1、Designation: D7541 11Standard Practice forEstimating Critical Surface Tensions1This standard is issued under the fixed designation D7541; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parent
2、heses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice covers procedures for estimating values ofthe critical surface tension of surfaces by observing the wettingand dewetting of a series of l
3、iquids (usually organic solvents)applied to the surface in question.1.2 Another technique, measurement of the contact angles,u, of a series of test liquids and plotting cos u versus surfacetension (Zisman plots), provides data that allow the determi-nation of more exact values for critical surface t
4、ension.1.3 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establi
5、sh appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D2578 Test Method for Wetting Tension of Polyethyleneand Polypropylene Films2.2 Nordtest Standards:3NT poly 176 Spreading Surface Tension by
6、the AppliedDroplet Method.3. Terminology3.1 Definitions:3.1.1 critical surface tension, nthe surface tension of ahypothetical liquid that would just spontaneously spread ifapplied as a drop to the surface in question; any liquid with asurface tension lower than the critical surface tension willsprea
7、d spontaneously.4. Summary of Practice4.1 In this practice, a series of liquids of gradually increas-ing surface tension are applied to a surface in the form ofdrops, narrow strips, or spots. Drops may be applied using adropper, syringe or other device capable of producing indi-vidual drops. Liquid
8、strips or spots are applied to the surface byswabbing with saturated cotton swabs or by another type ofapplicator, such as one that is similar to a marker pen. In thecase of the drop, the observer determines whether the dropstays in place or spreads. In the case of the liquid strip or spot,the quest
9、ion is whether the liquid stays in place or dewets andcrawls. In each case, the break point between wetting anddewetting provides the critical surface tension.5. Significance and Use5.1 Knowledge of the critical surface tension of substrates,primers and other coatings is useful for explaining or pre
10、dict-ing wettability by paints and other coatings applied to thosesurrfaces. Surfaces with low critical surface tensions usuallyare prone to suffer defects such as crawling, picture framing,cratering and loss of adhesion when painted. Low or irregularvalues, or both, often are indicative of contamin
11、ation that couldreduce adhesion. Surfaces with high critical surface tensionsare easy to wet and usually provide an excellent platform forpainting.5.2 The swab, marking pen and draw-down tests all simu-late the application of a film5.3 The swab and marking pen techniques are simple andrapid and are
12、particularly useful for testing in the field or oncurved, irregular or porous surfaces where contact anglescannot be measured. The drop test does not work well on suchsurfaces and the draw-down method requires a flat specimenthat is relatively large.5.4 The estimation of critical surface tension has
13、 beenuseful in characterizing surfaces before and after cleaningprocesses such as power washes and solvent wipes in order toevaluate the efficiency of the cleaning.5.5 One or more of these techniques could be the basis of ago/no-go quality control test where if a certain liquid wets, thesurface is a
14、cceptable for painting, but if that liquid retracts andcrawls, the surface is not acceptable.5.6 Another go/no go test is possible where the test liquid isa paint and the surface is a substrate, primer or basecoat. Aform of this test has been used for coatings for plastics.1This practice is under th
15、e jurisdiction of ASTM Committee D01 on Paint andRelated Coatings, Materials, and Applications and is the direct responsibility ofSubcommittee D01.23 on Physical Properties of Applied Paint Films.Current edition approved Feb. 1, 2011. Published February 2011. Originallyapproved in 2009. Last previou
16、s edition approved in 2009 as D7541 - 09. DOI:10.1520/D7541-11.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM websit
17、e.3For Nordtest standards, see or contactNordtest, Tekniikantie 12, FIN-02150 Espoo, Finland.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.6. Interferences6.1 The specimen must be clean in order for results to bemeaningful. The su
18、rface must not be touched or rubbed.6.2 The surface tensions of test liquids, especially those thatare mixtures, are subject to change with time. Test liquidsurface tensions should be confirmed before they are first used,measured periodically after that and whenever change issuspected.6.3 Test liqui
19、ds may become contaminated, in which caseresults with them will be meaningless. Test liquid surfacetensions should be confirmed before they are first used,measured periodically after that and whenever contamination issuspected.6.4 High ambient temperature may cause rapid evaporationof test liquids a
20、nd make it difficult to determine whetherretraction has occurred or shrinkage is due to evaporation.7. Apparatus7.1 Several of one of the following types of applicators:7.1.1 Cotton swab (small ball of cotton at the end of a stick).7.1.2 Marker pen type applicator.7.1.3 Dropper or syringe.7.1.4 Othe
21、r device with the ability to apply a drop, strip, orspot.7.2 Drawdown Baronly for draw-down test.7.3 Instrument or devices for measuring temperature andhumidity.8. Materials8.1 Swab, drop and draw-down tests.8.1.1 Test liquids.8.1.1.1 The original publication on the swab test4specifiedthe liquids in
22、 Table 1 (listed along with their surface tensions).This set of liquids has a large surface tension gap between 24and 35 dynes/cm.8.1.1.2 Test Method D2578 specifies mixtures of formamideand ethylene glycol monomethyl ether (both reagent grade).Mixtures can be designed so as to produce any combinati
23、on ofsurface tension values.8.1.1.3 The drop test publications5,6specify mixtures ofethanol and water, but do not give details of the proportions.8.1.1.4 Nordtest Method NT poly 1763includes a table ofsurface tensions for ethanol/water mixtures at 23C, whichgives values ranging from 22 to 72 mN/m in
24、 2 mN/m intervals.8.1.1.5 Other liquids covering a range of surface tensionscould be used. If possible, highly volatile solvents should beavoided as it is difficult to tell whether they are dewetting orjust evaporating.9. Preparation of Specimens9.1 The areas tested shall not contain visible blemish
25、es ordefects and shall not be touched with the fingers or be allowedto be contaminated in any way.9.2 Specimens may be cleaned, bearing in mind that thesurface of the specimen may be affected by the cleaningprocess. Any cleaning method should be chosen only afterconsidering how the process may alter
26、 the surface. Cleaningmust be clearly indicated in the report.10. ProcedureCotton Swab10.1 Beginning with the lowest surface tension liquid in thetest series, saturate the cotton ball at the end of the stick andapply three uniform strips 0.5 to 1 cm wide and 2 to 5 cm longto the test specimen.10.2 O
27、bserve whether the liquid remains as an intact film,retracts (crawls) or completely beads up. Allow 3 seconds forretraction or beading to occur. Longer times may be used, butevaporation of the liquid may cause retraction that appears tobe dewetting, but is not.10.3 If the liquid strip does not retra
28、ct or bead up within 3seconds, repeat the procedure on an untested section of thespecimen with a clean cotton swab and the next higher surfacetension liquid. If the strip does retract or bead in the initial test,a lower surface tension test liquid must be found and used.10.4 Each of the liquids in t
29、he series is used to test thespecimen until one of them clearly retracts. There are twodifferent conventions for determining the end point and esti-mating the critical surface tension:10.4.1 The critical surface tension of dewetting is taken asbeing intermediate between the surface tension value of
30、the lastliquid that wet the surface and the first one that did not. Forexample, if a 34 mN/m liquid wets the specimen and a 36mN/m liquid does not, the critical surface tension will beconsidered to be approximately 35 mN/m.10.4.2 The critical surface tension is taken as the highestsurface tension li
31、quid that just wets the surface. Using thiscriterion, the critical surface tension in the example in 10.4.1would be considered to be approximately 34 mN/m.11. ProcedureMarker Pen Applicator11.1 Begin with the marker pen with the lowest surfacetension.11.2 Press the applicator tip firmly on the corne
32、r of thespecimen until the tip is fully saturated with the ink.11.3 Lightly draw the pen across the specimen in threeparallel passes. One of the pen manufacturers specifies onlyevaluating the last pass.11.4 If the last ink strip remains wetted for 3 seconds ormore, repeat steps 11.2 and 11.3 on an u
33、ntested portion of thespecimen with the next higher surface tension marker pen.4Hansen, C. M., J. Coat. Technol., 44 (570), 57 (1972).5Hansen, C. M., European Coatings J., 94, 838 (1994).6Hansen, C. M., Pigment and Resin Technol., 27, 374 (1998).TABLE 1 Test Liquids and Their Surface TensionsLiquidS
34、urfact TensionmN/m (= dynes/cm)Acetone 23.7Dimethyl formamide 35.22-pyrollidone 37.6N-methyl-2-pyrollidone 39.0Dimethyl sulfoxide 43.0Ethylene cyanohydrin 44.4Formamide 56.0Water 72.8D7541 11211.5 Continue testing until the paint strip clearly retracts.Aswith the cotton swab test, there are two conv
35、entions fordetermining the end point and estimating the critical surfacetension. See 10.4.1 and 10.4.2 for details.12. ProcedureDrop Test12.1 Beginning with the lowest surface tension test liquid,place a small drop of the test liquid on the test specimen.12.2 Observe whether the liquid spreads. If i
36、t does, apply adrop of the next higher surface tension liquid.12.3 Continue with higher and higher surface tension liq-uids until a drop does not spread.12.4 See 10.4.1 and 10.4.2 for the two conventions used inestimating the critical surface tension from the observations.12.5 An example is shown in
37、 Fig. 1. The surface has acritical surface tension between 22 and 26 dynes/cm. Liquidswith surface tensions equal to or higher than 26 dynes/cm donot wet the surface and, therefore, retain their droplet form.13. ProcedureDraw-Down Test13.1 Aflat specimen, preferably on the order of 20 by 25 cmis pla
38、ced on and clamped to a work bench or table.13.2 Several test liquid drops are placed across the top ofthe specimen with space between them. The liquids shouldrange from low to high surface tension, increasing from left toright. A draw-down bar is placed above the drops and pulleddown. The resultant
39、 draw-downs are quickly examined forwetting and dewetting behavior.13.3 As with the other methods, there should be a breakpoint between the draw-down strips that wet and those thatdewet and retract.14. Report14.1 The report shall contain the following informationwhen applicable and available.14.1.1
40、Date, time, and place of the measurement.14.1.2 Description of the test specimen.14.1.3 Whether specimen is as-received or whether cleaninghas been done. If the latter, then describe the cleaning process.14.1.4 Temperature and humidity in the area of the test.14.1.5 Identification of the test and ap
41、plicator that wereused.14.1.6 If the drop test is used, indicate the drop size.14.1.7 Any deviations from the method.14.1.8 Identification of which convention was used to esti-mate the critical surface tension.14.1.9 The estimated value for the critical surface tension inmN/m.15. Keywords15.1 critic
42、al surface tension; dewetting; surface contamina-tion; wettability; wettingASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity
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45、received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copie
46、s) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org). Permission rights to photocopy the standard may also be secured from the ASTM website (www.astm.org/COPYRIGHT/).FIG. 1 Drops of Different Surface Tension Liquids on a Low Surface Tension Surface. Left to Right: Low to High Surface TensionLiquids; Spreading to BeadingD7541 113
