1 IntroductionNow-a-days, conductive polymers aregreatly used in various applications like light-emitting diodes, batteries,electromagnetic shielding, antistatic coating, gas sensors etc. Conductingpolymers are combined with other insulating polymers that are good atmechanical properties. Polyaniline is preferred over other conductive polymersbecause of its stability, low raw material cost and ease of synthesis 1.
It was discovered by Runge in 1835 and initially called aniline black. Itconsists of reduced benzoid rings and oxidized quinoid rings. There are threeoxidation states of polyaniline namely leucoemeraldine (fully reduced),pernigraniline (fully oxidized), emeraldine base (half oxidized) 2. Figure 1 Different oxidation states ofpolyaniline (y = 1: leucoemeraldine, y = 0.5: emeraldine and y = 0: pernigraniline2Due to infusibility and insolubility,PANI is difficult to process.
In order to improve its processibility, PANI isdoped with organic acids having long non-polar tails like dodecylbenzenesulfonic acid (DBSA) and camphor sulfonic acid (CSA). This makes polyanilinesoluble in many organic solvents such as chloroform, m-cresol and xylene. Thisalso makes possible the solution processing of polyaniline with other polymers3. Polyaniline requires polaron state to be electrically conducting.
For thispurpose, organic dopants such as dodecylbenzene sulfonic acid (DBSA), sodiumdodecyl sulfonate (SDS), sodium dodecylbenzene sulfonate (DBSNa), Tetra-decyl-tri-methyl-ammoniumbromide (TTAB), sodium bis (2-ethylhexyl) sulfosuccinate (AOT) and inorganicdopants such as HCl, H2SO4, HBF4, H3PO4, CrO3 etc. are used 4,5.Poly vinyl pyrrolidone (PVP) also calledPovidone and it is the polymer of vinyl pyrrolidone.
Because of its outstandingabsorption and complexes abilities; like PVP added to iodine forms complexcalled povidone-iodine that possesses disinfectant properties due to thepresence of iodine, a bactericidal component thus it has been extensively usedin pharmaceutical, cosmetic and food industry as well as in various technicalapplications 10. PVP is water soluble polymer and hygroscopic in nature andhas good thermal stability. In solution it has excellent wetting properties andreadily forms films so this makes it good as a coating. Due to its high polarity it bindsexceptionally well to polar molecules. Adhesive and cohesive properties arealso good. It is soluble in polar solvents and also dissolved in variousorganic solvents and insoluble in esters, acetone, ethers, ketones andhydrocarbons 10.Figure 2 Structure of PVP82 Experimental2.
1 MaterialsAniline (DAEJUNG), dodecylbenzene sulfonic acid(DBSA; DAEJUNG), acetone, distilledwater, ammonium persulfate (APS; Riedel deHaen), hydrochloric acid (HCl;Scharlau), polyvinylpyrrolidone (PVP K 30; DAEJUNG), N methyl-2-pyrrolidone(NMP;LAB-SCAN), chloroform (Riedel deHaen), xylene (DAEJUNG), ethylene glycol(DAEJUNG),N,N-Dimetylformamide (DMF; DAEJUNG), m-cresol (Scharlau). 2.2 Preparation of the PANI/DBSA powderAniline (8 g) was mixed with 22 g DBSA and 400 mldistilled water. Use magnetic stirrer to form a homogeneous milky whitedispersion of anilinium-DBSA complex. Under constant stirring, the dispersionwas cooled to 0~5 0C.
The APS solution (20 g APS in 100 ml water)was pre cooled to 0~5 0C and then added into milky solution dropwise. The milky solution turns into dark green. To terminate the polymerizationadd the 100 ml acetone, it will not only terminate the polymerization but alsodecrease the viscosity and remove the extra DBSA. After this filtrate thesample and wash with distilled water several time until the filtrate wascolorless and dry in oven for 48 hr at 500C. 2.3 Preparation of PANI-HClPrepare 1M solution of aniline in 1M HCl.
Use themagnetic stirrer to form a homogenous solution. During the stirring keep thetemperature of reaction 10C. Prepare the 0.25 M solution of APS inde-ionized water and pre cooled it at 10C for 1 hr.
Add the APSsolution drop wise and sample turns into dark green color. After 3 hr, filterthe sample and wash it with distilled water for several times until thefiltrate obtained was colorless, then dry the sample at 500C for 1day.2.4 Preparation of blend5g PVP and 0.1 g PANDB were added into chloroform(60 ml) at room temperature. Keep on stirring until a homogeneous and viscoussolution formed, then poured the sample on glass substrate. The evaporation ofsolvent was carried out at 40 0C for 72 hr.
2.5 PVP film castingPVPfilms were synthesized in different solvents (distilledwater (1000C), N methyl-2-pyrrolidone (2020C; NMP),chloroform (61.20C), xylene (138.40C), ethylene glycol(197.30C), ethanol (78.
370C), methanol (64.70C),dimetylformamide (1530C; DMF) and m-cresol (202.80C), toobtain a flexible film. Films obtained by all these solvents were brittleexcept NMP.3 Characterization3.1 TGA analysis (TGA)Themogravimetricanalysis was conducted to measure the weight loss of samples.
Thermograms wereobtained by using Shimadzu TA-60 in temperature range of 20-600 oCwith heating rate 10 0C/ min under nitrogen atmosphere. The weightlosses of all samples were analyzed at different stages. 3.2 DSC thermal analysis (DSC)Differential scanning calorimeter was used to studythe thermal properties of samples.
The glass transition temperature of sampleswere obtained by using Shimadzu DA-50 with scan rate of 100C/ min and temperature range from 20-250oC.3.3 Fourier transform infrared spectroscopy (FTIR)FTIR spectra of samples were obtained by Alpha FTIR withcomputer software. The characterization was performed in 4000-600 cm-1wave number. Formation of hydrogen bonding and interactionbetween the elements in (PANI-DBSA) and its blend was investigated by FourierTransform Infrared Spectroscopy (FTIR).4 Results:4.
1 FTIR:Figure 3 FTIR spectra of PANI/HCl,PANI/DBSA and PANI/PVP blend FTIR analysisshows the nature and extent of interaction between polymers. Mixing atmolecular level resulted into the change in peaks. FTIR shows the Quinoid ring and benzoid ring at 1574cm-1and 1488cm-1 respectively, C-N+. Stretching 1235cm-1,NH+= bending 1128cm-1 in PANI doped with HCl 7.In PANI doped with DBSA, Quinoid ring 1542cm-1 and benzoid ring 1460cm-1, NH+= bending 1086 cm-1are identified by FTIR 6.
In PANI/DBSA-PVP blend, hydrogen bonding is developedbetween Carbonyl stretching (C=O) band of PVP and NH+– of the PANI.The Carbonyl stretching band of PVP isshifted at 1652cm-1 on the addition of 10% PANI from 1660cm-1.Quinoid and Benzoid rings are identified at 1574cm-1 and 1488cm-1respectively 7.4.2 DSC Analysis:DSC curves are obtained by the usingDA-50 which gives the information about glass transition temperature Tg.
Figure 4 DSC spectra of PANI/HCl, PANI/DBSAand blendDSC curves provide the information about glasstransition temperature.PANI doped with HCl showed the endothermic peak isat 122.71oC while PANI doped with DBSA showed the 133.
55oC12.Pure PVP shows the Tg at 162.3oC 3.PANI doped with DBSA blended with PVP shows the Tgat 153.75oC 3.4.3 TGA Analysis:Thermogravimetric analysis was carried out using TA-60 Shimadzu in a temperaturerange of 15-600oC.
TGA curves of PANI doped with organic acid”Dodecylbenzenesulphonic acid” (DBSA) and inorganic acid i.e. HCl and PANI-DBSAblended with PVP are shown in the given below. Three major stages are obtainedin Thermogrames. Figure 5 Thermograms of PANI/HCl, PANI/DBSAand blend At 100oC, moisture is evaporated. Thesecond weight loss is associated with the destruction of linkage between NH+—SO-3and PANI chain in a temperature range of 320-370oC and the thirdweight loss is associated with the degradation started about 410-460oC9.
In case of HCl doped PANI, first weight loss isassociated to the volatility of water that is absorbed by the polymer in theform of moisture in between 60-110oC about 23%. In second stage,weight loss is attributed to dopants or smaller oligomer chains, started at 358oCand finally the decomposition of main chain of polymer at 568oC 10.Similarly in PANI/PVP blend, the weight loss ofmoisture is upto 100OC.
the decomposition temperature of blend is higherthan the PANI-DBSA i.e. about 402-432oC. After that PANI chain isstarted to decompose at 432oC 11.5 Conclusion Conductiveblend of polyaniline doped with dodecylbenzene sulfonic acid (PANI-DBSA) andpolyvinylpyrrolidone (PVP) was prepared. Thermal characterization was carriedout by using DSC, TGA and FTIR.
To obtain the conductivity and flexibility, PVPfilms were synthesized in different solvents. a comparative study of effect ofPVP grades and effect of solvents on the properties of blend will be carriedout in next term.