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Comparison of corrosion protection between double strands of polyaniline and poly-o-anisidine with poly (acrylic acid-co-acryl amide) on steel

Comparison of corrosion protection between double strands of polyaniline and poly-o-anisidine with poly (acrylic acid-co-acryl amide) on steel
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  See discussions, stats, and author profiles for this publication at: Comparison Of Corrosion Protection BetweenDouble Strands Of Polyaniline And Poly-O-Anisidine With Poly(Acrylic...  Article   in  Journal of Coatings Technology and Research · January 2012 DOI: 10.1007/s11998-011-9345-y CITATIONS 6 READS 29 3 authors:Some of the authors of this publication are also working on these related projects: Electrocatalysis, electrochemical sensors, energy conversion and storage, biomaterials. View projectDevelopment of graphene based electrochemical DNA biosensors for environmental pollutants.   ViewprojectM.R. MahmoudianUniversity of Malaya 39   PUBLICATIONS   402   CITATIONS   SEE PROFILE Wan Jeffrey BasirunUniversity of Malaya 205   PUBLICATIONS   1,082   CITATIONS   SEE PROFILE  Yatimah AliasUniversity of Malaya 180   PUBLICATIONS   1,486   CITATIONS   SEE PROFILE All content following this page was uploaded by Wan Jeffrey Basirun on 12 February 2015. The user has requested enhancement of the downloaded file. All in-text references underlined in blue are added to the srcinal documentand are linked to publications on ResearchGate, letting you access and read them immediately.  Comparison of corrosion protection between double strandsof polyaniline and poly- o -anisidine with poly(acrylic acid- co -acrylamide) on steel M. R. Mahmoudian, W. J. Basirun, Y. Alias   ACA and OCCA 2011 Abstract  Double strands of polyaniline (PAn) andpoly( o -anisidine) (POAn) with poly(acrylic acid- co -acryl amide) (PAA- co -AA) were successfully preparedon steel as undercoating, by immersion of the pre-treated surfaces into a PAn: (PAA- co -AA) and POAn:(PAA- co -AA) saturated DMF solution separately.The undercoatings formed on the steel were charac-terized by Fourier transform infrared spectroscopy(FTIR) techniques. A commercial paint (Nippon Paint,nonadded Chrome) was used as topcoating. Electrode/electroactive polymer/paint/electrolyte system wasstudied by electrochemical impedance spectroscopy(EIS). The EIS studies show that during the first18 days immersion time in 3.5% solution of NaCl,paint/PAn coating has better corrosion resistance thanpaint/POAn coating while in the final week of immer-sion time, the pore resistance ( R po ) and coatingcapacitance ( C  c ) of paint/POAn are higher and lowerthan the paint/PAn, respectively. Keywords  Steel, Paint, Aniline, Pore resistance,Coating Introduction In recent years, conducting polymers have attractedconsiderable interest for the development of advancedmaterials. These compounds are organic materials thatgenerally possess an extended conjugated  p -electronsystem along a polymer backbone. Polyaniline (PAn)and its derivatives such as poly- o -anisidine (POAn) areconducting polymers which, due to their high electricalconductivity, have been suggested to be used asprotective coatings on oxidizable metals. 1–3 Organic coatings are commonly used to protectmetals against corrosion. Paints are used for a widevariety of protective coatings because of their excellentadhesion,goodmechanicalproperties,andtheirnotablechemical resistance under different aggressive environ-ments, such as wet and high humidity conditions. 4,5 Inaddition, they possess a low cost, ease of manufacturingand application, and a wide range of products available.Many researchers have employed conducting polymercoatings, both electropolymerized and polymer pig-mented paint, f or corrosion protection. 6–8 Racicot et al. 9 used double-strand PAn for corrosionprotection of aluminum. The double-strand PAn is amolecular complex of two polymers: (1) PAn and (2) apolyanion. These two linear polymers are bondednoncovalently in a side-by-side fashion to form a stablemolecular complex. They used poly(methylacrylate- co -acrylic acid) as polymeric dopant and prepared amolecular complex with PAn as an undercoating. Theyreported that the rate of interfacial redox or chargetransfer reaction could be relatively high compared toother solid coating because the material is electricallyconductive.In this study, we have studied the corrosion protec-tion behavior of double-strand PAn and POAn sepa-rately on steel in 3.5% sodium chloride solution. Theeffect of electroactive polymer type on the capacitanceof coatings ( C  c ) and the pore resistance ( R po ) as afunction of immersion time and the polarizationresistance ( R p ) of coating were investigated in thisresearch. Experimental All the chemicals used were from Aldrich. The pureaniline (An) and  o -anisidine (OAn) used in the M. R. Mahmoudian ( & ), W. J. Basirun,Y. AliasDepartment of Chemistry, University of Malaya,Kuala Lumpur 50603, Malaysiae-mail: M_R_mahmoudian@yahoo.comJ. Coat. Technol. Res.,  9  (1) 79–86, 2012DOI 10.1007/s11998-011-9345-y79  experiment were always stored in darkness beforesynthesis. The elemental composition analysis of thesteel plate substrate of 3.14 cm 2 was wt%: 2.71% C,0.49% Si, and 94.79% Fe. Graphite counter electrodewas a rod measuring 0.2 cm in radius and 1.5 cm inheight and area of 2 cm 2 . A saturated calomel elec-trode (SCE) was used as the reference; all the potentialvalues were referred to this electrode. The steel plateworking electrodes were degreased in ethanol anddried at 45  C after being mechanically polished withfine emery paper of 320–1200 grades.To polymerize the monomers in the presence of thepoly(acrylic acid- co -acryl amide) (PAA- co -AA), themethod of Racicot 9 was used. 2.74 g of PAA- co -AA(sodium salt,  M  w  200,000, 70% carboxyl, Polysciences)which contains 0.022 mol carboxyl group was treatedwith 25 mL 3 M HCl to completely convert the saltform to the acid form which was then separated as aprecipitate from the solution. The precipitate waswashed with distilled water three times to remove theelectrolytes. The precipitate was then dissolved in25 mL DMF and 0.011 mol of monomer was addedand stirred for 0.5 h. After 50 mL 3 M HCl and 1 mLof 3 M FeCl 3  were added, 1.25 mL of 30% H 2 O 2 (0.011 mol) was added drop wise. After 2 min, solu-tions including the aniline monomer turned green,while the solution color containing the OAn monomerturned to red. The reaction was completed in 8 h.The PAn: PAA- co -AA and POAn: PAA- co -AAfilms were applied on the steel surfaces by immersionof the coupons in PAn: PAA- co -AA and POAn: PAA- co -AA saturated DMF solution. The prepared elec-troactive polymer can be used as undercoating andcommercial paint topcoating formulation containingorganic solvent (Thinner) and titanium oxide pigments(Nippon Paint Co., Malaysia, Kuala Lumpur), wasapplied as topcoating. The commercial paint as topco-ating covered the coated steel with undercoating by jetspraying 120–150 mg. Characterization The thickness of the electroactive polymer: PAA- co -AA and also of the paint films were measured using aMechanical Profiler (KLA-Tencor, P-6) equipment.The thickness of electroactive polymer: PAA- co -AAas undercoating and topcoating was approximately 2and 28  l m, respectively. In addition, a control sampleof coated steel with paint with the same thickness butwithout undercoat was also prepared.Spectrum 400 (FTIR/FTFIR spectrometer) equip-ment was used to obtain the Fourier transform infrared(FTIR) spectra of doped PAn and POAn films on steelsurfaces. An iCamscope-305A (magnification 40 9 ) wasused to take the sample images.The impedance spectra were obtained over thefrequency range of 100 kHz–10 mHz, with acquisitionof 10 points per decade, with a signal amplitude of 5 mV around the open circuit potential. A Potentio-stat/Galvanostat Model PGSTAT-30 from Autolab,controlled by an USB_IF030 interface and by theFRA.EXE software both installed in a PC computerwas used to perform these experiments (FrequencyResponse Analysis [FRA] for Windows version 4.9).Each surface was exposed to a 3.5% NaCl aqueoussolution. The analysis of the impedance spectra wasdone by fitting the experimental results to equivalentcircuits using the nonlinear least-square fitting proce-dure. The quality of fitting to equivalent circuit was judged first by the  v 2 value (i.e., the sum of the squareof the difference between theoretical and experimentpoint) and second by limiting the relative error in thevalue of each element in the equivalent circuit to 5%. Results and discussion  FTIR spectroscopy The FTIR spectrum of doped PAn and POAn films onsteel surfaces is shown in Fig. 1. The peak at 1700.81and 1702.68 cm  1 in the FTIR spectrum of doped PAnand POAn, respectively, is due to the carbonyl groupof the acrylic acid units, whereas the peak at 1656.91and 1657.53 cm  1 in Figs. 1a and 1b, respectively, is due to the carbonyl group of the acrylamide units. 10 Inthe FTIR spectrum of doped PAn and POAn, peaksbetween 2600 and 3400 cm  1 can be attributed to N–Hand O–H bonds. The strong bands in the range of 1000–1300 cm  1 can be associated with aliphatic C–O.FTIR spectrum of doped POAn indicates the charac-teristic bands for C–O (aryl ether) at 1282.38 and1038.73 cm  1 . In Fig. 1, peaks between 690 and800 cm  1 are related to aromatic C–H bond. Thestructure of synthesized polymer films is shown inFig. 2.      %     T  r  a  n  s  m   i   t  a  n  c  e 4000 3600OHNHOHNH3196.573195.362948.063348.133348.25 2951.471702.68 1657.531282.381038.73798.84697.721656.911700.811228.531019.87793.61 695.41 (a)(b) aromatic C–Haromatic C–H3200 28002400200018001600140012001000800 600 400 Wavenumber (cm –1 ) Fig. 1: FTIR spectra of (a) doped polyaniline (PAn) and(b) doped poly- o  -anisidine (POAn) films on steel surface J. Coat. Technol. Res.,  9  (1) 79–86, 201280   EIS  Electrochemical impedance spectroscopy (EIS) in3.5% NaCl solution was used to analyze the elec-trode/electroactive polymer/paint/electrolyte system.The electrochemical parameters were evaluated byemploying the ZSimpWin software. We observed anexcellent agreement between experimental results andthe parameters obtained from the  R ( C  [ R ( RQ )])( RQ )and the  R ( C  [ R ( RQ )])( RC  ) equivalent circuit model forelectrode/POAn/paint/electrolyte and electrode/PAn/paint/electrolyte, respectively, where the chi-squared( v 2 ) minimized at 10  4 value (Fig. 3). The  R s ( C  c [ R po ( R p Q 1 )])( R CF Q 2 ) and  R s ( C  c [ R po ( R p Q 1 )])( R CF C  2 ) equiv-alent circuit model was used in the simulation of theimpedance behavior of electrode/POAn/paint/electro-lyte and electrode/PAn/paint/electrolyte, respectively,from the experimentally obtained impedance data. Themodel of electrode/POAn/paint/electrolyte was builtusing series components; the first is the bulk solutionresistance of the electrolyte  R s , the second is theparallel combination of the capacitance of the polymercoating  C  c  and  R po . The  R po  is the pore resistancewhich is due to the formation of ion conducting pathsacross the coating. The constant phase element (CPE)is defined by the admittance ( Y  ) and the power indexnumber  n: Y   =  Y  o (  j x ) n and for  n  = 1,  Y  o ( Q ) becomes acapacitor ( C  ). The CPE which is  Q 1  is parallel with  R p .The  R p  is the polarization resistance of the area at themetal/coating interface where corrosion occurs. Thelast component, a CPE which is  Q 2  is in parallel with acharge transfer resistor  R CF , corresponding to the porein the surface of the oxide layer. The equivalent circuitmodel for electrode/PAn/paint/electrolyte was similarto electrode/POAn/paint/electrolyte, except the CPE( Q 2 ) in electrode/POAn/paint/electrolyte was replacedwith the capacitance  C  CF . Simulation results for elec-trode POAn/paint/electrolyte and electrode PAn/paint/electrolyte show that this electrical equivalentcircuit was successfully applied to the experimentaldata to explain the interface between the electrode/coating.For intact coatings, the coating resistance  R po  ismuch higher compared with the electrochemical reac-tion parameters. 11 tan h  ¼  x C  c R po  ð 1 Þ where  x  = 2 p  f   and  f   is the applied frequency. Equation(1) indicates that for an intact coating without mac-rodefects, the measured (tan  h ) is related to theapplied frequency, coating capacitance ( C  c ), and poreresistance ( R po ). 11 During performance of the coatingin corrosive environments, the electrolyte solutiongradually permeates into the coating, and the poreresistance decreases and the coating capacitanceincreases. As a result, the current which flows throughthe pore resistance  R po  gradually increases and the  h  atthe given frequency gradually decreases with immer-sion time. The decreasing rate of the  h  depends on theapplied frequency and the relative values of coating N··N··NNNHNOCH 3  OCH 3  OCH 3  OCH 3 NH (a)(b) H Oxidized partReduced partOxidized partReduced part H nn ··N·· Fig. 2: The structure of (a) polyaniline (PAn) and (b) poly- o  -anisidine (POAn)    l  o  g      |    Z      |    (      Ω    )   l  o  g      |    Z      |    (      Ω    )   P   h  a  s  e  a  n  g   l  e   (   °   ) –2 –1 0 1  R s  R s C  c C  c C  2 Q 1 CPECPECPE Q 2 Q 1  R CF  R CF  R p  R p  R po  R po 2 3 4 501020304050    P   h  a  s  e  a  n  g   l  e   (   °   ) 5101520253035 log  f   (Hz) –2 –1 0 1 2 3 4 5 log  f   (Hz) (a)(b) Fig. 3: Agreement between experimental results andparameters from the equivalent circuit model: (a) elec-trode/poly- o  -anisidine (POAn)/paint/electrolyte and (b) elec-trode/polyaniline (PAn)/paint/electrolyte after 28 daysexposure time in 3.5% NaCl solution J. Coat. Technol. Res.,  9  (1) 79–86, 201281  resistance and capacitance. After the permeation of theelectrolyte into the coating reaches the saturation, thecoating capacitance would remain a relatively stablevalue while the pore resistance may keep decreasing,resulting in quick decrease of the  h . Therefore, thevariations of the  h  or tan  h  are related to the changes of the pore resistance and the capacitance, and mayreflect the performance of coatings. From the mea-sured EIS spectra, the  R po  variations and tan  h  atvarious high frequencies (10 5 Hz) with immersion timewere obtained for the paint/POAn and paint/PAncoating as shown in Fig. 4. In Fig. 4, the variation range for tan  h  is between 3.5 and 1. With the increase of immersion time, tan  h  measured at high frequenciesreduces until 8 days. It is noted that tan  h  and  R po showed similar decreasing tendencies. This may beexplained by equation (1), since at a given frequencythe measured tan  h  varies with the value of   C  c R po , andthe decreasing rate of the pore resistance  R po  is muchgreater than the increasing rate of  capacitance  C  c during the early period of immersion. 12 Figures 5a and 5b show results of the three parallel testsfor( R po )ofPAn:(PAA- co -AA)andPOAn:(PAA- co -AA) at 10 5 Hz, respectively. The results from threemeasurements follow the same trend and are very closeto each other. The mean values and standard deviationsof the data from Fig. 5 are shown in Tables 1 and 2. For most of the data, the standard deviations are less than 1and 2 for PAn: (PAA- co -AA) and POAn: (PAA- co -AA), respectively, except the first 4 days of POAn:(PAA- co -AA) that are more than 2. Hence, the coatingresistance ( R po ) measurement by using equivalent cir-cuit shows good reproducibility.Figures 6a and 6b show the comparison between the variation tan  h  and  R po  of both coatings. The resultsshow after 28 days the  R po  of paint/POAn is more thanthe  R po  of paint/PAn. This result confirms the variationof tan  h  (10 5 Hz) . A better estimate of the change in coating deteri-oration can be obtained from the variation of   R po  and C  c  with the immersion time. As can be seen fromFig. 7,  R po , which shows the extent of ionic conductionthrough the coating in electrolytic environments,decreases with rising immersion time, indicating anincrease in ionic conductivity for the coating and lowerprotective properties as a result of electrolyte penetra-tion. Figures 7a and 7b show the  R po  variation value of POAn/paint and PAn/paint. For  R po  of POAn/paint(Fig. 7a), there is an initial increase in up to 5 days andthen a sharp decrease up to 8 days, and it increased alittle up to the ninth day and decreased again andfinally increased until 28 days of immersion (Fig. 7a).The trend of   R po  variation of PAn/paint is similar toPOAn/paint but in the two parts of the immersiontime, their  R po  variation is different. During the firstand last weeks of immersion time, the amount of   R po  of POAn/paint was more than PAn/paint. The decreaseand minimum of   R po  values have been associated withthe formation and rupture of blisters and the sub-sequent increase and maximum with the deposition of corrosion products in the blisters. 13 05101520253000.511.522.533.5    T  a  n   (   °   )    R   p  o   (   k      Ω    c  m    2    ) 0 5 10 15 Time (days) (a) 20 2511223005101520253000.511.522.53    T  a  n   (   °   )    R   p  o   (   k      Ω    c  m    2    ) 0 5 10 15 Time (days) (b) 20 25 30 Fig. 4: The variation of the pore resistance ( R  po ) and tan  h at high frequency (10 5 Hz) with immersion time for (a) poly- o  -anisidine (POAn)/paint and (b) polyaniline (PAn)/paint 05101520253000.511.522.533.5    T  a  n   (   °   )   T  a  n   (   °   )    R   p  o   (   k      Ω    c  m    2    ) 0 5 10 15 Time (days) (a) 20 25 3005101520253000.511.522.53    R   p  o   (   k      Ω    c  m    2    ) 0 5 10 15 Time (days) (b) 20 25 30 Fig. 5: The variation of the pore resistance ( R  po ) and tan  h at 10 5 Hz with immersion time. The three parallel tests for R  po  of (a) PAn: (PAA- co  -AA) and (b) POAn: (PAA- co  -AA),respectively J. Coat. Technol. Res.,  9  (1) 79–86, 201282
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