ASTM D7541-11(2022)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D7541 − 11 (Reapproved 2022)
Standard Practice for
Estimating Critical Surface Tensions
This standard is issued under the fixed designation D7541; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 3. Terminology
1.1 This practice covers procedures for estimating values of 3.1 Definitions:
the critical surface tension of surfaces by observing the wetting 3.1.1 critical surface tension, n—the surface tension of a
and dewetting of a series of liquids (usually organic solvents) hypothetical liquid that would just spontaneously spread if
applied to the surface in question. applied as a drop to the surface in question; any liquid with a
surface tension lower than the critical surface tension will
1.2 Another technique, measurement of the contact angles,
spread spontaneously.
θ, of a series of test liquids and plotting cos θ versus surface
tension (Zisman plots), provides data that allow the determi-
4. Summary of Practice
nation of more exact values for critical surface tension.
4.1 In this practice, a series of liquids of gradually increas-
1.3 The values stated in SI units are to be regarded as
ing surface tension are applied to a surface in the form of
standard. No other units of measurement are included in this
drops, narrow strips, or spots. Drops may be applied using a
standard.
dropper, syringe or other device capable of producing indi-
1.4 This standard does not purport to address all of the vidualdrops.Liquidstripsorspotsareappliedtothesurfaceby
safety concerns, if any, associated with its use. It is the swabbing with saturated cotton swabs or by another type of
responsibility of the user of this standard to establish appro- applicator, such as one that is similar to a marker pen. In the
priate safety, health, and environmental practices and deter- case of the drop, the observer determines whether the drop
mine the applicability of regulatory limitations prior to use. stays in place or spreads. In the case of the liquid strip or spot,
1.5 This international standard was developed in accor- the question is whether the liquid stays in place or dewets and
dance with internationally recognized principles on standard- crawls. In each case, the break point between wetting and
ization established in the Decision on Principles for the dewetting provides the critical surface tension.
Development of International Standards, Guides and Recom-
5. Significance and Use
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee. 5.1 Knowledge of the critical surface tension of substrates,
primers and other coatings is useful for explaining or predict-
2. Referenced Documents
ing wettability by paints and other coatings applied to those
surfaces. Surfaces with low critical surface tensions usually are
2.1 ASTM Standards:
prone to suffer defects such as crawling, picture framing,
D2578 TestMethodforWettingTensionofPolyethyleneand
cratering and loss of adhesion when painted. Low or irregular
Polypropylene Films
values,orboth,oftenareindicativeofcontaminationthatcould
2.2 Nordtest Standards:
reduce adhesion. Surfaces with high critical surface tensions
NT poly 176 Spreading Surface Tension by the Applied
are easy to wet and usually provide an excellent platform for
Droplet Method.
painting.
5.2 The swab, marking pen and draw-down tests all simu-
late the application of a film
This practice is under the jurisdiction of ASTM Committee D01 on Paint and
Related Coatings, Materials, and Applications and is the direct responsibility of
5.3 The swab and marking pen techniques are simple and
Subcommittee D01.23 on Physical Properties of Applied Paint Films.
rapid and are particularly useful for testing in the field or on
Current edition approved July 1, 2022. Published July 2022. Originally approved
in 2009. Last previous edition approved in 2015 as D7541 – 11 (2015). DOI:
curved, irregular or porous surfaces where contact angles
10.1520/D7541-11R22.
cannot be measured. The drop test does not work well on such
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
surfaces and the draw-down method requires a flat specimen
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on that is relatively large.
the ASTM website.
5.4 The estimation of critical surface tension has been
For Nordtest standards, see www.nordicinnovation.net/nordtest.cfm or contact
Nordtest, Tekniikantie 12, FIN-02150 Espoo, Finland. useful in characterizing surfaces before and after cleaning
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7541 − 11 (2022)
processes such as power washes and solvent wipes in order to 8.1.1.2 TestMethodD2578specifiesmixturesofformamide
evaluate the efficiency of the cleaning. and ethylene glycol monomethyl ether (both reagent grade).
Mixtures can be designed so as to produce any combination of
5.5 One or more of these techniques could be the basis of a
surface tension values.
go/no-go quality control test where if a certain liquid wets, the
5,6
8.1.1.3 The drop test publications specify mixtures of
surface is acceptable for painting, but if that liquid retracts and
ethanol and water, but do not give details of the proportions.
crawls, the surface is not acceptable.
8.1.1.4 Nordtest Method NT poly 176 includes a table of
5.6 Another go/no go test is possible where the test liquid is
surface tensions for ethanol/water mixtures at 23 °C, which
a paint and the surface is a substrate, primer or basecoat. A
gives values ranging from 22 to 72 mN/m in 2 mN/m intervals.
form of this test has been used for coatings for plastics.
8.1.1.5 Other liquids covering a range of surface tensions
could be used. If possible, highly volatile solvents should be
6. Interferences
avoided as it is difficult to tell whether they are dewetting or
6.1 The specimen must be clean in order for results to be
just evaporating.
meaningful. The surface must not be touched or rubbed.
6.2 The surface tensions of test liquids, especially those that
9. Preparation of Specimens
are mixtures, are subject to change with time. Test liquid
9.1 The areas tested shall not contain visible blemishes or
surface tensions should be confirmed before they are first used,
defects and shall not be touched with the fingers or be allowed
measured periodically after that and whenever change is
to be contaminated in any way.
suspected.
9.2 Specimens may be cleaned, bearing in mind that the
6.3 Test liquids may become contaminated, in which case
surface of the specimen may be affected by the cleaning
results with them will be meaningless. Test liquid surface
process. Any cleaning method should be chosen only after
tensions should be confirmed before they are first used,
considering how the process may alter the surface. Cleaning
measuredperiodic
...