- Email: [email protected]
alum composites
Polymer Testing 23 (2004) 739–745 www.elsevier.com/locate/polytest
Material Properties
Physical properties of polystyrene/alum composites S.A. Saq’an a, A.S. Ayesh b, A.M. Zihlif b, , E. Martuscelli c, G. Ragosta c a
c
Physics Department, Jordan University of Science and Technology, Irbid, Jordan b Department of Physics, University of Jordan, Amman, Jordan Institute of Research and Technology of Plastic Materials, CNR, Via Campi Flegrei, Pozzuoli, Napoli, Italy Received 9 January 2004; accepted 15 April 2004
Abstract The mechanical, thermal, optical and electrical properties of polystyrene/alum composites have been studied as a function of alum content and applied field frequency. The mechanical properties, glass transition temperature, optical energy gap, dielectric constant and AC electrical conductivity of the composites sheets showed frequency and filler content dependence. Analysis and correlation between the collected physical quantities are presented. # 2004 Elsevier Ltd. All rights reserved. Keywords: Mechanical; Optical; Dielectric constant; Energy gap; Conductivity; Glass transition temperature; Alum
1. Introduction Considerable research has been devoted to the modification of the mechanical, thermal and optical properties of polymer composites to meet the requirements of advanced technical and industrial applications [1,2]. Much of this attention is currently focused on obtaining new structural components to be used in electrical conduction, thermal insulation, and electromagnetic shielding applications [3,4]. The nature of the fillers, including their composition, particle dimensions, homogeneity of distribution and adhesion level in a polymeric matrix, is important for the physical properties of the composites. Many research works have demonstrated that the addition of an optimum amount of an electrolytic filler greatly enhances the ionic conductivity and affects the bulk properties of the composites. The interactions of an alkaline ion with a polymer matrix determine its possible application in energy batteries and other solidstate electrochemical devices [5–8]. Interesting effects were observed by us on the optoelectrical properties of PEO/alum and PEO/manganese composites [9,28].
Corresponding author. Fax: +962-65348932. E-mail address: [email protected] (A.M. Zihlif).
Generally, the observed ion conduction in the composite bulk was mainly attributed to ionic interactions and impurity activity taking place during the passage of an electric current into the composite. In this paper, the effects of alum concentration (by weight) and the applied electric field frequency on the physical properties of polystyrene/alum composites such as yield stress, glass transition temperature, dielectric constant, AC conductivity and optical energy gaps are reported. 2. Experimental work 2.1. Materials and composite preparation The polymeric matrix used in the present study was polystyrene (PS) resin of molecular weight 23 700. Polystyrene has good thermal and electrical insulation properties. The alum filler, ordinary commercial potassium sulfate (potassium alum), AlK3(SO4)212H2O, was in the form of glassy transparent crystals and soluble in water. The solid alum was ground into a fine powder of average particle size 18 lm and kept in an v oven overnight at 40 C to reduce the water content. The alum filler is one of a series of crystallized double sulfates containing some impurities. It was added to the PS matrix to make an electrolytic composite, i.e. an
0142-9418/$ - see front matter # 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymertesting.2004.04.008
740
S.A. Saq’an et al. / Polymer Testing 23 (2004) 739–745
ionic polymer composite which would be used in solid batteries or as an ion-exchange electrode [10,11]. The method of composites preparation has been described elsewhere [12]. It involved mixing alum fine powder with PS resin in a Brabender apparatus at v 180 C for 10 min. The compression molded composite sheets obtained were about 1.5 mm thick containing 10, 20, 30, and 40 wt% alum particles randomly distributed. 2.2. Tensile tests Tensile tests were carried out using an Instron machine (TX automated floor model) on dumbbellshaped specimens. The gauge length was 23 mm and width 4 mm. The crosshead speed was 1 mm/min. The v tests were done at 20 C. The Instron machine was connected to a computer programmed to give the required mechanical parameters. 2.3. Differential scanning calorimetry Measurements of the glass transition temperature (Tg) were carried out using a Perkin Elmer DSC, calibrated with the melting transition of indium, at a heatv ing rate of 10 C/min. The midpoint on the DSC thermogram was taken as the glass transition temperature. 2.3.1. The optical absorption spectra Absorption spectra of the prepared PS/alum sheets were measured in the wavelength range k ¼ 250 850 nm (uv–visible) using a spectrophotomer. The absorption coefficient, a(x), was calculated from the absorbance A after correction for reflection losses using the formula aðkÞ ¼ 2:303AX 1
3. Results and discussion 3.1. Mechanical and thermal results Fig. 1 shows the dependence of Young’s modulus and the yield stress on alum content for the composites. The elastic modulus is enhanced and the yield stress decreased with increasing the alum concentration. The modulus enhancement is normally expected in fibre and particulate composites. The observed decrease in the tensile yield stress with increasing the alum concentration is due to weak interfacial adhesion between the alum particles and the PS matrix. This weak adhesion could be attributed to existence of some structural irregularities as cavities and voids [15–17]. Other possible explanation is may be due to brittleness of the alum grains themselves. However, many investigations showed that the effect of solid fillers on the strength of polymers may be positive or negative, depending on such factors as filler shape and size, internal stresses, surface nature, and aspect ratio [18]. The yield strain and the energy to yield shown in Fig. 2 decreased with increasing the filler content. The glass transition temperature (Tg) is an important physical parameter to characterize the structural property of an amorphous polymer in terms of chain rigidity and intermolecular forces. Fig. 3a shows a DSC thermogram of PS/alum composite (10 wt%). The values of the Tg determined from the measured thermographs are shown in Fig. 3b as a function of filler concentration. The results show that there was a small v change in the value of Tg, within 5 C, with increasing alum content up to 20 wt%. The effect of a filler on Tg was observed by Briscoe [19] and Avella and colleagues [20] who observed a slight increase in Tg, and reported that addition of a rigid filler into a polymer matrix is generally responsible for a slight increase in Tg, usually v about 6 C.
ð1Þ
where X is the sample thickness [13,23]. 2.3.2. Impedance measurements Impedance measurements were made with a HP 4194A-impedance analyzer over the frequency range 100 Hz–13 MHz at room temperature. Calibration (short and open) of the impedance analyzer was done before the measurements. Disk shaped specimens were cut from the composite sheets (10, 20, 30, 40 wt% alum) and placed between the copper plates (10 mm diameter) of a test sample holder placed in a shielded cell designed for this purpose. The two leads of the holder were connected to the terminals of the impedance analyzer [11–14].
Fig. 1. Young’s modulus and yield stress versus alum concentration (wt%).
S.A. Saq’an et al. / Polymer Testing 23 (2004) 739–745
741
3.2. Optical results The absorption edge of non-crystalline materials gives a measure of the band strength or energy band gap. The absorption coefficient a for these materials has the following frequency x dependence [21,22]: aðxÞ hx ¼ bð hx Eopt Þr
Fig. 2. Yield strain and energy to yield versus alum concentration.
Fig. 3.
ð2Þ
where h is Plank’s constant, b is a constant, and r is an exponent which can take values of 1, 2, 3, 12 or 32 depending on the nature of the electronic transitions (direct or non-direct) responsible for optical absorption [23,24]. The application of Eq. (2) was demonstrated in our previous papers [13,25–28]. Fig. 4 represents the spectra of the optical absorbance A for samples of neat
(a) DSC thermographs for alum composite (10 wt%). (b) The glass transition temperature versus alum composition.
742
S.A. Saq’an et al. / Polymer Testing 23 (2004) 739–745
Fig. 4.
The variation of the absorption coefficient (a) with the wavelength.
PS, 10, 20, 30 and 40 wt% alum-filled composites. The optical energy gaps, listed in Table 1, were determined from graphs representing the product of the optical absorption coefficient and the photon energy ða hxÞ2 versus photon energy ð hxÞ. The values of Eopt were obtained by extrapolating the straight lines to intercept the photon energy coordinate ð hxÞ. At low absorption levels, the absorption coefficient a(x) is described by the Urbach formula [22,23]: hx aðxÞ ¼ a0 exp ð3Þ DE where a0 is a constant, and DE is an energy which is interpreted as the width of the tail of localized states in the forbidden band gap. The tailing of states at the Urbach band edges is caused by structural disorder. Such tail states give a contribution to the optical absorption at photon energies below the band gab energy, i.e. characteristic absorption behavior in the subgap region [24].
Table 1 Optical energy gaps
Fig. 5 shows the natural logarithm of the optical absorption coefficient versus the incident photon energy. It represents the Urbach plot for composites with different alum concentrations, and the exponential dependence of a(x) on ð hxÞ for these composites suggests that it obeys Urbach’s rule [22]. The calculated values of Eopt and DE are listed in Table 1 which shows that both the optical energy gap and the energy tail DE decreased with increasing alum content. The decrease in the energy gap of these composites can be understood by considering the mobility concept proposed by Davis and Mott [21]. The optical energy gap, in general, represents the energy difference between the localized states in the valence band and extended states in the conduction band. On this basis, the energy sum Eopt þ D E can be taken to represent the mobility gap of the charge carriers existing in the conducting specimens. Table 1 shows that the energy gap decreased with increasing alum concentration. The overall behavior of the optical energy gap and energy tails is consistent with previously reported results for PVA [29] and PEO [30] doped with chlorides. 3.3. Electrical results
Samples AlK3 ðSO4 Þ2 12H2 0 (wt%)
Eopt (eV)
DE (eV)
Eopt þ DE ðeVÞ
0 10 20 30 40
4.14 3.90 3.85 3.79 3.6
0.67 0.29 0.23 0.14 0.28
4.71 4.19 4.08 3.93 3.88
Impedance measurements were conducted on two composites of filled PS with alum concentration 10 and 40 wt% at room temperature and in the frequency range 100 Hz and 13 MHz using a HP4142A impedance analyzer. It was noticed that the phase angle was always negative, indicating that the composites were capacitive and could be represented by parallel RC networks connected in series. Fig. 6 shows the impedance
S.A. Saq’an et al. / Polymer Testing 23 (2004) 739–745
743
Fig. 5. The logarithm of the absorption coefficient with photon energy.
(real component) frequency dependence. Impedance values decrease with increasing frequency and increasing alum concentration. The observed decrease in impedance with alum content is due to protonic migration transporting the oxygen, K, Al elements and impurities existing in the alum filler [9,11]. This motion leads to higher electrical conduction in the filled composites. The dielectric loss e00 , the imaginary part of the complex dielectric constant, was calculated from impedance data as shown elsewhere [9,11,26]. The ACconductivity rAC for an ionic electrolyte material is
Fig. 6.
calculated from the relation rAC ¼ 2pf e0 e00
ð4Þ
where f is the applied field frequency, and e0 is the permittivity of free space. Fig. 7 shows the variation of the dielectric loss e00 with frequency. It decreased with frequency and increased with alum concentration. The dependence of the calculated AC-conductivity on frequency is shown in Fig. 8. It increased when the alum content increased. At high frequency (>105 Hz), the conductivity increased rapidly. This increase in rAC is expected, since at higher applied field frequency more
The variation of the real component of impedance with frequency.
744
S.A. Saq’an et al. / Polymer Testing 23 (2004) 739–745
Fig. 7. The dependence of the dielectric loss on the frequency.
Fig. 8.
The dependence of the AC-conductivity on frequency.
ions and impurities are moved. A correlation between the observed energy gap Eopt and the conductivity rAC can be noticed from Table 1 and Fig. 8. Similar effects of the filler concentration on rAC and energy gap were recently observed by us in PEO/salt complexes [9,28,30].
quency and alum concentration dependence. The observed enhancement in the AC-conductivity is attributed to ionic interactions and impurity motion taking place in the bulk of electrolyte polymer composites.
4. Conclusion
The authors would like to thank the staff of the pharmacy college of Jordan University for technical help. One of us (A. Zihlif) is very grateful to the International Centre for Theoretical Physics (ICTP) in Trieste, Italy for support and co-operation.
The tensile parameters, glass transition temperature, optical energy gap, dielectric constant and AC-electrical conductivity of the prepared composites exhibit fre-
Acknowledgements
S.A. Saq’an et al. / Polymer Testing 23 (2004) 739–745
References [1] G. Lubin, Handbook of Composites, Van Nostrand, London, 1982. [2] Z. Jastrzebski, The Nature and Properties of Engineering Materials, second ed., John Wiley, New York, 1977, (Chapter 10). [3] D. Bigg, W. Mirick, D. Stutz, Polym. Testing 5 (1985) 169. [4] A. Haj-Daoud, A. Zihlif, M. Abdelazeez, J. Mater. Sci. Mater. Lett. 15 (1992) 104. [5] R. Saraswathi, M. Geraro, B. Malhotra, J. Appl. Polym. Sci. 74 (1999) 145. [6] P.V. Wright, Br. Polym. J. 7 (1975) 319. [7] M. Armand, Solid State Ionics 9–10 (1983) 745; M. Armand, Ann. Rev. Mater. Sci. 16 (1986) 254. [8] Y. Tajita, J. Mater. Sci. 31 (1996) 2081. [9] Y. Ramadin, S. Saq’an, A. Zihlif, J. Thermoplast. Comp. Mater. 13 (2000) 497; Y. Ramadin, S. Saq’an, A. Zihlif, J. Thermoplast. Comp. Mater. 13 (2000) 451. [10] B. Scrosati, in: J. MacCallum, C. Vincent (Eds.), Polymer Electrolyte Reviews, Elsevier, New York, 1989. [11] A. Eid, Y. Ramadin, A. Zihlif, Inter. J. Polym. Mater. 47 (2000) 387. [12] V. Di Liello, E. Martuscelli, G. Ragosta, A. Zihlif, J. Mater. Sci. 26 (1992) 2100. [13] Y. Ramadin, A. Zihlif, S. Al-Ani, Optical Mater. 5 (1996) 69. [14] F. Hussain, A. Zihlif, J. Thermoplast. Comp. 6 (1993) 120. [15] V. Di Liello, E. Martuscelli, G. Ragosta, A. Zihlif, J. Polym. Mater. 17 (1992) 93.
745
[16] V. Di Liello, E. Martuscelli, G. Ragosta, A. Zihlif, Inter. J. Mater. Sci. 25 (1990) 706; V. Di Liello, E. Martuscelli, G. Ragosta, A. Zihlif, Inter. J. Mater. Sci. 26 (1991) 2100. [17] M. Abu-Samra, M. Ahmed, A. Zihlif, Polym. Eng. Sci. 24 (1984) 936. [18] A. Cross, R. Howard, Polymer 19 (1972) 677. [19] J. Briscoe, in: K. Friedrich (Ed.), Friction and Wear of Polymer Composites, vol. 1, Elsevier, Amsterdam, 1986. [20] M.L. DI Lorenzo, M. Errico, M. Avella, J. Mater. Sci. 37 (2002) 2351. [21] E. Davis, N. Mott, Phil. Mag. 22 (1970) 903. [22] F. Urbach, Phys. Rev. 92 (1953) 1324. [23] S. Al-Ani, I. Al-Hassany, Z. Al-Dahan, J. Mater. Sci. 30 (1995) 3720; S.K. Al-Ani, A.A. Higozi, J. Mater. Sci. 26 (1991) 3670. [24] S.R. Elliot, The Physics and Chemistry of Solids, Wiley, 1998, pp. 392, (Chapter 5). [25] Y. Ramadin, A. Zihlif, S. Al-Ani, Optical Mater. 59 (1996) 69. [26] M.H. Aballa, Y. Ramadin, A. Zihlif, Appl. Phys. A 60 (1995) 437. [27] M. Ahmed, A. Zihlif, E. Mastuscelli, G. Rogosta, Polym. Composites 13 (1992) 53. [28] S. Saq’an, A. Ayeth, A. Zihlif, Optical and thermal properties of PEO doped with MnCl2 salt, Optical Mater. 24 (4) (2003) 629. [29] M. Khaled, M. El-Ocker, H. Risk, H. Elzahed, J. Mater. Sci. Mater. Electronics 6 (1995) 424. [30] S. Saq’an, A. Zihlif, Inter. J. Polym. Mater. 52 (2003) 387.
Material Properties
Physical properties of polystyrene/alum composites S.A. Saq’an a, A.S. Ayesh b, A.M. Zihlif b, , E. Martuscelli c, G. Ragosta c a
c
Physics Department, Jordan University of Science and Technology, Irbid, Jordan b Department of Physics, University of Jordan, Amman, Jordan Institute of Research and Technology of Plastic Materials, CNR, Via Campi Flegrei, Pozzuoli, Napoli, Italy Received 9 January 2004; accepted 15 April 2004
Abstract The mechanical, thermal, optical and electrical properties of polystyrene/alum composites have been studied as a function of alum content and applied field frequency. The mechanical properties, glass transition temperature, optical energy gap, dielectric constant and AC electrical conductivity of the composites sheets showed frequency and filler content dependence. Analysis and correlation between the collected physical quantities are presented. # 2004 Elsevier Ltd. All rights reserved. Keywords: Mechanical; Optical; Dielectric constant; Energy gap; Conductivity; Glass transition temperature; Alum
1. Introduction Considerable research has been devoted to the modification of the mechanical, thermal and optical properties of polymer composites to meet the requirements of advanced technical and industrial applications [1,2]. Much of this attention is currently focused on obtaining new structural components to be used in electrical conduction, thermal insulation, and electromagnetic shielding applications [3,4]. The nature of the fillers, including their composition, particle dimensions, homogeneity of distribution and adhesion level in a polymeric matrix, is important for the physical properties of the composites. Many research works have demonstrated that the addition of an optimum amount of an electrolytic filler greatly enhances the ionic conductivity and affects the bulk properties of the composites. The interactions of an alkaline ion with a polymer matrix determine its possible application in energy batteries and other solidstate electrochemical devices [5–8]. Interesting effects were observed by us on the optoelectrical properties of PEO/alum and PEO/manganese composites [9,28].
Corresponding author. Fax: +962-65348932. E-mail address: [email protected] (A.M. Zihlif).
Generally, the observed ion conduction in the composite bulk was mainly attributed to ionic interactions and impurity activity taking place during the passage of an electric current into the composite. In this paper, the effects of alum concentration (by weight) and the applied electric field frequency on the physical properties of polystyrene/alum composites such as yield stress, glass transition temperature, dielectric constant, AC conductivity and optical energy gaps are reported. 2. Experimental work 2.1. Materials and composite preparation The polymeric matrix used in the present study was polystyrene (PS) resin of molecular weight 23 700. Polystyrene has good thermal and electrical insulation properties. The alum filler, ordinary commercial potassium sulfate (potassium alum), AlK3(SO4)212H2O, was in the form of glassy transparent crystals and soluble in water. The solid alum was ground into a fine powder of average particle size 18 lm and kept in an v oven overnight at 40 C to reduce the water content. The alum filler is one of a series of crystallized double sulfates containing some impurities. It was added to the PS matrix to make an electrolytic composite, i.e. an
0142-9418/$ - see front matter # 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymertesting.2004.04.008
740
S.A. Saq’an et al. / Polymer Testing 23 (2004) 739–745
ionic polymer composite which would be used in solid batteries or as an ion-exchange electrode [10,11]. The method of composites preparation has been described elsewhere [12]. It involved mixing alum fine powder with PS resin in a Brabender apparatus at v 180 C for 10 min. The compression molded composite sheets obtained were about 1.5 mm thick containing 10, 20, 30, and 40 wt% alum particles randomly distributed. 2.2. Tensile tests Tensile tests were carried out using an Instron machine (TX automated floor model) on dumbbellshaped specimens. The gauge length was 23 mm and width 4 mm. The crosshead speed was 1 mm/min. The v tests were done at 20 C. The Instron machine was connected to a computer programmed to give the required mechanical parameters. 2.3. Differential scanning calorimetry Measurements of the glass transition temperature (Tg) were carried out using a Perkin Elmer DSC, calibrated with the melting transition of indium, at a heatv ing rate of 10 C/min. The midpoint on the DSC thermogram was taken as the glass transition temperature. 2.3.1. The optical absorption spectra Absorption spectra of the prepared PS/alum sheets were measured in the wavelength range k ¼ 250 850 nm (uv–visible) using a spectrophotomer. The absorption coefficient, a(x), was calculated from the absorbance A after correction for reflection losses using the formula aðkÞ ¼ 2:303AX 1
3. Results and discussion 3.1. Mechanical and thermal results Fig. 1 shows the dependence of Young’s modulus and the yield stress on alum content for the composites. The elastic modulus is enhanced and the yield stress decreased with increasing the alum concentration. The modulus enhancement is normally expected in fibre and particulate composites. The observed decrease in the tensile yield stress with increasing the alum concentration is due to weak interfacial adhesion between the alum particles and the PS matrix. This weak adhesion could be attributed to existence of some structural irregularities as cavities and voids [15–17]. Other possible explanation is may be due to brittleness of the alum grains themselves. However, many investigations showed that the effect of solid fillers on the strength of polymers may be positive or negative, depending on such factors as filler shape and size, internal stresses, surface nature, and aspect ratio [18]. The yield strain and the energy to yield shown in Fig. 2 decreased with increasing the filler content. The glass transition temperature (Tg) is an important physical parameter to characterize the structural property of an amorphous polymer in terms of chain rigidity and intermolecular forces. Fig. 3a shows a DSC thermogram of PS/alum composite (10 wt%). The values of the Tg determined from the measured thermographs are shown in Fig. 3b as a function of filler concentration. The results show that there was a small v change in the value of Tg, within 5 C, with increasing alum content up to 20 wt%. The effect of a filler on Tg was observed by Briscoe [19] and Avella and colleagues [20] who observed a slight increase in Tg, and reported that addition of a rigid filler into a polymer matrix is generally responsible for a slight increase in Tg, usually v about 6 C.
ð1Þ
where X is the sample thickness [13,23]. 2.3.2. Impedance measurements Impedance measurements were made with a HP 4194A-impedance analyzer over the frequency range 100 Hz–13 MHz at room temperature. Calibration (short and open) of the impedance analyzer was done before the measurements. Disk shaped specimens were cut from the composite sheets (10, 20, 30, 40 wt% alum) and placed between the copper plates (10 mm diameter) of a test sample holder placed in a shielded cell designed for this purpose. The two leads of the holder were connected to the terminals of the impedance analyzer [11–14].
Fig. 1. Young’s modulus and yield stress versus alum concentration (wt%).
S.A. Saq’an et al. / Polymer Testing 23 (2004) 739–745
741
3.2. Optical results The absorption edge of non-crystalline materials gives a measure of the band strength or energy band gap. The absorption coefficient a for these materials has the following frequency x dependence [21,22]: aðxÞ hx ¼ bð hx Eopt Þr
Fig. 2. Yield strain and energy to yield versus alum concentration.
Fig. 3.
ð2Þ
where h is Plank’s constant, b is a constant, and r is an exponent which can take values of 1, 2, 3, 12 or 32 depending on the nature of the electronic transitions (direct or non-direct) responsible for optical absorption [23,24]. The application of Eq. (2) was demonstrated in our previous papers [13,25–28]. Fig. 4 represents the spectra of the optical absorbance A for samples of neat
(a) DSC thermographs for alum composite (10 wt%). (b) The glass transition temperature versus alum composition.
742
S.A. Saq’an et al. / Polymer Testing 23 (2004) 739–745
Fig. 4.
The variation of the absorption coefficient (a) with the wavelength.
PS, 10, 20, 30 and 40 wt% alum-filled composites. The optical energy gaps, listed in Table 1, were determined from graphs representing the product of the optical absorption coefficient and the photon energy ða hxÞ2 versus photon energy ð hxÞ. The values of Eopt were obtained by extrapolating the straight lines to intercept the photon energy coordinate ð hxÞ. At low absorption levels, the absorption coefficient a(x) is described by the Urbach formula [22,23]: hx aðxÞ ¼ a0 exp ð3Þ DE where a0 is a constant, and DE is an energy which is interpreted as the width of the tail of localized states in the forbidden band gap. The tailing of states at the Urbach band edges is caused by structural disorder. Such tail states give a contribution to the optical absorption at photon energies below the band gab energy, i.e. characteristic absorption behavior in the subgap region [24].
Table 1 Optical energy gaps
Fig. 5 shows the natural logarithm of the optical absorption coefficient versus the incident photon energy. It represents the Urbach plot for composites with different alum concentrations, and the exponential dependence of a(x) on ð hxÞ for these composites suggests that it obeys Urbach’s rule [22]. The calculated values of Eopt and DE are listed in Table 1 which shows that both the optical energy gap and the energy tail DE decreased with increasing alum content. The decrease in the energy gap of these composites can be understood by considering the mobility concept proposed by Davis and Mott [21]. The optical energy gap, in general, represents the energy difference between the localized states in the valence band and extended states in the conduction band. On this basis, the energy sum Eopt þ D E can be taken to represent the mobility gap of the charge carriers existing in the conducting specimens. Table 1 shows that the energy gap decreased with increasing alum concentration. The overall behavior of the optical energy gap and energy tails is consistent with previously reported results for PVA [29] and PEO [30] doped with chlorides. 3.3. Electrical results
Samples AlK3 ðSO4 Þ2 12H2 0 (wt%)
Eopt (eV)
DE (eV)
Eopt þ DE ðeVÞ
0 10 20 30 40
4.14 3.90 3.85 3.79 3.6
0.67 0.29 0.23 0.14 0.28
4.71 4.19 4.08 3.93 3.88
Impedance measurements were conducted on two composites of filled PS with alum concentration 10 and 40 wt% at room temperature and in the frequency range 100 Hz and 13 MHz using a HP4142A impedance analyzer. It was noticed that the phase angle was always negative, indicating that the composites were capacitive and could be represented by parallel RC networks connected in series. Fig. 6 shows the impedance
S.A. Saq’an et al. / Polymer Testing 23 (2004) 739–745
743
Fig. 5. The logarithm of the absorption coefficient with photon energy.
(real component) frequency dependence. Impedance values decrease with increasing frequency and increasing alum concentration. The observed decrease in impedance with alum content is due to protonic migration transporting the oxygen, K, Al elements and impurities existing in the alum filler [9,11]. This motion leads to higher electrical conduction in the filled composites. The dielectric loss e00 , the imaginary part of the complex dielectric constant, was calculated from impedance data as shown elsewhere [9,11,26]. The ACconductivity rAC for an ionic electrolyte material is
Fig. 6.
calculated from the relation rAC ¼ 2pf e0 e00
ð4Þ
where f is the applied field frequency, and e0 is the permittivity of free space. Fig. 7 shows the variation of the dielectric loss e00 with frequency. It decreased with frequency and increased with alum concentration. The dependence of the calculated AC-conductivity on frequency is shown in Fig. 8. It increased when the alum content increased. At high frequency (>105 Hz), the conductivity increased rapidly. This increase in rAC is expected, since at higher applied field frequency more
The variation of the real component of impedance with frequency.
744
S.A. Saq’an et al. / Polymer Testing 23 (2004) 739–745
Fig. 7. The dependence of the dielectric loss on the frequency.
Fig. 8.
The dependence of the AC-conductivity on frequency.
ions and impurities are moved. A correlation between the observed energy gap Eopt and the conductivity rAC can be noticed from Table 1 and Fig. 8. Similar effects of the filler concentration on rAC and energy gap were recently observed by us in PEO/salt complexes [9,28,30].
quency and alum concentration dependence. The observed enhancement in the AC-conductivity is attributed to ionic interactions and impurity motion taking place in the bulk of electrolyte polymer composites.
4. Conclusion
The authors would like to thank the staff of the pharmacy college of Jordan University for technical help. One of us (A. Zihlif) is very grateful to the International Centre for Theoretical Physics (ICTP) in Trieste, Italy for support and co-operation.
The tensile parameters, glass transition temperature, optical energy gap, dielectric constant and AC-electrical conductivity of the prepared composites exhibit fre-
Acknowledgements
S.A. Saq’an et al. / Polymer Testing 23 (2004) 739–745
References [1] G. Lubin, Handbook of Composites, Van Nostrand, London, 1982. [2] Z. Jastrzebski, The Nature and Properties of Engineering Materials, second ed., John Wiley, New York, 1977, (Chapter 10). [3] D. Bigg, W. Mirick, D. Stutz, Polym. Testing 5 (1985) 169. [4] A. Haj-Daoud, A. Zihlif, M. Abdelazeez, J. Mater. Sci. Mater. Lett. 15 (1992) 104. [5] R. Saraswathi, M. Geraro, B. Malhotra, J. Appl. Polym. Sci. 74 (1999) 145. [6] P.V. Wright, Br. Polym. J. 7 (1975) 319. [7] M. Armand, Solid State Ionics 9–10 (1983) 745; M. Armand, Ann. Rev. Mater. Sci. 16 (1986) 254. [8] Y. Tajita, J. Mater. Sci. 31 (1996) 2081. [9] Y. Ramadin, S. Saq’an, A. Zihlif, J. Thermoplast. Comp. Mater. 13 (2000) 497; Y. Ramadin, S. Saq’an, A. Zihlif, J. Thermoplast. Comp. Mater. 13 (2000) 451. [10] B. Scrosati, in: J. MacCallum, C. Vincent (Eds.), Polymer Electrolyte Reviews, Elsevier, New York, 1989. [11] A. Eid, Y. Ramadin, A. Zihlif, Inter. J. Polym. Mater. 47 (2000) 387. [12] V. Di Liello, E. Martuscelli, G. Ragosta, A. Zihlif, J. Mater. Sci. 26 (1992) 2100. [13] Y. Ramadin, A. Zihlif, S. Al-Ani, Optical Mater. 5 (1996) 69. [14] F. Hussain, A. Zihlif, J. Thermoplast. Comp. 6 (1993) 120. [15] V. Di Liello, E. Martuscelli, G. Ragosta, A. Zihlif, J. Polym. Mater. 17 (1992) 93.
745
[16] V. Di Liello, E. Martuscelli, G. Ragosta, A. Zihlif, Inter. J. Mater. Sci. 25 (1990) 706; V. Di Liello, E. Martuscelli, G. Ragosta, A. Zihlif, Inter. J. Mater. Sci. 26 (1991) 2100. [17] M. Abu-Samra, M. Ahmed, A. Zihlif, Polym. Eng. Sci. 24 (1984) 936. [18] A. Cross, R. Howard, Polymer 19 (1972) 677. [19] J. Briscoe, in: K. Friedrich (Ed.), Friction and Wear of Polymer Composites, vol. 1, Elsevier, Amsterdam, 1986. [20] M.L. DI Lorenzo, M. Errico, M. Avella, J. Mater. Sci. 37 (2002) 2351. [21] E. Davis, N. Mott, Phil. Mag. 22 (1970) 903. [22] F. Urbach, Phys. Rev. 92 (1953) 1324. [23] S. Al-Ani, I. Al-Hassany, Z. Al-Dahan, J. Mater. Sci. 30 (1995) 3720; S.K. Al-Ani, A.A. Higozi, J. Mater. Sci. 26 (1991) 3670. [24] S.R. Elliot, The Physics and Chemistry of Solids, Wiley, 1998, pp. 392, (Chapter 5). [25] Y. Ramadin, A. Zihlif, S. Al-Ani, Optical Mater. 59 (1996) 69. [26] M.H. Aballa, Y. Ramadin, A. Zihlif, Appl. Phys. A 60 (1995) 437. [27] M. Ahmed, A. Zihlif, E. Mastuscelli, G. Rogosta, Polym. Composites 13 (1992) 53. [28] S. Saq’an, A. Ayeth, A. Zihlif, Optical and thermal properties of PEO doped with MnCl2 salt, Optical Mater. 24 (4) (2003) 629. [29] M. Khaled, M. El-Ocker, H. Risk, H. Elzahed, J. Mater. Sci. Mater. Electronics 6 (1995) 424. [30] S. Saq’an, A. Zihlif, Inter. J. Polym. Mater. 52 (2003) 387.