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JOURNAL OF COLLOID AND INTERFACE SCIENCE182,465472(1996)ARTICLE NO.0489Dynamic and Equilibrium Phase Behavior in theC12E5Abietic AcidH2O SystemSTEPHENP.BEAUDOIN,1RUBENG.CARBONELL,2ANDCHRISTINES.GRANTDepartment of Chemical Engineering,North Carolina State University,Raleigh,North Carolina 27695Received March 8,1995;accepted April 17,1996The studies identified a multistage cleaning mechanism con-Previous research has investigated the removal of representativesisting of the following steps:(1)surfactant and water pene-flux residues(abietic acid(AA)in isopropyl alcohol(IPA)fromtration into the AA/IPA,(2)shear-driven removal of anprinted wiring assemblies using aqueous solutions of a nonionicAAsurfactantwater liquid phase,and(3)shear-driven re-surfactant(pentaethylene glycol mono-n-dodecyl ether(C12E5).moval of isolated AAsurfactantwater aggregates directlyTo optimize cleaning with this surfactant,greater understandingfrom the FR-4 surface.of the equilibrium and dynamic phase behavior in the AA-C12E5-In emulsification-based cleaning of liquid oily soils fromH2O system is required.In this research,partial ternary phasesurfaces,the first step is adsorption and penetration of surfac-diagrams were developed at 60 and 457C(above the binary cloudtant into the contaminant(47).The surfactant and waterpoint).Increasing the AA content of the system caused isotropicsurfactant(L2)and lamellar liquid crystalline(La)phases to formthen mix with the oil(contaminant)phase to form water-at lower temperatures than in the binary C12E5H2O system.Asin-oil or oil-in-water emulsions.Droplets of these emulsionsthe temperature increased,the solubility of AA in the L2 phasemay be displaced from the surface by hydrodynamic forces.increased considerably,while the AA content of the La phase wasThese steps are consistent with the cleaning observed in thenot affected as strongly.The dynamic phase behavior resultingC12E5waterAA system.from contact of micellar C12E5solutions with AA or AA/IPA parti-The research presented here investigates the dynamic andcles at 247C(below the binary cloud point)and 457C was alsoequilibrium behavior observed when particles and films ofobserved.When AA or AA/IPA particles were contacted with 4.1AA/IPA are contacted with aqueous solutions of C12E5at1 1003M C12E5solutions,the surfactant and water penetratedseveral temperatures.These investigations enhance under-into the particles to create isotropic liquid aggregates.When parti-standing of the cleaning process by allowing the phasescles were contacted with more concentrated micellar C12E5solu-formed to be related to the controlling parameters seen intions(0.25 M),a new concentrated surfactant phase surroundedthe particles and solubilized the AA.q 1996 Academic Press,Inc.the cleaning.This also facilitates optimization of cleaningKey Words:micelles;nonionic surfactants;surfactant phase be-conditions for the removal of flux residues from PWAs usinghavior;detergency;solubilization.aqueous surfactant solutions.EXPERIMENTAL PROCEDURESINTRODUCTIONMaterialsThe removal of solid films of abietic acid(AA)containingThe AA used in this study was supplied by Alfa Specialtyup to 45%isopropyl alcohol(IPA)from disks of FR-4 ep-Chemicals and was approximately 90%pure.Its density wasoxyglass laminate(Fig.1)by aqueous solutions of a non-determined to be 1.08 g/ml by comparison with sucroseionic surfactant(pentaethylene glycol mono-n-dodecylsolutions of known density.The IPA and tetrahydrofuranether,C12E5)has been studied under controlled hydrody-(THF)(Fisher Chemicals)were HPLC grade,and the C12E5namic conditions(1,2).This work resulted from a need to(Nikko Chemicals of Japan)was 99%pure,as verified byeliminate the use of CFC-113-based solutions to removegas chromatography at Nikko.All chemicals were used asflux residues from printed wiring assemblies(PWAs).FR-received.The water used in this work was 18.3 MV-cm DI4 laminate is a common substrate used in PWAs,while thewater from a Barnstead Nanopure system.mixture of AA and IPA is representative of flux residue.Equilibrium Phase Diagrams1Current address:Arizona State University,Dept.of Chemical,Bio.,andTo construct ternary AAC12E5water phase diagrams,Materials Engineering,Tempe,AZ 85287.2To whom correspondence should be addressed.mixtures of C12E5,water,and AA were allowed to equilibrate4650021-9797/96$18.00Copyrightq1996 by Academic Press,Inc.All rights of reproduction in any form reserved.AIDJCIS 4355/6g14$24108-23-96 10:08:55coidaAP:Colloid466BEAUDOIN,CARBONELL,AND GRANTFIG.1.Brominated epoxy resin typical of FR-4(3).for periods ranging from three weeks to two months at con-the AA.The UV detector was calibrated using solutions ofknown AA concentration.A Rheodyne injector with a 200stant temperature in a Fisher Isotemp Model 615A oven.The solutions were held in tapered,airtight vials of Teflon-ml liquid-phase injection loop was used for sample injection.Thus,the water and AA contents of the phases were mea-PFA(ColeParmer)during the equilibration.The vials wereagitated vigorously at least once each day so that all phasessured,and the C12E5content was determined by total massbalance.were well mixed.Optical microscopy was used to determinethe equilibrium phase structures of the samples,and theirIn later stages of the work,the lyophilization was omittedand the samples were dissolved directly in THF and injectedcompositions were determined using gel-permeation chro-matography.Phases were sampled with a 1 ml Hamiltoninto the GPC apparatus.In this case,a 1000 AmStyragelcolumn and two Shodex kf-801 GPC columns in series wereGas-Tight syringe.Approximately half of each sample wasplaced in a new glass capillary tube(VitroDynamics;0.8used for the separation and a Waters 410 Differential Refrac-tometer(RI apparatus)was placed downstream of the UVmm path length,8 mm width,rectangular capillaries;flame-sealed at one end)for analysis of its phase structure.Thedetector.The RI apparatus was calibrated against C12E5solu-tions of known concentration.In this method,the AA andremainder of each sample was used to determine its composi-tion(discussed below).Between sampling and analysis,C12E5contents of the solution were measured and the watercontent was determined by mass balance.Replicate sampleseach capillary tube was maintained at the equilibrium tem-perature in a Fisher recirculating water bath,although theanalyzed by both methods showed good agreement,althoughthere was less variation between samples analyzed by thelag time between sampling and analysis was always lessthan 5 min.The samples were studied at 1001magnificationsecond method.under both unpolarized and polarized light using an opticalmicroscope(Olympus BH-P)equipped with an Olympus C-Dynamic Phase Behavior35 AD2 camera and photographic system.A red filter wasused to assist in the detection of birefringence and to identifyThe dynamic behavior of aqueous C12E5solutions in con-tact with pure AA or AA/IPA particles was studied usingthe rotation of Maltese crosses in the lamellar liquid crystal-line(La)phase(8,9).A hot stage(Sensortek TS-4 ERthe optical microscope at 1001magnification.AA particleswere obtained directly from the material provided by Alfa,Controller and Hot Stage)was used to maintain the capillar-ies at the equilibrium temperature during viewing.Phaseswhile mixed AA/IPA particles were obtained from AA/IPAfilms on disks of FR-4 laminate.These films were madewere identified by comparing their optical characteristics(birefringence,oily streaks,Maltese crosses)to those ofwhen 42%(mass)solutions of AA in IPA were spin-coatedonto FR-4 disks using a Headway Research,Model CB15representative surfactant phases(8,9).The presence of AAwas inferred from the yellowbrownorange color of thespin-coating apparatus(1,2).After drying in a desiccatorfor 24 h,these films were less than 4mm thick.A razorphases.To determine the phase compositions,the second portionblade was used to scrape the dried film samples from thedisks.The particles(AA or AA/IPA)were placed on aof each phase sample(see above)was placed in a pre-weighed glass vial with a Teflon-lined screw top lidglass microscope slide with a cover slip,and aqueous C12E5solution was placed at the edges of the cover slip using(Fisher),and the mass was recorded.In the initial stages ofthe work,these samples were freeze-dried using a Virtis 10-a clean 1 ml Hamilton Gas-Tight syringe.The surfactantsolutions flowed under the cover slip to contact the particles.324 lyophilization apparatus,and their water content wasdetermined by the change in mass during drying.The sam-The contacting was observed through the microscope andphotographs were taken to document changes in both theples were then dissolved in THF and analyzed using gel-permeation chromatography(GPC)to determine their AAparticles and the aqueous solution with time.An excess ofsurfactant solution was maintained at the edges of the covercontent.With this method,a THF mobile phase was pumpedthrough threemStyragel columns(1000,100,and 10 Aporeslip during contacting,and the slide was maintained at thedesired temperature using a hot stage.Prior to addition todiameter)in series using a Waters 6000A Isocratic Pump.A Waters 440 UV Absorbance Detector(UV detector)setthe slides,the surfactant solutions were maintained at thecontacting temperature using a Fisherbrand Recirculatingat 254 nm was placed downstream of the columns to detectAIDJCIS 4355/6g14$24208-23-96 10:08:55coidaAP:Colloid467C12E5ABIETIC ACIDH2O PHASE BEHAVIORFIG.2.Ternary C12E5AAH2O phase diagram at 607C.Lalamellar liquid crystalline phase containing solubilized AA;L2isotropic surfactantliquid containing solubilized AA;Ssolid AA;Wdilute aqueous phase.Water Bath.To search for characteristics of the La phase,and AA,although it is above the point of equal solubilizationthe polarized lenses of the microscope were crossed and aat 607C.The range of compositions in the LaW system atred filter was employed.The microscope stage was tilted457C is similar to that seen in the 607C case,indicating thatduring the contacting to see if flow birefringence(a charac-the effect of temperature on the composition of this phaseteristic of the sponge-like liquid crystal(L3)phase)wasis small.exhibited by any of the phases.To further investigate the effect of AA on the phase transi-tions in the ternary system,the effect of AA on the cloudRESULTS AND DISCUSSIONpoint of a micellar C12E5solution was studied.The CMC ofC12E5at 247C is 6.411005M,and is insensitive to smallEquilibrium Phase Diagrams at 60 and 457Ctemperature changes(6).A 4.111003M C12E5solutionwithout AA had a cloud point of 32.57C,while 1.411004The partial phase diagrams obtained for the H2O-C12E5-M AA in the same solution reduced the cloud point to 29.57C.AA system at 60 and 457C are presented in Figs.2 and 3.Other researchers also have found that oils in watersurfac-The regions of extremely low surfactant or AA concentrationtant systems cause a change in the cloud point(11,12).were not investigated.Also,surfactant and water contentsThe reductions in the temperatures of the cloud point andof the solid phases of each diagram were not evaluated.Itof L2 phase formation indicate that AA makes aqueous C12E5was assumed that the solid was pure AA.solutions more hydrophobic.Comparison of Figs.2 and 3 reveals that the L2 phaseWhen the concentration of AA in the La phase was high,forms at 607C in the presence of approximately 12 to 42%this phase was denser than the W phase,and when the con-AA in solution and at lower AA levels at 457C.At thesecentration of AA in the La phase was low,the W phase wassurfactant concentrations,the L2 phase does not form in thedenser.In the regions of WL2solid AA phase equilibriumbinary system below approximately 827C,although it is seen(above42%AA in solution at 607C;above18%AA inat 607C when the surfactant content of the system is greatersolution at 457C),the solid AA was the densest phase.Thethan roughly 80%by mass(10).At 457C,the L2WAAL2 phase was always more dense than the W phase,whethervertex(which represents the solubility limit of AA in theL2 phase)is below the point of equal solubilization of waterthey were present in a two-or three-phase system.The L2AIDJCIS 4355/6g14$24208-23-96 10:08:55coidaAP:Colloid468BEAUDOIN,CARBONELL,AND GRANTFIG.3.Ternary C12E5AAH2O phase diagram at 457C.Lalamellar liquid crystalline phase containing solubilized AA;L2isotropic surfactantliquid containing solubilized AA;Ssolid AA;Wdilute aqueous phase.phase was usually clear,in contrast to the La phase,whichphase containing solubilized AA at 607C.One unit step onthe grid in Figure 4 is equal to 15mm(as for all photographswas usually turbid.Figure 4 is a photograph(in polarized light)of the Lain this paper).The Maltese crosses on the right-hand sideFIG.4.Photograph of La phase containing solubilized AA;607C,approximately 20%(wt)C12E5,5%(wt)AA,75%(wt)H2O.AIDJCIS 4355/6g14$24208-23-96 10:08:55coidaAP:Colloid469C12E5ABIETIC ACIDH2O PHASE BEHAVIORFIG.5.Photograph of L2 phase containing solubilized AA;607C,approximately 45%(wt)C12E5,40%(wt)AA,15%(wt)H2O.of Fig.4 and the streaky birefringence on the left-hand sideand streamed into the bulk solution(not shown).No solubi-lization in the aqueous phase was observed at any conditionof this photo are characteristic of the La phase(13).The L2 phase occasionally contained roughly sphericalin the absence of concentrated surfactant layers such as this.In the 111003M photos(Figs.6A,6B),the size of theinternal structures,as shown in Fig.5(607C,unpolarizedlight).No birefringent regions were detected in this phase,AA/C12E5aggregates increased during the liquefaction,sug-and it did not exhibit flow birefringence.The spheres aregesting that water penetrated into the surfactant-laden AA.thought to be regions of local order.They showed no ten-As the temperature increased,the rate of liquefaction ofdency to move out of the bulk phase,even when it wasthe AA/IPA particles increased,as shown in Fig.7.It hasdispersed into the W phase by vigorous mixing.The spheresbeen shown that the saturation concentration of C12E5inhad the same color and texture as the bulk phase,and theAA/IPA films increases with increasing temperature(1,2),number and size of the spheres were not affected by theperhaps due to a reduction in the solubility of the surfactantintensity or frequency of mixing.These observations suggestin the aqueous phase(14).This may explain the increasedthat the spheres were not emulsified water droplets,but wererate of penetration at 457C.Although the diffusion coeffi-characteristic of this L2 phase.cients for surfactant and water in both the organic and aque-ous phases is thought to increase with increasing tempera-Dynamic Phase Behaviorture,it is unlikely that this effect alone accounted for thechange in liquefaction rate.Figure 6 presents photographs of the contacting of 11Figures 6 and 7 at 247C show that the liquefaction of the1003M(in unpolarized light)and 0.25 M(in polarizedAA/