is often used to describe PTA. NTA is a subset of PTA since PTA covers larger range of particle
sizes than nanoscale.
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Table 1 (continued)
Bubble measurands
Number
International
Size concentra- Measure-
Techniques
Standard
Size distribu- tion ment
tion (bubbles time
per ml)
Single particle light interaction ISO 21501-2 0,1 μm - Number- 30 s -
8
SPOS < 10
a
methods ISO 21501-3 100 μm based 5 min
ISO 13322-1 0,5 μm - Number- Typical
8
Static image analysis methods — > 10
> 1 000 μm based 15 min
0,5 μm - Number-
a 8
Dynamic image analysis methods — ISO 13322-2 > 10 > 5 min
> 1 000 μm based
8 12
SMLS Under 10 nm - No 10 - 10 ~10 s
Static multiple light scattering
development 100 μm
a
Technique may require a special procedure or detector for obtaining appropriate results.
b
Nanoparticle tracking analysis (NTA) is often used to describe PTA. NTA is a subset of PTA since PTA covers larger range of particle
sizes than nanoscale.
6 Characterization techniques
This clause deals with individual techniques and how they are applied to characterizing fine bubble
samples. Most samples are assumed to be in a transparent liquid, but some reference to opaque samples
may be found for techniques that allow their treatment.
6.1 Dynamic light scattering
6.1.1 General
Dynamic light scattering (DLS) is also known as photon correlation spectroscopy (PCS). It measures
the hydrodynamic particle size by measuring the Brownian motion of the fine bubbles in a sample.
The technique uses a laser which is passed through a sample and the light scattering measured on
a detector. The detector(s) could be at a variety of angles. The intensity of light is measured over a
rapid timescale. The change in scattering intensity over time as particles diffuse in and out of the
measurement zone is related to their size, small particles diffuse rapidly and large particles slowly. The
translational diffusion coefficient is measured which can be turned into the hydrodynamic diameter by
the Stokes Einstein equation [see ISO 22412:2017, Formula (A.5)].
This intensity change is expressed as a correlation function which examines the signal change over time.
From this information on the size and polydispersity of the sample can be obtained. A size distribution
is derived by applying an appropriate algorithm to the correlation function. It is an intensity-based
technique.
6.1.2 Reference standard
ISO 22412, Particle size analysis — Dynamic light scattering (DLS)
NOTE Originally, there were two International Standards relating to this technique ISO 13321 and ISO 22412
now merged into one single document, ISO 22412.
6.1.3 Size
The lowest size in DLS will depend on the system sensitivity, and for most systems will be sufficient
for sizing fine bubbles. The upper size range will depend on when the bubbles no longer behaving as
objects undergoing Brownian motion. In the case of particles this is normally sedimentation, but for
bubbles, rising is more likely.
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6.1.4 Size distribution
Dynamic light scattering measures an intensity-based distribution. This leads to sensitivity on the
large particle end of the distribution as they scatter light with more intensity. In size area of interest,
6
there is a 10 dependence of scattering intensity with size. This may lead to issues obtaining accurate
data if large particles or contaminants are present. For a clean sample, the technique is able to provide
a distribution for fine bubbles in the size area of interest.
6.1.5 Concentration
Most dynamic light scattering instruments are set up to auto adjust for concentrations ranging from
low to high. Number concentration of bubbles required for appropriate measurements is generally
9
higher than that given for particles. A concentration of (or over) 10 bubbles per ml is normal.
6.1.6 Measurement time
As for PTA (see 6.3), theoretical derivation of Stokes-Einstein equation [see ISO 22412:2017,
Formula (A.5)] assumes no change in particle population, their size or number on the time scale of the
measurement. This may not be true for dynamically changing
...