The Use of Le Bail Method to Analyze the Semicrystalline Pattern of a Nanocomposite Based on Polyaniline Emeraldine-Salt Form and α-Al 2 O 3

1Programa de Pós-Graduação em Ciência e Engenharia de Materiais (PPGCEM), Programa de Pós-Graduação em Fı́sica (PPGFIS), Universidade Federal do Amazonas (UFAM), 69077-000 Manaus, AM, Brazil 2Departamento de Fı́sica (DF), Universidade Federal do Amazonas (UFAM), 69077-000 Manaus, AM, Brazil 3Nanomed Inovação em Nanotecnologia, 13560-460 São Carlos, SP, Brazil 4Instituto de Fı́sica de São Carlos (IFSC), Universidade de São Paulo (USP), 13566-590 São Carlos, SP, Brazil

Intrinsically conducting polymers (ICPs) have been widely studied due to its great potential in technological applications, representing a class of materials with mechanical, electrical, and optical properties similar to metals and inorganic semiconductors [17][18][19][20][21].Among ICPs, polyaniline emeraldine-salt form (PANI-ES) has a prominent position due to the low cost of monomer, ease of synthesis, and doping and chemical stability [22][23][24][25][26]. Aluminum oxide (-Al 2 O 3 ) is one of the most important advanced ceramic materials due to its good corrosion resistance, hardness, good mechanical properties, and adsorption capacity, which favor its use in several technological applications [27][28][29][30][31].
Despite the importance of PANI in the ICPs class, there are some limitations that hinder its use in industrial scale, such as low solubility in organic solvents, low mechanical 2 Advances in Materials Science and Engineering flexibility, and processability [32,33].A widely used mechanism for improving its solubility and processability is the introduction of polar functional and long flexible alkyl groups mainly bonded to the main chain [34].Furthermore, PANI is one of the most promising industrial alternatives to obtain nanocomposites or blends.Then, one can combine the electrical properties of PANI with mechanical properties of the insulating matrix, such as alumina [35].
Nanocomposite constituted by -Al 2 O 3 microparticles reinforced by PANI-ES nanoparticles was prepared by in situ polymerization.Fourier-transform infrared spectroscopy (FTIR) was used for bonds of structural information; XRD was used for the determination of cell parameters and crystallinity percentage estimative; Le Bail method was performed to refine cell parameters and to obtain crystallite size and shape; SEM was carried out for the determination of solid nanocomposite morphology.These results were correlated with electrical properties.The crystal structure investigation of semicrystalline materials is an important research topic in many areas and remains in full development.Understanding the structure of semicrystalline nanocomposites constituted by polymer/ceramic materials is essential to the development of new technological applications.

Experimental
2.1.Nanocomposite Synthesis.PANI-ES/-Al 2 O 3 synthesis was performed based on Zhang (2006) [8] and Sanches et al. (2013) [25], with some modifications.Aniline (ANI) monomer was purchased from Sigma-Aldrich and further distilled.-Al 2 O 3 was obtained from Sapra, SA; São Carlos, SP, in December 2013.Two solutions were prepared.In Solution I, 20 mL of distilled aniline (ANI) was dissolved in 500 mL of hydrochloric acid (HCl) 1.0 M, added to 167 g of -Al 2 O 3 powder under stirring.In Solution II, 11.5 g of ammonium persulfate (APS) was added to 200 mL of hydrochloric acid (HCl) 1.0 M.Then, Solution II was rapidly added to Solution I allowing the polymerization.System remained under stirring for 3 h.Then, the dispersion of green color with -Al 2 O 3 particles was vacuum filtered and washed with acetone.

Fourier-Transformed Infrared Spectroscopy (FTIR).
Infrared spectra were measured in Nanomed Inovac ¸ão em Nanotecnologia in a spectrophotometer Bomem-MB Series-Hartmann and Braun in the range of 400-2000 cm −1 .Samples were prepared in KBr pellet with mass ratio of 1 : 100.

X-Ray Diffraction and Crystallinity
Percentage.XRD data were obtained at the Laboratory of X-ray Crystallography of IFSC/USP, São Carlos, SP, using a Rigaku Rotaflex diffractometer equipped with graphite monochromator and rotating anode tube, operating with Cu K, 50 kV, and 100 mA.Powder diffraction patterns were obtained in step scanning mode, 2 = 5-55 ∘ , step of 0.02 ∘ , and 3 s/step.Using routine software, crystallinity percentage was estimated using the diffractogram pattern and separating and then measuring the integrated intensities from the crystalline and noncrystalline phases.The integration was carried out over the whole range 2 = 5 ∘ to 55 ∘ , where  is the Bragg angle.The estimated crystallinity (E.C.), given as a percentage, was obtained by E.C. = 100  /(  +   ), where   and   are, respectively, the crystalline and noncrystalline integrated intensities [36].

SEM Analysis and DC Conductivity Measurements.
SEM experiments were performed in equipment Supra 35, Carl Zeiss.Powder samples were deposited on a carbon tape and the surface morphology was obtained at room temperature.For DC conductivity measurements, samples processed into pellets were coated with silver ink on both sides in which electrical connections were made.Measurements were performed at room temperature (300 K) using a Keithley Model 2612 A from 500 mV to 2 V.

Results and Discussion
3.1.FTIR Analysis.Figure 1 shows the FTIR spectra of the nanocomposite (PANI-ES/-Al 2 O 3 ), PANI-ES, and -Al 2 O 3 .For PANI-ES spectrum, bands were found between 1556 and 1457 cm −1 (band 1), which were related to C=C double bonds; bands between 1300 and 1234 cm −1 (band 2) are due to the C-N stretching; a band located at 1132 cm −1 (band 3) is attributed to vibration of C-H bond and 794 cm −1 (band 4) to the out-of-plane angular vibration of C-H aromatics.Regarding the -Al 2 O 3 phase, bands between 649 and 457 cm −1 correspond to the condensed AlO 6 octahedra which compose the building blocks in -Al 2 O 3 structure [48].Thus, in the FTIR nanocomposite spectrum bands related to both materials were observed.No additional bands related to new chemical bonds were found, suggesting that the nanocomposite was formed by physical deposition. .Figure 2 shows the nanocomposite XRD pattern.Crystallinity percentage was estimated from the whole nanocomposite XRD pattern.

X-Ray
Figure 3 shows the superposition of the diffraction pattern of nanocomposite (PANI-ES/-Al 2 O 3 ) (black), the supposed profile related to the noncrystalline phase (red), and the corresponding profile of the supposed crystalline phase (dark blue).Nanocomposite crystallinity percentage was estimated around 70%.

SEM Analysis and DC Conductivity Measurements.
Scanning electron microscopy (SEM) technique revealed that the ceramic material has particles with a range of micrometric sizes with plates-like morphology.For PANI-ES  An increasing about 1,300 times in nanocomposite DC electrical conductivity (0.24 S/cm) was verified when compared to the pure sample of PANI-ES [25].This is surprising since alumina is an electrical insulator with DC electrical conductivity about 10 −14 S/cm.The pure PANI-ES conductivity was found around 1.84 × 10 −4 S/cm for Sanches et al. [25], as expected.
We suggest that the most compact PANI-ES interface between the -Al of 0.17 S/cm for core-shell structured alumina-polyaniline particles.Michálek et al. [49] studied the electrical conductivity in alumina/multiwall carbon nanotubes (MWCNT) that obtained an increase from 10 −14 S/cm (pure alumina) to 2.7 ⋅ 10 −3 S/cm for composites.However, the DC electrical conductivity can decrease in the case of a better interaction between the composite components: Teoh et al. [50] synthesized nanofibers composite by oxidative polymerization of aniline with alumina nanofibers and the DC electrical conductivity decreased with increasing alumina nanofibers from 0.18 S/cm to 10 −3 S/cm for alumina loading from 0% to 20%.

Le Bail Method Analysis.
A process using iteratively the Rietveld decomposition formula for whole powder pattern decomposition (WPPD) purposes was first applied in 1988 [37] and called much later the "Le Bail method" or "Le Bail fit, " or "pattern matching" as well as "profile matching" in the FullProf Rietveld program [40].In the original computer program first applying that method, arbitrarily all equal  2 (calc) values are first used, instead of using structure factors calculated from the atomic coordinates, resulting in " (obs) " which are then reinjected as new  2 (calc) values at the next iteration, while the usual profile and cell parameters (but not the scale) are refined by least squares.Equipartition of  [43] and Lutterotti and Scardi (1990) [44]  exactly overlapping reflections comes from the strictly equal result for Bragg peaks at the same angles which would have starting equal calculated intensities.Not starting from a set of all equal  2 (calc) values would produce  (obs) values keeping the same original ratio for the exactly overlapping reflections.It is understandable that such an iterative process requires as good starting cell and profile parameters as the Rietveld method itself [51].
To perform Le Bail method the crystal symmetry and unit cell for PANI and aluminum oxide obtained, respectively, by Evain et al. [43] and Lutterotti and Scardi [44] were used as input data.The refinement steps were followed by refining the peak width, refinement of , , and  and , , , , , and .This sequence was addressed for both phases.Figure 7 shows the final refinement, with the observed ( obs , black) and the calculated ( calc , red) diffractograms, as well as the residual line ( obs - calc , blue).Table 1 shows the refined parameters.
The refined parameters values were compared with those obtained in literature [43,44].It is important to stress that the standard deviation appearing in the global average apparent size is calculated using the reciprocal lattice directions so it is a measure of the degree of anisotropy, not of the estimated error.The crystallite size projections for ES-PANI are showed in Figure 8(a).The crystallite shape can be described as a prolate ellipsoidal shape with its longer axis roughly parallel to [110] [25].There was an average crystallite size around 41 Å with standard deviation (anisotropy) of 10 Å.There are a smaller apparent size of 30    kept its lattice parameters and provide structural information about crystallite size and shape.

Conclusions
We successfully obtained polyaniline emeraldine-salt form/ -aluminum oxide (PANI-ES/-Al 2 O 3 ) nanocomposite by in situ polymerization.XRD analysis showed that nanocomposite presents a semicrystalline pattern (with estimated crystallinity around 70%) with peaks related to both materials.SEM analysis showed that PANI-ES was polymerized over the -Al 2 O 3 plates.FTIR technique revealed that nanocomposite has characteristic absorption bands related to both materials, suggesting that nanocomposite has preserved the original structural characteristics of its constituents.Conducting polymer/inorganic nanocomposite can be classified into two types: physical deposition, in which the polymer is absorbed on the surface of inorganic particles, and chemical deposition, in which there is a covalent bond between them [11].So, FTIR analysis showed that there was no chemical interaction between PANI-ES and -Al 2 O 3 .
The great contribution of this work is to obtain structural information using the Le Bail whole powder pattern decomposition method applied to a semicrystalline system consisting of semicrystalline polymeric/highly crystalline ceramic materials.The purpose of this work is also to promote this important structural characterization tool, which can be properly applied for semicrystalline materials.This method allowed the determination of cell parameters and crystallite size/shape for all phases.The refined cell parameters, so closed to the original values, showed that all phases have kept its structural characteristics after synthesis.For PANI-ES and -Al 2 O 3 there were, respectively, average crystallite sizes around 41 and 250 Å.
With respect to conductivity measurements, this work showed that it is possible to increase the conductivity of polyaniline by synthesizing a nanocomposite using an insulating matrix.It was observed that the polymerization of PANI-ES over -Al 2 O 3 particles promoted an increasing of conductivity around 1,300 times when compared to pure sample of PANI-ES.To explain this increasing in conductivity, we suggested that the interface between PANI-ES/-Al 2 O 3 probably created easier paths for charge carriers in nanocomposite.We hope that the structural information provided in this study may be useful in the area of materials science and, more specifically, in several technological applications that require conducting nanocomposites with electrical conductivity in the obtained range.
and 35 Å in the [010] and [001] directions, respectively, and others almost equivalent (46 Å) along [100].The crystallite size projections for -Al 2 O 3 are showed in Figure 8(b).There was an average crystallite size around 250 Å with standard deviation (anisotropy) of 40 Å.There is a largest apparent size of 140 Å in the [100] and [010] directions, and other smaller (90 Å) along [001].Through Le Bail method it was verified that nanocomposite phases have