1、Designation: D7334 08 (Reapproved 2013)Standard Practice forSurface Wettability of Coatings, Substrates and Pigmentsby Advancing Contact Angle Measurement1This standard is issued under the fixed designation D7334; the number immediately following the designation indicates the year oforiginal adoptio
2、n or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () 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
3、liquid is applied 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
4、to make themeasurements, 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 t
5、est liquid on a solid substrate.1.6 Although contact angles are governed by surfacetension, this standard cannot be used to measure surfacetension directly.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 d
6、oes not purport 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 St
7、andards:2D1193 Specification for Reagent WaterD5725 Test Method for Surface Wettability and Absorbencyof Sheeted Materials Using an Automated Contact AngleTester (Withdrawn 2010)33. Terminology3.1 Definitions:3.1.1 advancing contact angle, nthe contact angle that ismeasured immediately after the ses
8、sile drop is placed on thesurface.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 addit
9、ional area. This is the contact 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 f
10、ormed by a liquid atthe three phase boundary where a liquid, gas (air) and solidintersect.3.1.3 receding contact angle, nthe contact angle measuredwhen material is removed from the drop so that it contracts.3.1.3.1 DiscussionThe liquid-solid interfacial area willdecrease. This is the “de-wetting ang
11、le.”3.1.4 sessile drop, ndrop 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 un
12、its. They are measures of an effectthat arises from unbalanced molecular cohesive forces at asurface that cause the surface to contract and behave like a filmor membrane. The surface molecules have higher free energythan those in the bulk material. The excess free energy is whatwe call surface energ
13、y, which has units of energy/unit area suchas Joules/cm2. However, what we measure is surface tension,1This 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
14、 of Applied Paint Films.Current edition approved June 1, 2013. Published June 2013. Originallyapproved in 2008. Last previous edition approved in 2008 as D7334 08. DOI:10.1520/D7334-08R13.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at service
15、astm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3The last approved version of this historical standard is referenced onwww.astm.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 1
16、9428-2959. United States1the force necessary to break a film of a given length, usually indynes/cm or Newtons/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
17、of two methods:4.2.1 by viewing the sessile drop through a microscopefitted with a goniometer scale for direct 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
18、Use5.1 This standard is useful for characterizing the wettabilityof surfaces. A surface that is easy to wet 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.
19、2 This standard also can be used to test pigment surfacesfor wettability, particularly by potential surfactant- 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 t
20、hosepigments well.5.3 Although the contact angle is governed by the surfacetensions of the test liquid and test surface, the angle cannotprovide a surface tension value directly.5.4 Alow advancing contact angle value (90) or somewhere in-between (angle of 45 to 90). Water contact angles have beenuse
21、d to estimate surface cleanliness before and after cleaningoperations, ease of wettability of surfaces by waterbornecoatings 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
22、will depend on the surface tensions of the liquidand the test surface. A low surface tension (energy) 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 liqui
23、d that is a potential dispersant for a test pigmentmust wet the pigment well or it will not work as a 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 ana
24、lytical methods such as infrared microscopywould be needed to identify the chemical moieties that give 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. Interference
25、s6.1 The following factors may interfere with results:6.1.1 Dirt or fingerprints on the surface being 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 tes
26、tliquid such that the contact angle changes rapidly.7. Apparatus7.1 A horizontal stage onto which a flat 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 v
27、apor(particularly useful in measuring water angles).7.4 A light source to illuminate the three-phase 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 digital
28、video cameras (CCTV) provided with appropriate software toprocess the image and determine the contact angle. A descrip-tion of an automated instrument for measuring angle of contactand a method for using it can be found in Test Method D5725.8. Test Liquids8.1 The liquid(s) selected for testing purpo
29、ses are chosenbased on the characteristics of the surface that are of interest.8.2 Water is used to 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 b
30、e of reagentgrade or better.8.4 WaterType II reagent water (distilled) in accordancewith Specification D1193.8.5 Paint may be used as a test liquid to evaluate the abilityof that paint to wet a substrate or primer.A = contact angleD=dropofliquidP = specimenT = tangent at specimen surfaceFIG. 1 Measu
31、ring Angle of ContactD7334 08 (2013)28.6 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 panel of interest is too large to fit on thestage, then test specimens should be
32、 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 shall not be touched with the fingersor contaminated in any other way.9.3 If con
33、tamination or improper handling is suspected, thespecimen may be rinsed with water or washed with laboratorydetergent and water. However, cleaning may affect the resultsand must be noted on the report.9.4 Pigment specimens shall be in the form of disksprepared in a press such as those used to prepar
34、e 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 stage in accordancewith the manufacturers instructions.10.3 Place the test specimen on t
35、he 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 hypodermicneedle at the distance from the surface recommended by themanufacturer of the instrument
36、(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 (usually 5 L). With manual equipment, 20 L is commonly used. Forbest results, drop size should
37、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 thetwo points of contact of the drop can be determined (see Fig.1) or focus the camera or v
38、ideo 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 different, the valuesshould be eliminated and the test repeated. The contact anglefor the speci
39、men 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 following information:11.1.1 Apparatus used.11.1.2 Identification of the specimen.11.1.
40、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 angle measurement.12. Keywords12.1 advancing contact angles; contact angles; surface ten
41、-sions; wettability; wettingsASTM 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 of any such patent rights, and the riskof inf
42、ringement 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 reapproved or withdrawn. Your comments are invited either for revision of this stand
43、ard 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 you feel that your comments have not received a fair hearing you shouldmake your vi
44、ews 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). Permission rights to photocopy the standard may also be secured from the ASTM website (www.astm.org/COPYRIGHT/).D7334 08 (2013)3
