SPECTROSCOPIC STUDY ON POLY(ACRYLIC ACID-CO-ACRYLAMIDE)-GRAFT–POLYANILINE AS A RADIATION DOSIMETER FOR ALPHA PARTICLES

SPECTROSCOPIC STUDY ON POLY(ACRYLIC ACID-CO-ACRYLAMIDE)-GRAFT–POLYANILINE AS A RADIATION... Abstract Poly(acrylate-co-acrylamide) was a synthesis by chemical oxidation polymerization of an aqueous binary mixture of acrylate/acrylamide (1:1 mole ratio) using ammonium persulphate as an initiator at 70°C under the nitrogen atmosphere. The obtained copolymer was introduced for grafting with polyaniline. The grafting process was performed by chemical oxidation polymerization of aniline using ammonium persulphate as an initiator in hydrochloric acid media at 40°C under the nitrogen atmosphere. Poly(acrylic acid-co-acrylamide)-graft–polyaniline samples irradiated with (alpha-particles) at different irradiation doses (0, 2.33, 8.73, 13.09 and 17.46 Gy) at the same linear energy transfer. The change in the morphology, optical properties and the energy gap of poly(acrylic acid-co-acrylamide)-graft–polyaniline samples were studied. INTRODUCTION When an ionizing radiations pass through a polymeric material, ionization and excitation process take place for molecules of the material(1). These leads to breaking of original bonds, chain scission, radical formation and cross-linking in the polymeric material(2, 3). Scission and cross-linking not only depend upon the polymer structure, but also upon the energy deposited per unit track length (linear energy transfer (LET))(4–6). This lead in modifying the structure and optical properties of polymers(7, 8). A radiation dosimeter is a system that either directly or indirectly determines the absorbed dose of ionizing radiation. Radiation dosimeters are important for many applications including environmental safety and remediation, medical imaging, industrial process monitoring, national security, military surveillance and even basic science(9). The electrical conductivity of polyaniline nano-films before and after irradiation (using alpha, beta and gamma radiation sources) was measured and evaluated(10). The changes of optical and electrical properties of aniline hydrochloride/polyvinyl alcohol films (AN/PVA) influenced by gamma radiation for gamma dosimetry application from 0 to 10 kGy were reported(11). The effect of alpha particle fluences on the morphology and optical properties of polyaniline in nano-scale was studied(12). The effect of gamma rays irradiated polyaniline blends with chlorine-containing polymers, copolymers and HCl-releasing compounds was studied(13). In addition, the ionizing radiations may also produce a random fracture of main chain and breaking of the original bonds, giving rise to the formation of free radicals, double/triple bonds, cross-linking(14), carbon cluster formation(15) and evolution of ionic species and gaseous components. Leucoemeraldine and polyemeraldine base (the non-conducting form of polyaniline) can be used as a detecting device for low-dose ionization radiation, but polyemeraldine salts (the conducting form) are possible for high dose detectors(16). Irradiation of polymers by high and low LET radiation is widely used in improving the physical and chemical properties of the polymeric material for high technology applications(17). In this work, we aimed to expose poly(acrylic acid-co-acrylamide)-graft–polyaniline samples to different doses of alpha-particles of the same of LET. To investigate their capability in alpha-particles dosimeter by studying the optical behavior and morphological structure of the graft samples after irradiation. EXPERIMENTAL Synthesis of poly(acrylate-co-acrylamide) For 25 ml solution of a binary mixture of acrylic acid (2.040 g) and acrylamide (2.015 g), sodium hydroxide solution (0.100 mol L−1) was added with stirring until the solution becomes slightly alkaline (pH = 7.2). The above binary mixture was thermostat at 70°C and then ammonium persulfate (APS) (0.052 g) was added as initiator. The copolymerization was performed under the nitrogen atmosphere at 70°C for 3 h. The formed copolymer was precipitated by the addition of methanol as non-solvent. The copolymer was washed with methanol and dried under vacuum at 70°C for constant weight. Preparation of poly(acrylic acid-co-acrylamide)-graft–polyaniline A mixture of the copolymer solution (15 ml = 1.2 g), aniline (2 ml, density = 1.2 g/cm3) and hydrochloric acid (2.5 ml, 33.3%) are thermostat at 40°C for 15 min, then 5.7 g APS is added. The grafting reaction is achieved at 40°C under N2 atmosphere for 2 h (grafting % = 72.5). The resulting graft was washed with distilled water several times, methanol and N-methylpyrrolidone for removing polyaniline homopolymer then dried under vacuum at 70°C. Irradiation techniques Poly(acrylic acid-co-acrylamide)-graft–polyaniline pellets (1.20 × 1.20 cm2 × 0.980 mm) pressed at 20 bars are irradiated in the air in contact with 241Am-source (at Nuclear and Radiation Research Lab, Beni-Suef University, Egypt). The energy of alpha particles emitted from 241Am-source was 5.486 MeV. The LET (electronic-LET + nuclear-LET) corresponding to the alpha particle energy was calculated(18). The calculated LET for the present irradiation graft was 12.18 eV/Å. The incident fluences were calculated(7) according to the irradiation times 0, 15, 60, 90 and 120 min, respectively. Accordingly, the irradiation doses can be calculated by the following equation(1):   Dose(Gy)=1.6×10−10(LET(MeV/cm)×Fluence(/cm2))/ρ(gm/cm3) (1) The calculated irradiation doses are (0, 2.33, 8.73, 13.09 and 17.46 Gy) for the same value of LET. Ultraviolet–visible spectroscopy Spectrophotometric analysis of the investigated polymeric samples before and after irradiation was carried out using Shimadzu visible spectrophotometer Double beam 2600, Japan. Scanning electron microscope and X-ray diffraction The Scanning electron microscope analysis was carried out using JSM-6510LA Scanning electron microscope (JEOL, Japan). The X-ray diffraction (XRD) patterns of the prepared samples were characterized with the help of Pananlytical Empryan X-ray diffractometer 202 964 (the Netherlands). The scan range was 5°–1400. RESULTS AND DISCUSSIONS Optical characteristics Poly(acrylic acid-co-acrylamide)-graft–polyaniline pellets were irradiated at different alpha particle doses (0, 2.33, 8.73, 13.09 and 17.46 Gy). The UV–Visible spectra of the samples before and after irradiation with alpha particles are graphically represented in Figure 1. The absorption peak at 275 nm is attributed to the π–π* transition of the benzenoid segment and the absorption peaks at 536 nm are attributed to the polaron and the bipolaron transition in polyaniline(19). This confirms the grafting of polyaniline onto poly(acrylic acid-co-acrylamide). From Figure 1, the irradiated polymeric pellet shift in the peaks toward the higher wavelength side (red shift) as well as an increase in the intensity of the peak at 563 nm suggests an increasing in the probability of re-interact between the graft chain, decrease in the energy band gap in the case of poly(acrylic acid-co-polyacrylamide)-graft–polyaniline and increase in the number of charge carriers. This shift can be due to the interaction between poly(acrylic acid-co-polyacrylamide)-graft–polyaniline chains. The broadening of absorption peaks increases with the increasing of irradiation dose which can be assigned to a generation of defects such as radicals, organic species or centers induced by radiation, resulting in the formation of new levels of energy(20). The dose respond (the difference between intensity of irradiated sample and virgin sample at each dose) of irradiated graft samples at different doses at 429 nm is shown in Figure 2 which show a linear increasing in (∆A) with an increasing the dose. Figure 1. View largeDownload slide UV–Vis spectra of poly(acrylic acid-co-acrylamide) before and after irradiation at different doses. Figure 1. View largeDownload slide UV–Vis spectra of poly(acrylic acid-co-acrylamide) before and after irradiation at different doses. Figure 2. View largeDownload slide Dose responds of poly(acrylic acid-co-acrylamide)-graft–polyaniline samples before and after irradiation at 429 nm at different irradiation dose. Figure 2. View largeDownload slide Dose responds of poly(acrylic acid-co-acrylamide)-graft–polyaniline samples before and after irradiation at 429 nm at different irradiation dose. Energy band gap The optical band gap energy (Eg) of poly(acrylic acid-co-acrylamide)-grafted polyaniline samples were calculated from Tauc’s plot(21, 22) is given by the equation:   α(v)=β(hv−Eg)nhv (2)where, α is the absorption coefficient, hv is the photon energy, B is the band gap tailing parameter, Eg is a characteristic energy which is termed as optical band gap and n is the transition probability index, which has discrete values n = 1/2, 3/2, 2 and 3 for direct allowed, direct forbidden, indirect allowed and indirect forbidden electronic transitions, respectively. The direct and indirect energy band gaps were estimated by the plot between (αhν)2 and (αhν)1/2 as a function of the photon energy (hν) and are shown in Figures 3 and 4, respectively. This behavior showed that the direct allowed transition (n = 1/2) was the most probable involved transition mechanism. The values of the direct and indirect energy gaps for virgin as well as irradiated samples are presented in Table 1. The value of (Eg) is slightly decreasing with the irradiation doses. The variations in (Eg) suggest the formation of defects (radicals and organic species) after alpha particles irradiations and/or the formation of carbon enriches clusters(23). This may be attributed to the formation of a conjugated system of bonds due to bond cleavage by radiation. Table 1. Direct and indirect optical band gaps energy of virgin and irradiated poly(acrylic acid-co-acrylamide) graft polyaniline samples. Irradiation dose (Gy)  Indirect band energy (eV)  Direct band energy (eV)  0  1.849  2.045  2.33  1.862  2.051  8.73  1.781  2.029  13.09  1.756  2.025  17.46  1.739  2.012  Irradiation dose (Gy)  Indirect band energy (eV)  Direct band energy (eV)  0  1.849  2.045  2.33  1.862  2.051  8.73  1.781  2.029  13.09  1.756  2.025  17.46  1.739  2.012  Figure 3. View largeDownload slide Tauc’s plot corresponding to direct band gap of poly(acrylic acid-co-acrylamide)-graft–polyaniline samples before and after irradiation at different doses. Figure 3. View largeDownload slide Tauc’s plot corresponding to direct band gap of poly(acrylic acid-co-acrylamide)-graft–polyaniline samples before and after irradiation at different doses. Figure 4. View largeDownload slide Tauc’s plot corresponding to indirect band gap of poly(acrylic acid-co-acrylamide)-graft–polyaniline samples before and after irradiation at different doses. Figure 4. View largeDownload slide Tauc’s plot corresponding to indirect band gap of poly(acrylic acid-co-acrylamide)-graft–polyaniline samples before and after irradiation at different doses. Carbon cluster The carbonaceous cluster is one of the important parameters that enhance the optical properties of the polymeric material. This is due to that the carbonaceous clusters are rich with charge carrier, which enhances the surface conductivity of the polymers. The number of carbon atoms per cluster can be calculated by the following equation(23):   Eg=34.3/(N)0.5 (3) The number of carbon atoms per cluster (N) for virgin and irradiated graft samples for indirect and direct band gap varies from ~339.335 to 389.035 and 279.677 to 290.624, respectively, as shown in Table 2. The maximum value for cluster size was found in irradiation dose 17.46 Gy whereas the minimum value of the band gap energy was found at dose 2.33 Gy. Carbon enriched domains created in irradiated polyaniline samples may be responsible for the decreasing in the band gap. Table 2. The variation of number of carbon atoms per cluster (N) of samples before and after irradiation. Irradiation dose (Gy)  The number of carbon atoms per cluster (N)  Indirect  Direct  0  344.123  281.330  2.33  339.335  279.677  8.73  370.903  285.774  13.09  381.539  286.905  17.46  389.035  290.624  Irradiation dose (Gy)  The number of carbon atoms per cluster (N)  Indirect  Direct  0  344.123  281.330  2.33  339.335  279.677  8.73  370.903  285.774  13.09  381.539  286.905  17.46  389.035  290.624  Effect of irradiation doses on the morphological microstructure of poly(acrylic acid-co-acrylamide)-graft–polyaniline samples (SEM) The morphological microstructure of the unirradiated and irradiated poly(acrylic acid-co-acrylamide)-graft–polyaniline samples at different irradiation dose (0, 2.33, 8.73, 13.09 and 17.46 Gy) are characterized by SEM images which are shown in Figure 5 (A, B, C, D and E), respectively. Figure (5A) represented the sample before irradiation showed some microspores particles aggregation. Figure 5B represented poly(acrylic acid-co-acrylamide)-graft–polyaniline irradiated at 2.33 Gy showed increasing in the particles aggregation and enhancement particles structure. At irradiation dose 8.73 Gy, poly(acrylic acid-co-acrylamide)-graft–polyaniline is depicted in (Figure 5C) indicate that the clusters are large and clear, but its surface is not smooth and contains macro-granular structure with a diameter in the range of a few microns. At irradiation dose 13.09 Gy (Figure 5D) indicates that an enhancement in the crystallinity of the graft and the shape of the particles become in the sheet form with a diameter in the range (400 nm). Further irradiation at 17.46 Gy indicated that an increasing the crystallinity of the graft and the crystalline region becomes predominates and the crystal size decreasing to (300 nm) as shown in Figure 5E. This indicated that the crystallinity is increasing and the crystal size decreasing with increasing the irradiation doses. Figure 5. View largeDownload slide SEM images (A–E) of poly(acrylic acid-co-acrylamide)-graft–polyaniline samples before and after irradiation at different doses (0, 2.33, 8.73,13.09 and 17.46 Gy), respectively. Figure 5. View largeDownload slide SEM images (A–E) of poly(acrylic acid-co-acrylamide)-graft–polyaniline samples before and after irradiation at different doses (0, 2.33, 8.73,13.09 and 17.46 Gy), respectively. X-ray diffraction patterns The XRD of the unirradiated and irradiated samples of poly(acrylic acid-co-acrylamide)-graft–polyaniline with different irradiation doses (0, 2.33, 8.73, 13.09 and 17.46 Gy) are given in Figure 6. The graft sample before irradiation has semi-crystalline structure. It is clear also from this figure that, the intensity after irradiation increasing for all prominent peaks with increasing the irradiation dose. The increasing in the intensity indicated that the enhancement in the degree of crystallinity. This may be due to cross-linking of the polymer chain or by the formation of single or multiple helices, which induces more crystalline region in the graft samples. The degree of crystallinity was calculated by separating intensities due to the amorphous and crystalline phase of the diffraction pattern. Percentage of crystallinity (Xc, %) is measured as the ratio of the crystalline area to total area(24).   Xc(%)=[AcAa+Ac]×100%where, Ac = area of the crystalline phase and Aa = area of the amorphous phase. The degree of crystallinity of (0, 2.33, 8.73, 13.09 and 17.46 Gy) is (60.78, 64.33, 70.65, 73.75 and 79.24%), the degree of crystallinity of poly(acrylic acid-co-acrylamide)-graft–polyaniline increasing with increasing the dose as shown in Figure 7. The crystallite size of the particles before and after irradiation is shown in Table 3. The crystallite size decreasing with increasing the dose this agrees with the previous discussion in SEM part. Table 3. The variation of crystallite size of samples before and after irradiation. Irradiation dose (Gy)  The crystallite size (μm)  0  1.092  2.33  0.874  8.73  0.624  13.09  0.454  17.46  0.324  Irradiation dose (Gy)  The crystallite size (μm)  0  1.092  2.33  0.874  8.73  0.624  13.09  0.454  17.46  0.324  Figure 6. View largeDownload slide XRD of poly(acrylic acid-co-acrylamide)-graft–polyaniline samples before and after irradiation at different doses. Figure 6. View largeDownload slide XRD of poly(acrylic acid-co-acrylamide)-graft–polyaniline samples before and after irradiation at different doses. Figure 7. View largeDownload slide The change in crystallinty of poly(acrylic acid-co-acrylamide)-graft–polyaniline samples before and after irradiation at different doses Figure 7. View largeDownload slide The change in crystallinty of poly(acrylic acid-co-acrylamide)-graft–polyaniline samples before and after irradiation at different doses CONCLUSION From the spectroscopic study of poly(acrylic acid-co-acrylamide)-graft–polyaniline irradiated at different dose it is clear that at dose 17.46 Gy the band gap energy of the graft has the minimum value and cluster size have the maximum value. SEM images show an enhancement in the morphological structure in the graft samples with irradiation with alpha-particles. The change in XRD patterns before and after irradiation showed that the crystallinity of the graft with the increasing dose and the crystallite size decreasing with increasing the dose. All the previous data confirmed that poly(acrylic acid-co-acrylamide)-graft–polyaniline can be used as a radiation dosimeter for α-particles in the range from 0 to 17.46 Gy. REFERENCES 1 Durrani, S. A. and Bull, R. K. Solid state nuclear track detection: principles. In: Methods and Applications  ( Oxford: Pergamon Press) ( 1987). 2 Lee, E. H. ion-beam modification of polymeric materials—fundamental, principles and applications. Nucl. Instrum. Methods B  151, 29– 41 ( 1999). Google Scholar CrossRef Search ADS   3 IAEA TECDOC. Controlling of degradation effects in Radiation processing of polymers IAEA , Vienna ( 2009). 4 Yates, B. W. and Shinozaki, D. M. Radiation degradation of poly(methyl methacrylate) in the soft x-ray region. J. Polymer Sci.  31, 1779– 1784 ( 1993). Google Scholar CrossRef Search ADS   5 Kudoh, H., Sasuga, T., Seguchi, T. and Katsumura, Y. High-energy-ion-irradiation effects on polymer materials: 3. The sensitivity of cellulose triacetate and poly(methyl methacrylate). Polymer (Guildf)  37, 2903– 2908 ( 1996). Google Scholar CrossRef Search ADS   6 Lee, E. H., Rao, G. R. and Mansur, L. K. Hardness enhancement and crosslinking mechanisms in polystyrene irradiated with high energy ion-beams. Mater. Sci. Forum  248, 135– 146 ( 1997). Google Scholar CrossRef Search ADS   7 Eissa, M. F. Study the effect of post-irradiation gamma ray doses on optical and spectral response of CR-39 polymer track recorder. Int. J. Low Radiat.  8, 10– 19 ( 2011). Google Scholar CrossRef Search ADS   8 Eissa, M. F., kaid, M. A. and Kamel, N. A. Study of the effects of low and high linear energy transfers on poly(methylmethacrylate) samples. J. Appl. Polymer Sci.  125, 3682– 3687 ( 2012). Google Scholar CrossRef Search ADS   9 Laranjeira, J. M. G., Khoury, H. J., de Azevedo, W. M., de Vasconcelos, E. A. and da Silva, E. F., Jr Polyaniline nanofilms as a monitoring label and dosimetric device for gamma radiation. Mater. Charact.  50, 127– 130 ( 2003). Google Scholar CrossRef Search ADS   10 Lima Pacheco, A. P., Araujo, E. S. and de Azevedo, W. M. Polyaniline/poly acid acrylic thin film composites: a new gamma radiation detector. Mater. Charact.  50, 245– 248 ( 2003). 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SPECTROSCOPIC STUDY ON POLY(ACRYLIC ACID-CO-ACRYLAMIDE)-GRAFT–POLYANILINE AS A RADIATION DOSIMETER FOR ALPHA PARTICLES

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Abstract

Abstract Poly(acrylate-co-acrylamide) was a synthesis by chemical oxidation polymerization of an aqueous binary mixture of acrylate/acrylamide (1:1 mole ratio) using ammonium persulphate as an initiator at 70°C under the nitrogen atmosphere. The obtained copolymer was introduced for grafting with polyaniline. The grafting process was performed by chemical oxidation polymerization of aniline using ammonium persulphate as an initiator in hydrochloric acid media at 40°C under the nitrogen atmosphere. Poly(acrylic acid-co-acrylamide)-graft–polyaniline samples irradiated with (alpha-particles) at different irradiation doses (0, 2.33, 8.73, 13.09 and 17.46 Gy) at the same linear energy transfer. The change in the morphology, optical properties and the energy gap of poly(acrylic acid-co-acrylamide)-graft–polyaniline samples were studied. INTRODUCTION When an ionizing radiations pass through a polymeric material, ionization and excitation process take place for molecules of the material(1). These leads to breaking of original bonds, chain scission, radical formation and cross-linking in the polymeric material(2, 3). Scission and cross-linking not only depend upon the polymer structure, but also upon the energy deposited per unit track length (linear energy transfer (LET))(4–6). This lead in modifying the structure and optical properties of polymers(7, 8). A radiation dosimeter is a system that either directly or indirectly determines the absorbed dose of ionizing radiation. Radiation dosimeters are important for many applications including environmental safety and remediation, medical imaging, industrial process monitoring, national security, military surveillance and even basic science(9). The electrical conductivity of polyaniline nano-films before and after irradiation (using alpha, beta and gamma radiation sources) was measured and evaluated(10). The changes of optical and electrical properties of aniline hydrochloride/polyvinyl alcohol films (AN/PVA) influenced by gamma radiation for gamma dosimetry application from 0 to 10 kGy were reported(11). The effect of alpha particle fluences on the morphology and optical properties of polyaniline in nano-scale was studied(12). The effect of gamma rays irradiated polyaniline blends with chlorine-containing polymers, copolymers and HCl-releasing compounds was studied(13). In addition, the ionizing radiations may also produce a random fracture of main chain and breaking of the original bonds, giving rise to the formation of free radicals, double/triple bonds, cross-linking(14), carbon cluster formation(15) and evolution of ionic species and gaseous components. Leucoemeraldine and polyemeraldine base (the non-conducting form of polyaniline) can be used as a detecting device for low-dose ionization radiation, but polyemeraldine salts (the conducting form) are possible for high dose detectors(16). Irradiation of polymers by high and low LET radiation is widely used in improving the physical and chemical properties of the polymeric material for high technology applications(17). In this work, we aimed to expose poly(acrylic acid-co-acrylamide)-graft–polyaniline samples to different doses of alpha-particles of the same of LET. To investigate their capability in alpha-particles dosimeter by studying the optical behavior and morphological structure of the graft samples after irradiation. EXPERIMENTAL Synthesis of poly(acrylate-co-acrylamide) For 25 ml solution of a binary mixture of acrylic acid (2.040 g) and acrylamide (2.015 g), sodium hydroxide solution (0.100 mol L−1) was added with stirring until the solution becomes slightly alkaline (pH = 7.2). The above binary mixture was thermostat at 70°C and then ammonium persulfate (APS) (0.052 g) was added as initiator. The copolymerization was performed under the nitrogen atmosphere at 70°C for 3 h. The formed copolymer was precipitated by the addition of methanol as non-solvent. The copolymer was washed with methanol and dried under vacuum at 70°C for constant weight. Preparation of poly(acrylic acid-co-acrylamide)-graft–polyaniline A mixture of the copolymer solution (15 ml = 1.2 g), aniline (2 ml, density = 1.2 g/cm3) and hydrochloric acid (2.5 ml, 33.3%) are thermostat at 40°C for 15 min, then 5.7 g APS is added. The grafting reaction is achieved at 40°C under N2 atmosphere for 2 h (grafting % = 72.5). The resulting graft was washed with distilled water several times, methanol and N-methylpyrrolidone for removing polyaniline homopolymer then dried under vacuum at 70°C. Irradiation techniques Poly(acrylic acid-co-acrylamide)-graft–polyaniline pellets (1.20 × 1.20 cm2 × 0.980 mm) pressed at 20 bars are irradiated in the air in contact with 241Am-source (at Nuclear and Radiation Research Lab, Beni-Suef University, Egypt). The energy of alpha particles emitted from 241Am-source was 5.486 MeV. The LET (electronic-LET + nuclear-LET) corresponding to the alpha particle energy was calculated(18). The calculated LET for the present irradiation graft was 12.18 eV/Å. The incident fluences were calculated(7) according to the irradiation times 0, 15, 60, 90 and 120 min, respectively. Accordingly, the irradiation doses can be calculated by the following equation(1):   Dose(Gy)=1.6×10−10(LET(MeV/cm)×Fluence(/cm2))/ρ(gm/cm3) (1) The calculated irradiation doses are (0, 2.33, 8.73, 13.09 and 17.46 Gy) for the same value of LET. Ultraviolet–visible spectroscopy Spectrophotometric analysis of the investigated polymeric samples before and after irradiation was carried out using Shimadzu visible spectrophotometer Double beam 2600, Japan. Scanning electron microscope and X-ray diffraction The Scanning electron microscope analysis was carried out using JSM-6510LA Scanning electron microscope (JEOL, Japan). The X-ray diffraction (XRD) patterns of the prepared samples were characterized with the help of Pananlytical Empryan X-ray diffractometer 202 964 (the Netherlands). The scan range was 5°–1400. RESULTS AND DISCUSSIONS Optical characteristics Poly(acrylic acid-co-acrylamide)-graft–polyaniline pellets were irradiated at different alpha particle doses (0, 2.33, 8.73, 13.09 and 17.46 Gy). The UV–Visible spectra of the samples before and after irradiation with alpha particles are graphically represented in Figure 1. The absorption peak at 275 nm is attributed to the π–π* transition of the benzenoid segment and the absorption peaks at 536 nm are attributed to the polaron and the bipolaron transition in polyaniline(19). This confirms the grafting of polyaniline onto poly(acrylic acid-co-acrylamide). From Figure 1, the irradiated polymeric pellet shift in the peaks toward the higher wavelength side (red shift) as well as an increase in the intensity of the peak at 563 nm suggests an increasing in the probability of re-interact between the graft chain, decrease in the energy band gap in the case of poly(acrylic acid-co-polyacrylamide)-graft–polyaniline and increase in the number of charge carriers. This shift can be due to the interaction between poly(acrylic acid-co-polyacrylamide)-graft–polyaniline chains. The broadening of absorption peaks increases with the increasing of irradiation dose which can be assigned to a generation of defects such as radicals, organic species or centers induced by radiation, resulting in the formation of new levels of energy(20). The dose respond (the difference between intensity of irradiated sample and virgin sample at each dose) of irradiated graft samples at different doses at 429 nm is shown in Figure 2 which show a linear increasing in (∆A) with an increasing the dose. Figure 1. View largeDownload slide UV–Vis spectra of poly(acrylic acid-co-acrylamide) before and after irradiation at different doses. Figure 1. View largeDownload slide UV–Vis spectra of poly(acrylic acid-co-acrylamide) before and after irradiation at different doses. Figure 2. View largeDownload slide Dose responds of poly(acrylic acid-co-acrylamide)-graft–polyaniline samples before and after irradiation at 429 nm at different irradiation dose. Figure 2. View largeDownload slide Dose responds of poly(acrylic acid-co-acrylamide)-graft–polyaniline samples before and after irradiation at 429 nm at different irradiation dose. Energy band gap The optical band gap energy (Eg) of poly(acrylic acid-co-acrylamide)-grafted polyaniline samples were calculated from Tauc’s plot(21, 22) is given by the equation:   α(v)=β(hv−Eg)nhv (2)where, α is the absorption coefficient, hv is the photon energy, B is the band gap tailing parameter, Eg is a characteristic energy which is termed as optical band gap and n is the transition probability index, which has discrete values n = 1/2, 3/2, 2 and 3 for direct allowed, direct forbidden, indirect allowed and indirect forbidden electronic transitions, respectively. The direct and indirect energy band gaps were estimated by the plot between (αhν)2 and (αhν)1/2 as a function of the photon energy (hν) and are shown in Figures 3 and 4, respectively. This behavior showed that the direct allowed transition (n = 1/2) was the most probable involved transition mechanism. The values of the direct and indirect energy gaps for virgin as well as irradiated samples are presented in Table 1. The value of (Eg) is slightly decreasing with the irradiation doses. The variations in (Eg) suggest the formation of defects (radicals and organic species) after alpha particles irradiations and/or the formation of carbon enriches clusters(23). This may be attributed to the formation of a conjugated system of bonds due to bond cleavage by radiation. Table 1. Direct and indirect optical band gaps energy of virgin and irradiated poly(acrylic acid-co-acrylamide) graft polyaniline samples. Irradiation dose (Gy)  Indirect band energy (eV)  Direct band energy (eV)  0  1.849  2.045  2.33  1.862  2.051  8.73  1.781  2.029  13.09  1.756  2.025  17.46  1.739  2.012  Irradiation dose (Gy)  Indirect band energy (eV)  Direct band energy (eV)  0  1.849  2.045  2.33  1.862  2.051  8.73  1.781  2.029  13.09  1.756  2.025  17.46  1.739  2.012  Figure 3. View largeDownload slide Tauc’s plot corresponding to direct band gap of poly(acrylic acid-co-acrylamide)-graft–polyaniline samples before and after irradiation at different doses. Figure 3. View largeDownload slide Tauc’s plot corresponding to direct band gap of poly(acrylic acid-co-acrylamide)-graft–polyaniline samples before and after irradiation at different doses. Figure 4. View largeDownload slide Tauc’s plot corresponding to indirect band gap of poly(acrylic acid-co-acrylamide)-graft–polyaniline samples before and after irradiation at different doses. Figure 4. View largeDownload slide Tauc’s plot corresponding to indirect band gap of poly(acrylic acid-co-acrylamide)-graft–polyaniline samples before and after irradiation at different doses. Carbon cluster The carbonaceous cluster is one of the important parameters that enhance the optical properties of the polymeric material. This is due to that the carbonaceous clusters are rich with charge carrier, which enhances the surface conductivity of the polymers. The number of carbon atoms per cluster can be calculated by the following equation(23):   Eg=34.3/(N)0.5 (3) The number of carbon atoms per cluster (N) for virgin and irradiated graft samples for indirect and direct band gap varies from ~339.335 to 389.035 and 279.677 to 290.624, respectively, as shown in Table 2. The maximum value for cluster size was found in irradiation dose 17.46 Gy whereas the minimum value of the band gap energy was found at dose 2.33 Gy. Carbon enriched domains created in irradiated polyaniline samples may be responsible for the decreasing in the band gap. Table 2. The variation of number of carbon atoms per cluster (N) of samples before and after irradiation. Irradiation dose (Gy)  The number of carbon atoms per cluster (N)  Indirect  Direct  0  344.123  281.330  2.33  339.335  279.677  8.73  370.903  285.774  13.09  381.539  286.905  17.46  389.035  290.624  Irradiation dose (Gy)  The number of carbon atoms per cluster (N)  Indirect  Direct  0  344.123  281.330  2.33  339.335  279.677  8.73  370.903  285.774  13.09  381.539  286.905  17.46  389.035  290.624  Effect of irradiation doses on the morphological microstructure of poly(acrylic acid-co-acrylamide)-graft–polyaniline samples (SEM) The morphological microstructure of the unirradiated and irradiated poly(acrylic acid-co-acrylamide)-graft–polyaniline samples at different irradiation dose (0, 2.33, 8.73, 13.09 and 17.46 Gy) are characterized by SEM images which are shown in Figure 5 (A, B, C, D and E), respectively. Figure (5A) represented the sample before irradiation showed some microspores particles aggregation. Figure 5B represented poly(acrylic acid-co-acrylamide)-graft–polyaniline irradiated at 2.33 Gy showed increasing in the particles aggregation and enhancement particles structure. At irradiation dose 8.73 Gy, poly(acrylic acid-co-acrylamide)-graft–polyaniline is depicted in (Figure 5C) indicate that the clusters are large and clear, but its surface is not smooth and contains macro-granular structure with a diameter in the range of a few microns. At irradiation dose 13.09 Gy (Figure 5D) indicates that an enhancement in the crystallinity of the graft and the shape of the particles become in the sheet form with a diameter in the range (400 nm). Further irradiation at 17.46 Gy indicated that an increasing the crystallinity of the graft and the crystalline region becomes predominates and the crystal size decreasing to (300 nm) as shown in Figure 5E. This indicated that the crystallinity is increasing and the crystal size decreasing with increasing the irradiation doses. Figure 5. View largeDownload slide SEM images (A–E) of poly(acrylic acid-co-acrylamide)-graft–polyaniline samples before and after irradiation at different doses (0, 2.33, 8.73,13.09 and 17.46 Gy), respectively. Figure 5. View largeDownload slide SEM images (A–E) of poly(acrylic acid-co-acrylamide)-graft–polyaniline samples before and after irradiation at different doses (0, 2.33, 8.73,13.09 and 17.46 Gy), respectively. X-ray diffraction patterns The XRD of the unirradiated and irradiated samples of poly(acrylic acid-co-acrylamide)-graft–polyaniline with different irradiation doses (0, 2.33, 8.73, 13.09 and 17.46 Gy) are given in Figure 6. The graft sample before irradiation has semi-crystalline structure. It is clear also from this figure that, the intensity after irradiation increasing for all prominent peaks with increasing the irradiation dose. The increasing in the intensity indicated that the enhancement in the degree of crystallinity. This may be due to cross-linking of the polymer chain or by the formation of single or multiple helices, which induces more crystalline region in the graft samples. The degree of crystallinity was calculated by separating intensities due to the amorphous and crystalline phase of the diffraction pattern. Percentage of crystallinity (Xc, %) is measured as the ratio of the crystalline area to total area(24).   Xc(%)=[AcAa+Ac]×100%where, Ac = area of the crystalline phase and Aa = area of the amorphous phase. The degree of crystallinity of (0, 2.33, 8.73, 13.09 and 17.46 Gy) is (60.78, 64.33, 70.65, 73.75 and 79.24%), the degree of crystallinity of poly(acrylic acid-co-acrylamide)-graft–polyaniline increasing with increasing the dose as shown in Figure 7. The crystallite size of the particles before and after irradiation is shown in Table 3. The crystallite size decreasing with increasing the dose this agrees with the previous discussion in SEM part. Table 3. The variation of crystallite size of samples before and after irradiation. Irradiation dose (Gy)  The crystallite size (μm)  0  1.092  2.33  0.874  8.73  0.624  13.09  0.454  17.46  0.324  Irradiation dose (Gy)  The crystallite size (μm)  0  1.092  2.33  0.874  8.73  0.624  13.09  0.454  17.46  0.324  Figure 6. View largeDownload slide XRD of poly(acrylic acid-co-acrylamide)-graft–polyaniline samples before and after irradiation at different doses. Figure 6. View largeDownload slide XRD of poly(acrylic acid-co-acrylamide)-graft–polyaniline samples before and after irradiation at different doses. Figure 7. View largeDownload slide The change in crystallinty of poly(acrylic acid-co-acrylamide)-graft–polyaniline samples before and after irradiation at different doses Figure 7. View largeDownload slide The change in crystallinty of poly(acrylic acid-co-acrylamide)-graft–polyaniline samples before and after irradiation at different doses CONCLUSION From the spectroscopic study of poly(acrylic acid-co-acrylamide)-graft–polyaniline irradiated at different dose it is clear that at dose 17.46 Gy the band gap energy of the graft has the minimum value and cluster size have the maximum value. SEM images show an enhancement in the morphological structure in the graft samples with irradiation with alpha-particles. The change in XRD patterns before and after irradiation showed that the crystallinity of the graft with the increasing dose and the crystallite size decreasing with increasing the dose. All the previous data confirmed that poly(acrylic acid-co-acrylamide)-graft–polyaniline can be used as a radiation dosimeter for α-particles in the range from 0 to 17.46 Gy. REFERENCES 1 Durrani, S. A. and Bull, R. K. Solid state nuclear track detection: principles. 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Radiation Protection DosimetryOxford University Press

Published: Mar 1, 2018

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