Progressive Intercalation and Exfoliation of Clay in Polyaniline–Montmorillonite Clay Nanocomposites and Implication to Nanocomposite Impedance

Abstract

Conducting polymers, such as polyaniline (PANi) and polypyrrole (PPy), and their nanocomposites, are desired in a wide range of applications, including supercapacitors, lithium ion battery, chemical sensors, biosensors, barrier thin films, and coatings, because of their interesting electrical and electrochemical properties. It is well known that the properties of polymer nanocomposites depend on their chemical structure, as well as their microstructure, yet scientists and engineers have not fully understood how to properly control the structure of polymer nanocomposites. In this study, it is shown that the structure of polyaniline–montmorillonite clay nanocomposites (PACN) can be controlled by varying the ammonium persulfate (APS, oxidant) concentration. The structure of polyaniline and Cloisite 20A clay are, therefore, profoundly affected during the synthesis of PACN nanocomposites. The thickness of polyaniline crystal decreased with increasing oxidant concentration. Fourier transform infrared spectroscopy (FTIR) was used to determine the oxidation state of PANi. The structure of the nanocomposites was studied by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), wide-angle X-ray diffraction (WAXD), wide-angle X-ray scattering (WAXS), and small-angle X-ray scattering (SAXS). Electrochemical impedance spectroscopy (EIS) analysis of polyimide nanocomposite coatings containing PACN with varying levels of intercalation and exfoliation indicate that the coating impedance decreased with exposure time for some coating systems. It is shown that polyimide–PACN nanocomposite coating containing highly intercalated clay was more durable and maintained constant impedance after 20 weeks of exposure in a corrosive medium.

1. Introduction

Composite materials constituted of intrinsically conducting polymers (ICPs) and inorganic particles have been synthesized by using either chemical or electrochemical methods [1,2,3,4,5,6,7,8,9,10,11] and evaluated for various applications. Such nanocomposites have been shown to possess excellent corrosion resistance [7,9], good EMI shielding ability [8], and are effective in heavy metal and dye removal [6,11], because the ICP can improve their special properties when combined with the inorganic fillers.

In the recent years, there has been a heightened interest in formulating nanocomposites constituted of inorganic clay and an organic polymer matrix on a nanometer scale. Reports show that incorporation of nanosized clay fillers into a polymer matrix resulted in a remarkably improved strength, modulus, thermal resistance, fire retardant ability, and decreased permeability of the nanocomposites [1]. It was demonstrated that dramatic enhancement in properties was gained from minimal clay loading of about 2 volume %. Giannelis and his colleagues found that polymer and clay can form nanocomposites by melt processing [2,3,4,12]. Subsequently, tremendous work has been conducted using the concept of organic–inorganic nanocomposite based on clay and organic polymers, such as epoxies [13,14,15], nylon [16,17,18], polyimide [19,20], polyurethane [21], and polypropylene [22].

The remarkable advancement of nanotechnology is another factor that has inspired people to combine the two special materials, conducting polymers and clay, to form nanocomposites. The area of conducting polymer–clay nanocomposites represents an exciting new trend in materials science in that it has vast potential applications due to the special nature of both components.

Conducting polymers are a class of synthetic metals that show an unusually high electrical conductivity. These polymers show high electrical conductivity in their doped state. Alan G. MacDiarmid et al. won the Nobel Prize in chemistry in 2000 for their work on intrinsically conducting polymers (ICPs) [23].

Polyaniline (PANi) is a widely investigated ICP because of its chemical and environmental stability. Because of PANi’s remarkable electrical, electronic, and mechanical properties, it is suggested for applications in antistatic coating, corrosion inhibition additives, capacitors, and lithium-ion batteries.

Figure 1 shows the three major oxidation states of PANi, viz., leucoemeraldine base (LB), emeraldine base (EB), and pernigraniline base (PNB).

Montmorillonite (MMT) belongs to the structural family known as the 2:1 phyllosilicates. It is composed of layers of crystals stacked together periodically. The crystal structure usually consists of layers made up of two silica tetrahedral sandwiching an octahedral sheet of either alumina or magnesia, in which oxygen atoms are shared between the octahedral sheet and the silica tetrahedral sheet (Figure 2). Isomorphic replacement of trivalent metal ions (i.e., Al³⁺) by bivalent ions (i.e., Mg²⁺) within the layers causes a permanent net negative charge. The positive charge deficiency is usually balanced by insertion of cations, such as Ca²⁺ or Na⁺, inside the galleries. The layers of clay align themselves in a parallel manner and form stacks and are attracted to each other by van de Waals force. The gap between the layers is called gallery and the distance, called d₀₀₁ spacing, can vary over a wide range depending on the size of the cations adsorbed.

Recently, there has been a number of reports on the preparation, structure, and properties of PANi filled with layered silicate materials [24,25,26,27,28,29,30,31]. However, none of these studies provide a synthesis route for achieving progressive intercalation and exfoliation of clay.

It has been demonstrated that PANi is electrically conductive when doped. It is, therefore, a viable candidate material for energy storage applications in electromagnetic interference shielding, solar cells, electrochromic displays, sensors, lithium-ion batteries, anticorrosive materials [32,33,34,35,36,37,38], and supercapacitors [39]. Polyaniline coating can be applied to stainless steel bipolar plate in a polymer electrolyte membrane fuel cell to prevent corrosion of the electrode during operation.

PANi has been suggested for use as a supercapacitor electrode material because of its high specific capacitance of over 100 F/g [39]. However, the specific capacitance of PANi can decrease by about 15% during usage. Improvement of the energy storage ability, cyclability, and anticorrosive properties of PANi can be achieved by structural modification of PANi and by reinforcement with nanofillers, such as organoclay and graphene. It is widely believed that, by controlling the structure of PANi during synthesis, a more efficient and high-performing PANi electrode material and membrane can be prepared [39,40].

In this paper, the structure of polyaniline and polyaniline–montmorillonite clay nanocomposite (PACN) were progressively varied by varying the oxidant concentration. A correlation between the structure of PACN and the impedance of hybrid polyimide/PACN nanocomposite coatings on Al 2024-T3 substrate exposed to corrosive 3.5 wt.% NaCl solution was made.

2. Experimental

2.1. Materials

Aniline, N-methyl-2-pyrrolidinone (NMP), and ammonium persulfate ((NH₄)₂S₂O₈) (APS) were purchased from Aldrich Inc., (Milwaukee, WI, USA) and were used as received. Cloisite^® Clay Na+ and Cloisite^® 20A clay were obtained from Southern Clay Products, Inc. (Gonzales, TX, USA). Reagent-grade oxydianiline (ODA) and pyromellitic dianhydride (PMDA) were purchased from Aldrich Inc. (Milwaukee, WI, USA).

2.1.1. Preparation of the Nanocomposites

Synthesis of the nanocomposites was carried out by in situ polymerization technique in aqueous medium. An appropriate amount of aniline was dissolved in distilled water. Then, clay was added to the solution under vigorous magnetic stirring. In the case of organoclay, a small amount of methanol was used to disperse clay before adding it to the solution. After clay was well dispersed in the solution using ultrasonic bath, ammonium persulfate ((NH₄)₂S₂O₈, APS) dissolved in water was added in a dropwise manner. The mixture was stirred for 48 h before filtration. The filtrate was rinsed with 1000 mL distilled water. The obtained composite material was dried in an oven under vacuum at 100 °C. The composites were then ground, weighed, and stored in vials for later use.

2.1.2. Preparation of Polyimide/PACN Coatings

Poly(amic acid) (PAA) resin was prepared by reacting an equimolar amount of ODA and PMDA in dimethyl acetamide (DMAc) with mechanical stirring at 5 °C. An amount of 0.1 wt.% of PACN was dispersed in 11.25 mL of DMAc with magnetic stirring for 2.5 h. A total of 3.5 mL of PAA was then added to the solution with continuous stirring for an additional 2 h. The coating was solution cast onto ultrasonically cleaned Al 2024-T3 substrate. The coating was then thermally treated initially at 60 °C and later at 100 °C for 1.5 h. Final curing of the coatings was carried out at 200 °C for 2.5 h.

2.2. Characterization

Polyaniline-montmorillonite clay nanocomposites, PACN were characterized by using a Bio-Rad FTS-40 FTIR spectrometer (Bio-rad, Richmond, CA, USA). FTIR was used to determine the chemical structure and composition of the nanocomposites. FTIR spectra were collected at a resolution of 4 cm⁻¹ and averaged over 256 scans. The incident angle was set at 50° for all the samples. Nanocomposite powders were pressed into pellets made from mixtures of 95 vol % of KBr and 5 vol % of the nanocomposites using a hydraulic press. A background spectrum of pure KBr pellet was subtracted from the collected spectra.

X-ray diffraction (XRD) patterns were collected from Philips X’pert Diffractometer equipped with Cu-Kα radiation source (λ = 1.54 Å). The samples were prepared by dispersing a thin layer of the powder onto a double-sided tape affixed to a glass slide. The X-ray diffractometer was operated for 1 s at 30 KV and 25 mA and a scanning step of 0.05° in two-theta angle.

The SAXS data were collected on a Molecular Metrology SAXS camera with a double-focusing design using a bent Au-coated mirror to focus on the vertical plane and a bent asymmetric Si (111) monochromator to focus on the horizontal plane. The focus is in the plane of the detector to preclude de-smearing. The detector is a two-dimensional multi-wire detector from Molecular Metrology, and the sample-to-detector distance is 127.6 cm. The X-ray source is a Rigaku R-200 rotating anode generator with a copper target and a real focus of 0.3 × 3 mm² cathode assembly. The generator was run at 45 KV and 70 mA for 30 minutes.

The WAXS data were collected on a Bruker D8 Discover X-ray diffraction system with a ¼ cradle and a GADDS system. The focusing is performed with a single Gobel mirror with a 0.5 mm collimator. The detector used is a two-dimensional multi-wire detector with a sample-to-detector distance of 20.2 cm. The diffractograms were collected in the transmission mode. The X-ray source is a sealed copper tube operated at 40 KV and 40 mA for 10 min.

Scanning electron microscopy (SEM) was used to study the microstructure of PANi and PACN. Hitachi S-900 SEM was used to carry out SEM study. The samples were immersed in liquid nitrogen and then fractured with a pair of tweezers to provide fresh cross-sectional surface for study. The samples were then coated with a Polaron SC7640 sputter coater. Transmission electron microscopy (TEM) was used to investigate the structure of PANi–clay nanocomposites (PACN) using Jeol JEM-2000 FX Electron Microscope. Electrochemical impedance spectroscopy (EIS) is one of the most advanced electrochemical techniques for determining the impedance and durability of organic coatings. EIS measurements were performed by using a Solartron 1250 frequency response analyzer connected to an EG&G model 273A Princeton Applied Research, PAR Potentiostat. The EIS test was run in a frequency range from 0.01 Hz to 1 MHz. Samples were tested in an aerated 3.5 wt.% NaCl solution.

3. Results and Discussion

3.1. Compositions

PANi synthesized by in situ polymerization showed typical emeraldine structure. The characteristic PANi absorption bands occur at 3265 and 3203 (doublet), 1584, 1511, 1300, 847 and 864 (doublet) cm⁻¹. These peaks are due to the secondary amine, C=N stretching, C-N stretching, N-H deformation, and p-substituted benzene ring, respectively. The characteristic FTIR spectrum of clay (Cloisite^® 20A) shows a doublet at 2854 and 2928 cm⁻¹, a broad peak at 1054 cm⁻¹, and another doublet at 450–600 cm⁻¹. The FTIR spectra for PANi, Cloisite 20A, and their nanocomposite show that characteristic peaks of both PANi and Cloisite clay were present in the spectrum of PACN nanocomposite (Figure 3). The FTIR spectrum of PACN showed no specific change or shift in the PANi peaks in the spectrum, indicating that the incorporation of clay does not affect the chemical structure of PANi (Figure 3).

Figure 4 shows the effect of oxidant concentration on the quinoid:benzenoid peak area ratio for PACN (Figure 4A) and neat PANi (Figure 4B). It is shown that the quinoid-to-benzenoid peak area ratio is about 0.5 for both PANi and PACN, indicating that the PANi synthesized is of the emeraldine form.

3.2. Scanning Electron Microscopy (SEM)

The morphology of Cloisite 20A clay was observed by using scanning electron microscopy (SEM) (Figure 5A). The SEM micrograph of 20A clay shows large two-dimensional disks with a size distribution ranging from about 1 μm to 10 μm. The size of the particles observed is in agreement with data provided by Southern Clay Product, Inc. The thickness of the 2D clay particles lies between 20 and 50 nm. This shows that a single clay particle consists of layers of silicate platelet (~1 nm thick) stacked together.

The PACN containing high clay concentration can be considered as PANi-modified clay, the morphology of which is shown in the SEM micrographs in Figure 5B,C for PACN synthesized by using 0.7 and 3.5 wt.% of oxidant, respectively. The main feature of the morphology of PACN is the presence of platelets, which reflects the high concentration of clay (Figure 5B). For PACN synthesized by using low oxidant concentration of 0.7 wt.%, the platelets are much thicker and small pieces are peeled off from bigger particles (Figure 5B). A comparison of the PACN samples synthesized with 0.7 and 3.5 wt.% of oxidant is shown in Figure 5B,C. Figure 5B shows that the PACN particle thickness is significantly higher than that for 20A clay particle (thickness of about 50 nm), indicating the expansion of the clay galleries. It was determined that the d-spacing is expanded to about 44 Å. This result is in agreement with wide-angle X-ray diffraction patterns and the small-angle X-ray scattering results. Figure 5C shows smaller particles of PACN in elongated clusters, but the distinctive sharp feature of clay is not clearly shown, maybe due the high fraction of polyaniline that completely envelopes the clay particles. From the SEM micrograph of PACN prepared by using 3.5 wt.% of the oxidant, APS, shown in Figure 5C, one can see a significant increase in polymer content, since the platelet structure of clay has completely disappeared. It is shown in the later sections that PACN synthesized by using 3.5 wt.% APS is constituted of exfoliated clay particles.

3.3. Wide-Angle X-ray Diffraction (WAXD)

Figure 6 shows the WAXD pattern of mineral clay Cloisite Na⁺ clay and organoclay Cloisite 20A clay. Na⁺ clay contains Na⁺ cations inside the gallery, while 20A is the organically modified clay.

As shown in Figure 6, Cloisite 20A clay has a lower 2θ angle peak than the sodium clay, indicating that Cloisite 20 A clay gallery spacing is higher. The remaining peaks that are shown at higher 2θ angles are associated with the crystalline structure of the clay platelets. The crystal miller indices for both Cloisite 20A and Cloisite Na+ clay are indicated in Figure 6.

Figure 7 shows the comparison of WAXD patterns of PANi, PACN, and Clay 20A. It should be noted that the PANi polymer crystal plane (100) peak is located around a 2θ angle of 6.6°, which is different from clay d-spacing. The lower 2θ peak associated with the d-spacing of clay is not detected in the PACN spectrum shown in Figure 7. This may be due to a high level of intercalation or exfoliation of clay. Figure 8 shows WAXD patters of PANi synthesized at different oxidant concentrations and the crystal indices are marked on the respective peaks. From the powder diffraction patterns, PANi crystalline unit cell type can be identified as tetragonal, in agreement with Nicolau and Djurado’s report [27]. The intensity of the d₁₀₀ peak for PANi decreases with increasing oxidant concentration (Figure 8). Figure 8 also shows the shifting of the d₍₁₀₀₎ peak to a low angle with increasing APS wt.%.

The WAXD patterns of a series of PACN samples synthesized at different oxidant concentrations are shown in Figure 9. As shown in the WAXD patterns for all the PACN samples, the clay d-spacing peak is no longer present in the detectable 2θ° angle range of the WAXD instrument, which suggests that clay maybe highly intercalated or partially exfoliated. Note that the galleries were expanded from 10.4 Å to ≥ 44.1 Å. The small peak located at a 2θ° angle of 6.55° for PACN samples synthesized with 0.5, 0.7, and 0.8 wt.%, respectively, corresponds to PANi d₁₀₀ crystalline peak and it can be observed in Figure 9. Figure 9 also shows that there is a shift of the d-spacing peak to the lower angle, due to the expansion of the galleries of clay with the increasing amount of oxidant used in PACN preparation.

A partially crystalline polymer contains defects that cause peak broadening in the XRD patterns, which can be used to determine crystalline domain size. The crystalline domain size for PANi was calculated by using the Scherrer equation [28]:

$$L=\frac{0.9\lambda }{\Delta (2\theta )\cos \theta }$$

(1)

where L is the crystal domain size, λ is the X-ray wavelength, Δ(2θ) is the half-height width of the peak (here we use the peak at around 20°), and θ is half of the 2θ position of the peak. The L values for both PACN and PANi are plotted in Figure 10. The size of the crystal domains is about 20–60 Å. As the oxidant concentration increases, the crystal domain size decreases for both PANi and PACN (Figure 10). From FTIR analysis, it is shown that the oxidant concentration affects the oxidation states of the polymer, and may affect the rigidity and conformation of the chain [29,30]. The size of the crystal domain is, therefore, affected. It is also shown in Figure 10 that the crystal domain size of PANi in PACN nanocomposite is smaller than that of neat PANi due to the presence of clay. The arrangement of the polymer chain could be affected during polymerization inside the clay galleries. The small distance between the adjacent platelets imposes a confinement effect on the crystal structure of PANi; thus, crystal domain size is smaller.

From the TEM micrographs, the intercalated clay galleries have a d-spacing of about 40 Å, which is of the same order of the crystal domain size of nanocomposites. This is an indication that one crystal domain is aligned in the galleries along the perpendicular direction of clay sheet. The schematic representation of the structure of PACN obtained during the in situ polymerization is shown in Figure 11. It shows that PANi chains exist both on the outside as well as inside the clay galleries. The d-spacing of the intercalated clay is shown to lie between 40 and 60 angstroms.

In summary, WAXD results show that in situ polymerization method results in a gallery expansion of at least 30 Å. Further expansion of the gallery is not detectable by wide-angle X-ray diffraction. Small-angle X-ray scattering and TEM analysis, discussed in the following sections, will provide complementary information.

3.4. Wide-Angle X-ray Scattering (WAXS) and Small-Angle X-ray Scattering (SAXS)

Wide-angle X-ray scattering (WAXS) and small-angle X-ray scattering (SAXS) were used to investigate the shifting of the d₍₀₀₁₎ spacing peak at low angles. The WAXS patterns of PACN synthesized by using different oxidant, APS, concentrations are shown in Figure 12. It can be seen that there is a progressive shift of the d-spacing peak to the lower angle with increasing APS concentration, which indicates a systematic expansion of the galleries of clay with the increasing amount of oxidant used in the synthesis. This observation is important, since it provides a strategy for synthesizing PACN with a controlled intercalation level and structure.

PACN0 and PACNna are two samples of the nanocomposites synthesized at an extremely high APS concentration of 3.5 wt.%. As shown in the WAXS patterns for these two samples in Figure 12, no d-spacing peak is observed in the WAXS spectra for PACN0 and PACNna, indicating exfoliation of clay. PACN6, PACN5, and PACN1 were prepared by using 0.8, 0.7, and 0.1 wt.% oxidant. It is shown that, as the oxidant concentration increases, the d-spacing increases as shown by decreasing low 2θ angle peak. SAXS is used to detect the peak at an extremely low angle in order to ascertain whether PACNna and PACN0 are exfoliated. SAXS patterns for the samples are shown in Figure 13 and Figure 14. Figure 13 shows the presence of a peak at 2θ angle between 2 and 3° for PACN6, PACN5, and PaCN1, respectively. Figure 14 gives a combined chart of SAXS and WAXS for all samples, from which it can be seen that there is no observable peak at a lower q value for PACNna and PACN0. It is noted that the scattering vector q is the reciprocal of the d-spacing. These results suggest that, at extremely high oxidant concentration, an exfoliated structure can be obtained.

In summary, the WAXD results showed that in situ polymerization method resulted in a gallery expansion of at least 23 Å for the clay particles. A progressive expansion of the gallery was obtained as a result of increasing the oxidant concentration. At high oxidant concentrations of 3.5 wt.%, exfoliated structures are obtained, as shown in Figure 12, Figure 13 and Figure 14.

3.5. Transmission Electron Microscopy (TEM)

Figure 15 shows the TEM micrograph of one clay particle at a magnification of 600 k, with sharp edge attached to lacey carbon. A TEM micrograph for PACN nanocomposites with clay loading of 52 wt.% has been reported earlier [30]. In the TEM micrographs of PACN [30], it was shown that the distance between the parallel lines is about 40 Å or higher, which indicates intercalation of PANi into MMT clay gallery. This observation is in agreement with the WAXD, WAXS, and SAXS data reported in the previous sections, which confirm progressive intercalation and exfoliation of clay. Evidence of platelets peeled off from the tactoids was shown in the TEM micrograph for PACN [30]. Thus, both exfoliated clay and intercalated tactoids are present in PACN, in agreement with the findings of Yeh et al. [31].

From the above analysis, a structural model of partially exfoliated PACN (Figure 16) is suggested. This structural model visualizes two coexisting forms of clay in the nanocomposites. One is exfoliated single platelets randomly dispersed in the PANi matrix and the other is intercalated tactoids containing PANi chains inside the galleries. Single platelets randomly dispersed in the matrix and clay tactoids containing polyaniline crystal in the galleries are the dominant structure.

Figure 17 shows that the EIS spectra for PACN powder dispersed in polyimide matrix to form PACN/PI coatings were nearly capacitive with high impedance of between 1 × 10⁹ and 5 × 10⁹ Ohms during the first few hours (0 days) of testing in a 3.5% NaCl solution. The freshly prepared bare Al alloy substrate and the fresh neat PI coating have much lower impedance of 10⁴ Ohms and 10⁷ Ohms, respectively, during the first few hours (0 days) of testing. As indicated in Figure 17, the electrolyte has permeated into the solution/metal interface and PI coatings/metal interface for bare Al-2024-T3 substrate and the PI/Al2024-T3 coating, respectively, shortly after exposure to the corrosive 3.5 wt.% NaCl solution. The permeation of electrolyte onto the substrate is marked by the first time constant (change in slope of the impedance versus frequency curve), which occurred at about 1000 Hz (0.001 s) for bare Al-2024-T3 substrate and PI/Al-2024-T3 coating, respectively (Figure 17).

Figure 18 shows the EIS impedance spectra of all the samples tested after 20 weeks of exposure to the corrosive environment. It is shown that the impedance for most of the samples had significantly decreased due to coating debonding, coating delamination, and concomitant charge transfer process.

As shown in Figure 18, the PACN/PI coating containing highly intercalated clay, PACN06/PI, prepared by using 0.8 wt.% ammonium persulphate (APS) solution, maintained the highest impedance after 20 weeks of exposure to the corrosive condition. The PACN06/PI coating system retained the initial high impedance of ≥10^9.5 Ohms after 20 weeks of exposure in a 3.5 wt.% NaCl solution. The impedance of the PACN/PI coatings containing exfoliated clays, PACN0/PI and PACNna/PI, were degraded substantially after 20 weeks of exposure to about 10⁸ Ohms. The nanocomposite coatings containing exfoliated clays also showed the occurrence of charge transfer and development of Warburg impedance at a frequency of about 1 × 10⁻¹ Hz, indicating that the electrolyte has not only permeated to the coating/substrate interface, but that debonding and delamination of the coating are commonplace. The neat PI coating and PANi/PI coating were fully degraded after 20 weeks of exposure. These coatings are, therefore, not as durable as the coating prepared with highly intercalated clay, PACN06/PI. It is suggested, therefore, that, for outstanding barrier property and effective protection of Al alloy substrate against degradation, highly intercalated clays rather than fully exfoliated clays are the best practice.

4. Conclusions

The structure of PACN nanocomposites constituted of PANi and MMT clay was systematically investigated. By using in situ polymerization technique, this study successfully created novel PACN nanocomposites with a wide range of structural levels. By systematically controlling the oxidant concentration, the intercalation levels and the exfoliation clay were remarkably controlled. The PACN nanocomposites synthesized by using low oxidant concentrations ranging from 0.1 to 0.8 wt.% showed progressively intercalated and partially exfoliated structures. Exfoliated clay structure was obtained at a higher oxidant concentration of 3.5 wt.%. This study provides the synthesis methodology for formulating PACN with controlled intercalation and exfoliation. A correlation between synthesis conditions and the resulting structure of the PACN nanocomposites was made. It is shown that the extent of intercalation and exfoliation of clay can be remarkably controlled by varying the oxidant concentration.

WAXD results confirmed that PANi synthesized is semicrystalline. The size of the PANi crystal domain was shown to be between 20 and 60 Å. As the APS concentration increases, the crystal domain size decreases for both PANi and PACN. The crystal domain size of PANi in the PACN nanocomposite is smaller than that of neat PANi due to the presence of clay. The nucleation and growth of PANi crystals and the arrangement of PANi chain are affected by the presence clay. EIS results for polyimide nanocomposite coatings containing PACN with varying levels of intercalated and exfoliated clays indicate that the nanocomposite impedance increases with the increasing level of intercalation of clay. It is also demonstrated that nanocomposite coating containing highly intercalated clay was more durable and showed no sign of debonding and delamination, and maintained high impedance after 20 weeks of exposure to the corrosive environment compared to those containing exfoliated clays.