LPTE #763380, VOL 52, ISS 9
In Situ Polymerization and Characterization of Aniline and O-Anthranilic Acid Copolymer / Pyrogenic Silica Nanocomposites A. S. Al-Hussaini, M. Sh. Zoromba, and N. A. El-Ghamaz QUERY SHEET This page lists questions we have about your paper. The numbers displayed at left can be found in the text of the paper for reference. In addition, please review your paper as a whole for correctness. Q1: Au: In CAF2, is the city=region of the university correctly written as Mansoura? Q2: Au: The sizes of Figures 6, 7, 8, and 9 are so small that they cannot be read. Please send new figures 6-9 in a larger format that can be more easily read. Q3: Au: In reference 7, what is the title of hte article?.
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Polymer-Plastics Technology and Engineering, 52: 1–8, 2013 Copyright # Taylor & Francis Group, LLC ISSN: 0360-2559 print=1525-6111 online DOI: 10.1080/03602559.2013.763380
In Situ Polymerization and Characterization of Aniline and O-Anthranilic Acid Copolymer / Pyrogenic Silica Nanocomposites A. S. Al-Hussaini1, M. Sh. Zoromba1, and N. A. El-Ghamaz2 1
Department of Chemistry, Faculty of Science, Port-Said University, Port-Said, Egypt Department of Physics, Faculty of Science, Damietta Branch, Mansoura University, Q1 Mansoura, Egypt 5
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as an insoluble powder[19]. In an attempt to improve the polymer solubility, co-polymerization of aniline with aniline derivatives was proposed[20,21]. The co-polymerization of aniline with o-anthranilic acid (AA) is an example that depends on the relative reactivity of aniline and AA. Aniline is 7000 times more reactive than AA. The presence of the carboxyl group sterically increases the inter-chain distance, weakening the interchain hydrogen bonds, could interact with the solvents and thus increases the solubility[22]. Therefore, the electrochemical polymerization rate of polyanthranilic acid (PAA) was slower than that of PANI; hence, the rate of aniline=AA co-polymerization is increased with increasing the aniline content[23]. The chemical co-polymerization of aniline with o-anthranilic acid (AA) to form copolymer films has been made in aqueous hydrochloric acid medium and the effect of AA concentration in the film formation was investigated[24]. The literature dealing with the synthesis of PANI by different methods like solution, emulsion, miniemulsion, micro-emulsion, inverse miniemulsion, and electrochemical[25,26] and conduction mechanism[27,28] is very well studied. But the literature dealing with aniline o-anthranilic acid copolymer is relatively less. The coating of PANI on fillers like clay, silica, silicates, carbon black, poly(methyl methacrylate), etc. can produce conductive filler[29,30]. But the literature dealing with the coating of poly(aniline and o-anthranilic acid) on silica fillers at different percentages of silica nanoparticles, their electric and thermal properties was not studied. The PANI = nano-silica nanocomposite was synthesized by an in situ chemical oxidative polymerization of aniline in presence of nano-silica (Aerosil 200, amorphous fumed silica, average size of 12 nm). The morphology of nanocomposite showed better dispersion of nano-silica particles in the PANI matrix[31]. The present article deals with the in situ oxidative chemical polymerization of aniline and o-anthranilic acid which
Copolymers of aniline and o-anthranilic acid / amorphous fumed silica nanocomposite are synthesized by 5:1 molar ratios of the respective monomers with different percentages of silica nanoparticles via in situ chemical co-polymerization. The electrical conductivity and spectral characteristics upon incorporation of o-anthranilic acid units into the polyaniline backbone in presence of silica nanoparticles are investigated. The results are justified by measuring the UV-Vis absorption spectra, FT-IR for PANAA copolymer, and in situ PANAA/silica nanocomposite. Also, the thermal gravimetric analysis for the copolymer powder formed in the bulk in absence and in presence of silica nanoparticles are carried out. Keywords Aniline and o-anthranilic acid copolymer; Dielectric constant; In situ polymerization; Nano-silica; Nanocomposite; Semi-conductive polymer nanocomposites
INTRODUCTION The research on the preparation of conductive polymer composites with inorganic materials such as metal oxides[1,2], layered silicates[3–5] or other polymers that are in the form film[6], fiber[7], and fabric[8] has been enlarged. These efforts are aimed to improve the use of conductive composites in various technological fields. For example, nanocomposites[9,10] having high electrical conductivity, thermal stability, mechanical properties and flame retardance were prepared by conductive polymers inorganic composites. It was reported that conductive nanocomposites could be used as biosensors, super capacitors, light emitting diodes, catalysts and rechargeable batteries[11,12]. Polyaniline (PANI) can be used as an electrode material[13,14], in microelectronics[15,16], as an electrochromic device[17], in radiation shielding and in recordable optical discs[18]. On the contrary, the commercial usefulness of PANI has been limited by its intractable nature especially in the doped form, which is normally produced chemically Address correspondence to A. S. Al-Hussaini, Department of Chemistry, Faculty of Science, Port-Said University, Port-Said 42526, Egypt. E-mail:
[email protected]
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was performed in absence and in presence of different percentages of nano-silica. Morphology and thermal property of the synthesized nanocomposite were examined by scanning electron microscope (SEM), as well as, thermogravimetric analysis (TGA). A comparison of electrical 85 properties of the synthesized PANAA, and PANAA=silica nanocomposite was investigated.
Characterization FT-IR Spectra The IR spectra of different powder were recorded using 130 FT-IR Spectrometer, Spectrum RX 1, USA. The samples were prepared in the pellet form by mixing the Powder with KBr by the ratio 1:10 and pressing it in the Perkin Elmer hydraulic device using 15 tons pressure.
EXPERIMENTAL Materials All reagents were used without any further purification: 90 Aniline and anthranilic acid were purchased from Aldrich, potassium dichromate (Merck), ammonia solution and hydrochloric acid (ADWIC), Pyrogenic or fumed silica (Aerosil R972, Degussa: specific surface area (BET ¼ 110 20 m2=g, tapped density ¼ approx. 50 g = lit, Loss on drying 95 300 C, under this experimental concentration and conditions. When the temperature was increased to 700 C, both of the two samples were not fully degraded and still residual remnant, where the PANAA = nano-silica composite (1f) possessed 33% residual. Therefore, the mass content of nano-silica in the nanocomposite can be confirmed. This result is in accordance with that of the mass of used nanosilica during the synthesis (7%). It may be caused by the nano-silica, which was completely embedded in the PANAA matrix.
Figures 4a and 4b for pure PANAA at 1000x and Figures 4c and 4d for PANAA=SiO2 nanocomposite 1500x, 250 it is observed that the silica particles are nano-sized with nearly spherical shapes. Aggregation of silica nanoparticles occurred, which is a typical problem for nanosized particles. Well dispersion of nano-silica in the whole system was not completely confirmed, similar results have been reported[31]. 255 From nano-silica particles were seen in composite micrographs given at 1000x and 1500x in Figures 4b and 4d, it may be said that aniline and anthranilic acid polymerization was achieved on the surface of silica particles or PANAA formed in the polymerization medium com- 260 pletely absorbed on the silica surface particles. AC Conductivity and Dielectric Properties of PANAA The AC conductivity is related to the dielectric constant (e ¼ er þ iei) according to the relation[44]: rac ¼ xeo ei
ð1Þ
Morphology Analysis The scanning electron microscope micrographs of PANAA and PANAA=SiO2 nanocomposits at different magnifications are shown in Figures 4a-d. In both
FIG. 4. SEM micrographic of: (a) pure PANAA at 1000x (1), (b) PANAA = nano-silica containing 7% nano-silica at1000x (1f), (c) pure PANAA at 1500x, and (d) PANAA = nano-silica containing 7% nano-silica at1500x.
FIG. 5. (a) Plot of lnrac versus 1=T for the PANAA and (b) frequency dependence of DEac for PANAA.
PYROGENIC SILICA NANOCOMPOSITES
where ei is the imaginary part of the dielectric constant, eo is the permittivity of free space and x is the angular frequency. The real part of the dielectric constant, er, can be calculated by the relation. er ¼
Cp d eo A
ð2Þ
where Cp is the capacitance of the sample measured in parallel mode. The imaginary part of the dielectric constant, ei, can be calculated by the relation ei ¼ er tan d
ð3Þ
where d ¼ 90- u and u is the phase angle. The temperature dependence of the ac conductivity rac for PANAA at the temperature range 303–523 K is shown in Figure 5a. The rac values for PANAA are in the semiconductor range. The values of rac increase with increasing 280 frequency in general while all curves corresponding to different frequencies showed different temperature dependence behaviours depending on the temperature range.
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On the other hand, at low frequency, rac is sensitive to temperature, while it becomes less sensitive to temperature upon increasing the frequency. 285 In the temperature region 365–450 K (region II), the conductivity decreases with increasing temperature giving negative activation energy. This behaviour was reported by El-Ghamaz et al.[45] and Yakuphanoglu et al.[44], which may be explained as a response to increase of the dielectric 290 constant at this temperature region and this can be attributed to the dehydration of the sample during the heating process[45]. At regions I and III, the rac increases with increasing temperature and thus the electrical activation energy of this sample is positive. This behaviour can be 295 explained by the Arrhenius equation, which is expressed as
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FIG. 6. Temperature dependence of the dielectric constant for PANAA: (a) the real part, er, and (b) the imaginary part, ei.
rac ¼ ro expðDEac =kT Þ
ð5Þ
where ro is the pre-exponential factor, DEac is the thermal activation energy for ac electrical conductivity, and k is the Boltzmann constant. The values of DEac were calculated 300 from the slopes at regions I and III. The values of DEac were
FIG. 7. Plot of lnrac versus 1=T for the PANAA=silica nanocomposite: (a) at test frequency 103 Hz and (b) at test frequency 105 Hz.
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found to decrease with increasing frequency. The frequency dependence of the calculated DEac for PANAA corresponding to the regions I and III are presented in Figure 5b. The real and imaginary parts of the permittivity, er and ei 305 for PANAA as a function of temperature and at different frequencies are shown in Figures 6a and 6b, respectively. Both of er and ei were characterized by a maximum value at temperature around 370 K, which is independent of the test fre310 quencies. This confirms the dehydration during the heating process. The values of both er and ei decrease with increasing test frequency and become less sensitive to the changes of temperature in the considered range of temperature. AC Conductivity and Dielectric Properties of PANAA= Silica Nanocomposite The effect of introducing nano-silica (Aerosil R972, amorphous fumed silica, average size of 20–40 nm) to the PANAA on rac, in the temperature range 303–523 K is shown in Figures 7a and 7b for test frequencies, 103 and 5 320 10 Hz, respectively. Generally, the values of rac increased 315
FIG. 9. Temperature dependence of ei for PANAA=silica nanocomposites: (a) at test frequency 103 Hz and (b) at test frequency 105 Hz.
with increasing of nano-silica percentage until 4%. At 4%, the rac increased by about three orders of magnitude. However, the greater increase of nano-silica percentage, the greater the decease of rac. This behaviour can be attributed to the aggregation of silica nano particles which has 325 already been detected by the morphology measurements. This result is in agreement with results reported by Bhadra et al.[38]. The effect of doping of PANAA with silica nano particles on er and ei is presented in Figures 8a and 8b and 9a and 9b. The values of both er and ei measured at 105 Hz 330 were nearly independent of temperature for all samples except for 4% nano-silica sample in which the values of both er and ei increase with increasing temperature. FIG. 8. Temperature and dopant concentration dependence of er for PANAA=silica nanocomposites: (a) at test frequency 103 Hz and (b) at test frequency 105 Hz.
CONCLUSION In this work, PANAA = nano-silica nanocomposites were successfully prepared by in situ chemical oxidative
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polymerization technique of aniline and o-anthranilic acid in the presence of fumed nano-silica particles. The PANAA=nano-silica nanocomposites were characterized 340 by FT-IR, UV-Vis absorption spectra. As a result, the UV spectrum of PANAA showed significant difference over that of PANAA=nano-silica nanocomposite. The morphology of PANAA=nano-silica nanocomposite was observed by SEM images which showed better 345 dispersion of nano-silica particles in the PANAA matrix. Also, Mass percentage of the nano-silica in the nanocomposite was confirmed to be about 7% by TGA data. Furthermore, the values of both the real and the imaginary parts of the dielectric constant as a function of temperature 350 were also investigated. In our system, the conductivity increases with increasing silica nonoparticle percentages. At low frequencies, rac is sensitive to temperature, while it becomes less sensitive to temperature upon increasing the frequency. 355
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