1、Designation: D 7334 08Standard Practice forSurface Wettability of Coatings, Substrates and Pigmentsby Advancing Contact Angle Measurement1This standard is issued under the fixed designation D 7334; the number immediately following the designation indicates the year oforiginal adoption or, in the cas
2、e of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice covers the measurement of the angle ofcontact when a drop of liquid is appli
3、ed to a coated surface,substrate, or preformed disk of pigment.1.2 There are two types of contact angles, advancing andreceding. This standard deals only with advancing contactangles.1.3 This practice is intended to supplement the manufactur-ers instructions for the device being used to make themeas
4、urements, but is not intended to replace them.1.4 A common test liquid is water, but many other liquidssuch as solvents, surfactant and dispersant solutions and evenliquid paints can be used.1.5 This practice is based on goniometry, which involves theobservation of a sessile drop of test liquid on a
5、 solid substrate.1.6 Although contact angles are governed by surface ten-sion, this standard cannot be used to measure surface tensiondirectly.1.7 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.1.8 This standard does not purpo
6、rt to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 11
7、93 Specification for Reagent WaterD 5725 Test Method for Surface Wettability and Absor-bency of Sheeted Materials Using an Automated ContactAngle Tester3. Terminology3.1 Definitions:3.1.1 advancing contact angle, nthe contact angle that ismeasured immediately after the sessile drop is placed on thes
8、urface.3.1.1.1 DiscussionThe drop has the maximum volumeallowable for the liquid-solid interfacial area: any addition willmake the drop expand and increase the liquid-solid interfacialarea. This can be thought of as the “wetting angle” because thedrop is ready to wet additional area. This is the con
9、tact angleused in this method and in most coating measurements.3.1.2 contact angle, nthe interior angle that a drop makesbetween the substrate and a tangent drawn at the intersectionbetween the drop and the substrate as shown in Fig. 1.3.1.2.1 DiscussionThis is the angle formed by a liquid atthe thr
10、ee phase boundary where a liquid, gas (air) and solidintersect.3.1.3 receding contact angle, nthe contact angle mea-sured when material is removed from the drop so that itcontracts.3.1.3.1 DiscussionThe liquid-solid interfacial area willdecrease. This is the “de-wetting angle.”3.1.4 sessile drop, nd
11、rop of liquid on the upper side of ahorizontal surface (as in Fig. 1).3.1.5 surface tension, n, and surface energy, nthe termssurface tension and surface energy are often used interchange-ably.3.1.5.1 DiscussionThey are the same numerically, al-though they have different units. They are measures of
12、an effect1This practice is under the 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. 15, 2008. Published March 2008.2For ref
13、erenced 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 website.A = contact angleD=dropofliquidP = specimenT = tangent at specimen su
14、rfaceFIG. 1 Measuring Angle of Contact1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.that arises from unbalanced molecular cohesive forces at asurface that cause the surface to contract and behave like a filmor membrane. The surface
15、 molecules have higher free energythan those in the bulk material. The excess free energy is whatwe call surface energy, which has units of energy/unit area suchas Joules/cm2. However, what we measure is surface tension,the force necessary to break a film of a given length, usually indynes/cm or New
16、tons/m.4. Summary of Practice4.1 A drop of a specified volume of water or another agreedupon test liquid is applied to a test specimen using a syringe.4.2 The contact angle is measured by either of two methods:4.2.1 by viewing the sessile drop through a microscopefitted with a goniometer scale for d
17、irect measurement of theangle,4.2.2 by capturing an image of the drop, then measuringwith a protractor or using appropriate software to process theimage and measure the angle.5. Significance and Use5.1 This standard is useful for characterizing the wettabilityof surfaces. A surface that is easy to w
18、et is one over which acoating is more likely to give good adhesion and appearanceand less likely to suffer surface tension related defects such ascrawling, cratering, pinholing and orange peel.5.2 This standard also can be used to test pigment surfacesfor wettability, particularly by potential surfa
19、ctant- or resin-based dispersants or mill bases. Easily wetted pigments aremore likely to be easy to disperse and dispersants/mill basesthat wet pigments of interest are more likely to disperse thosepigments well.5.3 Although the contact angle is governed by the surfacetensions of the test liquid an
20、d test surface, the angle cannotprovide a surface tension value directly.5.4 A low advancing contact angle value ( 90) or somewherein-between (angle of 45 to 90). Water contact angles havebeen used to estimate surface cleanliness before and aftercleaning operations, ease of wettability of surfaces b
21、y water-borne coatings and the effectiveness of rinsing processes.5.6 An organic liquid such as a solvent also can be used tocharacterize a substrate, coating or pigment. The resultantcontact angle will depend on the surface tensions of the liquidand the test surface. A low surface tension (energy)
22、test surfacewill not be wet by a high surface tension liquid.5.7 In addition to water and solvents, a surfactant dispersionor dispersant solution can be used to test a pigment surface.Any test liquid that is a potential dispersant for a test pigmentmust wet the pigment well or it will not work as a
23、dispersant.5.8 Contact angle measurements can be used to map sur-faces in terms of hydrophilicity, presence of low surfacetension components or contaminants, or variations in compo-sition. Other analytical methods such as infrared microscopywould be needed to identify the chemical moieties that give
24、 thecontact angle differences.5.9 This test method can be used on nearly all coatings andsubstrates and may be extended to pigments by compressingthe pigment powder into a solid disk.6. Interferences6.1 The following factors may interfere with results:6.1.1 Dirt or fingerprints on the surface being
25、tested.6.1.2 A rough or porous test surface such that the drop sinksin rapidly.6.1.3 A curved test surface such that angles are difficult tomeasure.6.1.4 Low humidity ( 50 % RH) when water is the testliquid such that the contact angle changes rapidly.7. Apparatus7.1 A horizontal stage onto which a f
26、lat surface is mounted,7.2 A device (generally a syringe) to place a droplet on thesurface.7.3 An enclosure (if desired) to prevent interference ofvapor-borne impurities and to secure saturation of vapor(particularly useful in measuring water angles).7.4 A light source to illuminate the three-phase
27、contactregion from behind.7.5 A microscope which magnifies the contact area. It mustbe able to travel along when the drop advances. Nowadayseyepieces and still cameras usually are replaced by digitalvideo cameras (CCTV) provided with appropriate software toprocess the image and determine the contact
28、 angle. A descrip-tion of an automated instrument for measuring angle of contactand a method for using it can be found in Test Method D 5725.8. Test Liquids8.1 The liquid(s) selected for testing purposes are chosenbased on the characteristics of the surface that are of interest.8.2 Water is used to
29、determine wetting characteristics of thatliquid on the coating or substrate and/or to characterize thehydrophilicity and hydrophobicity of that surface.8.3 Organic test liquids such as solvents must be of reagentgrade or better.8.4 WaterType II reagent water (distilled) in accordancewith Specificati
30、on D 1193.8.5 Paint may be used as a test liquid to evaluate the abilityof that paint to wet a substrate or primer.8.6 A mill base, dispersant solution or surfactant dispersionmay be used as a test liquid to evaluate the ability of thatmaterial to wet a pigment.9. Test Specimens9.1 If the part or pa
31、nel of interest is too large to fit on thestage, then test specimens should be cut to a size appropriatefor the instrument being used. They shall be cut in such a wayas to be thoroughly representative of the sample.9.2 The actual test areas tested shall not contain visibleblemishes or defects and sh
32、all not be touched with the fingersor contaminated in any other way.9.3 If contamination or improper handling is suspected, thespecimen may be rinsed with water or washed with laboratoryD7334082detergent and water. However, cleaning may affect the resultsand must be noted on the report.9.4 Pigment s
33、pecimens shall be in the form of disksprepared in a press such as those used to prepare KBr disks forinfrared analysis.10. Procedure10.1 Test the specimens at a temperature of 23 6 2C (73.56 3.5F) and at a relative humidity $ 50 % unless otherwiseagreed upon.10.2 Set up the goniometer and level the
34、stage in accordancewith the manufacturers instructions.10.3 Place the test specimen on the instrument, if necessaryholding it in close contact with the stage by means of smallweights, clips, or whatever fixtures are associated with theinstrument.10.4 Contact angle drop set the tip of the hypodermicn
35、eedle at the distance from the surface recommended by themanufacturer of the instrument (3 mm (18 in.) has worked wellfor testing coatings) and deposit a drop of test liquid no greaterthan 20 Lin size on the specimen. With automated equipment,use the drop size recommended by the manufacturer (usuall
36、y 5 L). With manual equipment, 20 L is commonly used. Forbest results, drop size should be controlled to 60.1 L. Thecontact angle measured on this drop will be an advancingcontact angle.10.5 Adjust the goniometer eye piece and the internalmeasuring mechanism so that the interior angle of each of the
37、two points of contact of the drop can be determined (see Fig.1) or focus the camera or video device so that the image of thedrop can be captured.10.6 Make two angle measurements (one on each dropedge) of each of three drops on the specimen. If the contactangles on two edges are significantly differe
38、nt, the valuesshould be eliminated and the test repeated. The contact anglefor the specimen shall be the average of the six anglesmeasured.10.7 Water contact angles must be measured rapidly (within30 s of depositing the drop) to avoid changes in angle as thewater evaporates.11. Report11.1 Report the
39、 following information:11.1.1 Apparatus used.11.1.2 Identification of the specimen.11.1.3 Identification of the test liquid.11.1.4 Average contact angle liquid on the specimen.11.1.5 If the specimen was cleaned, this must be noted.11.1.6 Whether or not a humidity chamber was used for awater contact
40、angle measurement.12. Keywords12.1 advancing contact angle; contact angle; surface ten-sion; 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 advi
41、sed that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either
42、reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If
43、 you feel that your comments have not 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 copies) 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).D7334083
