Ahmed, M A

El-Dine, Tag M

Ellil, Abo M S

IACS Institutional Repository

Indian J. P hys. 79(6), 651-655 (2005)a: %U P  ?E n h a n c e m e n t  o f  t h e  t r a n s p o r t  a n d  c |ie le c tr ic  b e h a v io u r  o f  p u r e  a n db le n d e d  C P V C  b|^ m e ta l  io n sM A Ahmed*» M S Abo Ellil and M Tag El-Dine Department of Physics, Faculty of Science Cairo University, Giza, EgyptE -m ail: moala47@h|ftmail.comR e c e i v e d  2 3  J u l y  2 0 0 4 ,  a c c e ^ d  1 7  M a r c h  2 0 0 5\A bstract : The AC conductivity and the dielectric properties were mealatred as a function of temperature and frequency for the pure and blended chlorinated polyvinyl chloride (CPVC) polymer samples. The DC con0uctivity was measured in the same range of temperature. The effect o f metal ion concentration as well as its ionic radius on the above propcnics was studied. The measurements of conductivity showed the existence of more than one conduction mechanism. Both DC and AC conductivities increase with increasing the metal ion content. The obtained values of the activation energy indicate the .semi conducting behaviour for metal-doped samples.Keywords : Polymer, AC and DC conductivity, dielectric property. PACS Nos. : 72.80-r, 77.84JdThe electrical properties o f chlorinated polyvinyl chloride (CPVC) are o f great interest because of their wide range of applications, which can be considered as one o f the easily molded insulation. These properties depend not only on their chemical composition and structural features but also on the degree of molecular order. The polymer conductivity depends on the presence o f free ions, which are not connected chemically with the polymer chain while the main chain may not participate in the charge transfer process. Thus, the polymer conductivity depends greatly on the presence o f low molecular weight impurities, which can serve as an ion source [1]. In polymers, there are two possible ion sources, the former is the dipole orientation by thermal agitation and the latter is the ions, which are injected from the metal electrode into the polymer system [2.3]. The chlorinated polyvinyl chloride (CPVC) is known to undergo thermal and chem ical dehydrochlorination [4 ,5 ]. Thermal degradation is believed to proceed almost exclusively by dehydrochlorination resulting in polyene sequences when the temperature is raised at a constant rate. The investigation o f dielectric properties o f polymeric materialsis one o f the most convenient methods o f unraveling the origin o f dielectric dispersion and relevant phenomena [6-8]. The AC conductivity measurements are very important to characterize the nature o f the conduction process. Studies o f polymers provide valuable information about molecular motion and their interaction in the composite materials. The aim of the present work is to find a good correlation betw een the metal ion concentration as a dopant material and the electrical properties o f the CPVC and also to find the effect of the ionic radii o f different dopants used on such properties.The samples under investigation are prepared using the standard casting method in which the pure CPVC is dissolved in dry tetra hydroflurine (THF) [British Drug House (BDH)]. The inorganic compounds (metal acetates) are also dissolved in (THF) and then blended with CPVC in proper weights (1, 2, 3 and 4 wt%). The resulting mixture is casted in a level petridish o f diameter 10 cm and left to dry in a level dissicator for 3 days. The obtained uniform thickness thin films are checked for good drying waA then cut in the form o f disks with diameter 10 mm and thickness 0.05 mm. Differential*CorrespcMiding Author<D 2005 lACS652 M A Ahmed, M S Abo Ellil and M Tag El-Dinescanning calorimetry (DSC) thermographs are performed for all prepared samples in the same range o f temperature including the glass transition temperature. For measuring the electrical properties, two surfaces o f each film are coated with silver paint and checked for good conduction. The two-probe method has been used for measuring all electrical projxsrtics, where Hioki LCR-Z Hi tester (Japan) m odel 3531 is used for such m easurem ents. DC  conductivity o f all samples are measured at a fixed voltage o f 600 V, not exceeding 1.2 x 10  ^ V/cm. The temperature o f  the sample is measured using T-typ)e thermocouple with its junction Just in contact with the sample where the accuracy was ± 1 X \D C  e le c tr ic a l  c o n d u c tiv ity  :The dependence o f  Ooc on the reciprocal o f the absolute temperature for CPVC, pure and Cu-doped sample is shown in Figure 1. The results show that the conductivity for all sam ples is increased with increasing both temperature and the metal ion concentration. It must also be noted that the conductivity o f the doped samples is always more than that o f the pure one. The increase in Oiyc at high temperature is due to liberation o f  more electrons or/and ions through the amorphous region where the thermal energy is sufficiently large. With heating, a microstrain is expected to takes place in the sample, which affects directly on the motion o f charge carriers as well as their conductivity [9,10], This is because the microstrain initiates small polarons move and participate2.2 2.51000/T(K *) 2.8 3.1 3.4F igure  1. Representation o f the DC conductivity (In oeic) v s , IGOO/Tof pure CPVC and their blends with different c oncentration (1, 2, 3 and 4 wt*^ ) ofin conductivity. Two breaks in the figure are observed for all investigated samples. The lower temperature break corresponds to the glass transition temperature (T ,^), while the other is related to the crystalline region [11]. The obtained data showed that the DC conductivity increases with decreasing ionic radius o f  the metal ion where < tn, < rpe < /"cr* A lso cJbc increases with increasing the metal ion concentration. This result is due to the diffusion o f the dopant material into the polymer matrix. At higher temperature (above 7\,), the increase in the free volume would facilitate the motion o f the ionic charge carriers. Evidently, all the plots o f  In cr v e rsu s  l / T  indicate the maintenance o f  the two segments obeying the normal Arrhenius equation cr =  (To exp i—AE IkT) where ao is the preexponential factor, A E  is the thermal activation energy and k  is the Boltzman constant. The values o f the activation energy were calculated from the slopes o f In o  ve rsu s  l / T  for low (£']) and high (En) temperature regions respectively and are reported in Table 1. The reportedTable 1. Activation energies E(cV) calculated for CPVC doped with differcni metal ion concentration in regions I and 11.Sample Region I Region 11Pure Cpvc 1.20 0.80C ul wt% 0.81 0.72Cu2 wi% 0.71 0.61Cu3 wl% 0.69 0.58Cu4 wt% 0.64 0.53N il wt% 0.85 0.73Ni2 wt% 0.79 0.55Ni3 wt% 0.72 0.58Ni4 wl% 0.67 0.56Pel wt% 0.87 0.75Fc2 wt% 0.82 0.68Fe3 wi% 0.74 0.60Fc4 wt% 0.68 0.58C rl wt% 0.89 0.79Cr2 wt% 0.85 0.70Cr3 wt% 0.77 0.63Cr4 wt% 0.70 0.60data show that the activation energies are decreased with increasing metal ion concentration. In general, the values o f  the activation eneigy more than 0 .6  eV  would normally be associated with ionic transport [31. The value of activation energy less than 0 .2  eV  should be associated with electronic mechanism. Therefore, it is acceptable to suggest here that at the tw o regions I and II, the conduction may be due to ionic mechanism and space charge limited current. The CPVC doped with Cu^  ^ ionEnhancement o f the transport and dielectric behaviour o f pure and blended CPVC by metal ions 653has the lowest value o f  activation energy in comparison with other samples. In fact, transition metals such as and Cr ’^*^ reside at various sites when introduced in CPVC. They may go substitutionaly into the polymer chain or reside at the amorphous -crystalline boundaries and d iffu se  preferentia lly  through the amorphous regions and/or charge transfer com plexes (CTC) or they may exist in the form o f molecular aggregates [12,13]. Thus, it is quite likely that ions o f  these metals may diffuse in the amorphous phase o f the polymer and thus forming (CTC) with polymer chain f l4 ]. Consequently, the maximum conductivity in CPVC samples is obtained when they arc doped with Cu^  ^ ions.A C  c o n d u c tiv ity  :Figure 2 is a typical curve illustrating the dependence o f  AC conductivity on the reciprocal o f absolute temperature for Cr doped CPVC (concentration o f Cr 1 wt%) at different frequencies (10 kHz-1 MHz). From Figure 2, it is clear that nearly same trend was obtained with a large plateau extended over a wide range o f  temperature. The values o f  the activation energy in the low temperature region increase with decreasing frequency. This means that in this frequency region, the frequency acts as a2.2 2.4 2.61(KX)/T(K ») 2.8 3,0 3.2 3.4pumping force f l5 ]  and helps in transferring the charge carriers sp ec ia lly  e lectron s betw een  the d ifferent conduction states. At high temperature and high frequency (600 kHz—1 MHz), no detectable increase in the mobility o f  the charge carriers because the recovering effect o f  derm al energy increases. The experimental data o f the investigated samples showed that increases withequency. The real cause o f increasing for Cu^  ^ than le other metal ions is due to its small ionic radius as eviously discus.sed in Oj^ ,. The pumping force o f  the •plied frequency helps in pushing the metal ions o f j|mailer radius to be m oved between the different Conduction states with the result o f  increasing This beans that the increase o f  conductivity in CPVC sample ^or all metal ions is mainly due to thermally activated Inobility o f  ions as the majority o f charge carriers and Hot due to thermally activated creation o f charge carriers, ifhe mobility in case o f Cu^  ^ ions is much greater than any other metal ions used. The dependence o f ctac on the applied frequency at temperatures 416, 357 and 312 K is shown in Figure 3. It is known that AC conductivity can-16-22-24•  416K• 357 K• 3 I 2 K8 15Figure 2. Representation of the AC conductivity at different frequencies (Ino&c) vs. 1000/T of CPVC doped with (Cr^ "^ ) at concentration 1 wt%.» 10 11 12 13 14Ln(f)F igure  3. Variation o f In with In frequency.be represented over many decades o f  frequency by an empirical relation o f  the form [16] :654 M A Ahmed, M S Abo Ellil and M Tag ETDine<Tac = Aco^ (1)where A  is constant and the index s  is the exponent o f  frequency. The calculated values o f s  are found 1.53, 1.58 and 1.55 at 416, 357 and 312 K respectively. The values for s  are significantly higher than unity and independent on temperature. Accordingly, the data gave the prediction that the quantum mechanical tunneling model is the most suitable mechanism to explain the AC conduction behaviour in the considered system [17]. From the comparison between <Jac and cTdc» il could be concluded that the higher conductivity and lower activation energy o f AC measurements than those o f DC, enhances the dependence o f  AC conductivity on frequency. Consequently, it can be suggested that the free radicals (carriers) which appear only within CPVC macro­molecules, can be more detected in AC than DC measure­ments. These carriers are retarded by the established barriers between polymer m olecules. Thus, the frequency o f  the applied electric field facilitates the AC conductivity in the sample by means o f the Maxwell-Wagner two- layer condenser model [18].D ie le c tr ic  co n s ta n t :The variation o f the activation energy between large values in DC measurement and small values in DC  measurement means that both electrons and ions participate in conduction mechanism. The small positive polaron role cannot be neglected in the conduction process. Figure 4 shows the temperature dependence o f  the real part o fthe dielectric constant { s ' )  for pure CPVC at various frequencies in the temperature range (300—430 K). From the figure, it is clear that as the frequency increases, the dielectric constant decreases. This decrease is attributed to the fact that the dipoles o f  the main chain o f CPVC cannot follow up the field variation [19]. The gradual increase o f  e* with temperature for all frequencies and the sharp increase above 326 K indicate the glass transition temperature (7] )^ o f  the samples. The increase o f e* with temperature is mainly due to the increase of the polarization arising from the molecular motion of polymer chain segm ents which in turn, allow s the orientation o f  dipolar units in the applied electric field. But at the same time, the contribution o f interfacial polarization gives rise to the space charge mechanism[20]. Figure 5 shows the variation o f  (e*)  with temperature for pure C PV C  and dop ed  w ith  m etal (Cu^^) concentrations (1, 2, 3 and 4 wt%) at a frequency o f  100 kHz. From this figure, it is noted that { f ') increases with increasing Cu content. Such a behaviour was expected because more conducting centers are available in the dielectric medium which absorb the electric enei^y pa.ssing through the medium resulting into the damping o f  the dipolar motion o f  the dielectric medium and hence increases the value o f  (£*') for the samples [21].9.47.45.43.4•  Pure pvc D C ul wt% A Cu2 wt% 0 ‘ Cu3 wi% X Cu4 wt%oXooX X X X X X ^oo A O AO o'o"  - oO A_ ^ o ^ oOOOOOOO Q ^o o o o O o ° g »• • • • • •290 340 390 440T(K)F igure  4. The variation o f the dielectric constant e '  with temeperature at frequencies (10 kHz -1  M Hz) for pure CPCV.F igure  5. The variation o f dielectric constant £ '  with temperature for pure CPVC and doped with metal (Cu '^**) concentrations (1, 2, 3 and 4 wt%) at (100 kHz).References[ 1) A F  Ioffe P h y s ic s  o f  S e m ic o n d u c to r s  (London : Infosearch) (1960) [21 M M  Migahed, R El Khodary and M  Hainan J . M a ter. ScL  25 2795 (1990)Enhancemtm o f the ttm sport and dielectric behaviour o f pure and blended CPVC by metal ions 655(3] A K Jonschcr Thin Solid Film  1 213 (1%7)[4] A Wirscn and P Flodin /  Appl. Polym. Set. 22 3039 (1978)|5] M Rogested and T Hjenbcry Macromolecules 26 60 (1993)[6] 11 Pcrepchko An Introduction to Polymer Physics (Moscow ; Mir Publisher) (1981)[71 K Liang, G Balhcgyl, F E Koresr. and W J Macknight J. Polym. Set. PflrfB29 649(1991)(81 C Fonggao, G A Sounders, E F Lanabson, R N Hampton, O Carini, G Di Marco and M Lanza J. Polym. Sci. Pan B 34 425 (1996)(91 B E Springteb J. Appl. Phys. 44 2925 (1973)(10] M Amin, H H Hassan and E Abdel Bary J. Polym. ScL, Polym. CAem.Ed. 12 2651 (1974)(11) P D Garrcnt and D T Grubb J. Polym. Sci. Pan 26 2509 (1998)112) D Kiessling and B Mundorfer Plasle, Kautsch 16 348 (1969)(13] T J Lewis and D M Tbylor J. Phys. D5 1964 (1972)(14] S Ghand and P C Mehendu J. Phys. D19 857 (1986)(15] M A Ahmed and M A Alahdal Ini. J. Polym. Mater SI 243 (2002)(16] SR Elliott Adv. Phy.t. .36 135 (1987)(17] MM Wakkad Indian J. Pure Appl. Phys. 34 235 (1996)I If I K C Kao and W Hwang Electrical Transport in Solids (New York • Pergamon)(1961)1 A A Zaky and R Hawely Dielectric Solids (New York : [)over) Ch 3 1 (1970)[2 f] A Triapathi, A K Triapathi and P K Pillai J. Mater. Sn. 25 1947 (1990)] R A Jangid, Neru, D Bhatnagar and J M Gandhi Indian J. Pure Appl. P/»w.34 316(1996)

Enhancement of the Transport and Dielectric Behaviour of Pure and Blended CPVC by Metal Ions

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Enhancement of the Transport and Dielectric Behaviour of Pure and Blended CPVC by Metal Ions

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