ASTM_D_7334_-_08_2013.pdf

Designation:D733408(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 adoption 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 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 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 test 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 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 establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards: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Test Method for Surface Wettability and Absorbencyof Sheeted Materials Using an Automated Contact AngleTester(Withdrawn 2010)33.Terminology3.1 Definitions:3.1.1 advancing contact angle,nthe contact angle that ismeasured immediately after the sessile drop is placed on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 additional 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 formed 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 angle.”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 units.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 energy,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 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 serviceastm.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 19428-2959.United States1 the 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 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