Specific Electrical Conductivity of Thin Films of Polyaniline Doped with Sulfuric Acid

Transcription

1 Volue-5, Issue-5, October-05 International Journal of Engineering and Manageent Research Page Nuber: 47-5 Specific Electrical Conductivity of Thin Fils of Polyaniline Doped with Sulfuric Acid Izet Gazdić, Aledina Modrić-Šahbazović, Suada Sulejanović 3 Departent of Physics, Faculty of atheatics and natural sciences, University of Tuzla, BOSNIA AND HERZEGOVINA 3 Departent of Physics, Faculty of atheatics and natural sciences, University of Sarajevo, BOSNIA AND HERZEGOVINA ABSTRACT This paper presents the specific electrical conductivity of thin fils of polyer polyaniline which was doped with sulfuric acid. Polyaniline in the undoped state is an insulator and doping can convert it into a conductor of electrical current. Polyaniline aterial (PANI) which was the subject of the research in this study was synthesized in our laboratory with the ethod of oxidative polyerization reaction at 0 C and at roo teperature of 0 C. Doping was carried out directly in the production process. Fro the thus obtained doped aterials (PANI-H SO 4 ) were ade thin fils by the ethod of rotating disk at different speeds. Based on the easured electrical resistance of each fil individually, we calculated specific electrical conductivity. It is shown that this conductivity depends on the teperature at which the doping is carried out with sulfuric acid, as well as on the speed of the rotating disk on which the individual thin fils were obtained. Keywords---- polyer, polyaniline, insulator, thin fils, doping, sulfuric acid, electrical resistance, specific electrical conductivity, conductor. I. INTRODUCTION Macroolecular copounds fored by stringing basic substance olecules (onoers) into acroolecules with a large nuber of atos (000 and ore) are referred to as polyers. The process of connecting into acroolecular substances, without the foration of by-products, is polyerization. The basic repeating structural unit of a polyer acroolecule is er (in etals an ato). The nuber of olecules (onoers), of which a polyer olecule consists, deterines the degree of polyerization. With the increasing degree of polyerization there occures changing of the physical properties of polyers (viscosity, hardness, solubility, etc.). Each olecule is represented by the length of the chain consisting of specific ebers which by their cheical coposition can be of the sae or different type. Polyaniline belongs to a group of synthesized polyers. It was first synthesized in 86 [] and was alost forgotten as it had no iportant technological applications because it did not conduct electrical current. However, the discovery of MacDiarid et al in 986, that a relatively siple cheical process can transfor it into a conductive state [] started a sudden interest in this aterial. In the very beginning of the study on conducting polyers the ain objective of the research was the understanding of fundaental processes in the, while today the ain goal is iproving the conductivity and its technological applications. This is especially evident after the discovery of a polyer LED (light eitting diode) in 990 by Richard Friend [3]. Polyers are substances coposed of acroolecules. Most of these are organic acroolecules that are coposed of the sae type of building blocks - the onoers, which are interconnected by covalent bonds. Each olecule is represented by the length of the chain consisting of specific ebers which by their cheical coposition can be of the sae or different type. Depending on the degree of order and density of utual arrangeent of chains a polyer can be: partially crystalline and copletely aorphous. Crystalline polyers have inside the loosely packed parts of the olecules that ake up its aorphous phase. The crystal phase has a greater ipact on the physical and echanical properties. When switching fro the aorphous polyer to the crystalline state, increased are the tensile strength, hardness and resistance to heat. Aorphous state of a syste reduces its stiffness and akes it elastic. This phenoenon is used in production processes where it is necessary to provide good elasticity of aterial used. In ters of the states the polyers can exist 47 Copyright 0-5. Vandana Publications. All Rights Reserved.

2 in two states of atter: liquid and solid. They can not have the gaseous aggregate state, because the vapor pressure is negligible and vapor decoposes. The discovery of conducting polyers began a new field of research on the border between cheistry and condensed atter physics. Conductive polyers paved the way for the iproveent of fundaental understanding of physics and cheistry. Polyaniline is characterized by a very high degree of cheical stability which akes it very interesting for exploration and technical application. It is available in the for of volue (bulk) or as a thin fil, which is the subject of this paper. By doping it is converted to a conductive state. Polyaniline doped with acids such as HCl, H SO 4, H PO 4 is not soluble in any organic solvent, while the undoped polyaniline (eeraldine base) is very well soluble in N-ethylpyrrolidinone. Solubility is an iportant technological feature of polyaniline because it enables the production of thin polyer fils. It can be said that the polyers have a huge variety of properties. Sall changes in the physical paraeters (e.g., teperature) or a very ild cheical treatent can drastically change the properties of the polyer. This fascinating feature is typical of all soft atter, and by that ter we ean: liquid crystals, polyers, detergents, colloidal beads and porous aterials. II. MATERIAL AND METHODS Polyaniline doped with sulfuric acid (PANI- H SO 4 ) that was researched in this study was synthesized in our laboratory with the ethod of oxidative polyerization reaction. The process of obtaining and doping was carried out siilarly as in the work listed under [4] in References. The polyerization of polyaniline was carried out by cheical oxidation of aniline in aqueous solution (95%) of sulfuric acid ( M aq H SO 4 ), wherein the used oxidizer was aoniu peroxodisulphate (NH 4 ) S O 4 (APS). There have been several synthesis perfored as follows: in two containers (A and B) was placed 94 l of deionized water; M H SO 4 was placed in each container, that is 5.4 l of 95% sulfuric acid. in the first vessel (A) was placed 8 L ( ole) of aniline (C 6 H 5 NH ). Aniline is a very weak base; the ixture is stirred until coplete dissolution of aniline to obtain transparent and light-colored solution; in another container (B) was placed 0.08 g of APS, which was stirred until coplete dissolution; slowly, while stirring continuously, the contents of the container B is added into the vessel A; whole ixture was stirred for 4 hours with a agnetic stirrer (see Figure ), and then left to stand without stirring for 4 h; after 4 hours in resting state of the ixture on the botto of the container a green precipitate was fored; by decantation the precipitate is separated fro the water in which the synthesis was carried out; after decanting the precipitate was rinsed with ethanol until the liquid above the residue becoes transparent, to reove any unwanted polyerization products (Figure ). then the precipitate was rinsed with deionized water to copletely reove the ethanol and a filtration was perfored with filter paper; before the doped polyaniline (PANI-H SO 4 ) was transfored into solid state, we started the production of thin fils. Figure. Mixture of PANI-H SO 4 in an ice bath, placed on a agnetic stirrer. Figure. View of the precipitate PANI-H SO 4 after the rinse with ethanol. It is very iportant, in the described process of obtaining a polyaniline doped with sulfuric acid, to have sufficient tie passed between each step, that is before each next step it is necessary to wait until all the reactions are copleted in the syste so that the syste is in balance. III. EXPERIMENTAL RESULTS AND DISCUSSION Thin fils of PANI-HCl were produced by using a spin coater (Model P-6708D, Specialty Coating Systes, Indianapolis, IN) whose rotational speed can reach 8000 revolutions/inute. On the spin coater was attached a vacuu pup type D.V.P. Vakuu Technology s.r.l Italy and a copressor fro the sae anufacturer, so that 48 Copyright 0-5. Vandana Publications. All Rights Reserved.

3 the entire process for obtaining thin fils took place in a vacuu. On the vacuu head of the spin coater which was ade in the shape of a disk with the diaeter of 50, is set an inkjet transparency fil (insulator) with thickness of 0.08 on which is applied the ixture PANI-H SO 4 in constantly the sae aount of 400 µ l. In the process of obtaining thin fils by Specialty Coating Systes we can control the following paraeters: rotation speed of rev/ in, with the possibility of prograing three levels (RPM of rev/in, RPM RPM rev/in, RPM3 RPM rev/in), acceleration tie of rotating disk (RAMP, RAMP, RAMP 3) of -30 seconds, rotation length (TIME, TIME, TIME 3) up to 999 seconds. deceleration tie (RAMP 4) fro -30 seconds. All these entioned paraeters are very iportant for obtaining a high-quality fil of polyaniline doped with sulfuric acid. In order to obtain high quality fils it is necessary first to set a lower speed of rotation, and then to accelerate the disk over specific tie (00; 400; 600 revolutions/inute). As described in part we ade two identical series of doping PANI-H SO 4 at roo teperature (0 C). Fro each series were ade 8 fils at different speeds of rotation disk (rp). After drying in the desiccator we easured the electrical resistance of a part of the fil at a length of c, and based on this data we calculated the electrical conductivity for each saple of the thin fil by the relation σ = L G/S where G= /R and is called conductance. The obtained results of these two series of experients are shown in Table. N u be r of sa pl es Table. Results of easureents for thin fils PANI-H SO 4 obtained at 0 C Rotational speed (rp disk/ inute) -RPM Electrical resistance (kω) Specific electrical conductivity (0 - S/) 00,400, ,500, ,600, ,900, ,400, ,000, ,3000, ,4000, specific electrical conductivity 0 e (-) S/ PANI-H SO 4 at 0 C,8,6,4 0,8 0,6 0,4 0, rp Figure 3. Change of specific electric conductivity depending on the speed of rotation for thin fils PANI- H SO 4 obtained at 0 C In exactly the sae way was perfored the doping of polyaniline with sulfuric acid (PANI-H SO 4 ), but now at 0 C. The entire process took place in containers with ice, with a constant teperature control. Of the aterial so obtained were ade two series of saples of thin fils ( 3 and 4). The experiental results for these two series are presented in Table. N u be r of sa pl es Table. Results of easureent for thin fils of PANI-H SO 4 obtained at 0 C Rotational speed (rp disk / inute)-rpm Electrical resistance (kω) Specific electrical conductivity (0 - S/) 00,400, ,500, ,600, ,900, ,400, ,000, ,3000, ,4000, The dependence of the specific electrical conductivity for these two series ( 3 and 4) on the rotation speed of the disk is shown in Figure 4. The dependence of the specific electrical conductivity of thin fils of PANI-H SO 4 obtained at roo teperature on the speed of rotating disk is shown in Figure Copyright 0-5. Vandana Publications. All Rights Reserved.

4 specific electrical conductivity 0 e (-) S/,,8,6,4 0,8 0,6 0,4 0, 0 PANI-H SO 4 at 0 C rp 3 4 Figure 4. Change of specific electric conductivity depending on the speed of rotation for thin fils PANI- H SO 4 obtained at 0 C Fro the figures 3 and 4 we can see an exponential dependence of the specific electrical conductivity on the rotation speed of the disk for the saples of thin fils of all series. Using nonlinear ethod of least squares we ade fitting of experientally obtained graphics (Figures 5, 6, 7,8) Figure 7. Fitted curve for the PANI-H SO 4 obtained at 0 C ( 3 and 4).. Figure 8. Fitted curve for the PANI-H SO 4 obtained at 0 C in the sei-logarithic distribution ( 3 and 4) Figure 5. Fitted curve for the PANI-H SO 4 obtained at 0 C ( and ) Figure 6. Fitted curve for the PANI-H SO 4 obtained at 0 C in the sei-logarithic distribution ( and ). Fro Figure 5 one can conclude that the experiental data for the PANI-H SO 4 obtained at 0 C ake a good fit on the exponential function y=0,083 exp(- 675x). Figure 6 shows the sae inforation but in a sei-logarithic distribution where the exponential function is converted to a linear function (straight line). On the basis of that iage one can better observe that the greater deviations fro the line occur for higher values of rotating speed of the disk. Figures 7 and 8, respectively, show the sae function but for the experiental data PANI-H SO 4 obtained at 0 C. The experiental results are fitted to a function y = exp (-0.90 x). In all entioned functions, x is the rotating speed of the disk (kilo rp). After that, we perfored infrared spectroscopy (IR) of the aterial PANI-H SO 4 obtained at 0 C and 0 C. Infrared spectroscopy was perfored on a PerkinEler FT-IR Syste Spectru BX so that the infrared radiation is passed through a paste ade fro the powder ixture of PANI-H SO 4 and KBr at the ratio :9. After passing through the cuvette with an unknown copound, the intensity of the incident bea is reduced, 50 Copyright 0-5. Vandana Publications. All Rights Reserved.

5 thus with a coputer we obtain the dependence of the transparency coefficient on the reciprocal value of the wavelength in c -. %T c Figure 9. Infrared spectroscopy of PANI-H SO 4 obtained at 0 C %T IV CONCLUSION Fro the shown tables, as well as the graphical display of conductivity, it can be seen that fils PANI- H SO 4 obtained at higher speeds of rotating disk have a lower specific electric conductivity. When disk rotation speeds are greater than 6000 rp we can not get thin fils that can conduct electricity. Also, by coparing fils of all series it can be concluded that polyaniline fils doped with sulfuric acid, which are obtained by the synthesis at 0 C ( 3 and 4), have a greater specific electrical conductivity than those obtained at 0 C ( and ) which is in line with the work [4]. Based on the experientally obtained graphics and fitted functions it can be concluded in this paper too that the conductivity of thin fils doped with sulfuric acid is given by relation a exp( b x) σ = where x is the rotating speed of the disk (kilo rp), and the constants a and b are correctly deterined for each series of saples. The echanis of conductivity in such aterials can be described by the odel of Variable Range Hopping - VRH [4] [5]. Fro the tables and and the figures 3 and 4 it can be seen that there exists a conductivity of thin fils of PANI-H SO 4, and that it varies depending on the nuber of revolutions of the disk and the way of obtaining, whereas undoped saples (fils) do not conduct electricity [6]. On the basis of infrared spectroscopy of aterials it can be concluded that the dependence for both the PANI-H SO 4 at 0 C and the PANI-H SO 4 at 0 C, is alost the sae. The only difference is that for the aterial PANI- H SO 4 obtained at 0 C there occurs additional peak at 04 c -, which indicates the additional C-O connection. After coparing the graphics obtained by infrared spectroscopy with the graphics obtained fro database, there is a siilarity of the PANI-H SO 4 at 0 C with a 86,995%,3,5-Tetrachlorobenzene, and of the PANI- H SO 4 at 0 C with a % Triethylene glycol onochlorohydrine. REFERENCES []. H. Letheby, J. Che. Soc. 5, 6 (86). []. J. C.Chiang, A. G.MacDiarid, Synth. Met. 3, 93 (986) [3]. J. H. Burroughes, D. D. C. Bradley, A. R. Brown, R. N. c- Figure 0. Infrared spectroscopy of PANI-H SO 4 obtained Marks, R. H. Friend, P. L. Burns, A. H. Hoes, Nature at 0 C 347, 539 (990). [4]. Izet Gazdić, Aledina Modrić-Šahbazović, Senada Fro the iages 9 and 0 we can see that the Avdić, Suada Sulejanović, "Reproducibility of Obtaining dependence of both the PANI-H SO 4 at 0 C and the thin Fils of Polyaniline by Direct Doping" TEM Journal- PANI-H SO 4 at 0 C, is alost the sae. Technology, Manageent, Inforatics, ISSN: The peak at 670 c - indicates that there is a benzene ring; (print). eissn: (Online), Vol.4, No., May peaks at 370 c - and 345 c - that the coposition has 05, pp 30-36, nitrites, and the peak at 560 c - that there is nitro [5]. N. F. Mott, Metal-Insulator Transition, Taylor and copound NO. The appearance of peaks between 3900 Francis, Bristol (990). c - and 3500 c - indicate that in the tested aterial there [6]. Izet Gazdić, Senada Avdić, Suada Sulejanović, Suada are O-H and N-H bonds. Bikić, Aledina Modrić-Šahbazović Teperature Dependence of the Conductivity of Polyaniline Saples, Journal of Trends in the Developent of Machinery and Associated Technology Vol. 7, No., ISSN (online), p.p , (03), 5 Copyright 0-5. Vandana Publications. All Rights Reserved.