Effect of Iodine Doping on the Polyaniline /Clay Nano Composite Thin Films Prepared by Mechanochemical Intercalation Method

Document Type : Research Paper


1 Physics Department, College of Education, Basra University, Basra, Iraq

2 Department of Material Sciences, Polymer Research Center, Basra, Iraq

3 Ministry of Education General Directorate, Basra, Iraq



A mechanochemical approach is used to make a polyaniline:AIcaulan clay nano composite in this study. The presence of a green color indicates the formation of polyaniline/clay. Thin sheets of iodine-doped polyaniline/clay that have been pre-prepared are used. The weight percent of iodine in the nanocomposite films was 16%, 33%, and 50% wt percent of the total weight of PANI/ clay. These as-deposited films were analyzed for physicochemical and optoelectronic features using Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray absorption spectra, and optical absorption spectra. FT-IR The chemical activity of both pure and iodine-doped thin polyaniline/clay sheets is then investigated using spectroscopic measurements.SEM images reveal an uneven distribution of grains throughout the subsurface, according to morphological analysis.
The optical band gaps of the films are then investigated using absorption spectrum measurements. Indirect transitions' energy transition gaps are characterized and determined. The energy band gap will be shown to vary depending on the content of polyaniline and clay iodine. As iodine concentration rises, the optical band gap decreases from 3.47to 2.18eV.


The effect of incorporating electrically active polymers such as (PANI), polypyrrole (PPy), and others with added clay particles improves the mechanical strength of the polymer, its colloidal stability and electrical properties due to the unique properties of clay represented by its surface area and electrostatic charge[1]. Various researches have been conducted by scientists on the insertion of electronically conductive polymer with clay[2]. The electrochemical structure of chemical materials was described and found that the materials have a higher anisotropic nano conductivity than the PANI-clay composite made from anilinium – montmorillonite[3].
A solvent-free polyaniline-clay nanocomposite, and the electro rheological properties of polyaniline-clay with montmorillonite clay was reported [4] . The interaction of the polymer and the clay results in an exfoliated structure, because the polymer utilizes the entire surface of the clay layers, who claimed that exfoliated nanocomposites are more exquisite[5].  The polymerization of aniline in the interlayers of clay made Pani/montmorillonite has a higher conductivity than pure polyaniline, which reduces defects and polymer bridges, as a result of the formation of a long chain[6]. The discovery of halogen doping of polyacetylene, which increased electrical conductivity significantly, had a significant impact on the development of practical applications of conductive polymers such as electrical devices and transistors in the field of (FTE) and others [7-11], which is a new approach in plastic electronics. Iodine doping has a wide range of applications, whether in vapor or solution, until the effect of halogen doping on polymer conductivity is discovered.In their natural state,( π-conjugated polymers) are insulators. Low donor electron concentrations in the doping process result in an increase in conductivity and charge carriers.
The charge transfer process is useful in the process of iodine uptake by (π -conjugated polymers )because iodine has multiple properties such as chemical stability and good conductivity.  (PANI) is one of the conductive polymers in comparison to the rest of the polymers in terms of low production costs and polymerization in an aqueous medium that is non-toxic to the environment[12]. 
Iodine has a high vapor pressure at room temperature and a low sublimation temperature, making it difficult to treat iodine accumulation in air and water, and this vapor state complicates iodine accumulation even more. Iodine doping with (PANI) in the past [13-16]. Many practical applications of conductive polymers include capacitors and transistors [17],as well as optoelectronic devices [18]. PANI is a p-type conductive polymer that is easy to polymerize, chemically and environmentally stable[19,20]. The variable conductivity of PANI, which can be tuned using the doping/de b vdoping procedure, has sparked a lot of interest [21,22] .
(PANI) has been doped with various metals to improve its electrical properties [23,26], and a few researchers have also published a study on the interaction of (PANI) with iodine in addition to its conductive and electrical properties. The conductivity increased by eight times by volume when doping (PANI) with iodine in ethanol solution[27], and the conductivity increased by five times due to proton (PANI) with hydrogen iodide (HI) [28], where iodine I2 had a significant effect on the regularity of the polymer chain.
Solvent casting, physical vapor deposition (PVD), and other techniques were used to make (PANI) films that were characterized as mechanically solid and thermally stable [29,30], and it is believed that once the plasma produces thin films of (PANI) that are good and uniform. Because of their chemical stability, moderate charge transfer capabilities, and environmental friendliness, n-type inorganic nanomaterials (TiO2,ZnO) and P-type organic materials (PANI) are considered conductive polymers [31]. The combination of PANI (P-Type) and TiO2 n-type has been used in a wide range of electrical devices, including solar energy systems [32] and Schottky diodes. It has been demonstrated that PANI/ZnO heterogeneous junctions have poor electrical properties when compared to PANI/TiO heterogeneous junctions, which generate a large volume of charge carriers and thus improve electrical properties [33,34].
Nanopolymers are a new type of compound made up of particles with a molecular dimension of 1 to 100 nanometers dispersed throughout [35]. Carbon nanotubes and clay  are two of the most commonly used particles in strengthening polymer nanocomposites [36]. The composite (polymer / nanoclay) is a novel material family in which the nanoclay is influenced by the polymer matrix [35]. clay with a low levels.Through a previous study for nanocomposites based on saturated polyester UP/clay with a clay content of up to 5% by weight, and found an increase in tensile strength and tensile modulus[37 ],also in another study, the compound has better mechanical and thermal properties[38], and increasing the clay loading leads to an increase in the tensile modulus and fracture toughness[39], in addition to the fact that the brittleness in nanocomposites is a defect that limits their applications.

Alcaulan was broken down using an electric machine until it was reduced to soft clay particles. Alcaulan clay is mixed with aniline monomer (7.27 mol), which is then dissolved in 1M H2SO4 and placed in a three-necked flask. The aniline: H2SO4 is then added, and the mixture is stirred continuously in an ice bath for 3-4 hours. The oxidizing agent, ammonium per sulphate (NH4)2S2O8, is dissolved in 1M H2SO4 and slowly and carefully added to the solution in the flask to begin the polymerization. The reactor mixture is then continuously stirred for 24 hours. When the polymerization is complete, the color of the solution changes from greenish black to greenish black. After that, the product is cleaned with acid before being packaged. Before being characterized, the filtered powder is dried in a 50°C oven. To evaluate all samples in the wavelength range 400-4000 cm-1 under equal conditions, Fourier Shemadzu Co model 8400 Series uses transform infrared (FT IR) spectra with solid KBr discs.

FT-IR analysis
The FT-IR spectrum of iodine doped Pani/ clay shows in Fig. 1a, b, and c.
The aromatic ring is retained in the polymer, as indicated by the peak at 1581cm-1 [40]. At 3211 cm-1, the N-H vibration is detected. Peaks of substituted benzene can also be found at 798 and 609 cm-1. Table 1 shows the band assignments for the FT-IR absorption bands for pure, polymerized, and iodine-doped polyaniline/clay thin films.
In the iodine-doped polyaniline/clay, there is a shift in N-H stretching and C-N stretching bands, as shown in the Table 1. The N-H stretch absorbed in the N-H and C-N stretching bands indicated that iodine atoms may be attaching to polyaniline’s amine nitrogen sites [41]. The key bands in the iodine-doped polyaniline that correspond to the aromatic rings are found to be shifted towards high wave number. This suggests that iodine doping alters the structure of aniline samples.

Morphological Analysis SEM
Polyaniline’s as-deposited surface morphology Scanning electron microscopy is used to examine thin films. The technique of scanning electron microscopy (SEM). Fig. 2 depicts a SEM image of the sample.
In Fig. 2a  PANI/ clay showed several micrometer areas dark and bright contrast are present , the dark portion indicates to clay particles with diameter 21.37 nm, the bright portion is due to PANI chains, the diameter of 410 nm. In Fig. 2b  PANI/ clay/iodine showed small ball with diameter 14.14 nm attracted to clay and PANI.

Structural properties of the PANI/clay and PANI/clay/iodin
Fig. 3a shows the PANI/clay X-ray diffraction pattern. The amorphous nature of PANI/clay is suggested by its X-ray diffraction pattern. The X-ray diffraction pattern of PANI/clay/iodine is shown in Fig. 3b. The crystalline nature of the composite is indicated by the iodine peak, as shown in the figure. The additional peaks in Fig. 3b correspond to the iodine dispersion in PANI/clay when comparing the XRD patterns of PANI/clay/iodine.

UV-VIS absorption studies
Fig. 4  shows the UV-visible spectra of intercalated PAni/clay/iodine. For the n-π*transition of PAni/clay/iodine dopent, sharp UV absorption peaks were observed between (350-390) nm [42]. 
Enough light energy must be absorbed to transfer electrons from the valence band to the conduction band; this energy is equal to the energy gap, and the relationship that shows the absorbed energy (h) is[43,44].


where α is the absorption coefficient , hʋ  is the photon energy , A a constant. The symbol represents the power coefficient. It’s calculated by examining the various types of electronic transitions that are possible, with 1/2 indicating direct permitted and 3/2 indicating direct prohibited [45,46].The plotting of (αhʋ)1/2 against hʋ as shown in Fig. 5 of polyaniline / clay in iodine doped form .
Fig. 5 shows that when the weight ratios of iodine are added to PANI/clay, the energy gap narrows as the percentage of addition increases, clearly demonstrating the effect of iodine on the PANI/clay compound as shown in Table 2. Table 2 shows the effect of iodine on the PANI/clay compound. It is seen that the iodine doping decrease the optical band gaps from 2.6 eV for Pani/clay doped with  16% iodine to 1.8 eV for Pani doped with 50% iodine
The adjustment of the polymer structure is responsible for the change in the optical band gap. Due to the insertion of the charged species, doping causes structural ordering of the polymers. 

Electrical conductivity (σdc)
Because electrical conductivity is a property of polymeric materials and materials due to the presence of an ionic impurity, materials are categorized into three categories based on their continuous electrical conductivity (insulators, semiconductors, conductors, and superconductors) [47]. The electrical conductivity of materials can change by adding impurities, a process known as doping, hence the electrical conductivity of these materials is low. And when impurities are impurities, this ability alters, and depending on the type of impurities employed (maturations or donors), a type (n) or a type (p) can be obtained [48].
 The following equation [49] can be used to compute electrical conductivity (σdc).


Where: R stands for electrical resistance, measured in Ω, d: thickness of the embrane.
           A: Electrode area.
According to the equation [50], the value of electrical conductivity changes exponentially with absolute temperature.

where σo: conductivity at a temperature (00C), Ea: the value of the activation energy,
T: temperature in Kelvin, KB: Boltzmann’s constant.
The membrane’s characteristic (current-voltage) at various temperatures within the range (303-34300K).
The current-voltage feature is shown in Fig. 6 for temperatures ranging from 303 to 3430K. The conduction mechanism has improved compared to the undoped membrane, and this is due to the proportion of doping by the oxidizing agent iodine.
For PANI/clay films, a relationship was made between the reciprocal of temperature 1000/T and lnσd.c, from which the activation energy Ea could be estimated from the slope of the straight line using the following relationship [49]:

Table 3 shows the values of activation energy Ea for PANI/clay with deferent ratio I2.
Table -4 shows the values of electric conductivity for PANI/clay pure and (PANI /clay+I2) in variant temperature. 

Our findings show that a method of Mechanochemical in intercalation can be used to obtain Pani-H2SO4/Alculan clay.
Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray absorption spectra, and optical absorption spectra were used to examine the deposited films for physicochemical and optoelectronic features.
SEM revealed that PANI/clay/iodine has a small ball with a diameter of 14.14 nm that is attracted to clay and PANI, and the X-ray diffraction pattern revealed the amorphous nature of PANI/clay and the crystalline nature of PANI/clay/iodine. The energy gap narrows as the percentage of iodine added increases, clearly demonstrating the effect of iodine on the PANI/clay compound. Iodine doping decreases the optical band gaps from 2.6 eV for Pani/clay doped with 16% iodine to 1.8 eV for Pani/clay doped with 50% iodine.
The temperature change with PANI/clay and PANI/clay/I2 electrical conductivity was investigated. The electrical conductivity of PANI/clay was 0.5˟10-7 s.cm-1 at room temperature, while it was 6×10-7 s.cm-1   at 50 percent of the same temperature, according to the findings. It was discovered that as the proportion of doping increases and the temperature rises, the electrical conductivity rises as well.

The authors declare that there is no conflict of interests regarding the publication of this manuscript.


1.    Dubois P, Alexandre M. Performant Clay/Carbon Nanotube Polymer Nanocomposites. Adv Eng Mater. 2006;8(3):147-154.
2.    Carrado KA, Xu L. In Situ Synthesis of Polymer−Clay Nanocomposites from Silicate Gels. Chem Mater. 1998;10(5):1440-1445.
3.    Inoue H, Yoneyama H. Electropolymerization of aniline intercalated in montmorillonite. Journal of Electroanalytical Chemistry and Interfacial Electrochemistry. 1987;233(1-2):291-294.
4.    Yoshimoto S, Ohashi F, Ohnishi Y, Nonami T. Solvent free synthesis of polyaniline–clay nanocomposites from mechanochemically intercalated anilinium fluoride. Chem Commun. 2004(17):1924-1925.
5.    Review of Narayanan et al. Copernicus GmbH; 2020.
6.    Zhu J-F, Xu R-Q, Zhao H-Y, Luo Z-Y, Pan B-J, Rao C-Y. Fundamental mechanical behavior of CMMOSC-S-C composite stabilized marine soft clay. Applied Clay Science. 2020;192:105635.
7.    Shirakawa H. The Discovery of Polyacetylene Film: The Dawning of an Era of Conducting Polymers (Nobel Lecture). Angew Chem Int Ed. 2001;40(14):2574-2580.
8.    MacDiarmid AG. “Synthetic Metals”: A Novel Role for Organic Polymers (Nobel Lecture). Angew Chem Int Ed. 2001;40(14):2581-2590.
9.    Heeger AJ. Semiconducting and Metallic Polymers: The Fourth Generation of Polymeric Materials (Nobel Lecture). Angew Chem Int Ed. 2001;40(14):2591-2611.
10.    Sandman DJ. A review of: “Advances in Synthetic Metals Twenty Years of Progress in Science and Technology” edited by P. Bernier, S. Lefrant, and G. Bidan, Elsevier Science S.A., 1999; ISBN 0 444 72003 0 (hardback); 0 444 72004 9(paperback); xii + 445 pages; $198.00; 390.00 NLG(hardback). Molecular Crystals and Liquid Crystals Science and Technology Section A Molecular Crystals and Liquid Crystals. 2000;348(1):337-340.
11.    Goto H, Yoneyama H, Togashi F, Ohta R, Tsujimoto A, Kita E, et al. Preparation of Conducting Polymers by Electrochemical Methods and Demonstration of a Polymer Battery. J Chem Educ. 2008;85(8):1067.
12.    Goto H. Electrically conducting paper from a polyaniline/pulp composite and paper folding art work for a 3D object. Textile Research Journal. 2010;81(2):122-127.
13.    Wang L, Jing X, Wang F. On the iodine-doping of polyaniline and poly-ortho-methylaniline. Synth Met. 1991;41(1-2):739-744.
14.    Gizdavic-Nikolaidis M, Bowmaker GA. Iodine vapour doped polyaniline. Polymer. 2008;49(13-14):3070-3075.
15.    Sarkar A, Ghosh P, Meikap AK, Chattopadhyay SK, Chatterjee SK, Chowdhury P, et al. Electrical-transport properties of iodine-doped conducting polyaniline. J Appl Polym Sci. 2008;108(4):2312-2320.
16.    Sajeev US, Mathai CJ, Saravanan S, Ashokan RR, Venkatachalam S, Anantharaman MR. On the optical and electrical properties of rf and a.c. plasma polymerized aniline thin films. Bull Mater Sci. 2006;29(2):159-163.
17.    Advanced organic chemistry Third edition), by G. W. Wheland. Pp. xi + 871. John Wiley & Sons Inc., New York; John Wiley & Sons Ltd, London. 1960. E7 net. Endeavour. 1961;20(79):171.
18.    Ameen S, Shaheer Akhtar M, Husain M. A Review on Synthesis Processing, Chemical and Conduction Properties of Polyaniline and Its Nanocomposites. Science of Advanced Materials. 2010;2(4):441-462.
19.    MacDiarmid AG, Epstein AJ. Science and Technology of Conducting Polymers. Frontiers of Polymer Research: Springer US; 1991. p. 259-270.
20.    Ameen S, Ali V, Zulfequar M, Haq MM, Husain M. Preparation and measurements of electrical and spectroscopic properties of sodium thiosulphate doped polyaniline. Current Applied Physics. 2009;9(2):478-483.
21.    Huang W-S, Humphrey BD, MacDiarmid AG. Polyaniline, a novel conducting polymer. Morphology and chemistry of its oxidation and reduction in aqueous electrolytes. Journal of the Chemical Society, Faraday Transactions 1: Physical Chemistry in Condensed Phases. 1986;82(8):2385.
22.    Blinova NV, Stejskal J, Trchová M, Prokeš J, Omastová M. Polyaniline and polypyrrole: A comparative study of the preparation. Eur Polym J. 2007;43(6):2331-2341.
23.    Hasik M, Kurkowska I, Bernasik A. Polyaniline incorporating cobalt ions from CoCl2 solutions. React Funct Polym. 2006;66(12):1703-1710.
24.    Dimitriev OP. Doping of polyaniline by transition metal salts: effect of metal cation on the film morphology. Synth Met. 2004;142(1-3):299-303.
25.    Hirao T. Conjugated systems composed of transition metals and redox-active π-conjugated ligands. Coord Chem Rev. 2002;226(1-2):81-91.
26.    Hirao T. A Novel Redox System for the Palladium(II)-Catalyzed Oxidation Based on Redox of Polyanilines. Tetrahedron Lett. 1995;36(33):5925-5928.
27.    Zeng X-R, Ko T-M. Structure?conductivity relationships of iodine-doped polyaniline. J Polym Sci, Part B: Polym Phys. 1997;35(13):1993-2001.
28.    Stejskal J, Trchová M, Blinova NV, Konyushenko EN, Reynaud S, Prokeš J. The reaction of polyaniline with iodine. Polymer. 2008;49(1):180-185.
29.    Zaharias GA, Bent SF. Growth Process of Polyaniline Thin Films Formed by Hot Wire CVD. Chem Vap Deposition. 2009;15(4-6):133-141.
30.    Inagaki N, Matsunaga M. Preparation of carboxylate groups-containing thin films by plasma polymerization. Polym Bull. 1985;13(4).
31.    Ameen S, Akhtar MS, Kim YS, Yang OB, Shin H-S. Polyaniline/gallium doped ZnO heterostructure device via plasma enhanced polymerization technique: Preparation, characterization and electrical properties. Microchimica Acta. 2010;172(3-4):471-478.
32.    Ameen S, Akhtar MS, Kim G-S, Kim YS, Yang OB, Shin H-S. Plasma-enhanced polymerized aniline/TiO2 dye-sensitized solar cells. J Alloys Compd. 2009;487(1-2):382-386.
33.    Ameen S, Akhtar MS, Kim YS, Yang OB, Shin H-S. Diode Behavior of Electrophoretically Deposited Polyaniline on TiO2 Nanoparticulate Thin Film Electrode. Journal of Nanoscience and Nanotechnology. 2011;11(2):1559-1564.
34.    Alexandre M, Dubois P. Polymer-layered silicate nanocomposites: preparation, properties and uses of a new class of materials. Materials Science and Engineering: R: Reports. 2000;28(1-2):1-63.
35.    Paul DR, Robeson LM. Polymer nanotechnology: Nanocomposites. Polymer. 2008;49(15):3187-3204.
36.    Baran Inceoglu A, Yilmazer U. Synthesis and mechanical properties of unsaturated polyester based nanocomposites. Polymer Engineering & Science. 2003;43(3):661-669.
37.    Şen S. Effect of both silane-grafted and ion-exchanged organophilic clay in structural, thermal, and mechanical properties of unsaturated polyester nanocomposites. Polym Compos. 2009;31(3):482-490.
38.    Kornmann X, Berglund LA, Sterte J, Giannelis EP. Nanocomposites based on montmorillonite and unsaturated polyester. Polymer Engineering & Science. 1998;38(8):1351-1358.
39.    Obayes OK, Shahad HAK. Experimental Investigation of Flame Speed of Gasoline Fuel-Air Mixture. International Journal of Current Engineering and Technology. 2018;8(02).
40.    Norcia VD. Corporations and Morality Thomas Donaldson Englewood Cliffs, NJ: Prentice-Hall, 1982. Pp. ix, 214. $12.95, cloth; $8.95, paper - Business EthicsNorman Bowie Prentice-Hall Series in Occupational Ethics Englewood Cliffs, NJ: Prentice-Hall, 1982. Pp. xiii, 159. $7.95, paper. Dialogue. 1983;22(2):364-366.
41.    Kalaivasan N, Shafi SS. Synthesis of Various Polyaniline / Clay Nanocomposites Derived from Aniline and Substituted Aniline Derivatives by Mechanochemical Intercalation Method. E-Journal of Chemistry. 2010;7(4):1477-1483.
42.    Baishya U, Sarkar D. Structural and optical properties of zinc sulphide-polyvinyl alcohol (ZnS-PVA) nanocomposite thin films: effect of Zn source concentration. Bull Mater Sci. 2011;34(7):1285-1288.
43.    Mansour SA, Yakuphanoglu F. Electrical-optical properties of nanofiber ZnO film grown by sol gel method and fabrication of ZnO/p-Si heterojunction. Solid State Sciences. 2012;14(1):121-126.
44.    Aziz S, Rasheed M, Ahmed H. Synthesis of Polymer Nanocomposites Based on [Methyl Cellulose](1−x):(CuS)x (0.02 M ≤ x ≤ 0.08 M) with Desired Optical Band Gaps. Polymers. 2017;9(12):194.
45.    Aziz SB, Mamand SM, Saed SR, Abdullah RM, Hussein SA. New Method for the Development of Plasmonic Metal-Semiconductor Interface Layer: Polymer Composites with Reduced Energy Band Gap. Journal of Nanomaterials. 2017;2017:1-9.
46.    Yamasaki S, Koga T, Ohura H, Yano J. Electrical conductivity effect of polyaniline addition to poly(ethylene oxide) electrolyte film containing lithium perchlorate. J Mater Sci Lett. 1996;15(3):225-226.
47.    Ali GG, Ahmed MA, Sulaiman AA. Structural properties of AuNPs/PSi nanostructure. Digest Journal of Nanomaterials and Biostructures. 2022;17(2):473-480.
48.    Abdallh MS. Synthesis and Optical Properties Study of Some Metal Complexes of Poly (Vinyl Chloride)-Pyridine-4-Carbohydrazide. Journal of Al-Nahrain University Science. 2013;16(2):24-29.
49.    Ullmann’s Encyclopedia of Industrial Chemistry:  Sixth, Completely Revised Edition. Volumes 1−40 Edited by Wiley-VCH. Wiley-VCH:  Weinheim. 2003. 30 000 pp. $5500. ISBN 3-527-30385-5. Journal of the American Chemical Society. 2003;125(35):10768-10768.