Characterization and Application of Nanomaterials (2023) Special Issue: Nanocomposites processing, characterization, and applications doi:10.24294/can.v6i2.3361 1 Review Article Cutting-edge conjugated nanocomposites—Fundamentals and anti- corrosion significance Ayesha Kausar1,2,*, Ishaq Ahmad1,2 1 NPU-NCP Joint International Research Center on Advanced Nanomaterials and Defects Engineering, Northwestern Polytechnical University, Xi’an 710072, China. 2 UNESCO-UNISA Africa Chair in Nanosciences/Nanotechnology, iThemba LABS, Somerset West 7129, South Africa. * Corresponding author: Ayesha Kausar, dr.ayeshakausar@yahoo.com ABSTRACT This review is merely designed to throw light on the cutting-edge conjugated nanocomposites based on conjugated or conducting polymers and appropriate nanofillers. An important aspect of the conjugated nanocomposites has been observed in the anticorrosion of metals or metallic substrates. Particularly, including carbon nanoparticles (fullerene, graphene, and carbon nanotube) and inorganic nano-additives to the conjugated matrices have enhanced the physical features (morphology, electrical conductivity, mechanical stability, adhesion, and barrier properties) as well as corrosion resistance. To access the anti-corrosion potential, the conjugated nanocomposites have been coated on metal substrates using facile techniques of solution, spraying, dipping, and others. Accordingly, competent anti-corrosion conjugated nanocomposites have found potential for energy or electronic devices, engineering structures, and so on. Keywords: conjugated; nanocomposites; matrix; conductivity; anti-corrosion ARTICLE INFO Received: 20 November 2023 Accepted: 6 December 2023 Available online: 30 December 2023 COPYRIGHT Copyright © 2023 by author(s). Characterization and Application of Nanomaterials is published by EnPress Publisher LLC. This work is licensed under the Creative Commons Attribution- NonCommercial 4.0 International License (CC BY-NC 4.0). https://creativecommons.org/licenses/by- nc/4.0/ 1. Introduction Nanocarbon nanoparticles have been considered important fillers for nanocomposites and applied for technical applications[1,2]. Corrosion has been identified as a serious problem for metals employing industries[3]. To thwart corrosion related challenges, polymer based materials and nanomaterials have been focused in literature[4]. Here, conjugated or conductive materials have gained special emphasis to treat the corrosion issues of metals or other affected materials[5]. A basic problem has been documented as the interaction of corrosion causing species to metal surfaces causing harmful effects[6]. In this concern, the coating of conjugated materials on metal surfaces has been used to prevent corrosion[7]. Mechanism of corrosion prevention has also been examined[8]. Adding nanoparticles in conjugated nanocomposites has been found to further enhance the performance of these anti-corrosion coatings[9]. The conjugated nanocomposite coatings have been explored using numerous chemical, electrochemical, and physical practices[10,11]. According to the literature, the application of conjugated coatings on metal surfaces enhanced the adhesion strength and wear resistance, relative to neat steel metal[12]. Fine nanoparticle dispersion has been found to enhance the nanocomposite coating performance to prevent the corrosion issue. 2 This article basically offers a cutting-edge review of conjugated nanocomposite coatings for anti- corrosion of metal surfaces. Fundamentals of corrosion, corrosion protection mechanisms, and coating processes have been stated. The importance of using nanocomposites and conjugated nanocomposites for corrosion protection utilizations has been analysed. Specifically, adding nanocarbon nanoparticles has been found to considerably enhance the anti-corrosion performance of these conjugated nanocomposite coatings. Morphology, physical features, and anti-corrosion performance of the conjugated nanocomposites have been deliberated. Resulting anti-corrosion coatings have been used in essential technical sectors. This is an all- embracing, revolutionary, and up-to-date review of corrosion resistance of conjugated polymers and derived nanocomposites covering design, properties, and technological relevance. To the best of our knowledge, the anticorrosion potential of conjugated polymer/nanocarbon nanocomposites has not been reviewed comprehensively in the literature before. Consequently, this article is undoubtedly a radical contribution in the field of corrosion resistance conjugated nanocomposites. Future growths in the field of anticorrosion conjugated polymer/nanocarbon nanocomposites are not possible for the field scientists or researchers before getting prior compiled literature knowledge on these materials. 2. Conjugated materials for corrosion protection Conjugated polymers or conducting polymers have been considered as important materials for corrosion protection of metals[13–15]. Conjugated polymers like polyaniline, polypyrrole, and others have been frequently applied in anti-corrosion coatings. Corrosion effects can be perceived in these coatings due to the surface cracking leading to the approach of corrosive species to metal surfaces. Polyaniline coatings have been deposited on the steel or iron surface to prevent corrosion effects[16]. A direct relation has been observed between the electrical conductivity and corrosion resistance of the materials. An increase in electrical conduction has improved the electrochemical and anti-corrosion performance of the conjugated polymers[17]. The corrosion process is usually prevented by increasing the electrical conductivity of the anticorrosion coating applied on the metal surface. Therefore, a direct relationship exists between the rise in electrical conductivity and improving corrosion resistance. Metal corrosion usually occurs when metal atoms interact with atmospheric molecules to form oxides, hydroxides, and other molecules to cut the electron flow of metal atom’s orbitals. In other words, when metal atoms are corroded, electrons cannot hop through the metal for electron conduction. Once the metal surface is corroded, electron flow pathways are restricted, so lowering the electrical conductivity. Conjugated polymers usually form a protection layer over the metal surface. Research revealed that the formation of a conductive polymer layer on the metal surface offers corrosion protection via the formation of passive oxide layer involving oxidation-reduction reactions and also the barrier effect. Consequently, the likelihood of the corrosion phenomenon is delayed. Nevertheless, complex corrosion protection mechanisms have been found to be involved in corrosion protection by conducting polymers. The mechanism of corrosion protection by conducting polymers is in turn affected by numerous parameters. The amount of coated material may also affect the corrosion rate. In addition, polypyrrole has been used to form anti-corrosion coatings on iron or aluminum metal surfaces[18,19]. The corrosion rate greatly relies on factors like amounts, surfactants, pH, and other ecological factors. For conjugated polymers, anti-corrosion performance has been found to be upsurged using nanofillers as well as inhibitors[20,21]. 3. Nanocomposites of conjugated polymers for corrosion resistance Undoubtedly, conjugated polymers have been found functional for the anti-corrosion of metals[22]. Conjugated polymers have the efficiency to better interact with the metal surfaces to avert the harmful effects[23]. Metal surfaces commonly act as anodes and conjugated polymers perform as cathodes to encounter corrosion issues through electrochemical reactions[24]. Temporarily, anti-corrosion occurs due to metal- conjugated polymer interface reactions[25]. Adding additives or nanoparticles has been preferred to supplement 3 the anti-corrosion performance by averting the corrosive media from the metal surfaces[26]. Consequently, conjugated nanocomposites have been designed to have superior anti-corrosion and scratch/wear resistance features, than pristine conjugated polymers[27]. High performance coatings of conjugated nanocomposites of polyaniline, polypyrrole, and others have been reported[28,29]. These nanocomposite coatings have been frequently deposited using the chemical or electrochemical approaches and electron conduction and charge transference effects have been examined. 4. Conjugated nanocomposites with nanocarbon for anti-corrosion Conjugated nanocomposites have been designed using the conducting polymer matrix and carbon nanoparticle reinforcements[30–32]. Adding nanocarbons to conjugated nanocomposites has resulted in efficient coatings with facile synthesis, physical features, and technological uses. Among carbon nano-reinforcements, carbon nanotube has been adopted as a widely used and effective nanofiller to the conjugated polymers to augment the physical profile[33–35]. Deshpande et al.[36] specified nanocomposite coatings of polyaniline filled with multi-walled carbon nanotubes to protect carbon steel. Open circuit potential studies were used to assess the corrosion resistance performance. Anti-corrosion coatings of polypyrrole and carbon nanotube have also been developed[37]. Han et al.[38] formed high performance anti-corrosion polypyrrole/multi-walled carbon nanotube nanocomposite coatings. Richard Prabakar and Pyo[39] designed multi-walled carbon nanotube reinforced poly(3,4-ethylenedioxythiphene) nanocomposite coatings for corrosion prevention. The nanomaterial coatings had electrostatic repulsions to avert the corrosion causing anions from the metal surface. Mariano et. al.[40] reported on polyaniline and carbon nanotube based nanocomposites focusing on electron conduction and corrosion resistance profiles. Including 1 wt.% carbon nanotube revealed high electrical conductivity of 0.06 Scm–1, i.e., five orders higher than neat polyaniline (Figure 1). On the other hand, lower carbon nanotube loading of 0.25 wt.% exposed minor electrical conductivity of about ∼10−7 Scm–1. Figure 2 presents a model for the conductive carbon nanotube filled polyaniline matrix. It was proposed that the carbon nanotube bundles were uniformly aligned in the matrix and separated by an insulating polyaniline layer. The aligned nanofillers developed conduction paths through the polymer for efficient electrical conductivity. It was suggested that the coupling may occur among adjacent carbon nanotube bundles for better passage of electrons, in the direction of applied electric field. The tunnelling effects between the carbon nanotube bundles may be hindered due to the polymer layer in between. In addition to carbon nanotubes, graphene and graphene oxide nanofillers have been used to improve the electron conductivity, barrier, mechanical, and thermal features of the conjugated polymers[41–43]. Owing to the large surface area and surface properties, graphene and related nanoparticles exposed fine barrier properties and anti-corrosion resistance[44]. Chang et al.[45] studied tortuous ways in polyaniline/graphene nanocomposite coatings, responsible for averting H2O and O2 molecules due to barrier effects, so producing anti-corrosion effects[46]. Lin et al.[47] fabricated epoxy nanocomposite coatings filled with polyaniline functional graphene Figure 1. Conductivity as a function of carbon nanotube wt.% at 1 V[40]. Reproduced with permission from ACS. 4 Figure 2. (a) Schematic of polyaniline/carbon nanotube nanocomposite; and (b) fibrillar conduction path through two carbon nanotube bundles separated by an insulating polyaniline layer. This junction is modelled by two domains (open and filled) with two conductivities in series[40]. Reproduced with permission from ACS. oxide. The coatings have been reported for fine barrier and anti-corrosion features due to mutual interactions between the polyaniline, graphene oxide, and epoxy[48]. Corrosion inhibition effects of graphene oxide have been explored in literature[49]. Ramezanzadeh et al.[50] designed polyaniline nanocomposite coatings filled with graphene oxide and cerium. The nanomaterial coatings were coated on the mild steel and corrosion effects were studied. Functionalization of graphene oxide with nanoparticles further boosted the anti-corrosion performance of these coatings by developing twisted diffusion paths throughout the nanocomposites. Sheng et al.[51] fabricated polyaniline nanocomposites filled with graphene oxide and p-phenylenediamine functional graphene oxide nanofillers. The nanomaterials were prepared using the in situ redox polymerization. This study explored the synergistic effects between matrix and nanofiller on the morphology and anti-corrosion characteristics of the nanocomposites. Scanning electron microscopy and transmission electron microscopy micrographs of graphene oxide and p-phenylenediamine functional graphene oxide are given in Figure 3. It can be observed that the p-phenylenediamine functional graphene oxide had a more wrinkled nanosheet nanostructure owing to interactions between the p-phenylenediamine and graphene oxide. Comparatively, pristine graphene oxide has a lesser crumpled and smooth nanosheet nanostructure. Owing to the well- interacted phenylenediamine-graphene oxide nanostructure, the nanosheets avoid reaggregation tendency. Figure 4 depicts the Nyquist plots of polyaniline/phenylenediamine/graphene oxide nanocomposites with various nanofiller loading. Adding nano additives enhanced the semicircle diameters due to improvement in the charge transfer resistance or polarization of the nanomaterials. Consequently, the addition of nanofiller averted the diffusion of corrosive electrolyte molecules through the nanocomposite coating. According to equivalent circuit studies, electrolyte resistance, polarization resistance, and charge transfer resistance revealed corrosion resistance of the nanocomposite coatings. Figure 5 depicts the proposed model for the nanocomposites with corrosion diffusion pathways. Dispersion of functional nanofiller in polyaniline caused considerable hindrance to the penetrating corrosive molecules through nanocomposite coating towards metal. On the other hand, neat polymer coating had no resistance to the seeping corrosion species, so affecting the metal surface. Henceforth, these nanocomposite coatings had up to 99.9% anti-corrosion efficiency, as per potentiodynamic polarization results. Catt et. al.[52] filled graphene oxide in poly(3,4-ethylenedioxythiphene) matrix to develop the nanocomposite coatings using electro-polymerization. For anti-corrosion studies, the magnesium surface was focused. Figure 6 depicts the cracked surface of poly(3,4-ethylenedioxythiphene)/graphene oxide coating after corrosion. In corrosion current vs. voltage scans, lower or more positive corrosion current was experiential for coated sample, related to the non-coated surface. The result depicted higher anti-corrosion efficiency of the nanocomposite material. 5 Figure 3. High magnification scanning electron microscopy images of (a) graphene oxide and (b) p-phenylenediamine functional graphene oxide; and transmission electron microscopy images of (c) graphene oxide and (d) p-phenylenediamine functional graphene oxide[51]. Reproduced with permission from ACS. Figure 4. (a) Nyquist plots; and (b) equivalent circuit model of polyaniline/p-phenylenediamine functionalized graphene 3 wt.% (PPCc03), polyaniline/p-phenylenediamine functionalized graphene 5 wt.% (PPCc05), and polyaniline/p-phenylenediamine functionalized graphene 10 wt.% (PPCc10)[51]. Reproduced with permission from ACS. Figure 5. The model of corrosive diffusion pathways through the coatings[51]. PPC = polyaniline/p-phenylenediamine functionalized graphene; PSc = pristine polyaniline. Reproduced with permission from ACS. (a) (b) Figure 6. (a) Scanning electron microscopy image of a crack in PEDOT/GO film after corrosion with cracked scale like morphology indicated by an arrow; and (b) corrosion current vs. voltage scans of coated and uncoated surface[52]. PEDOT/GO = poly(3,4- ethylenedioxythiphene)/graphene oxide. Reproduced with permission from Elsevier. (a) (b) 6 The inclusion of graphene and derives in conjugated polymers has promoted electron conductivity. This rise in electrical conductivity can be attributed to the fine electron conduction of graphene having high symmetry. Graphene has advantage of developing widespread π electron delocalization[53]. The rise in electrical conduction of graphene coatings in turn supports oxidation-reduction reactions and barrier effects for corrosion resistance. Fullerene is a significant zero dimensional carbon nanofiller used in corrosion resisting polymeric nanocomposites[54–56]. Here, fullerene has capability to develop van der Waals or π-π interactions with the polymers[57]. The mutual interactions industrialised better diffusion trails for corrosion species and supported electron conduction through the coatings[58]. Consequently, the corrosion mechanism can be explained on the basis of matrix-nanofiller associations in charge of transporting conjugated polymer/fullerene systems[59]. Polyaniline and fullerene based nanomaterials have been designed[60–62]. Polyaniline has been reported to form a charge transfer complex with fullerene nanoparticles[63]. Cheng et al.[64] fabricated fullerene C60 filled polyaniline nanocomposites. The electrical conductivity was found to increase from 9 × 10–10 to 63.7 Sm–1, leading to efficient anti-corrosion performance. Gizdavic-Nikolaidis et al.[65] also prepared a nanocomposite coating of C60 nanoparticles reinforced polyaniline. Dispersion in the nanocomposite was premeditated using transmission electron microscopy. The nanoparticle sizes of 50–100 nm were observed in the matrix. Fine dispersion produced better electron transference routes to support charge transfer and anti-corrosion performance. Wang et al.[66] developed polyaniline and fullerene C60 nanowhisker derivative nanocomposites. Figure 7 illustrates the microstructure of polyaniline doped fullerene C60 nanowhiskers according to scanning electron microscopy. Adhesion of a thin polymer layer can be experiential on a fullerene nanorod surface due to the formation of a charge transfer complex. Such nanostructures have improved the electrical conductivity, leading to better corrosion confrontation[67]. Polypyrrole has also been filled with fullerene nanoparticles to form high-tech nanocomposites[68–70]. Wysocka-Zolopa et al.[71] reported on the polypyrrole and fullerene C60 based nanocomposites using chemical oxidative polymerization. Figure 8 depicts the in situ synthesis of polypyrrole and fullerene C60 resulting in nanocomposite. Here, the in situ route seemed effective in developing the well-interlinked polypyrrole-fullerene nanomaterial. Polythiophene is another conjugated matrix polymerized via electrochemical polymerization[72]. A doping process has been used to upsurge the electron conduction of polythiophene even higher than 100 Scm–1[73]. Polythiophene derived forms like poly(3-octylthiophene), poly(3-hexylthiophene), poly(3-octadecylthio- phene), etc., have also been focused[74,75]. Zabihi et al.[76] developed fullerene C60 filled poly(3-hexylthiophene) nanocomposite coatings. The nanomaterial had superior charge transfer and anti-corrosion due to matrix- (a) (b) Figure 7. Scanning electron microscopy images of (a) fullerene nanowhiskers; and (b) polyaniline doped nanowhiskers[66]. Reproduced from Hindawi (Published Open Access). 7 Figure 8. Development of polypyrrole and fullerene C60 derived nanocomposites[71]. Reproduced with permission from ACS. Table 1. Design, synthesis, and corrosion efficiency of conjugated polymer and nanocomposites. Material Synthesis Corrosion efficiency Ref Polyaniline In situ or electrochemical polymerization Icorr 0.112 µA cm–2; Ecorr –0.596 V 3.5% NaCl; 8 h [77] Polyaniline In situ polymerization ammonium persulfate; sulfuric acid ∼ 0.06 Scm–1 [40] Polyaniline/carbon nanotube In situ polymerization ammonium persulfate; sulfuric acid ∼ 10−7 Scm–1; Tunneling 11-15 Å vs. carbon nanotube contents [40] Polyaniline In situ chemical oxidative polymerization; ammonium persulfate 5.30 × 10–3 Scm–1 [78] Polyaniline/carbon nanotube 20 wt.% In situ chemical oxidative polymerization; ammonium persulfate 2.72 × 10–1 Scm–1; Visibly decreased corrosion relative to pristine sample [78] Polyaniline In situ chemical oxidative polymerization Icorr –610 µA cm–2; Ecorr 0.718 mV [79] Polyaniline/carbon nanotube 2 wt.% In situ chemical oxidative polymerization; ammonium persulfate Icorr –467 µA cm–2; Ecorr 0.31 mV [79] Polypyrrole In situ polymerization Icorr –0.943 µA cm–2; Ecorr 17.5 mV [80] Polypyrrole/carbon nanotube 1 wt.% In situ polymerization Icorr –0.294 µA cm–2; Ecorr 21.5 mV [80] Polythiophene In situ method Electrical conductivity σ 9.9 × 10–12 Scm–1 [81] Polythiophene/carbon nanotube In situ method Electrical conductivity σ 1.2 × 10–10 Scm–1 [81] Polyaniline Electrodeposition Icorr 2.46 × 10–8 A cm–2; Ecorr 0.086 V [82] Polyaniline/graphene oxide Electrodeposition Icorr 5.04 × 10–9 A cm–2; Ecorr 0.247 V [82] Polythiophene Solution method Icorr 3.47 × 10–5A cm–2; Ecorr –0.62 V [83] Polythiophene/graphene oxide Solution method Icorr 5.70 × 10–5A cm–2; Ecorr –0.578 V [83] Poly(3-hexyl-thiophene): phenyl-C61-butyric acid methyl ester Solution method Increase in corrosion efficiency to 100%; 100 h [84] nanofiller associations. Table 1 demonstrates important literature examples on the design, synthesis, and corrosion efficiency of pristine conjugated polymers as well as nanocarbon nanocomposites for comparison. Including nanocarbons have found to enhance the electrical conductivity as well as anticorrosion potential of the nanocomposites. 8 5. Prospects and conclusions Conducting nanocomposite coatings has gained an immense stance in the methodological and engineering industries[85,86]. Conjugated polymers may have optimum electron conductivity, however, there is a lack of structural resilience, limiting major applications. In this context, nanoparticles have been filled in the conjugated polymers to improve the adhesion, durability, and wear properties, when applied on the metal surfaces[87]. Especially, carbonaceous nanoparticles have been used to improve the barrier effects and corrosion inhibition features of the conjugated polymers. The main factors contributing to the anti-corrosion performance include the matrix-nanofiller associations, interface formation, development of charge transportation paths, and formation of resistive paths for the seeping of corrosive species[88]. All these aspects can contribute to the prevention of corrosive species approaching the metal surface for corrosion purposes. Corrosion prevention mechanisms have been mostly investigated in terms of barrier effects as well as the electrochemical defense of metals against corroding species[89]. For anti-corrosion coating fabrication, mostly in situ polymerization, electro-polymerization, and solution practices have been applied. Recently, sophisticated techniques like spin coating, spray coating, and dipping routes have been considered for the formation of evenly layered nanocomposites on metal surfaces. The fate of conjugated nanocomposite coatings depends upon the design and fabrication of efficient innovative self healing materials[90]. Consequently, the self-healing phenomenon can better promote the corrosion resistance of the nanocomposite coatings[91]. In effect, the self healing coatings have the potential to release self healing particles to recuperate the corrosion damage in the materials[92]. In such coatings, self healing nanocapsules can be loaded which can act in specific corrosion conditions[93]. Future labors are demanded to generate the self healing coatings of the conducting polymers and conjugated nanocomposites having outstanding anti-corrosion efficiency[94]. In this way, self healing anticorrosion coatings need to be designed for future electronics, automobile, and engineering industries[95]. This article is planned to schematically portray the impact of conjugated polymer and conjugated nanocomposites in the corrosion protection of metals. For the formation of conjugated nanocomposite coatings, conducting polymers like polyaniline, polypyrrole, polythiophene, and related derivatives have been used as matrices. These polymers were filled with nanocarbon nanofillers to enhance the anti-corrosion features. Facile routes have been adopted to fill the conjugated matrices with carbon nanoparticles. Subsequently, anti- corrosion properties and involved mechanisms were examined. Carbon nanoparticles have resulted in improved anti-corrosion performance due to fine nano-additive dispersion, mutual interactions, and the formation of charge or electron diffusion pathways throughout the nanocomposite. All these synergistic effects led to a fine anti-corrosion performance. Hence, the conjugated nanocomposites have been efficiently used to protect the metals and metallic components from harmful corrosion effects. Author contributions Conceptualization, AK; methodology, AK; data curation, AK; writing—original draft preparation, AK; writing—review and editing, AK, and IA; visualization, AK; supervision, AK; project administration, AK. All authors have read and agreed to the published version of the manuscript. Conflict of interest The authors declare no conflict of interest. References 1. Kausar A, Ahmad I, Dai Lam T. High-tech graphene oxide reinforced conducting matrix nanocomposites— Current status and progress. Characterization and Application of Nanomaterials 2023; 6(1): 2637. doi: 9 10.24294/can.v6i1.2637 2. Bellucci S. Decontamination of surface water from organic pollutants using graphene membranes. Characterization and Application of Nanomaterials 2023; 6(1): 2033. doi: 10.24294/can.v6i1.2033 3. Wang Q, Wang R, Zhang Q, et al. Application of biomass corrosion inhibitors in metal corrosion control: A review. Molecules 2023; 28(6): 2832. doi: 10.3390/molecules28062832 4. Kumar A. Role of conducting polymers in corrosion protection. World Journal of Advanced Research and Reviews 2023; 17(2): 45–47. doi: 10.30574/wjarr.2023.17.2.0238 5. Diao Y, Yang H, Lu Y, et al. Converting iron corrosion product to nanostructured conducting polymers: Synthetic strategies and applications. Accounts of Materials Research 2023; 4(7): 616–626. doi: 10.1021/accountsmr.3c00031 6. Naville W, Magnabosco R, Costa I. Uniaxial plastic strain effect on the corrosion-fatigue resistance of ISO 5832-1 stainless steel biomaterial. International Journal of Fatigue 2023; 173: 107701. doi: 10.1016/j.ijfatigue.2023.107701 7. Kausar A. Epitome of fullerene in conducting polymeric nanocomposite—Fundamentals and beyond. Polymer- Plastics Technology and Materials 2023; 62(5): 618–631. doi: 10.1080/25740881.2022.2121223 8. Góral-Kurbiel M, Drelinkiewicz A, Kosydar R, et al. Palladium content effect on the electrocatalytic activity of palladium–polypyrrole nanocomposite for cathodic reduction of oxygen. Electrocatalysis 2014; 5: 23–40. doi: 10.1007/s12678-013-0155-0 9. Ding C, Liu Y, Wang M, et al. Self-healing, superhydrophobic coating based on mechanized silica nanoparticles for reliable protection of magnesium alloys. Journal of Materials Chemistry A 2016; 4(21): 8041–8052. doi: 10.1039/C6TA02575G 10. Ribeiro DV, Abrantes JCC. Application of electrochemical impedance spectroscopy (EIS) to monitor the corrosion of reinforced concrete: A new approach. Construction and Building Materials 2016; 111: 98–104. doi: 10.1016/j.conbuildmat.2016.02.047 11. Yezer BA, Khair AS, Sides PJ, Prieve DC. Use of electrochemical impedance spectroscopy to determine double- layer capacitance in doped nonpolar liquids. Journal of Colloid and Interface Science 2015; 449: 2–12. doi: 10.1016/j.jcis.2014.08.052 12. Cano FJ, Castilleja-Escobedo O, Espinoza-Pérez LJ, et al. Effect of deposition conditions on phase content and mechanical properties of yttria-stabilized zirconia thin films deposited by Sol-Gel/Dip-coating. Journal of Nanomaterials 2021; 2021: 4449890. doi: 10.1155/2021/4449890 13. Umoren SA, Eduok UM. Application of carbohydrate polymers as corrosion inhibitors for metal substrates in different media: A review. Carbohydrate Polymers 2016; 140: 314–341. doi: 10.1016/j.carbpol.2015.12.038 14. Bhandari M, Preet Kaur D, Raj S, et al. Electrically conducting smart biodegradable polymers and their applications. In: Ali GAM, Makhlouf ASH (editors). Handbook of Biodegradable Materials. Springer, Cham; 2022. pp. 1–24. doi: 10.1007/978-3-030-83783-9_64-1 15. Van Nguyen T, Van Le Q, Peng S, et al. Exploring conducting polymers as a promising alternative for electrochromic devices. Advanced Materials Technologies 2023; 8(18): 2300474. doi: 10.1002/admt.202300474 16. Sazou D, Deshpande PP. Conducting polyaniline nanocomposite-based paints for corrosion protection of steel. Chemical Papers 2017; 71: 459–487. doi: 10.1007/s11696-016-0044-0 17. Gao F, Mu J, Bi Z, et al. Recent advances of polyaniline composites in anticorrosive coatings: A review. Progress in Organic Coatings 2021; 151: 106071. doi: 10.1016/j.porgcoat.2020.106071 18. Elkouh NA, Breedlove JJ, Pilvelait BR. Protective cover system including a corrosion inhibitor and method of inhibiting corrosion of a metallic object. U.S. Patent 7,759,265, 20 July 2010. 19. Ngwabebhoh FA, Sáha T, Stejskal J, et al. Conducting polypyrrole-coated leathers. Progress in Organic Coatings 2023; 179: 107495. doi: 10.1016/j.porgcoat.2023.107495 20. Kausar A. Nanodiamond reinforced polymer nanocomposite: Prospective corrosion protection materials. InL Phenomena and Theories in Corrosion Science, Methods of Prevention. NOVA Science Publishers Inc.; 2019. pp. 179–193. 21. Madhan Kumar A, Suresh Babu R, Ramakrishna S, de Barros ALF. Electrochemical synthesis and surface protection of polypyrrole-CeO2 nanocomposite coatings on AA2024 alloy. Synthetic Metals 2017; 234: 18–28. doi: 10.1016/j.synthmet.2017.10.003 22. Suthar V, de Souza FM, Asare MA, Gupta RK. Polymers and their nanocomposites for corrosion protection. In: Gupta RK (editor). Specialty Polymers: Fundamentals, Properties, Applications and Advances, 1st ed. CRC Press; 2023. 23. Li J, Bai H, Feng Z. Advances in the modification of silane-based sol-gel coating to improve the corrosion resistance of magnesium alloys. Molecules 2023; 28(6): 2563. doi: 10.3390/molecules28062563 24. Adamczyk L, Kulesza PJ. Fabrication of composite coatings of 4-(pyrrole-1-yl) benzoate-modified poly-3,4- ethylenedioxythiophene with phosphomolybdate and their application in corrosion protection. Electrochimica Acta 2011; 56(10): 3649–3655. doi: 10.1016/j.electacta.2010.12.078 25. Gobara M, Baraka A, Akidb R, Zorainyac M. Corrosion protection mechanism of Ce4+/organic inhibitor for AA2024 in 3.5% NaCl. RSC Advances 2020; 10(4): 2227–2240. doi: 10.1039/C9RA09552G 10 26. Qiang Y, Guo L, Li H, Lan X. Fabrication of environmentally friendly Losartan potassium film for corrosion inhibition of mild steel in HCl medium. Chemical Engineering Journal 2020; 406: 126863. doi: 10.1016/j.cej.2020.126863 27. Lai Q-T, Sun Q-J, Tang Z, et al. Conjugated polymer-based nanocomposites for pressure sensors. Molecules 2023; 28(4): 1627. doi: 10.3390/molecules28041627 28. Ananda Kumar S, Shree Meenakshi K, Sankaranarayanan TSN, Srikanth S. Corrosion resistant behaviour of PANI–metal bilayer coatings. Progress in Organic Coatings 2008; 62(3): 285–292. doi: 10.1016/j.porgcoat.2008.01.005 29. Li H, Huang W, Qiu B, et al. Effective removal of proteins and polysaccharides from biotreated wastewater by polyaniline composites. Advanced Composites and Hybrid Materials 2022; 5: 1888–1898. doi: 10.1007/s42114- 022-00508-0 30. Zhang H, Cui J, Sun J, He W. Corrosion inhibition of methanol towards stainless steel bipolar plate for direct formic acid fuel cell. International Journal of Hydrogen Energy 2020; 45(55): 30924–30931. doi: 10.1016/j.ijhydene.2020.08.038 31. Boppana SB, Dayanand S, Kumar MRA, et al. Synthesis and characterization of nano graphene and ZrO2 reinforced Al 6061 metal matrix composites. Journal of Materials Research and Technology 2020; 9(4): 7354–7362. doi: 10.1016/j.jmrt.2020.05.013 32. Wang S, Chen F, Zhuang G, et al. Synthesis of an all-carbon conjugated polymeric segment of carbon nanotubes and its application for lithium-ion batteries. Nano Research 2023; 16: 10342–10347. doi: 10.1007/s12274-023- 5530-4 33. Gergely A, Pászti Z, Hakkel O, et al. Corrosion protection of cold-rolled steel with alkyd paint coatings composited with submicron-structure types polypyrrole-modified nano-size alumina and carbon nanotubes. Materials Science and Engineering: B 2012; 177(18): 1571–1582. doi: 10.1016/j.mseb.2012.03.049 34. Jayakumari BY, Swaminathan EN, Partheeban P. A review on characteristics studies on carbon nanotubes-based cement concrete. Construction and Building Materials 2023; 367: 130344. doi: 10.1016/j.conbuildmat.2023.130344 35. Wang R, Sun L, Zhu X, et al. Carbon nanotube‐based strain sensors: Structures, fabrication, and applications. Advanced Materials Technologies 2023; 8(1): 2200855. doi: 10.1002/admt.202200855 36. Deshpande PP, Vathare SS, Vagge ST, et al. Conducting polyaniline/multi-wall carbon nanotubes composite paints on low carbon steel for corrosion protection: Electrochemical investigations. Chemical Papers 2013; 67: 1072– 1078. doi: 10.2478/s11696-012-0273-9 37. Madhusudhan CK, Muhammad F, Maruthi N, et al. Anticorrosion and supercapacitor applications of polypyrrole coated graphite nanocomposites. Sustainable Chemical Engineering 2023; 5: 17–31. doi: 10.37256/sce.5120243591 38. Han G, Yuan J, Shi G, Wei F. Electrodeposition of polypyrrole/multiwalled carbon nanotube composite films. Thin Solid Films 2005; 474(1–2): 64–69. doi: 10.1016/j.tsf.2004.08.011 39. Richard Prabakar S, Pyo M. Corrosion protection of aluminum in LiPF6 by poly(3,4-ethylenedioxythiophene) nanosphere-coated multiwalled carbon nanotube. Corrosion Science 2012; 57: 42–48. doi: 10.1016/j.corsci.2011.12.036 40. Mariano LC, Salvatierra RV, Cava CE, et al. Electrical properties of self-assembled films of polyaniline/carbon nanotubes composites. The Journal of Physical Chemistry C 2014; 118(43): 24811–24818. doi: 10.1021/jp502650u 41. Li J, Cui J, Yang J, et al. Silanized graphene oxide reinforced organofunctional silane composite coatings for corrosion protection. Progress in Organic Coatings 2016; 99: 443–451. doi: 10.1016/j.porgcoat.2016.07.008 42. Fu X, Lin J, Liang Z, et al. Graphene oxide as a promising nanofiller for polymer composite. Surfaces and Interfaces 2023; 37: 102747. doi: 10.1016/j.surfin.2023.102747 43. Gul W, Akbar Shah SR, Khan A, et al. Synthesis of graphene oxide (GO) and reduced graphene oxide (rGO) and their application as nano-fillers to improve the physical and mechanical properties of medium density fiberboard. Frontiers in Materials 2023; 10: 1206918. doi: 10.3389/fmats.2023.1206918 44. Liu S, Gu L, Zhang H, et al. Corrosion resistance of graphene-reinforced waterborne epoxy coatings. Journal of Materials Science & Technology 2016; 32(5): 425–431. doi: 10.1016/j.jmst.2015.12.017 45. Chang C-H, Huang T-C, Peng C-W, et al. Novel anticorrosion coatings prepared from polyaniline/graphene composites. Carbon 2012; 50(14): 5044–5051. doi: 10.1016/j.carbon.2012.06.043 46. Hemmasi AH, Khademi-Eslam H, Talaiepoor M, et al. Effect of nanoclay on the mechanical and morphological properties of wood polymer nanocomposite. Journal of Reinforced Plastics and Composites 2010; 29(7): 964–971. doi: 10.1177/0731684408101790 47. Lin Y-T, Don T-M, Wong C-J, et al. Improvement of mechanical properties and anticorrosion performance of epoxy coatings by the introduction of polyaniline/graphene composite. Surface and Coatings Technology 2019; 374: 1128–1138. doi: 10.1016/j.surfcoat.2018.01.050 48. Ramezanzadeh B, Bahlakeh G, Mohamadzadeh Moghadam MH, Miraftab R. Impact of size-controlled p- phenylenediamine (PPDA)-functionalized graphene oxide nanosheets on the GO-PPDA/Epoxy anti-corrosion, 11 interfacial interactions and mechanical properties enhancement: Experimental and quantum mechanics investigations. Chemical Engineering Journal 2018; 335: 737–755. doi: 10.1016/j.cej.2017.11.019 49. Zhu G, Cui X, Zhang Y, et al. Poly (vinyl butyral)/graphene oxide/poly (methylhydrosiloxane) nanocomposite coating for improved aluminum alloy anticorrosion. Polymer 2019; 172: 415–422. doi: 10.1016/j.polymer.2019.03.056 50. Ramezanzadeh B, Bahlakeh G, Ramezanzadeh M. Polyaniline-cerium oxide (PAni-CeO2) coated graphene oxide for enhancement of epoxy coating corrosion protection performance on mild steel. Corrosion Science 2018; 137: 111–126. doi: 10.1016/j.corsci.2018.03.038 51. Sheng X, Cai W, Zhong L, et al. Synthesis of functionalized graphene/polyaniline nanocomposites with effective synergistic reinforcement on anticorrosion. Industrial & Engineering Chemistry Research 2016; 55(31): 8576– 8585. doi: 10.1021/acs.iecr.6b01975 52. Catt K, Li H, Tracy Cui X. Poly (3,4-ethylenedioxythiophene) graphene oxide composite coatings for controlling magnesium implant corrosion. Acta Biomaterialia 2017; 48: 530–540. doi: 10.1016/j.actbio.2016.11.039 53. Cano FJ, Romero-Núñez A, Liu H, et al. Variation in the bandgap by gradual reduction of GOs with different oxidation degrees: A DFT analysis. Diamond and Related Materials 2023; 139: 110382. doi: 10.1016/j.diamond.2023.110382 54. Wang X, Tang F, Qi X, et al. Enhanced protective coatings based on nanoparticle fullerene C60 for oil & gas pipeline corrosion mitigation. Nanomaterials 2019; 9(10): 1476. doi: 10.3390/nano9101476 55. Kausar A. Fullerene nanofiller reinforced epoxy nanocomposites—Developments, progress and challenges. Materials Research Innovations 2021; 25(3): 175–185. doi: 10.1080/14328917.2020.1748794 56. Gao R, Liu Z, Liu Z, et al. Open-cage fullerene as a macrocyclic ligand for Na, Pt, and Rh metal complexes. Journal of the American Chemical Society 2023; 145(32): 18022–18028. doi: 10.1021/jacs.3c05733 57. Samadianfard R, Seifzadeh D, Habibi-Yangjeh A, Jafari-Tarzanagh Y. Oxidized fullerene/sol-gel nanocomposite for corrosion protection of AM60B magnesium alloy. Surface and Coatings Technology 2020; 385: 125400. doi: 10.1016/j.surfcoat.2020.125400 58. Turan ME, Sun Y, Aydin F, et al. Effects of carbonaceous reinforcements on microstructure and corrosion properties of magnesium matrix composites. Materials Chemistry and Physics 2018; 218: 182–188. doi: 10.1016/j.matchemphys.2018.07.050 59. Liu W, Speranza G. Functionalization of carbon nanomaterials for biomedical applications. C 2019; 5(4): 72. doi: 10.3390/c5040072 60. Zhang Y, Lang Y, Li G. Recent advances of non‐fullerene organic solar cells: From materials and morphology to devices and applications. EcoMat 2023; 5(1): e12281. doi: 10.1002/eom2.12281 61. Li W, Yang R, Sun M. Superior thermoelectric properties of bulk and monolayer fullerene networks. Journal of Materials Chemistry A 2023; 11(8): 3949–3960. doi: 10.1039/D2TA08537B 62. Idumah CI. Recent advancements in fire retardant mechanisms of carbon nanotubes, graphene, and fullerene polymeric nanoarchitectures. Journal of Analytical and Applied Pyrolysis 2023; 174: 106113. doi: 10.1016/j.jaap.2023.106113 63. Zubtsova YA, Kamanina N. The effect of fullerene on the temporal characteristics of a nematic liquid crystal- polyaniline-fullerene C60 system. Technical Physics Letters 2006; 32: 582–585. doi: 10.1134/S1063785006070108 64. Cheng X, Yokozeki T, Yamamoto M, et al. The decoupling electrical and thermal conductivity of fullerene/polyaniline hybrids reinforced polymer composites. Composites Science and Technology 2017; 144: 160–168. doi: 10.1016/j.compscitech.2017.03.030 65. Gizdavic-Nikolaidis M, Vella J, Bowmaker GA, Zujovic ZD. Rapid microwave synthesis of polyaniline–C60 nanocomposites. Synthetic Metals 2016; 217: 14–18. doi: 10.1016/j.synthmet.2016.03.009 66. Wang B, Gao X, Piao G. Preparation of polyaniline-doped fullerene whiskers. International Journal of Polymer Science 2013; 2013: 867934. doi: 10.1155/2013/867934 67. Keykhosravi S, Rietveld IB, Couto D, et al. [60] fullerene for medicinal purposes, a purity criterion towards regulatory considerations. Materials 2019; 12(16): 2571. doi: 10.3390/ma12162571 68. Goclon J, Winkler K. Band gap tuning in composites of polypyrrole derivatives and C60Pd3 polymer as models for p–n junction: A first principle computational study. ChemistrySelect 2018; 3(2): 373–383. doi: 10.1002/slct.201702752 69. Thummarungsan N, Pattavarakorn D, Sirivat A. Electrically responsive materials based on dibutyl phathalate plasticized poly(lactic acid) and spherical fullerene. Smart Materials and Structures 2022; 31: 035029. doi: 10.1088/1361-665X/ac5013 70. Zhou F, Ma Q, Huang Y, et al. Effects of phosphoric acid on the photovoltaic properties of photovoltaic cells with laminated polypyrrole-fullerene layers. Materials Science Forum 2011; 663–665: 861–864. doi: 10.4028/www.scientific.net/MSF.663-665.861 71. Wysocka-Zolopa M, Goclon J, Basa A, Winkler K. Polypyrrole nanoparticles doped with fullerene uniformly distributed in the polymeric phase: Synthesis, morphology, and electrochemical properties. The Journal of Physical Chemistry C 2018; 122(44): 25539–25554. doi: 10.1021/acs.jpcc.8b07681 72. Lim SP, Pandikumar A, Lim YS, et al. In-situ electrochemically deposited polypyrrole nanoparticles incorporated 12 reduced graphene oxide as an efficient counter electrode for platinum-free dye-sensitized solar cells. Scientific Reports 2014; 4: 5305. doi: 10.1038/srep05305 73. Kalagi SS, Patil PS. Secondary electrochemical doping level effects on polaron and bipolaron bands evolution and interband transition energy from absorbance spectra of PEDOT: PSS thin films. Synthetic Metals 2016; 220: 661– 666. doi: 10.1016/j.synthmet.2016.08.009 74. Causin V, Marega C, Marigo A, et al. Crystallization and melting behavior of poly(3-butylthiophene), poly(3- octylthiophene), and poly(3-dodecylthiophene). Macromolecules 2005; 38(2): 409–415. doi: 10.1021/ma048159+ 75. Qiao X, Wang X, Zhao X, et al. Nonisothermal crystallization of poly(3-dodecylthiophene) and poly(3- octadecylthiophene). Synthetic Metals 2000; 113(1–2): 1–6. doi: 10.1016/S0379-6779(99)00131-9 76. Zabihi F, Chen Q, Xie Y, et al. Fabrication of efficient graphene-doped polymer/fullerene bilayer organic solar cells in air using spin coating followed by ultrasonic vibration post treatment. Superlattices and Microstructures 2016; 100: 1177–1192. doi: 10.1016/j.spmi.2016.10.087 77. Rangel-Olivares FR, Arce-Estrada EM, Cabrera-Sierra R. Synthesis and characterization of polyaniline-based polymer nanocomposites as anti-corrosion coatings. Coatings 2021; 11(6): 653. doi: 10.3390/coatings11060653 78. Jeevananda T, Siddaramaiah, Kim NH, et al. Synthesis and characterization of polyaniline‐multiwalled carbon nanotube nanocomposites in the presence of sodium dodecyl sulfate. Polymers for Advanced Technologies 2008; 19(12): 1754–1762. doi: 10.1002/pat.1191 79. Madhan Kumar A, Gasem ZM. Effect of functionalization of carbon nanotubes on mechanical and electrochemical behavior of polyaniline nanocomposite coatings. Surface and Coatings Technology 2015; 276: 416–423. doi: 10.1016/j.surfcoat.2015.06.036 80. Madhan Kumar A, Sudhagar P, Fujishima A, Gasem ZM. Hierarchical polymer nanocomposite coating material for 316L SS implants: Surface and electrochemical aspects of PPy/f-CNTs coatings. Polymer 2014; 55(21): 5417– 5424. doi: 10.1016/j.polymer.2014.08.073 81. Patel RJ. Electrochemically Deposited Poly(thiophene)s and Their Composites with Carbon Nanotubes and Fullerenes [PhD thesis]. The Pennsylvania State University; 2011: AAT 3501021. 82. Qiu C, Liu D, Jin K, et al. Electrochemical functionalization of 316 stainless steel with polyaniline-graphene oxide: Corrosion resistance study. Materials Chemistry and Physics 2017; 198: 90–98. doi: 10.1016/j.matchemphys.2017.05.004 83. Mobin M, Ansar F. Polythiophene (PTh)–TiO2–reduced graphene oxide (rGO) nanocomposite coating: Synthesis, characterization, and corrosion protection performance on low-carbon steel in 3.5 wt% NaCl solution. ACS Omega 2022; 7(50): 46717–46730. doi: 10.1021/acsomega.2c05678 84. Bauld R, Fleury LM, Van Walsh M, Fanchini G. Correlation between density of paramagnetic centers and photovoltaic degradation in polythiophene-fullerene bulk heterojunction solar cells. Applied Physics Letters 2012; 101(10): 103306. doi: 10.1063/1.4749813 85. Pavase TR, Lin H, Shaikh Q, et al. Recent advances of conjugated polymer (CP) nanocomposite-based chemical sensors and their applications in food spoilage detection: A comprehensive review. Sensors and Actuators B: Chemical 2018; 273: 1113–1138. doi: 10.1016/j.snb.2018.06.118 86. Sun Z, Wang F, Kong L. Investigation of microwave-absorbing properties of aligned polyaniline/multi-walled carbon nanotubes nanocomposites. Fullerenes, Nanotubes and Carbon Nanostructures 2023. doi: 10.1080/1536383X.2023.2264994 87. Selim MS, Shenashen MA, El-Safty SA, et al. Recent progress in marine foul-release polymeric nanocomposite coatings. Progress in Materials Science 2017; 87: 1–32. doi: 10.1016/j.pmatsci.2017.02.001 88. Su L, Zhou Z, Shen P. Ni/C hierarchical nanostructures with Ni nanoparticles highly dispersed in N-containing carbon nanosheets: Origin of Li storage capacity. The Journal of Physical Chemistry C 2012; 116(45): 23974– 23980. doi: 10.1021/jp310054b 89. Zhu M-X, Chen T-X, Li M-T, et al. Tuning nanofillers in sprayed coating toward high flashover strength. IEEE Transactions on Dielectrics and Electrical Insulation 2023; 30(1): 299–307. doi: 10.1109/TDEI.2022.3210489 90. Teijido R, Ruz-Rubio L, Echaide AG, et al. State of the art and current trends on layered inorganic-polymer nanocomposite coatings for anticorrosion and multi-functional applications. Progress in Organic Coatings 2022; 163: 106684. doi: 10.1016/j.porgcoat.2021.106684 91. Chen Q, Zhu L, Chen H, et al. A novel design strategy for fully physically linked double network hydrogels with tough, fatigue resistant, and self‐healing properties. Advanced Functional Materials 2015; 25(10): 1598–1607. doi: 10.1002/adfm.201404357 92. Montemor MF. Functional and smart coatings for corrosion protection: A review of recent advances. Surface and Coatings Technology 2014; 258: 17–37. doi: 10.1016/j.surfcoat.2014.06.031 93. Abu-Thabit NY, Hamdy AS. Stimuli-responsive polyelectrolyte multilayers for fabrication of self-healing coatings–A review. Surface and Coatings Technology 2016; 303: 406–424. doi: 10.1016/j.surfcoat.2015.11.020 94. Anand Ganesh V, Raut HK, Sreekumaran Nair A, Ramakrishna S. A review on self-cleaning coatings. Journal of Materials Chemistry 2011; 21(41): 16304–16322. doi: 10.1039/C1JM12523K 95. Xu JW, Chua MH, Shah KW. Electrochromic Smart Materials: Fabrication and Applications. Royal Society of Chemistry; 2019. doi: 10.1039/9781788016667