ISO/TS 10689:2023

Nanotechnologies — Superhydrophobic surfaces and coatings: Characteristics and performance assessment

This document specifies requirements and recommendations for performance assessment methods for superhydrophobic surfaces and coatings subjected to mechanical stress, solar radiation and weathering, liquids, and thermal cycling, where applicable, based on the agreement between interested parties. The performance assessment is carried out based on comparative measurements of the advancing and receding angles and the calculation of the contact angle hysteresis before and after the above-mentioned working/environmental conditions. This document does not address safety and environmental related issues of such coatings. This document is applicable to any superhydrophobic surfaces and coatings (i.e. nanostructured) on which the measurement of the advancing and receding angles is possible.

Nanotechnologies — Surfaces et revêtements superhydrophobiques : Caractéristiques et évaluation de la performance

General Information

• Status: Published
• Publication Date: 07-Aug-2023
• ICS: 07.120 - Nanotechnologies
• Technical Committee: ISO/TC 229 - Nanotechnologies
• Drafting Committee: ISO/TC 229 - Nanotechnologies
• Current Stage: 6060 - International Standard published
• Start Date: 08-Aug-2023
• Due Date: 08-Jul-2025
• Completion Date: 08-Aug-2023

Standards Content (Sample)

TECHNICAL ISO/TS
SPECIFICATION 10689
First edition
2023-08
Nanotechnologies —
Superhydrophobic surfaces and
coatings: Characteristics and
performance assessment
Nanotechnologies — Surfaces et revêtements superhydrophobiques :
Caractéristiques et évaluation de la performance
Reference number
ISO/TS 10689:2023(E)
© ISO 2023

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ISO/TS 10689:2023(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2023
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: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
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ISO/TS 10689:2023(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Characteristics and measurement methods . 5
4.1 General . 5
4.2 Test piece . 5
4.3 Pre-treatment of the test piece . 6
4.4 Contact angle measurement — Dynamic method . 6
4.4.1 Advancing angle . 6
4.4.2 Receding angle . 6
4.4.3 Contact angle hysteresis . 6
4.5 Wettability regions . 6
5 Procedure .8
5.1 General . 8
5.2 Mechanical stress methods . 8
5.2.1 Water impacting test . 8
5.2.2 Wear resistance tests . 10
5.3 Determination of the resistance to solar radiation and weathering .12
5.3.1 General .12
5.3.2 Specimen preparation and conditioning .12
5.3.3 Procedure .13
5.3.4 Test report .13
5.4 Determination of resistance to liquids . 13
5.4.1 General .13
5.4.2 Preparation . 14
5.4.3 Procedure . 14
5.4.4 Test report . 14
5.5 Thermal cycling test . 14
5.5.1 General . 14
5.5.2 Procedure . 14
5.5.3 Test report .15
Annex A (informative) Superhydrophobic surfaces and coatings .16
Annex B (informative) Recommended standard test methods .18
Bibliography .19
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ISO/TS 10689:2023(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 document 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).
ISO draws attention to the possibility that the implementation of this document may involve the use
of (a) patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed
patent rights in respect thereof. As of the date of publication of this document, ISO had not received
notice of (a) patent(s) which may be required to implement this document. However, implementers are
cautioned that this may not represent the latest information, which may be obtained from the patent
database available at  www.iso.org/patents. ISO shall not be held responsible for identifying any or all
such patent rights.
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.
iv
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ISO/TS 10689:2023(E)
Introduction
Surfaces or coatings which are extremely difficult to wet with water can be considered as
superhydrophobic. Based on the scientific literature, superhydrophobic surfaces and coatings show
contact angles of above 150° as well as contact angle hysteresis less than 10°. Superhydrophobicity
phenomena is seen in some natural species, e.g. lotus leaves. Another related term is “lotus effect”
which arises for droplets in the Cassie-Baxter wetting state.
Various methods have been utilized for the production of superhydrophobic surfaces and coatings,
e.g. chemical vapour deposition, spin coating, sputtering, plasma deposition, chemical etching, sol-gel,
photolithography, anodizing and plasma electrolyte oxidation. The superhydrophobic surfaces and
coatings have numerous applications in different industries due to their properties, which can include
self-cleaning, anti-corrosion, anti-icing, anti-fog and antibacterial effects. Such coatings and surfaces are
gradually entering automotive, building and construction, healthcare, optical and electrical industries.
[1]
The market for superhydrophobic surfaces and coatings for 2020 was about $1,8 billion .
A common characteristic of superhydrophobic surfaces and coatings is their proper two-level
topography (i.e. micro- and nano-sized asperities) combined with low surface energy. This multiscale
(hierarchical) roughness would result in large water contact angle, low contact angle hysteresis, and
high wetting stability against the Cassie–Baxter to Wenzel transition. In other words, a large contact
angle is already achievable with a microscale surface roughness but for having a large contact angle
[3]
combined with small contact angle hysteresis, nanoscale roughness is needed . In other words, water
cannot penetrate into nano-scale surface asperities which results in small contact angle hysteresis. In
the absence of nano roughness, penetration of water into the micro-scale surface asperities results in
high contact angle hysteresis (see Annex A). Such surfaces (surfaces with contact angles above 150°
[3]
and contact angle hysteresis more than 10°) are called “pseudo-superhydrophobic” surfaces ; another
related term for pseudo-superhydrophobic is “sticky superhydrophobic”, that arises due to the rose
petal effect for droplets being in the Wenzel state.
Water droplets easily bead up and roll-off on superhydrophobic surfaces and coatings and this easy
roll-off is the root cause of all the interesting properties of superhydrophobic surfaces and coatings.
Advancing and receding angles are the parameters used to quantify the droplet mobility on surfaces. As
such, measuring the advancing and receding angles identifies if a coating/surface has superhydrophobic
properties. Also, measuring the advancing and receding angles before and after exposing the
surface to different working/environmental conditions can be used to assess the performance of
superhydrophobic surfaces and coatings.
The superhydrophobic surfaces and coatings are normally subjected to different working/
environmental conditions, for example, mechanical stress, ultra-violet (UV), visible and infrared (IR)
exposure, exposure to different liquids and thermal cycling. These conditions may lead to possible
alteration of the performance of superhydrophobic surfaces and coatings. Unfortunately, despite the
huge market, there is currently no standard to assess the durability of superhydrophobic surfaces
and coatings. This document aims to specify performance assessment methods of superhydrophobic
surfaces and coatings under different working/environmental conditions, where applicable, based on
the agreement between interested parties. The assessment criteria are comparison of advancing angle,
receding angle and contact angle hysteresis of the samples before and after being subjected to the above-
mentioned working/environmental conditions. Further, this document facilitates the communication
between the interested parties. Also, this document supports UN sustainable development goals (SDGs)
8 and 12 which are “decent work and economic growth” and “responsible consumption and production”.
v
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TECHNICAL SPECIFICATION ISO/TS 10689:2023(E)
Nanotechnologies — Superhydrophobic surfaces and
coatings: Characteristics and performance assessment
1 Scope
This document specifies requirements and recommendations for performance assessment methods
for superhydrophobic surfaces and coatings subjected to mechanical stress, solar radiation and
weathering, liquids, and thermal cycling, where applicable, based on the agreement between interested
parties. The performance assessment is carried out based on comparative measurements of the
advancing and receding angles and the calculation of the contact angle hysteresis before and after
the above-mentioned working/environmental conditions. This document does not address safety and
environmental related issues of such coatings.
This document is applicable to any superhydrophobic surfaces and coatings (i.e. nanostructured) on
which the measurement of the advancing and receding angles is possible.
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 2812-1, Paints and varnishes — Determination of resistance to liquids — Part 1: Immersion in liquids
other than water
ISO 7784-3, Paints and varnishes — Determination of resistance to abrasion — Part 3: Method with
abrasive-paper covered wheel and linearly reciprocating test panel
ISO 11997-3, Paints and varnishes — Determination of resistance to cyclic corrosion conditions — Part 3:
Testing of coating systems on materials and components in automotive construction
ISO 16474-2, Paints and varnishes — Methods of exposure to laboratory light sources — Part 2: Xenon-arc
lamps
ISO 19403-6:2017, Paints and varnishes — Wettability — Part 6: Measurement of dynamic contact angle
ISO/TR 21555:2019, Paints and varnishes — Overview of test methods on hardness and wear resistance of
coatings
3 Terms and definitions
For the purposes of this document, the following terms and definitions 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
abrasion
wear which is caused by removal of coating materials on a surface
[SOURCE: ISO/TR 21555:2019, 3.6]
1
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ISO/TS 10689:2023(E)
3.2
advancing angle
θ
a
contact angle (3.3), which is measured during advancing of the three-phase point
Note 1 to entry: Generally, the advancing angle is used for the determination of the interface energy, in which
case, the measurement should be carried out close to the thermodynamic equilibrium. This is approximately
reached if there is no influence of, for example, the dosing speed on the contact angle.
Note 2 to entry: See Figure 1.
Key
advancing angle
θ
a
Figure 1 — Illustration of an advancing angle by needle application of a drop
[SOURCE: ISO 19403-6:2017, 3.2, modified — Note 2 to entry has been added.]
3.3
contact angle
θ
angle to the base line within the drop, formed by means of a tangent on the drop contour through one of
the three-phase points
Note 1 to entry: see Figure 2.
2
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ISO/TS 10689:2023(E)
Key
1 three-phase point
2 liquid phase
3 solid phase
4 gas phase
5 base line
surface tension of the liquid surface
σ
l
surface free energy of the solid surface
σ
s
interfacial energy between solid surface and liquid surface
σ
sl
contact angle
θ
Figure 2 — Illustration of a contact angle in wetting equilibrium
o
Note 2 to entry: The contact angle is preferably indicated in degrees (°). 1 =π /180 . If the system is in
thermodynamic equilibrium, this contact angle is also referred to as thermodynamic equilibrium contact angle.
[SOURCE: ISO 19403-1:2022, 3.1.9, modified — the title of Figure 2 has been slightly modified.]
3.4
contact angle hysteresis
θ
ar
difference between advancing angle (3.2) and receding angle
[SOURCE: ISO 19403-6:2017, 3.4]
3.5
chemical homogeneity
chemically homogeneous composition of a surface to be examined
Note 1 to entry: The definition regards a purely qualitative assessment of the surface. Regarding the measurement
of the contact angle (3.3), a surface is considered chemically and topologically sufficiently homogeneous if no
significant differences of the contact angles can be determined when measuring on several areas on the surface.
The significance limits can be specified by the user in accordance with standard laboratory methods.
[SOURCE: ISO 19403-1:2022, 3.1.1, modified — "locations" has been replaced with "areas" in Note 2 to
entry.]
3
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ISO/TS 10689:2023(E)
3.6
double stroke
ds
complete reciprocal movement made by the abrasive wheel
[SOURCE: ISO 7784-3:2022, 3.2]
3.7
dynamic contact angle
contact angle (3.3), which is measured during advancing or receding of the three-phase point
Note 1 to entry: The advancing or receding of the three-phase point can be achieved by changing the volume of
the liquid drop to be measured, by relative movement (immersing and pulling out) of a solid body to an interface,
or by moving the drop over the interface (e.g. rolling off).
[SOURCE: ISO 19403-6:2017, 3.1]
3.8
receding contact angle
θ
r
contact angle (3.3), which is measured during receding of the three-phase point
Note 1 to entry: See Figure 3.
Key
receding angle
θ
r
Figure 3 — Illustration of receding angle by needle extraction of a drop
[SOURCE: ISO 19403-6:2017, 3.3, modified — Note 1 to entry has been added.]
3.9
static contact angle
angle between a plane solid surface and the tangent drawn in the vertical plane at the interface between
the plane solid surface and the surface of a droplet of liquid resting on the surface
[SOURCE: ISO 15989:2004, 3.4, modified — the symbol "θ" has been deleted.]
3.10
superhydrophobic coating
coated surface for which the contact angle (3.3) with a water droplet exceeds 150° and contact angle
hysteresis (3.4) is less than 10°
4
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ISO/TS 10689:2023(E)
3.11
superhydrophobic surface
surface made from hydrophobic material having nano-scale textures for which the contact angle (3.3)
with a water droplet exceeds 150° and the contact angle hysteresis (3.4) is less than 10°
3.12
topological homogeneity
uniformity of the macroscopic surface, including evenness and smoothness
Note 1 to entry: The definition regards a purely qualitative assessment of the surface. Regarding the measurement
of the contact angle (3.3), a surface is considered chemically and topologically sufficiently homogeneous if no
significant differences of the contact angles can be determined when measuring on several areas on the surface.
The significance limits can be specified by the user in accordance with standard laboratory methods.
[SOURCE: ISO 19403-1:2017, 3.1.2]
3.13
wear
irreversible change of a coating which is caused by the mechanical impact of moved objects
[SOURCE: ISO/TR 21555: 2019, 3.2]
3.14
wettability
degree of wetting
o
Note 1 to entry: Contact angle (3.3) θ = 0 indicates fully wetted and θ =180 indicates not wetted.
[SOURCE: ISO 19403-1:2017, 3.3.2, modified — Note 1 to entry has been added.]
4 Characteristics and measurement methods
4.1 General
The contact angle of water on superhydrophobic surfaces and coatings is larger than 150° and contact
angle hysteresis is less than 10°. Measuring the static contact angle on a superhydrophobic surface/
coating according to ISO 19403-2:2017, 7.2.2 is not possible (or at least it is challenging) as the drop
adheres to the needle and detaches from the surface during the procedure. As such, only dynamic
method (advancing and receding angles) shall be used. In other words, the following characteristics
shall be measured/calculated and reported after each test: advancing angle, receding angle and contact
angle hysteresis. The superhydrophobic surfaces and coatings to be tested for this document shall be
rigid, planar, macroscopically homogeneous and macroscopically smooth, on which measuring the
advancing and receding angles (dynamic contact angles) in accordance with ISO 19403-6 is possible.
A commercially available contact-angle meter, including a light source, optical system, specimen stage,
automatic liquid delivery system, and image processing algorithm is used according to ISO 19403-6.
4.2 Test piece
Cut out flat pieces of the substrate coated by superhydrophobic coating or substrate with
superhydrophobic surface. The cut pieces shall be proper representatives of the whole material used in
the real-world application. Caution shall be made not to contaminate the test piece with contaminants.
The shape and size of the test piece should allow the measurement of the advancing/receding angle
at minimum five different points, also allow performing the required tests mentioned in Clause 5 and
agreed by interested parties.
5
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ISO/TS 10689:2023(E)
4.3 Pre-treatment of the test piece
Measurements and determination of contact angle is extremely surface sensitive, especially to any
contamination. The risk of measuring useless results is therefore immense. Store the test pieces when
they will not be used immediately. Storage depends on the superhydrophobic material and substrate;
storage specifications shall be agreed upon by the interested parties.
4.4 Contact angle measurement — Dynamic method
4.4.1 Advancing angle
The advancing angle shall be measured in accordance with ISO 19403-6. In this method, by adding
the test liquids (i.e. water) to a drop on a surface, advancing angles are measured. The measurement
should be carried out close to the equilibrium. The standard deviation for the advancing angle should
not be more than 5°. In case the standard deviation is more than 5° for the dynamic method, the surface
chemical and topological homogeneities shall be checked. In order to improve the reliability, the mean
value can be calculated for smaller periods.
4.4.2 Receding angle
The receding angle shall be measured in accordance with ISO 19403-6. In this method, by subtracting
the test liquid (i.e. water) from a drop on a surface, receding angles are measured. The measurement
should be carried out close to the equilibrium. The standard deviation for the receding angle should not
be more than 5°. In case the standard deviation is more than 5° for the dynamic method, the individual
measuring values shall be checked. In order to improve the reliability, the mean value can be calculated
for smaller periods.
4.4.3 Contact angle hysteresis
The difference between advancing angle and receding angle is the contact angle hysteresis.
4.5 Wettability regions
The maximum water contact angle that can be attained on smooth surfaces (with lowering the surface
free energy) is 120° for a surface covered with CF groups, e.g. on Teflon. For heterogeneous surfaces
3
as shown by Cassie-Baxter relation, the apparent contact angle is the weighted average of the contact
angles of patches. As the contact angle of water on air is 180°, by roughening the surface, contact angles
can be larger than 120°. On rough or heterogeneous surfaces, the apparent contact angle is not unique.
The apparent contact angle changes between a minimum (receding angle) and a maximum (advancing
angle). From the wettability perspective, surfaces are categorized into: superhydrophobic, hydrophobic,
hydrophilic and superhydrophilic.
Adhesion of drops to substrates is linearly correlated to the contact angle hysteresis. The lower the
contact angle hysteresis, the lower the force required to shed (detach) a drop from its substrate. The
shedding force is usually gravity and/or stream. Comparing two drops with equal volumes, the one
with larger contact angle has larger area exposed to air. So, when the drops are exposed to free/forced
streams, to facilitate the shedding of drops, along with the low contact angle hysteresis, large contact
angle is important. As such, drops easily detach from superhydrophobic surfaces. In this document,
the following borders are suggested to better distinguish the superhydrophobics, hydrophobics,
hydrophilics and superhydrophilics. See Figure 4 and Table 1.
6
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ISO/TS 10689:2023(E)
Key
X receding angle (degree) B hydrophobic
Y advancing angle (degree) C hydrophilic
A superhydrophobic D superhydrophilic
Figure 4 — Superhydrophobic, hydrophobic, hydrophilic and superhydrophilic wettability
regions
Table 1 — Grades of superhydrophobic (×5), hydrophobic (×2), hydrophilic and
superhydrophilic wettability regions
Wettability Advancing angle Receding angle Contact angle hysteresis
Superhydrophobic I
θ >°150 θ >°140  θ <°10
a r ar
Superhydrophobic II
θ >°150 θ >°110 10°°<<θ 40
a r ar
Superhydrophobic III o
150°°>>θ 120 θ >°80
a r θ <40
ar
Superhydrophobic IV
θ >°120 θ >°30 40°°<<θ 90
a r ar
Superhydrophobic V —
θ >°120 90°<θ
a ar
Hydrophobic I
120°°>>θ 90 θ >°50 θ <°40
a r ar
Hydrophobic II —
120°°>>θ 90 40°<θ
a ar
Hydrophilic — —
90°°>>θ 10
a
Superhydrophilic — —
10°>θ
a
7
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ISO/TS 10689:2023(E)
Based on the above-mentioned discussion in this subclause, superhydrophobic grades IV and V (or
pseudo-superhydrophobics) are not always preferred to hydrophobic grade I. For example, for the
applications that the shedding force is not a free/forced stream, smaller contact angle hysteresis is
preferred to larger contact angle (i.e. hydrophobic grade I is preferred to superhydrophobic grades IV
and V). For the application that the surface is exposed to air, a higher contact angle is more important,
so superhydrophobic grades IV and V are preferred to hydrophobic grade I.
5 Procedure
5.1 General
Considering the fact that superhydrophobic surfaces and coatings are in practice subjected to different
environmental and working conditions, the performance assessment of superhydrophobic surfaces and
coatings shall be carried out and reported based on measuring the dynamic angles and calculating the
contact angle hysteresis before and after applying such working conditions. The working conditions
include mechanical stress (water impacting, and wear resistance), solar radiation and weathering,
liquid attacks, and thermal cycling (see Annex B). Depending on the applicati
...

© ISO 2023 – All rights reserved



ISO/DTS 10689:2023(E)
ISO TC 229/SC/WG 5
Secretariat: BSI
Nanotechnologies — Superhydrophobic surfaces and coatings: Characteristics and performance
assessment
Nanotechnologies — Surfaces et revêtements superhydrophobiques : caractéristiques et évaluation de la
performance

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ISO/DTS 10689:First edition
Date: 2023(E)-04-11

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© ISO /DTS 10689:2023(E), 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
[e-mail]
www.iso.org

iv © ISO 2023 – All rights reserved

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Contents
Contents      Page

Foreword . 7
Introduction . 9
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Characteristics and measurement methods . 7
4.1 General . 7
4.2 Test piece . 7
4.3 Pre-treatment of the test piece . 8
4.4 Contact angle measurement — Dynamic method . 8
4.4.1 Advancing angle . 8
4.4.2 Receding angle . 8
4.4.3 Contact angle hysteresis . 8
4.5 Wettability regions . 8
5 Procedure . 11
5.1 General . 11
5.2 Mechanical stress methods . 12
5.2.1 Water impacting test . 12
5.2.2 Wear resistance tests . 13
5.3 Determination of resistance to solar radiation and weathering . 16
5.3.1 General . 16
5.3.2 Specimen preparation and conditioning . 16
5.3.3 Procedure . 17
5.3.4 Test report . 17
5.4 Determination of resistance to liquids . 17
5.4.1 General . 17
5.4.2 Preparation . 18
5.4.3 Procedure . 18

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5.4.4 Test report . 18
5.5 Thermal cycling test . 18
5.5.1 General . 18
5.5.2 Procedure . 19
5.5.3 Test report . 19
Annex A (Informative) Superhydrophobic surfaces and coatings . 21
Annex B (Informative) Recommended standard test methods . 25
Bibliography . 26



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1.1.1.1.1.1 ISO/DTS 10689:2023(E)


1.2 Foreword

---------------------- Page: 6 ----------------------
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 documentsdocument 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 drawnISO draws attention to the possibility that some of the elementsimplementation of this
document may beinvolve the subjectuse of (a) patent(s). ISO takes no position concerning the evidence,
validity or applicability of any claimed patent rights in respect thereof. As of the date of publication of this
document, ISO had not received notice of (a) patent(s) which may be required to implement this
document. However, implementers are cautioned that this may not represent the latest information,
which may be obtained from the patent database available at  www.iso.org/patents. 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 ).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation onof 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.htmlthe following URL: .

The committee responsible for This document iswas 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

iv © ISO 2023 – All rights reserved

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ISO/DTS 10689:2023(E)
1.2.1.1.1.1 ISO/DTS 10689:2023(E)


.
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ISO/DTS 10689:2023(E)
Introduction
Surfaces or coatings which are extremely difficult to wet with water can be considered as
superhydrophobic. Based on the scientific literature, superhydrophobic surfaces and coatings show
o o
contact angles of above 150 150° as well as contact angle hysteresis less than 10 .10°.
Superhydrophobicity phenomena is seen in some natural species, e.g. lotus leaves. Other related terms are
“lotus effect” which arises for droplets being in “Cassie-Baxter” wetting state.
Various methods have been utilized for the production of superhydrophobic surfaces and coatings, e.g.
chemical vapour deposition, spin coating, sputtering, plasma deposition, chemical etching, sol-gel,
photolithography, anodizing, and plasma electrolyte oxidation. The superhydrophobic surfaces and
coatings have numerous applications in different industries due to their properties, which can include self-
cleaning, anti-corrosion, anti-icing, anti-fog, and antibacterial effects. Such coatings and surfaces are
gradually entering automotive, building and construction, healthcare, optical and electrical industries. The
[1]
market for superhydrophobic surfaces and coatings for 2020 was about $1.,8 billion. .
A common characteristic of superhydrophobic surfaces and coatings is their proper two-level topography
(i.e. micro- and nano-sized asperities) combined with low surface energy. This multiscale (hierarchical)
roughness would result in large water contact angle, low contact angle hysteresis, and high wetting
stability against the Cassie–Baxter to Wenzel transition. In other words, a large contact angle is already
achievable with a microscale surface roughness but for having a large contact angle combined with small
[3]
contact angle hysteresis, nanoscale roughness is needed. . In other words, water cannot penetrate into
nano-scale surface asperities which results in small contact angle hysteresis. In the absence of nano
roughness, penetration of water into the micro-scale surface asperities results in high contact angle
o
hysteresis (see AppendixAnnex A). Such surfaces (surfaces with contact angles above 150 150° and
o [3]
contact angle hysteresis more than 10 )10°) are called “pseudo-superhydrophobic” surfaces; other ;
another related term for pseudo-superhydrophobic is: “sticky superhydrophobic” that arises due to the
rose petal effect for droplets being in the Wenzel state.
Water droplets easily bead up and roll-off on superhydrophobic surfaces and coatings and this easy roll-
off is the root cause of all the interesting properties of superhydrophobic surfaces and coatings. Advancing
and receding angles are the parameters used to quantify the droplet mobility on surfaces. As such,
measuring the advancing and receding angles identify if a coating/surface has superhydrophobic
properties. Also, measuring the advancing and receding angles before and after exposing the surface to
different working/environmental conditions can be used to assess the performance of superhydrophobic
surfaces and coatings.
The superhydrophobic surfaces and coatings are normally subjected to different working/environmental
conditions, e.g.for example, mechanical stress, ultra-violet (UV), visible and infrared (IR) exposure,
exposure to different liquids, and thermal cycling. These conditions may lead to possible alteration of the
performance of superhydrophobic surfaces and coatings. Unfortunately, despite the huge market, there is
currently no standard to assess the durability of superhydrophobic surfaces and coatings. This
TSdocument aims to specify performance assessment methods of superhydrophobic surfaces and coatings
under different working/environmental conditions, where applicable based on the agreement between
interested parties. The assessment criteria are comparison of advancing angle, receding angle and contact
angle hysteresis of the samples before and after being subjected to the above-mentioned
working/environmental conditions. Further, this TSdocument facilitates the communication between the
interested parties. Also, this TSdocument supports UN sustainable development goals (SDGs) 8 and 12
which are “decent work and economic growth” and “responsible consumption and production”.
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TECHNICAL SPECIFICATION ISO/DTS 10689:2023(E)

1.2.1.1.1.2 ISO/DTS 10689:2023(E)


Nanotechnologies — Superhydrophobic surfaces and coatings:
Characteristics and performance assessment
21 Scope
This technical specification (TS) recommends thedocument specifies requirements and recommendations
for performance assessment method/smethods for superhydrophobic surfaces and coatings subjected to
mechanical stress, solar radiation and weathering, liquids, and thermal cycling, where applicable based on
the agreement between interested parties. The performance assessment is carried out based on
comparative measurements of the advancing and receding angles and calculatingthe calculation of the
contact angle hysteresis before and after the above-mentioned working/environmental conditions. This
document does not address safety and environmental related issues of such coatings.
Note 1. This TSdocument is applicable to any superhydrophobic surfaces and coatings (i.e.
nanostructured) on which measuring the measurement of the advancing and receding angles areis
possible.
32 2 Normative references
The following referenced documents are indispensable for the applicationreferred 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 2812–-1, Paints and varnishes— — Determination of resistance to liquids— — Part 1: Immersion in
liquids other than water
ISO 7784–-3, Paints and varnishes— — Determination of resistance to abrasion— — Part 3: Method with
abrasive-paper covered wheel and linearly reciprocating test panel
ISO /CD 11997--3, Paints and varnishes — Determination of resistance to cyclic corrosion conditions — Part
3: Testing of coating systems on materials and components in automotive construction
ISO 16474–-2, Paints and varnishes— — Methods of exposure to laboratory light sources— — Part 2:
Xenon-arc lamps
ISO 19403–1-6:2017, Paints and varnishes— — Wettability—Terminology and general principles
ISO 19403–2, Paints and varnishes—Wettability—Determination of the surface free energy of solid surfaces
by measuring the contact angle
ISO 19403–6, Paints and varnishes—Wettability— — Part 6: Measurement of dynamic contact angle
ISO/TR 21555:2019, Paints and varnishes— — Overview of test methods on hardness and wear resistance of
coatings
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ISO/DTS 10689:2023(E)

53 3 Terms and definitions
For the purposepurposes of this document, the following terms and definitions apply.
ISO maintains terminologicaland 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
abrasion
wear which is caused by removal of coating materials on a surface
[SOURCE: ISO/TR 21555:2019, 3.6]
3.2
advancing angle
θ
a
𝜃𝜃
a
contact angle, (3.3), which is measured during advancing of the three-phase point.
Note 1 to entry: Generally, the advancing angle is used for the determination of the interface energy, in which case,
the measurement should be carried out close to the thermodynamic equilibrium. This is approximately reached if
there is no influence of, for example, the dosing speed on the contact angle.
Note 2 to entry: See Figure 1.


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ISO/DTS 10689:2023(E)

Key
𝜃𝜃 , advancing angle
a
θ advancing angle
a
Figure 1 — Illustration of an advancing angle by needle application of a drop
[SOURCE: ISO 19403-6:2017, 3.2 -, modified] — Note 2 to entry has been added.]
3.3
contact angle
θ
𝜃𝜃
angle to the base line within the drop, formed by means of a tangent on the drop contour through one of
the three-phase points.
Note 1 to entry: see Figure 2.

Key
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ISO/DTS 10689:2023(E)
1 three-phase point

Deleted Cells
2 liquid phase

3 solid phase

4 gas phase

5 base line

σ 𝜎𝜎 surface tension of the liquid surface

l 𝑙𝑙
σ 𝜎𝜎 surface free energy of the solid surface

s 𝑠𝑠
interfacial energy between solid surface and liquid surface
σ 𝜎𝜎
𝑠𝑠𝑙𝑙
sl
θ𝜃𝜃 contact angle

Figure 2 — Illustration of a contact angle in wetting equilibrium
[SOURCE: ISO 19403-1:2022, 3.1.9 -, modified]

— the title of Figure 2 has been slightly modified and Note 2 to entry: has been deleted.]
o
𝑜𝑜
o
Note 2 to entry: The contact angle is preferably indicated in degrees (°). 1 =π /180 ( ). 1 =𝜋𝜋/180. If the
system is in thermodynamic equilibrium, this contact angle is also referred to as thermodynamic equilibrium contact
angle.
3.4
contact angle hysteresis
θ
ar
𝜃𝜃
ar
difference between advancing angle (3.2) and receding angle
[SOURCE: ISO 19403-6:2017, 3.4]
3.5
chemical homogeneity
chemically homogeneous composition of a surface to be examined.
Note 1 to entry: The definition regards a purely qualitative assessment of the surface. Regarding the measurement of
the contact angle, (3.3), a surface is considered chemically and topologically sufficiently homogeneous if no
significant differences of the contact angles can be determined when measuring on several areas on the surface. The
significance limits can be specified by the user in accordance with standard laboratory methods.
[SOURCE: ISO 19403-1, 3.1.1]:2022, 3.1.1, modified — "locations" has been replaced with "areas" in Note 2
to entry.]
3.6
double stroke
ds
one complete reciprocal movement made by the abrasive wheel
[SOURCE: ISO 7784-3:2022, 3.2]
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ISO/DTS 10689:2023(E)
3.7
dynamic contact angle
contact angle, (3.3), which is measured during advancing or receding of the three-phase point.
Note 1 to entry: The advancing or receding of the three-phase point can be achieved by changing the volume of the
liquid drop to be measured, by relative movement (immersing and pulling out) of a solid body to an interface, or by
moving the drop over the interface (e.g. rolling off).
[SOURCE: ISO 19403-6:2017, 3.1]
3.8
5.1.1.1 hardness
ability of a dry film or coat to resist indentation or penetration by a solid object
[SOURCE: ISO 4618:2014, 2.136]
3.9
receding contact angle
θ
r
𝜃𝜃
r
contact angle, (3.3), which is measured during receding of the three-phase point
Note 1 to entry: See Figure 3.


Key
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ISO/DTS 10689:2023(E)
𝜃𝜃 , receding angle
r
θ receding angle
r
Figure 3 — Illustration of receding angle by needle extraction of a drop
[SOURCE: ISO 19403-6, 3.:2017, 3 -.3, modified] — Note 1 to entry has been added.]
3.109
5.1.1.2 roll-off angle
𝛼𝛼
s
tipping of the surface of the solid body, due to which a liquid drop put down onto this surface rolls off.
[SOURCE: ISO 19403-7, 3.1]
3.11
static contact angle
angle between a plane solid surface and the tangent drawn in the vertical plane at the interface between
the plane solid surface and the surface of a droplet of liquid resting on the surface
[SOURCE: ISO 15989:2004, 3.4], modified — the symbol "θ" has been deleted.]
3.1210
superhydrophobic coating
o
a coated surface for which the contact angle (3.3) with a water droplet exceeds 150 150° and contact
o
angle hysteresis (3.4) is less than 10 .10°
3.1311
superhydrophobic surface
a surface made from hydrophobic material having nano-scale textures for which the contact angle (3.3)
o o
with a water droplet exceeds 150 150° and the contact angle hysteresis (3.4) is less than 10 .10°

o
(a surface where contact angle with a water droplet exceeds 150 and contact angle hysteresis is less than
o
10 made from hydrophobic material by engineering nano-scale surface textures.)

o
(a nano-scale textured hydrophobic surface for which the contact angle with a water droplet exceeds 150
o
and contact angle hysteresis is less than 10 .)

3.1412
topological homogeneity
uniformity of the macroscopic surface, including evenness and smoothness.
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ISO/DTS 10689:2023(E)
Note 1 to entry: The definition regards a purely qualitative assessment of the surface. Regarding the measurement
of the contact angle, (3.3), a surface is considered chemically and topologically sufficiently homogeneous if no
significant differences of the contact angles can be determined when measuring on several areas on the surface. The
significance limits can be specified by the user in accordance with standard laboratory methods.
[SOURCE: ISO 19403-1:2017, 3.1.2]
3.1513
wear
irreversible change of a coating which is caused by mechanical impact of moved objects
[SOURCE: ISO/TR 21555: 2019, 3.2]
3.1614
wettability
degree of wetting.
o
𝑜𝑜
Note 1 to entry: Contact angle 𝜃𝜃 = 0(3.3) indicates fully wetted and θ= 180 𝜃𝜃 = 180 indicates not
θ= 0
wetted.
[SOURCE: ISO 19403-1:2017, 3.3.2], modified — Note 1 to entry has been added.]
64 Characteristics and measurement methods
6.14.1 4.1 General
o
The contact angle of water on superhydrophobic surfaces and coatings is larger than 150 150° and contact
o
angle hysteresis is less than 10 .10°. Measuring the static contact angle on a superhydrophobic
surface/coating in accordance withaccording to ISO 19403-2:2017, 7.2.2 is not possible (or at least it is
challenging) as the drop adheres to the needle and detaches from the surface during the procedure. As
such, only dynamic method (advancing and receding angles) shall be used. In other words, the following
characteristics shall be measured/calculated and reported after each test: advancing angle, receding angle,
and contact angle hysteresis. The superhydrophobic surfaces and coatings to be tested for this
TSdocument shall be rigid, planar, macroscopically homogeneous, and macroscopically smooth;, on which
measuring the advancing and receding angles (dynamic contact angles)according to ISO 19403-6 is
possible.
A commercially available contact-angle meter, including a light source, optical system, specimen stage,
automatic liquid delivery system, and image processing algorithm is used in accordance withaccording to
ISO 19403-6:2017.
6.24.2 4.2 Test piece
Cut out flat pieces of the substrate coated by superhydrophobic coating or substrate with
superhydrophobic surface. The cut pieces shall be proper representatives of the whole material used in
the real-world application. Caution shall be made not to contaminate the test piece with contaminants. The
shape and size of the test piece should allow the measurement of the advancing/receding angle at
minimum five different points, also allow performing the required tests mentioned in Section Clause 5 and
agreed by interested parties.
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ISO/DTS 10689:2023(E)
6.34.3 4.3 Pre-treatment of the test piece
Measurements and determination of contact angle is extremely surface sensitive specially to any
contamination. The risk of measuring useless results is thereforthere for immense. Store the test pieces
when not to be used immediately. Storage depends on the superhydrophobic material and substrate; and
storage specifications shall be agreed upon by the interested parties.
6.44.4 4.4 Contact angle measurement (— Dynamic method)
6.4.14.4.1 4.4.1 Advancing angle
The advancing angle shall be measured in accordance with ISO 19403-6:2017. In this method, by adding
the test liquids (i.e. water) to a drop on a surface, advancing angles are measured. The measurement
should be carried out close to the equilibrium [SOURCE: ISO 19403:6, 3.2]. The standard deviation for the
o
advancing angle should not be more than 5 [SOURCE: ISO 19403-2, 8.1].5°. In case the standard deviation
is more than 5° for the dynamic method, the surface chemical and topological homogeneities shall be
checked. In order to improve the reliability, the mean value can be calculated for smaller periods.
6.4.24.4.2 4.4.2 Receding angle
The receding angle shall be measured in accordance with ISO 19403-6:2017. In this method, by
subtracting the test liquid (i.e. water) from a drop on a surface, receding angles are measured. The
measurement should be carried out close to the equilibrium [SOURCE: ISO 19403:6, 3.2]. The standard
o
deviation for the receding angle should not be more than 5 [SOURCE: ISO 19403-2, 8.1].5°. In case the
standard deviation is more than 5° for the dynamic method, the individual measuring values shall be
checked. In order to improve the reliability, the mean value can be calculated for smaller periods.
6.4.34.4.3 4.4.3 Contact angle hysteresis
The difference between advancing angle and receding angle is the contact angle hysteresis.
6.54.5 4.5 Wettability regions
The maximum water contact angle that one may attain on smooth surfaces (with lowering the surface free
energy) is 120° for a surface covered with CF groups, e.g. on Teflon. For heterogeneous surfaces as shown
3
by Cassie-Baxter relation, the apparent contact angle is the weighted average of the contact angles of
patches. As the contact angle of water on air is 180°, by roughening the surface, we may have contact
angles can be larger than 120°. On rough or heterogeneous surfaces, the apparent contact angle is not
unique. The apparent contact angle changes between a minimum (receding angle) and a maximum
(advancing angle). From the wettability perspective, surfaces are categorized into: superhydrophobic,
hydrophobic, hydrophilic and superhydrophilic.
Adhesion of drops to substrates is linearly correlated to the contact angle hysteresis. The lower the
contact angle hysteresis, the lower the force required to shed (detach) a drop from its substrate. The
shedding force is usually gravity and/or stream. Comparing two drops with equal volumes, the one with
larger contact angle has larger area exposed to air. So, when the drops are exposed to free/forced streams,
to facilitate the shedding of drops, along with the low contact angle hysteresis, large contact angle is
important. As such, drops easily detach from superhydrophobic surfaces. In this TSdocument, the
following borders are suggested to better distinguish the superhydrophobics, hydrophobics, hydrophilics
and superhydrophilics. See Figure 4 and Table 1.
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ISO/DTS 10689:2023(E)

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ISO/DTS 10689:2023(E)

Key
A Superhydrophobic
BX receding angle (degree) Hydrhydrophobic
Inserted Cells
o
p
h
o
b
i
c
B
CY advancing angle (degree) Hydrhydrophilic
o
p
h
i
l
i
c
C
DA superhydrophobic Supe superhydrophilic
r
h
y
d
r
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ISO/DTS 10689:2023(E)
o
p
h
i
l
i
c
D
Figure 4 — Superhydrophobic, hydrophobic, hydrophilic and superhydrophilic wettability regions
Table — The 1 — Grades of superhydrophobic (×5), hydrophobic (×2), hydrophilic and
superhydrophilic wettability regions
Wettability Advancing angle Receding angle Contact angle hysteresis
𝑜𝑜 𝑜𝑜
Superhydrophobic I
θ > 150°𝜃𝜃 > 150 θ > 140°𝜃𝜃 >  θ < 10°𝐶𝐶𝐶𝐶𝐶𝐶 < 10
a 𝐴𝐴 r 𝑅𝑅 ar
...

FINAL
TECHNICAL ISO/DTS
DRAFT
SPECIFICATION 10689
ISO/TC 229
Nanotechnologies —
Secretariat: BSI
Superhydrophobic surfaces and
Voting begins on:
2023-04-25 coatings: Characteristics and
performance assessment
Voting terminates on:
2023-06-20
Nanotechnologies — Surfaces et revêtements superhydrophobiques :
Caractéristiques et évaluation de la performance
RECIPIENTS OF THIS DRAFT ARE INVITED TO
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
Reference number
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
ISO/DTS 10689:2023(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN-
DARDS TO WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS. © ISO 2023

---------------------- Page: 1 ----------------------
FINAL
TECHNICAL ISO/DTS
DRAFT
SPECIFICATION 10689
ISO/TC 229
Nanotechnologies —
Secretariat: BSI
Superhydrophobic surfaces and
Voting begins on:
coatings: Characteristics and
performance assessment
Voting terminates on:
Nanotechnologies — Surfaces et revêtements superhydrophobiques :
Caractéristiques et évaluation de la performance
COPYRIGHT PROTECTED DOCUMENT
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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.
RECIPIENTS OF THIS DRAFT ARE INVITED TO
ISO copyright office
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
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THEY ARE AWARE AND TO PROVIDE SUPPOR TING
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DOCUMENTATION.
Phone: [phone]
IN ADDITION TO THEIR EVALUATION AS
Reference number
Email: [e-mail]
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
ISO/DTS 10689:2023(E)
Website: www.iso.org
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
Published in Switzerland
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN­
DARDS TO WHICH REFERENCE MAY BE MADE IN
ii
  © ISO 2023 – All rights reserved
NATIONAL REGULATIONS. © ISO 2023

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ISO/DTS 10689:2023(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Characteristics and measurement methods . 5
4.1 General . 5
4.2 Test piece . 5
4.3 Pre­treatment of the test piece . 6
4.4 Contact angle measurement — Dynamic method . 6
4.4.1 Advancing angle . 6
4.4.2 Receding angle . 6
4.4.3 Contact angle hysteresis . 6
4.5 Wettability regions . 6
5 Procedure .8
5.1 General . 8
5.2 Mechanical stress methods . 8
5.2.1 Water impacting test . 8
5.2.2 Wear resistance tests . 10
5.3 Determination of the resistance to solar radiation and weathering .12
5.3.1 General .12
5.3.2 Specimen preparation and conditioning .12
5.3.3 Procedure .13
5.3.4 Test report .13
5.4 Determination of resistance to liquids . 13
5.4.1 General .13
5.4.2 Preparation . 14
5.4.3 Procedure . 14
5.4.4 Test report . 14
5.5 Thermal cycling test . 14
5.5.1 General . 14
5.5.2 Procedure . 14
5.5.3 Test report .15
Annex A (informative) Superhydrophobic surfaces and coatings .16
Annex B (informative) Recommended standard test methods .18
Bibliography .19
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ISO/DTS 10689:2023(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 non­governmental, 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 document 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).
ISO draws attention to the possibility that the implementation of this document may involve the use
of (a) patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed
patent rights in respect thereof. As of the date of publication of this document, ISO had not received
notice of (a) patent(s) which may be required to implement this document. However, implementers are
cautioned that this may not represent the latest information, which may be obtained from the patent
database available at  www.iso.org/patents. ISO shall not be held responsible for identifying any or all
such patent rights.
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.
iv
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ISO/DTS 10689:2023(E)
Introduction
Surfaces or coatings which are extremely difficult to wet with water can be considered as
superhydrophobic. Based on the scientific literature, superhydrophobic surfaces and coatings show
contact angles of above 150° as well as contact angle hysteresis less than 10°. Superhydrophobicity
phenomena is seen in some natural species, e.g. lotus leaves. Other related terms are “lotus effect”
which arises for droplets being in “Cassie-Baxter” wetting state.
Various methods have been utilized for the production of superhydrophobic surfaces and coatings,
e.g. chemical vapour deposition, spin coating, sputtering, plasma deposition, chemical etching, sol­gel,
photolithography, anodizing and plasma electrolyte oxidation. The superhydrophobic surfaces and
coatings have numerous applications in different industries due to their properties, which can include
self­cleaning, anti­corrosion, anti­icing, anti­fog and antibacterial effects. Such coatings and surfaces are
gradually entering automotive, building and construction, healthcare, optical and electrical industries.
[1]
The market for superhydrophobic surfaces and coatings for 2020 was about $1,8 billion .
A common characteristic of superhydrophobic surfaces and coatings is their proper two-level
topography (i.e. micro- and nano-sized asperities) combined with low surface energy. This multiscale
(hierarchical) roughness would result in large water contact angle, low contact angle hysteresis, and
high wetting stability against the Cassie–Baxter to Wenzel transition. In other words, a large contact
angle is already achievable with a microscale surface roughness but for having a large contact angle
[3]
combined with small contact angle hysteresis, nanoscale roughness is needed . In other words, water
cannot penetrate into nano-scale surface asperities which results in small contact angle hysteresis. In
the absence of nano roughness, penetration of water into the micro­scale surface asperities results in
high contact angle hysteresis (see Annex A). Such surfaces (surfaces with contact angles above 150°
[3]
and contact angle hysteresis more than 10°) are called “pseudo-superhydrophobic” surfaces ; another
related term for pseudo-superhydrophobic is: “sticky superhydrophobic” that arises due to the rose
petal effect for droplets being in the Wenzel state.
Water droplets easily bead up and roll-off on superhydrophobic surfaces and coatings and this easy
roll-off is the root cause of all the interesting properties of superhydrophobic surfaces and coatings.
Advancing and receding angles are the parameters used to quantify the droplet mobility on surfaces. As
such, measuring the advancing and receding angles identify if a coating/surface has superhydrophobic
properties. Also, measuring the advancing and receding angles before and after exposing the
surface to different working/environmental conditions can be used to assess the performance of
superhydrophobic surfaces and coatings.
The superhydrophobic surfaces and coatings are normally subjected to different working/
environmental conditions, for example, mechanical stress, ultra-violet (UV), visible and infrared (IR)
exposure, exposure to different liquids and thermal cycling. These conditions may lead to possible
alteration of the performance of superhydrophobic surfaces and coatings. Unfortunately, despite the
huge market, there is currently no standard to assess the durability of superhydrophobic surfaces
and coatings. This document aims to specify performance assessment methods of superhydrophobic
surfaces and coatings under different working/environmental conditions, where applicable based on
the agreement between interested parties. The assessment criteria are comparison of advancing angle,
receding angle and contact angle hysteresis of the samples before and after being subjected to the above-
mentioned working/environmental conditions. Further, this document facilitates the communication
between the interested parties. Also, this document supports UN sustainable development goals (SDGs)
8 and 12 which are “decent work and economic growth” and “responsible consumption and production”.
v
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TECHNICAL SPECIFICATION ISO/DTS 10689:2023(E)
Nanotechnologies — Superhydrophobic surfaces and
coatings: Characteristics and performance assessment
1 Scope
This document specifies requirements and recommendations for performance assessment methods
for superhydrophobic surfaces and coatings subjected to mechanical stress, solar radiation and
weathering, liquids, and thermal cycling, where applicable based on the agreement between interested
parties. The performance assessment is carried out based on comparative measurements of the
advancing and receding angles and the calculation of the contact angle hysteresis before and after
the above-mentioned working/environmental conditions. This document does not address safety and
environmental related issues of such coatings.
This document is applicable to any superhydrophobic surfaces and coatings (i.e. nanostructured) on
which the measurement of the advancing and receding angles is possible.
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 2812­1, Paints and varnishes — Determination of resistance to liquids — Part 1: Immersion in liquids
other than water
ISO 7784­3, Paints and varnishes — Determination of resistance to abrasion — Part 3: Method with
abrasive-paper covered wheel and linearly reciprocating test panel
ISO 11997­3, Paints and varnishes — Determination of resistance to cyclic corrosion conditions — Part 3:
Testing of coating systems on materials and components in automotive construction
ISO 16474­2, Paints and varnishes — Methods of exposure to laboratory light sources — Part 2: Xenon-arc
lamps
ISO 19403­6:2017, Paints and varnishes — Wettability — Part 6: Measurement of dynamic contact angle
ISO/TR 21555:2019, Paints and varnishes — Overview of test methods on hardness and wear resistance of
coatings
3 Terms and definitions
For the purposes of this document, the following terms and definitions 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
abrasion
wear which is caused by removal of coating materials on a surface
[SOURCE: ISO/TR 21555:2019, 3.6]
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ISO/DTS 10689:2023(E)
3.2
advancing angle
θ
a
contact angle (3.3), which is measured during advancing of the three­phase point
Note 1 to entry: Generally, the advancing angle is used for the determination of the interface energy, in which
case, the measurement should be carried out close to the thermodynamic equilibrium. This is approximately
reached if there is no influence of, for example, the dosing speed on the contact angle.
Note 2 to entry: See Figure 1.
Key
advancing angle
θ
a
Figure 1 — Illustration of an advancing angle by needle application of a drop
[SOURCE: ISO 19403-6:2017, 3.2, modified — Note 2 to entry has been added.]
3.3
contact angle
θ
angle to the base line within the drop, formed by means of a tangent on the drop contour through one of
the three­phase points
Note 1 to entry: see Figure 2.
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ISO/DTS 10689:2023(E)
Key
1 three­phase point
2 liquid phase
3 solid phase
4 gas phase
5 base line
surface tension of the liquid surface
σ
l
surface free energy of the solid surface
σ
s
interfacial energy between solid surface and liquid surface
σ
sl
contact angle
θ
Figure 2 — Illustration of a contact angle in wetting equilibrium
[SOURCE: ISO 19403-1:2022, 3.1.9, modified — the title of Figure 2 has been slightly modified and Note
2 to entry has been deleted.]
o
Note 2 to entry: The contact angle is preferably indicated in degrees (°). 1 =π /180 . If the system is in
thermodynamic equilibrium, this contact angle is also referred to as thermodynamic equilibrium contact angle.
3.4
contact angle hysteresis
θ
ar
difference between advancing angle (3.2) and receding angle
[SOURCE: ISO 19403­6:2017, 3.4]
3.5
chemical homogeneity
chemically homogeneous composition of a surface to be examined
Note 1 to entry: The definition regards a purely qualitative assessment of the surface. Regarding the measurement
of the contact angle (3.3), a surface is considered chemically and topologically sufficiently homogeneous if no
significant differences of the contact angles can be determined when measuring on several areas on the surface.
The significance limits can be specified by the user in accordance with standard laboratory methods.
[SOURCE: ISO 19403-1:2022, 3.1.1, modified — "locations" has been replaced with "areas" in Note 2 to
entry.]
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ISO/DTS 10689:2023(E)
3.6
double stroke
ds
complete reciprocal movement made by the abrasive wheel
[SOURCE: ISO 7784­3:2022, 3.2]
3.7
dynamic contact angle
contact angle (3.3), which is measured during advancing or receding of the three­phase point
Note 1 to entry: The advancing or receding of the three-phase point can be achieved by changing the volume of
the liquid drop to be measured, by relative movement (immersing and pulling out) of a solid body to an interface,
or by moving the drop over the interface (e.g. rolling off).
[SOURCE: ISO 19403­6:2017, 3.1]
3.8
receding contact angle
θ
r
contact angle (3.3), which is measured during receding of the three­phase point
Note 1 to entry: See Figure 3.
Key
receding angle
θ
r
Figure 3 — Illustration of receding angle by needle extraction of a drop
[SOURCE: ISO 19403-6:2017, 3.3, modified — Note 1 to entry has been added.]
3.9
static contact angle
angle between a plane solid surface and the tangent drawn in the vertical plane at the interface between
the plane solid surface and the surface of a droplet of liquid resting on the surface
[SOURCE: ISO 15989:2004, 3.4, modified — the symbol "θ" has been deleted.]
3.10
superhydrophobic coating
coated surface for which the contact angle (3.3) with a water droplet exceeds 150° and contact angle
hysteresis (3.4) is less than 10°
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ISO/DTS 10689:2023(E)
3.11
superhydrophobic surface
surface made from hydrophobic material having nano-scale textures for which the contact angle (3.3)
with a water droplet exceeds 150° and the contact angle hysteresis (3.4) is less than 10°
3.12
topological homogeneity
uniformity of the macroscopic surface, including evenness and smoothness
Note 1 to entry: The definition regards a purely qualitative assessment of the surface. Regarding the measurement
of the contact angle (3.3), a surface is considered chemically and topologically sufficiently homogeneous if no
significant differences of the contact angles can be determined when measuring on several areas on the surface.
The significance limits can be specified by the user in accordance with standard laboratory methods.
[SOURCE: ISO 19403­1:2017, 3.1.2]
3.13
wear
irreversible change of a coating which is caused by mechanical impact of moved objects
[SOURCE: ISO/TR 21555: 2019, 3.2]
3.14
wettability
degree of wetting
o
Note 1 to entry: Contact angle (3.3) θ = 0 indicates fully wetted and θ =180 indicates not wetted.
[SOURCE: ISO 19403-1:2017, 3.3.2, modified — Note 1 to entry has been added.]
4 Characteristics and measurement methods
4.1 General
The contact angle of water on superhydrophobic surfaces and coatings is larger than 150° and contact
angle hysteresis is less than 10°. Measuring the static contact angle on a superhydrophobic surface/
coating according to ISO 19403­2:2017, 7.2.2 is not possible (or at least it is challenging) as the drop
adheres to the needle and detaches from the surface during the procedure. As such, only dynamic
method (advancing and receding angles) shall be used. In other words, the following characteristics
shall be measured/calculated and reported after each test: advancing angle, receding angle and contact
angle hysteresis. The superhydrophobic surfaces and coatings to be tested for this document shall be
rigid, planar, macroscopically homogeneous and macroscopically smooth, on which measuring the
advancing and receding angles (dynamic contact angles)according to ISO 19403-6 is possible.
A commercially available contact-angle meter, including a light source, optical system, specimen stage,
automatic liquid delivery system, and image processing algorithm is used according to ISO 19403-6.
4.2 Test piece
Cut out flat pieces of the substrate coated by superhydrophobic coating or substrate with
superhydrophobic surface. The cut pieces shall be proper representatives of the whole material used in
the real­world application. Caution shall be made not to contaminate the test piece with contaminants.
The shape and size of the test piece should allow the measurement of the advancing/receding angle
at minimum five different points, also allow performing the required tests mentioned in Clause 5 and
agreed by interested parties.
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ISO/DTS 10689:2023(E)
4.3 Pre-treatment of the test piece
Measurements and determination of contact angle is extremely surface sensitive specially to any
contamination. The risk of measuring useless results is there for immense. Store the test pieces when
not used immediately. Storage depends on the superhydrophobic material and substrate; storage
specifications shall be agreed upon by the interested parties.
4.4 Contact angle measurement — Dynamic method
4.4.1 Advancing angle
The advancing angle shall be measured in accordance with ISO 19403-6. In this method, by adding
the test liquids (i.e. water) to a drop on a surface, advancing angles are measured. The measurement
should be carried out close to the equilibrium. The standard deviation for the advancing angle should
not be more than 5°. In case the standard deviation is more than 5° for the dynamic method, the surface
chemical and topological homogeneities shall be checked. In order to improve the reliability, the mean
value can be calculated for smaller periods.
4.4.2 Receding angle
The receding angle shall be measured in accordance with ISO 19403-6. In this method, by subtracting
the test liquid (i.e. water) from a drop on a surface, receding angles are measured. The measurement
should be carried out close to the equilibrium. The standard deviation for the receding angle should not
be more than 5°. In case the standard deviation is more than 5° for the dynamic method, the individual
measuring values shall be checked. In order to improve the reliability, the mean value can be calculated
for smaller periods.
4.4.3 Contact angle hysteresis
The difference between advancing angle and receding angle is the contact angle hysteresis.
4.5 Wettability regions
The maximum water contact angle that one may attain on smooth surfaces (with lowering the surface
free energy) is 120° for a surface covered with CF groups, e.g. on Teflon. For heterogeneous surfaces
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as shown by Cassie-Baxter relation, the apparent contact angle is the weighted average of the contact
angles of patches. As the contact angle of water on air is 180°, by roughening the surface, contact angles
can be larger than 120°. On rough or heterogeneous surfaces, the apparent contact angle is not unique.
The apparent contact angle changes between a minimum (receding angle) and a maximum (advancing
angle). From the wettability perspective, surfaces are categorized into: superhydrophobic, hydrophobic,
hydrophilic and superhydrophilic.
Adhesion of drops to substrates is linearly correlated to the contact angle hysteresis. The lower the
contact angle hysteresis, the lower the force required to shed (detach) a drop from its substrate. The
shedding force is usually gravity and/or stream. Comparing two drops with equal volumes, the one
with larger contact angle has larger area exposed to air. So, when the drops are exposed to free/forced
streams, to facilitate the shedding of drops, along with the low contact angle hysteresis, large contact
angle is important. As such, drops easily detach from superhydrophobic surfaces. In this document,
the following borders are suggested to better distinguish the superhydrophobics, hydrophobics,
hydrophilics and superhydrophilics. See Figure 4 and Table 1.
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ISO/DTS 10689:2023(E)
Key
X receding angle (degree) B hydrophobic
Y advancing angle (degree) C hydrophilic
A superhydrophobic D superhydrophilic
Figure 4 — Superhydrophobic, hydrophobic, hydrophilic and superhydrophilic wettability
regions
Table 1 — Grades of superhydrophobic (×5), hydrophobic (×2), hydrophilic and
superhydrophilic wettability regions
Wettability Advancing angle Receding angle Contact angle hysteresis
Superhydrophobic I
θ >°150 θ >°140  θ <°10
a r ar
Superhydrophobic II
θ >°150 θ >°110 10°°<<θ 40
a r ar
Superhydrophobic III o
150°°>>θ 120 θ >°80
a r θ <40
ar
Superhydrophobic IV
θ >°120 θ >°30 40°°<<θ 90
a r ar
Superhydrophobic V —
θ >°120 90°<θ
a ar
Hydrop
...