pH-responsive nanostructured polyaniline capsules for self...

Scientia Iranica F (2017) 24(6), 3512{3520

Sharif University of TechnologyScientia Iranica

Transactions F: Nanotechnologywww.scientiairanica.com

pH-responsive nanostructured polyaniline capsules forself-healing corrosion protection: The in uence ofcapsule concentration

N. Pirhady Tavandashtia, M. Ghorbania,b;�, A. Shojaeia,c;�,J.M.C. Mold, H. Terrynd,e and Y. Gonzalez-Garciad

a. Institute for Nanoscience and Nanotechnology (INST), Sharif University of Technology, Tehran, P.O. Box 11155-8639, Iran.b. Department of Materials Science and Engineering, Sharif University of Technology, Tehran, P.O. Box 11155-9466, Iran.c. Department of Chemical and Petroleum Engineering, Sharif University of Technology, Tehran, P.O. Box 11155-9465, Iran.d. Department of Materials Science and Engineering, Delft University of Technology, 2628CD, Delft, The Netherlands.e. Group of Electrochemical and Surface Engineering, Vrije Universiteit Brussel, B-1050, Brussels, Belgium.

Received 8 August 2016; received in revised form 18 January 2017; accepted 22 April 2017

KEYWORDSNanostructuredpolyaniline capsules;MBT corrosioninhibitor;Organic coating;Corrosion protection.

Abstract. Nanostructured hollow polyaniline (PANI) capsules are good candidates forencapsulation of corrosion inhibitors and pH-responsive release when incorporated intoorganic coatings. In previous studies, the corrosion protection performance of PANIcapsules, containing organic inhibitor 2-Mercaptobenzothiazole (MBT), was demonstrated.The present work studies the in uence of capsule concentrations (i.e., 0.3, 1, and 2 wt%)on the corrosion protection properties of the coating system. Anti-corrosion properties ofdi�erent coatings were compared by means of Electrochemical Impedance Spectroscopy(EIS) and Scanning Vibrating Electrode Technique (SVET). MBT loaded PANI capsulesin epoxy ester coating on AA2024-T3 substrate allow for a self-healing e�ect to be obtainedduring the corrosion process. The results showed that the concentration of MBT loadedPANI capsules greatly in uences the corrosion protection properties of the coatings, andthe best corrosion protection performance was observed for the coating system containing1 wt% PANI capsules. The impedance value of the scratched area of this coating after 7days of immersion was one order of magnitude higher than that of the control sample.© 2017 Sharif University of Technology. All rights reserved.

1. Introduction

Due to the severe impact of corrosion on economy,industry, and environment, using strategies to preventor slow down the rate of corrosion is of great impor-tance. Application of organic coatings is one of themost widespread techniques for corrosion protection of

*. Corresponding authors. Tel: +98 21 66165219E-mail addresses: [email protected] (M. Ghorbani);[email protected] (A. Shojaei)

doi: 10.24200/sci.2017.4426

the metallic substrates. Since various external factorscan cause formation of pores and cracks in the coatingthrough which water and corrosive species can di�useand reach the metal surface; recently, considerable in-terest has been given to the use of corrosion protectionsystems that provide not only a physical barrier againstaggressive species, but also an active self-healing abil-ity [1-4]. One of the main strategies to achieve theactive e�ect is to apply micro/nanostructured hostingsystems for encapsulation of corrosion inhibitors andto incorporate the capsules into the coating system.Accordingly, the micro/nanostructured capsules willstore the inhibitors, and when corrosion starts (in case

N. Pirhady Tavandashti et al./Scientia Iranica, Transactions F: Nanotechnology 24 (2017) 3512{3520 3513

of degradation or damage in the coating), the capsulesrelease the corrosion inhibitor to stop the corrosionprocess, providing a self-healing e�ect.

Conducting polymer micro/nanostructures hasattracted much attention among researchers in recentyears because of their unique intrinsic properties. No-ticeably, the biggest advantage of nanostructured con-ducting polymers is that their structure and propertiescan be adjusted reversibly by doping-dedoping pro-cess [5], which can be controlled by adjusting electricpotential or changing solution pH [6,7]. Their responseto chemical or electrical stimuli can make a changein their conductivity, volume, color, permeability, andhydrophilicity [5,7-10]. These characteristics make theconducting polymers fascinating candidates to be usedas containers for encapsulation and smart release [5,11-13].

In our previous work [13], we studied the releaseof MBT from PANI capsules at di�erent pHs (i.e.,1.5, 7, 11). The results from UV-vis and SERSanalyses suggested that the encapsulation of MBTcorrosion inhibitor in polyaniline hollow microspheresis an e�cient way to achieve pH-controlled release ofthe inhibitor as well as to avoid its undesirable leachingfrom the coating. It was observed that the releaseof MBT from PANI capsules is triggered at pH�11.The corrosion process is usually accompanied by pHchanges in the local corrosion area; an increase in thelocal pH can take place during cathodic reaction ofreduction of the dissolved oxygen [14,15]. Thus, thelocal increase of pH due to corrosion process can triggerthe release of MBT from the capsules incorporatedinto the corrosion protective coatings, reducing therate of corrosion signi�cantly. The corrosion protectionproperties of MBT-loaded PANI capsules incorporatedinto epoxy ester coating were characterized. It wasdemonstrated that incorporation of MBT-loaded PANIcapsules in the coating resulted in enhanced activeprotection performance in case of a coating defect,without compromising the barrier properties of thecoating.

In the present work, the MBT corrosion inhibitorwas encapsulated in PANI hollow capsules, and dif-ferent concentrations of the capsules were embeddedinto epoxy ester coatings applied on AA2024 sub-strates. The anticorrosion properties of the coatedsamples and the e�ect of capsule concentration onthe coating performance were investigated by adhesionpull-o� tests, Scanning Vibrating Electrode Technique(SVET), and Electrochemical Impedance Spectroscopy(EIS) experiments.

2. Experimental procedure

2.1. MaterialsAniline (� 99:0%), ammonium persulfate (APS, �

98:0%), sodium hydroxide (� 98:0%, Pellets), hy-drochloric acid (37%), and Toluene (99.5%) werebought from Merck Chemicals. �-naphthalene sulfonicacid (�-NSA,� 90:0%) was acquired from Fluka Chem-icals, and 2-Mercaptobenzothiazole (MBT) (97.0%)was purchased from Sigma-Aldrich. All the chemicalswere used as received.

2.2. Fabrication of nanostructured PANIcapsules and encapsulation of MBT

Hollow microspheres of polyaniline (PANI) with nano-sized shell were synthesized using a soft templatemethod according to a procedure reported earlier [16].The encapsulation of organic corrosion inhibitor MBTin PANI capsules was performed via stirring a mixtureof PANI (50 mg) and MBT (0.3 g) in ethanol solution(10 mL) at 500 rpm for 3 h. Then, the solution wasevacuated using a vacuum pump along with stirring for10 min in order to increase the amount of encapsula-tion. The capsules were washed and centrifuged for3 times after the encapsulation procedure, followed byremoving the supernatant and drying the capsules atroom temperature overnight.

The loading of MBT in the capsules was in-vestigated by UV-Visible Spectroscopy (PerkinElmerLambda 950 instrument). The absorption at a wave-length of 324 nm, which is attributed to the ab-sorbance peak of MBT in ethanol, was monitored.The inhibitor-loaded PANI capsules were dispersedin ethanol. The dispersion was sonicated (UP400S,Hielscher Ultrasound Technology) for 20 min andcentrifuged (6000 rpm, 30 min). Then, the super-natant was studied via UV-vis spectroscopy. As areference, ethanol solutions of MBT with identi�edconcentrations were prepared and the calibration curvewas made. The quantity of 2-mercaptobenzothiazoleloaded into the hollow PANI microspheres is 1 wt%.

2.3. Coating preparationAluminum AA2024 alloy was used as substrates forcorrosion protection studies. Surface preparation forcoating application was as follows: the substrates wereground up to 1200 grit paper, washed with detergentand distilled water, and degreased in acetone in ultra-sound bath for 10 min. Epoxy ester resin (EE430S,Rezitan) was selected for coating preparation.

The MBT loaded PANI capsules were dispersedin toluene and introduced into epoxy ester resin viasonication for 10 min to get a homogeneous suspension.The mixture was then applied using a Metrohm Auto-lab spin-coater (at 500 rpm for 10 s, then at 2000 rpmfor 20 s) on AA2024 substrates. To investigatethe e�ect of capsules concentration on the corrosionprotection performance, the metallic substrates werecoated with di�erent coating systems containing 0.3, 1,and 2 wt% of MBT-loaded PANI-capsules. Moreover,

3514 N. Pirhady Tavandashti et al./Scientia Iranica, Transactions F: Nanotechnology 24 (2017) 3512{3520

pure epoxy ester coating (control) was also applied toAA2024 substrates for comparison. The mass loss onthe curing of the samples, calculated by weight, wasabout 60%. Using this value, the �nal compositions ofdi�erent coating systems in dried coating after curingwere estimated, as shown in Table 1. The dry �lmthickness of the coatings was 13:9�1:1 �m measured byeddy current method (ED10 Eddy, Dual Scope MP40,Germany).

Pull-o� tests, according to ASTM D4541, wereconducted with a hydraulic pull-o� tester (Elcometer,model HATE108) using a commercial 3M (M2000)adhesive cured for 24 h prior to testing.

2.4. Corrosion protection evaluationIn a typical EIS experiment, the coated substrateswere scratched (scratch length � 1 mm) and placedinto home-made cells, whereby an area of the samplewith 8 mm diameter was exposed to 0.3 wt% NaClsolution at room temperature for several days. A three-electrode setup in a Faraday cage was used, and theimpedance spectra were recorded at the open circuitpotential. An Ag/AgCl reference and a platinumcounter electrode were immersed in the cell, and themetal substrate functioning as the working electrodewas connected to an Impedance Analyzer (SolartronS1 1287). The current response was detected in thefrequency range of 100 kHz to 0.01 Hz, and the appliedvoltage perturbation was 10 mV. Ten frequencies wereassessed per decade. The spectra were obtained usingthe Zplot software and �tted with Zview. ConstantPhase Elements (CPE) were used in all �ttings insteadof capacitances because of the deviation from the idealcapacitance behavior (the phase angle of capacitorswas di�erent from �90�). The impedance of a CPEis de�ned as follows:

ZCPE(!) = Q�1(j!)�n;

where Z is the impedance, Q is the admittancecoe�cient, j2 = �1 is the imaginary number, !is the angular frequency (rad s�1), and n is theCPE exponent. The following equation was used tocalculate capacitance values for di�erent elements inthe equivalent circuit:

C = Q(!max)n�1;

where !max is the frequency at which the imaginaryimpedance reaches a maximum for the respective timeconstant [17].

The scanning vibrating electrode technique(SVET, Applicable Electronics (USA)) was applied toanalyze the anticorrosion properties of the coatings in0.3 wt% NaCl solution. The coating was scratched(scratch length � 1 mm) before the measurementto guarantee exposure of the metal to the aggressive

solution. Then, the coated samples were sealed withadhesive tape and only the area (� 3�3 mm2), includ-ing the scratch, was left uncovered. Measurements onareas with dimensions of � 1� 2 mm2 were performedevery 2 h during 24 h, and the mean acquisition timeper scan was � 20 min. The vibrating probe was a thinPt needle, with a platinum black sphere of ca. 20 �min diameter deposited on its tip. The current densityat 100 �m above the sample surface was detected. Thesubsequent analysis of the SVET data was performedwith the help of Quikgrid software. The repetition ofSVET experiments showed a consistent trend in theresults.

The surfaces of the scratched coatings after expo-sure to corrosive media were studied by JEOL JSM-IT300 SEM.

3. Results and discussions

Nanostructured hollow PANI microspheres were syn-thesized by Pirhady Tavandashti et al. via a soft tem-plate method [16]. The diameters of the microsphereswere mostly in the range of 1-2 �m, and they showedan average shell thickness of ca. 90 nm. The FTIR andUV-vis spectroscopies [13,16] showed that the capsuleshave a backbone polymer structure of polyaniline in anemeraldine salt form.

The encapsulation of organic corrosion inhibitor2-Mercaptobenzothiazole (MBT) was performed viastirring a mixture of PANI capsules and MBT inethanol solution. UV-vis and SERS spectroscopieswere used in the previous work [13] to con�rm theencapsulation of MBT in PANI containers. In brief,after the encapsulation procedure, the capsules werewashed and centrifuged for several times; then, thesupernatant of washing of the capsules was studiedusing UV-vis spectroscopy. The absorption at a wave-length of 324 nm was monitored, which correspondsto the absorbance peak of MBT in ethanol. No peakrelated to the presence of MBT was observed in thesupernatant of washing of the capsules. This was toeliminate the absorbed MBT on the surfaces of thecapsules. To investigate the presence of MBT inside thepolyaniline capsules, the capsules were broken by severeultrasonication for 20 min, and after centrifugation ofthe solution, the supernatant of broken capsules wasstudied by UV-vis spectroscopy. A strong absorptionpeak was detected in 324 nm, con�rming that MBTwas successfully loaded in PANI capsules. To provethe encapsulation of MBT in PANI containers further,Surface Enhanced Raman Spectroscopy (SERS) wasapplied. The capsules were dispersed in water and adrop of dispersion was put on a SERS probe (whichconsisted of silver particles (50-500 nm) in a gelatinmatrix on a glass substrate). When high laser power(i.e., 2.5 mW) was applied to the capsules, which


Table 1. Composition of di�erent coating systems.

Sample DescriptionControl Pure epoxy ester coatingCaps03 0.3 wt% of MBT loaded PANI capsules embedded into the coatingCaps1 1 wt% of MBT loaded PANI capsules embedded into the coatingCaps2 2 wt% of MBT loaded PANI capsules embedded into the coating

caused the capsules to burn o�, the characteristicSERS signals for MBT were evidenced in the resultingspectrum. It showed that after the capsules were burntout, MBT was released and absorbed on the surfaceof the SERS probe. Due to the surface enhancemente�ect of SERS probe, even the MBT encapsulated insingle PANI capsules was detectable. This result alsocon�rmed the encapsulation of MBT in the cavity ofthe capsules.

To investigate the e�ect of capsules concentrationon the corrosion protection performance of the coat-ings, the metallic substrates were coated with di�erentcoating systems containing 0.3, 1, and 2 wt% of MBTloaded PANI capsules. Furthermore, pure epoxy estercoating (control) was applied on AA2024 substratesfor comparison. The compositions of di�erent coatingsystems and codes used during the investigation areshown in Table 1.

3.1. Characterization of the coatingsSince epoxy ester coating is transparent, there is a pos-sibility to investigate the dispersion of hollow polyani-line capsules in the coating by optical microscopy(Figure 1). The optical microscopy images illustratedin Figure 1(a)-(d) were taken from the same area ofthe coating with a focus on di�erent focal depths. Itwas observed that the PANI capsules were uniformlydistributed in the coating matrix in three dimensions.

Besides barrier and active properties, the adhe-sion of the coatings is of great importance. Pull-o�test was applied to the study of the adhesion of thecoated samples. Figure 2 presents the results of pull-o� tests, showing that the coatings, containing MBTloaded PANI capsules, have superior adhesion to thatof pure epoxy ester coating (control). Moreover, theadhesion properties of the composite coatings signi�-cantly increased with increasing the concentration ofPANI capsules in the coatings.

Visual examination of the surfaces of the sampleand dolly (Table 2) revealed that by incorporation ofPANI capsules (� 1 wt%) in the coating system, thedelamination of the coatings decreased. Furthermore,as the capsule content increases, the percentage of coat-ing delamination decreases and the sample with 2 wt%of PANI capsules (Caps2) showed no signs of coatingdelamination with an adhesive fracture mode. Theseresults suggest that PANI capsule content increases theadhesion strength of the epoxy ester coating.

Figure 1. Optical microscopy of dispersion of MBTloaded PANI capsules in epoxy ester coating (Caps03) onAA2024 substrate: (a)-(d) The images were taken fromthe same area with focus on di�erent focal depths.

Figure 2. Pull-o� adhesion test of di�erent coatingsystems.

Table 2. Pull o� delamination results.

Sample Delamination (%)Control 80Caps03 90Caps1 � 1Caps2 0

3.2. Evaluation of the corrosion protection ofthe coatings

To study the self-healing properties of the coatings,EIS and SVET measurements were performed on thesamples immersed in 0.3 wt% NaCl solution. Prior to


corrosion tests, scratches with 1 mm length were madein the coatings using a scalpel in order to induce thecorrosion process.

3.2.1. EIS measurementsEIS measurements were performed on the scratchedsamples in 0.3 wt% NaCl solution to evaluate thecorrosion protection properties of the coated samples.In Figures 3 and 4, Bode plots of the scratchedsamples are shown after 1 and 7 days of immersion,respectively. After 1 day of immersion (Figure 3), thesample containing 1 wt% MBT-loaded PANI capsules(Caps1) presented higher impedance values than thoseof the other coating systems. The lowest impedancevalues were observed for Caps03 and control coatingsystems. After 7 days of immersion in 0.3 wt% NaClsolution (Figure 4), Caps1 coating system showedstill superior corrosion protection compared to othersamples. It presented the highest impedance valuesamongst other coating systems. Although Caps03and Caps2 coating systems showed poor protectionperformances with respect to sample Caps1, they stillhad higher impedance values than those of the control.

EIS results for all three coating systems showedthree time constants corresponding to capacitance ofthe coating, oxide layer of bare metal, and corrosionprocesses in the scratch [13]. EIS spectra were �ttedusing the equivalent circuit presented in Figure 5. Inthis equivalent circuit, Rsol is the solution resistance;Rcoat and CPEcoat are the resistance and capacitance

Figure 3. Bode plots of the scratched samples after 1 dayof immersion in 0.3 wt% NaCl solution.

Figure 4. Bode plots of the scratched samples after 7days of immersion in 0.3 wt% NaCl solution.

Figure 5. The equivalent circuit used for numerical�ttings of EIS data.

of the coating, respectively; Roxide is the resistance ofoxide layer and CPEoxide is the capacitance of oxidelayer; Rp and CPEdl are the polarization resistance anddouble-layer capacitance, respectively.

Figure 6(a) and (b) show the evolution of thecapacitance and resistance of the oxide layer forthe di�erent scratched coatings during immersion in0.3 wt% NaCl solution. In Figure 6(a), the controlsample showed higher capacitance values than thesystems containing MBT-loaded PANI capsules. Thesystems with MBT-loaded PANI capsules presentedlow, similar and stable capacitance values during 7days of immersion. This result indicates degradationin the oxide layer of the control coating with time.On the contrary, a more compact oxide layer wasformed in the coatings containing MBT loaded PANIcapsules. The evolution of the resistance of the oxidelayer, Roxide, with immersion time (Figure 6(b)) is inagreement with the capacitance behavior. The control(pure epoxy ester coating) shows the smallest values


Figure 6. Evolution of (a) capacitance and (b) resistanceof oxide layer for di�erent coating systems duringimmersion in 0.3 wt% NaCl solution.

of Roxide among other coating systems, con�rmingthat the control coating has the weakest oxide layeramong other systems. Nevertheless, it is importantto note that the concentration of inhibitor-loadedPANI capsules in the coating plays an important role.The largest resistance values of oxide layer amongall coating systems and during the total immersionperiod were measured for the coating containing 1 wt%MBT-loaded PANI capsules (Caps1). The resistanceincreases with immersion time reaching one order ofmagnitude higher value than that of the control sampleafter 7 days. This behavior indicates that the self-healing of the defect area in the coating containingMBT loaded PANI capsules, is taking place. SystemsCaps03 and Caps2 showed poorer self-healing behavior.The resistance values of oxide layer for Caps2 coatingsystem were similar to those of Caps1 during the �rst2 days of immersion. However, after 2 days, Roxide ofCaps2 declined. For the case of Caps03, the resistancevalues of oxide layer were only slightly higher thanthat of the control sample. This result indicates thatMBT-loaded capsule content in this coating was notsu�cient to make a great di�erence from pure epoxyester coating.

Figure 7. Evolution of polarization resistance fordi�erent coating systems during immersion in 0.3 wt%NaCl solution.

The evolution of polarization resistance for dif-ferent scratched coatings during immersion in 0.3 wt%NaCl solution is shown in Figure 7. It was observedthat Rp shows similar trend to the resistance of theoxide layer (Figure 6(b)). Control coating has thesmallest values of polarization resistance among othercoating systems, meaning that this coating has thehighest corrosion activity. Similarly, Caps03 coatingsystem has approximately comparable Rp values tothose of the control coating. The largest values of Rpfor the coating, containing 1 wt% MBT loaded PANIcapsules (Caps1), con�rm superior corrosion protectionproperties of this coating system.

In our previous work, it was observed that therelease of MBT from PANI capsules is triggered atpH�11 [13]. During corrosion in neutral aqueoussolutions, an increase in the local pH might takeplace through the reduction of the dissolved oxygen(1) [14,15]:

O2 + 2H2O + 4e� ! 4OH�: (1)

Therefore, the local increase of pH due to corrosionprocess is a trigger for MBT-loaded PANI capsulesincorporated in the coatings to release the corrosioninhibitor. The released MBT forms a protective layeron the attacked metal surface, reducing the rate of cor-rosion signi�cantly and providing a self-healing e�ect.However, EIS results show that the concentration ofMBT-loaded capsules plays an important role in theself-healing properties of the coating. If it is more thanan optimum amount, it can be even detrimental to thecorrosion protection performance.

Figure 8 shows the SEM images of the scratchedcoating systems after 4 days of exposure to 0.3 wt%NaCl solution. Good agreement is observed betweenthese SEM results, and the EIS results are discussedabove. Figure 8(a) demonstrates that, for the controlcoating system, large aggregates of corrosion productsare formed in the vicinity of scratch, evidencing the


Figure 8. SEM images of the scratched coating systems:(a) Control, (b) Caps03, (c) Caps1 [13], and (d) Caps2after 4 days of immersion in 0.3 wt% NaCl solution.

high corrosion activity. Moreover, the presence ofregions of undercoating corrosion was observed, andalso delamination of the coating in some areas wasdetected for this coating system. For the coatingsystems containing MBT loaded PANI capsules (Fig-ure 8(b)-(d)), no signs of delamination or undercoatingcorrosion were observed. However, the formation of theleast corrosion products in the scratch area of Caps1system con�rms its superior corrosion protection andself-healing ability compared to other coating systems.

3.2.2. SVET measurementsThe Scanning Vibrating Electrode Technique (SVET)was employed to assess the initial stages of corrosiondevelopment in the coatings and the self-healing per-formance. This technique can demonstrate localizedcorrosion activity by mapping the distribution of ca-

thodic and anodic ionic currents along the surface.SVET maps of the coating defect area immersed inthe 0.3 wt% NaCl solution were obtained every twohours. The current density maps of the scratchedcoatings after 18 h immersion in 0.3 wt% NaCl arepresented in Figure 9(a)-(d). Figure 9(a) shows thatthe pure epoxy ester (control) coating indicates highlylocalized corrosion activity in the scratch area after18 h immersion. For this coating, the defect wasactive during all tests, with a relatively increasingtrend of anodic and cathodic current densities withimmersion time. Figure 9(b)-(d) demonstrate that,in case of the epoxy ester coating containing MBT-loaded PANI capsules, the corrosion current density isfar less than that of the control coating, con�rmingthe improvement of corrosion protection performancefurther in case of incorporation of PANI microspheresinto the coating [13]. However, for this short immersiontime, it was not possible to visualize obviously thedi�erences between the coatings containing di�erentconcentrations of PANI capsules.

4. Conclusions

In this work, MBT corrosion inhibitor was encapsu-lated in PANI hollow microspheres, and the capsuleswere embedded into epoxy ester coatings applied toAA2024 substrates. The in uence of capsules con-centration on the corrosion protection performanceof the coatings was evaluated. EIS and SVET re-sults proved the superior corrosion protection of thecoatings, containing MBT-loaded PANI capsules, incomparison to the pure epoxy ester coating. Theresults showed that the content of MBT loaded PANIcapsules greatly in uences the corrosion protectionproperties of the coating. The best corrosion protec-tion performance was observed for the coating systemcontaining 1 wt% of PANI capsule (Caps1). However,

Figure 9. Current density maps of a scratch on (a) control, (b) Caps03, (c) Caps1, and (d) Caps2 coating systems after18 h exposure to 0.3 wt% NaCl solution. Scale units: �A.cm�2. Scanned area: � 1 mm� 2 mm.


incorporation of 0.3 wt% capsules (Caps03) into thecoatings did not su�ciently improve the corrosionprotection performance of epoxy ester coatings due tothe lack of corrosion inhibiting materials. Extremelyhigh concentration of PANI capsules (Caps02) in thecoatings has also shown a negative e�ect, especially onimmersion times longer than 2 days; it can be due tothe increase of water uptake and/or decrease of theintegrity of the coating by increase of PANI content.

Acknowledgments

The authors from Sharif University of Technologywould like to express their appreciation to the IranNational Science Foundation for �nancial support.

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Biographies

Nahid Pirhady Tavandashti received her PhD de-gree in Nanomaterials from Institute for Nanoscienceand Nanotechnology (INST), Sharif University of Tech-nology. She has worked on self-healing coatings from2007, when she started her MSc project. Her researchinterests are stimuli-responsive micro/nanocontainers,synthesis of nanocapsules and nanoreservoirs, smartself-healing coatings, and conducting polymers.

Mohammad Ghorbani is a Full Professor at theDepartment of Material Science and Engineering atSharif University of Technology in Tehran, Iran. Heearned his Master (1986) and doctoral (1991) degreesfrom Manchester University, UMIST, UK. His researchcovers a variety of coatings including electrodeposition


of metallic coatings, composite coatings, conversioncoatings, and nano coatings, leading to publication ofmore than one hundred ISI papers.

Akbar Shojaei is a Professor at the Department ofChemical & Petroleum Engineering of Sharif Universityof Technology. He received his PhD degree in PolymerComposite Processing from Amirkabir University ofTechnology in 2002. He joined Sharif University ofTechnology in 2003 as an Assistant Professor andinitiated a focused research program on polymericsystems. Currently, his main research interests areto develop advanced functional and structural poly-mer nano/composites for various applications suchas biomedical, smart/active surface coatings, foodpackaging, friction materials, and engineering load-

bearing components. Particularly, processing, fab-ricating, and unearthing relationships between mi-cro/molecular structure and macroscopic properties ofpolymer composites are under intensive investigation.Dr. Shojaei has published more than 70 refereed journalarticles and given scienti�c talks in many internationalconferences.

J.M.C. Mol. His/her biography was not available atthe time of publication.

H. Terryn. His/her biography was not available atthe time of publication.

Y. Gonzalez-Garcia. His/her biography was notavailable at the time of publication.

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