ISO/TS 10689

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: Not Published
• ICS: 07.120 - Nanotechnologies
• Technical Committee: ISO/TC 229 - Nanotechnologies
• Drafting Committee: ISO/TC 229 - Nanotechnologies
• Current Stage: 6000 - International Standard under publication
• Completion Date: 21-Jun-2023

Standards Content (Sample)

© 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

iv © ISO 2023 – All rights reserved
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1.1.1.1.1.1 ISO/DTS 10689:2023(E)
1.2 Foreword
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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

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”.

© ISO 2023 – All rights reserved ix
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ISO/DTS 10689:2023(E)
x © ISO 2023 – All rights reserved
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ISO/DTS 10689:2023(E)
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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
𝜃𝜃

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.
2 © ISO 2023 – All rights reserved
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ISO/DTS 10689:2023(E)
Key
𝜃𝜃 , advancing angle
θ advancing angle
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
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
© ISO 2023 – All rights reserved 3
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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
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.]

𝑜𝑜

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
𝜃𝜃
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
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
𝜃𝜃
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
θ receding angle
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

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

a coated surface for which the contact angle (3.3) with a water droplet exceeds 150 150° and contact

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°

(a surface where contact angle with a water droplet exceeds 150 and contact angle hysteresis is less than

10 made from hydrophobic material by engineering nano-scale surface textures.)

(a nano-scale textured hydrophobic surface for which the contact angle with a water droplet exceeds 150

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.
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

The contact angle of water on superhydrophobic surfaces and coatings is larger than 150 150° and contact

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

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

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

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.
8 © ISO 2023 – All rights reserved
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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
CY advancing angle (degree) Hydrhydrophilic
DA superhydrophobic Supe superhydrophilic
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ISO/DTS 10689:2023(E)

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
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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

iii
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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

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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 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

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expressions related to conformity assessment, as well as information about ISO's adherence to

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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.
© ISO 2023 – All rights reserved
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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”.

© ISO 2023 – All rights reserved
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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
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
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

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
surface free energy of the solid surface
interfacial energy between solid surface and liquid surface
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.]

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
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
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
contact angle (3.3), which is measured during receding of the three­phase point
Note 1 to entry: See Figure 3.
Key
receding angle
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

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

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
Superhydrophobic IV
θ >°120 θ >°30 40°°<<θ 90
a r ar
Superhydrophobic V —
θ >°120 90°<θ
a ar
Hydrop
...