ADVANCE MATERIALS GROWTH & CHARACTERIZATION
PREPARATION & XRD CHARACTERIZATION OF FLEXIBLE BLEND FILMS FORMED BY IN-SITU POLYMERIZATION OF PYRROLE IN POLY(VINYL ALCOHOL) M R RANGANATH & BLAISE LOBO Department of Physics, Karnatak Science College, Dharwad 580001, Karnataka, India *Email:
[email protected] Introduction: Conductive polymer blends are composed of conductive polymeric regions formed inside a matrix of non-conductive polymer containing an oxidizing agent. Conducting polymers like polyacetylene, polypyrrole (PPy) and Polyaniline (PANI) are known to be intractable. This difficulty in processibility limits their practical applicability, despite promise of potential applications like electrochromic devices, solid electrolytes for batteries, electromagnetic shielding materials, and corrosion resistant materials, among many others 1. One of the ways of circumventing this problem is the formation of flexible conducting polymeric blends. An example for such a sample is poly(vinyl alcohol)- polypyrrole (PVA-PPy) blend2. PPy is an intrinsically conductive polymer (ICP) which has been studied extensively due to its various interesting properties like high electrical conductivity and relatively good environmental stability. However, PPy is chemically synthesized as an intractable and unprocessable bulk powder precipitate due to the relatively rigid structure of its charged conjugated backbone. The conducting polymer blend of PVA and PPy , involves conductive PPy regions formed inside a matrix of PVA containing ferric chloride (FeCl3). The electrical, mechanical and optical properties of such a sample depend on the amount of doping and amount of conducting polymer in the non-conductive matrix. Electrical characteristics can vary from the limit of highly insulating materials (at low dopant levels) to that of a highly conductive polymeric film (at higher doping levels). PVA-PPy blends are used for patterning by photolithography3 and as a gas sensor4. The method of preparation plays a vital role in the bulk polymerization of pyrrole, when high transverse electrical conductivity is desired. H P de Oliveira et al5 have shown that the kinetics of polymerization in the bulk is very slow (taking hundreds of hours), compared to the surface (a few minutes), when solid films of ferric chloride doped PVA was exposed to pyrrole vapour. In this paper, we present a different preparative technique, wherein mobility of the monomer in the host polymer matrix is made obviously larger, by exposing the aqueous solution of ferric chloride doped PVA to pyrrole vapour, for a few hours (overnight). This leads to a visibly more homogeneous distribution of the conductive component (polypyrrole) in the PVA film, formed after solution casting. Careful control is achieved on the extent of polymerization and therefore the concentration of conductive component PPy, by adjusting the dopant level (of oxidizer FeCl3), rather than increasing the time of exposure. Experimental: The incorporation of PPy in PVA matrix is achieved by in-situ polymerization of pyrrole when PVA doped with FeCl3 is exposed to pyrrole vapor. An aqueous solution of PVA was formed by adding 2 gram of PVA granules to 50 ml of distilled water, dissolution being achieved using a magnetic stirrer (at 70 C). A few ml of an aqueous solution of FeCl 3, formed by dissolving 10g of FeCl3 in 250 ml distilled water was added to the PVA solution. Thus, FeCl 3 doped PVA solutions from 0.5 wt% to 44 wt% were prepared. Each of these was exposed for 16 hours to vapors of pyrrole. The resulting mixture was dried in an air cooled, temperature controlled furnace, maintained at 40°C. Solution casting method, with glass petridish as the substrate was utilized to obtain the PVA-PPy blend films. Thus different concentrations of PPy in the PVA matrix is achieved by controlled amounts (doping level) of the oxidizer (FeCl3). The resulting films were studied using XRD, DSC & UV-Visible Spectrometry. FTIR was utilized to endorse the presence of PPy in the final product (films). XRD spectra were acquired using the facility at Alagappa University, Karaikudi. Results and Discussion: The XRD spectra of the PVA-PPy blend films showed a variation from semi-crystalline nature to increasing amorphous 1
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A K Bakhshi “Electrically Conducting Polymers: From fundamental to applied research” Bulletin of Materials Science 18 (5), 469-495, 1995 H P de Oliveira, M V B dos Santos, C G dos Santos & C P de Melo “Preparation and electric and dielectric characterization of PVA/PPy blends” Materials Characterization 50, 223-226, 2003 O Yasushi, Y Shoji & K Masaki “Metal pattern formation by selective electroless metallization of polypyrrole films patterned by photochemical degradation of iron (β) chloride as an oxidizing agent” Synthetic Metals 144 (3), 265-269, 2004; Seung Hyung Cho, Ki Tae Song & Jun Young Lee “Recent Advances in Polypyrrole” Chapter 8 of Conjugated Polymers: Theory, Synthesis, Properties & Characterization Ed. Terze A Skotheim & John Reynolds, CRC Press 2006, pp 8-63 to 8-63 Linshu Jiang, Hee-Kwon Jun, Yong-Su Hoh, Jeong-Ok Lim, Duk-Dong Lee, Jeung-Soo Huh “ Sensing characteristics of Ppy-PVA methanol sensors prepared by in-situ vapor state polymerization” Sensors & Actuators B 105, 132-137, 2005 H P Oliveira, M V B dos Santos, C G dos Santos and C P de Melo “Electrical properties of PVA/PPy blends” Synthetic Metals 135-136, 447-448, 2003
structure, with increase in doping level. This is illustrated in figure 1. Note the decrease in intensity of the peak with increase in concentration of PPy. This indicates major microstructural changes in the PVA-PPy blend, the degree of crystallinity drastically decreasing with increase in the amount of PPy in the PVA matrix. Figure 2 confirms this trend showing XRD curves for 1 wt%, 5.7 wt% and 20 wt% PPy impregnated PVA films.
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M :- 2 wt% PPy in PVA I :- 10 wt% PPY in PVA C :- 44.4wt% PPy in PVA
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Figure 1. XRD Scan for 2 wt% , 10 wt% and 44.4 wt% (FeCl3 doped) PPy impregnated PVA.
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N:- 1 wt% PPy in PVA F:- 5.7 wt% PPy in PVA
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K:- 20 wt% PPy in PVA
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Figure 2. XRD Scan for 1 wt%, 5.7 wt% and 20 wt% PPy in PVA films, showing drop in degree of crystallinity with increase in PPy Concentration.
