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Microstructure change in poly(ethersulfone) films by swift heavy ions
Micron 41 (2010) 390–394
Contents lists available at ScienceDirect
Micron journal homepage: www.elsevier.com/locate/micron
Short communication
Microstructure change in poly(ethersulfone) films by swift heavy ions Vaibhav Kulshrestha a,*, Garima Agarwal a, Kamlendra Awasthi b,c, Balram Tripathi b, N.K. Acharya e, Devendra Vyas a, Vibhav K. Saraswat d, Y.K. Vijay b, I.P. Jain a a
Centre for Non-Conventional Energy Resources, University of Rajasthan, Jaipur 302004, India Department of Physics, University of Rajasthan, Jaipur 302004, India c DST Unit on Nanoscience, Department of Chemical Eng., Indian Institute of Technology, Kanpur 208016, India d Department of Physics, Banasthali University, Banasthali, Tonk, India e Applied Physics Department, Faculty of Technology & Engineering, The M.S. University of Baroda, Vadodara-390 001, India b
A R T I C L E I N F O
A B S T R A C T
Article history: Received 28 October 2009 Received in revised form 8 December 2009 Accepted 8 December 2009
PES membrane of thickness 25 mm was irradiated by Cl9+ ions of energy 100 MeV at IUAC, New Delhi. Microstructure changes due to exposure to high-energy ions were investigated by Fourier transform infrared (FTIR) and ultraviolet/visible (UV/vis) absorption spectroscopies, X-ray diffraction technique and by dynamic mechanical analysis (DMA). A significant loss of crystallinity is observed by the XRD data. Particle size or grain size calculated using Scherrer formula indicates measurable change in particle size of irradiated samples. The polymer chain scissions and structure degradations are expected to occur for irradiated samples. Optical properties of the films were changed due to irradiation that could be clearly seen in the absorption spectra. FTIR does not show the remarkable change in the irradiated samples, but there is some change in the surface roughness observed by AFM. ß 2009 Elsevier Ltd. All rights reserved.
Keywords: PES FTIR XRD DMA UV–vis AFM
1. Introduction High-energy ion bombardment induced modifications in polymeric materials have been attracting much attention, nowadays. The interaction between high-energy ions and the polymeric chain entanglements is described mostly in terms of primary excitation and ionization of the matrix leading to scissioning of original bonds, production of radicals and excited atoms (C), energetically feasible excimers (C–C), bond rearrangements and crosslinking of oligomeric fragments. These processes are responsible for polymer structural modification and the changes in fundamental properties changes. The ionization and electronic excitation processes are considered to lead chain scissioning and crosslinking in polymers [1]. Their ratio depends however on the system. Chain scissioning leads to decrease in molecular weight and crosslinking to increase it. Both effects change the polymer phase, chemical structure, crystallinity and the molecular weight. The breaking of atomic bonds and the rearrangements of polymer structure around the ion path result in a heavily modified cylindrical area, which is called latent track [2]. In such a small cylinder, the energy deposited along the ion path is extremely high and can approach up to several hundred eV/A˚. Taking into account
* Corresponding author. Tel.: +91 141 2711049. E-mail address: [email protected] (V. Kulshrestha). 0968-4328/$ – see front matter ß 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.micron.2009.12.003
that the energy of carbon bonds is only few eV, this high-energy deposition is sufficient to break all bonds in the track core. At lower distances, the ionization and excitations are caused by energetic electrons. The maximum range of the electron cascade depends on the ion velocity and may be up to 1000 nm. It has been observed that the irradiation effect depend not only on target properties but also on ion beam parameters such as ion current, fluence, energy, etc. Experiments showed that semicrystalline polymers become amorphous after irradiation by suitable ions [3,4], resulting from scission process of the main chains of the trans configuration of the ethylene glycol residue. In this case amorphization does not mean that an atom leaves the lattice site and moves to other neighbours, in this process the long molecular chains are damaged partially but not completely destroyed by the ion impacts. The localized energy deposition activates the movement of molecular chain and thus the atoms leave their position in the crystalline lattice, although the close neighbours in the chain are partially reserved [5,6]. The glass transition (Tg) is one of the most important properties exhibited by a polymer, determining its physical state and influencing other properties such as mechanical stiffness and toughness. Dynamic mechanical analysis is a good technique to study the variation in the transition regions due to the high-energy radiation treatment of the polymers. To the best of our knowledge, Ferain and Legras [7], Steckenreiter et al. [8] and Chipara and Reyes-Romero [9] have analyzed the swift heavy ion induced degradation in PC. Ferain
V. Kulshrestha et al. / Micron 41 (2010) 390–394
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studied the chemical modifications induced by SHI irradiations (Ar 4.5 MeV/amu) in a model compound, the diphenyl carbonate. Steckenreiter studied degradation processes in various polymers (PC, polyethyleneterephthalate, polyimide, polysulfone) induced by SHI irradiations. In situ Fourier transform infrared (FTIR) spectroscopy points out alkyne formation in all irradiated polymers. Chipara reported electron spin resonance (ESR) investigations on SHI irradiated PC. In present work chemical modifications induced by Cl9+ ions of 100 MeV energy at the ion fluences of 8 1010, 2 1011 and 4 1011 ion/cm2, have been studied using optical spectroscopy, XRD, thermomechanical and FTIR measurements. The choice of Cl9+ ion of 100 MeV due to its lower mass number but corresponding higher electronic energy loss, which is essential for track formation and the range of Cl9+ ion of 100 MeV is also much higher than the thickness of the films. The study of the detailed structure of ion track and its dependence on irradiation parameters is still on focus. 2. Experimental The poly(ethersulfone) PES material was procured in granular form from National Chemical laboratory, Pune, India (Fig. 1). The PES films of thickness 25 mm were prepared by the solution-cast method [10–12]. The films were dried under a low vacuum of 103 Torr at 60 8C (below the glass-transition temperature (Tg = 210 8C) for 10 h to complete removal of the solvent. These films were irradiated at fluence of 8 1010, 2 1011 and 4 1011 ion/cm2 by Cl9+ ion of 100 MeV. The range of the Cl9+ ion of 100 MeV in PES is 38 mm calculated by the SRIM 2007. The irradiation was performed under high vacuum of order 106 Torr at IUAC, New Delhi. The films were irradiated by the scanned beam of dimension, 1 1.5 cm2 [13]. X-ray diffraction patterns were obtained by means of a standard PW 1840 diffractometer, working at 40 kV and 25 mA, and equipped with a scintillation counter with single channel pulse height discriminator associated counting circuitry. The FeKa radiation (l = 1.93604 A˚) was collimated with soller slits. The Xray diffraction patterns were collected in a step-scanning mode with D2u = 0.0208 steps. Chemical modifications have also been analysed by Fourier transform infrared (FTIR) spectroscopy. FTIR spectroscopy was performed in transmission mode using NICOLET-550 FTIR spectrometer. The spectra were recorded in the wave number range of 1750–4000 cm1. Dynamic mechanical properties were studied using a rheometric dynamic mechanical thermal analyzer. Sample were cutted into strips of 15 mm 8 mm, and their dynamic loss tangent (tan d) was measured with in the range of 40–250 8C at heating rate of 3 8C/min. The spectra were recorded in the tensile mode, obtaining the dynamic loss tangent (tan d), at a frequency of 1 Hz, as a function of time. The UV/vis measurements were carried out on a HITACHI-U2900 spectrophotometer in absorption mode in the wavelength range of 800–190 nm. Topographical and roughness values of pristine and irradiated samples surface have been characterized by AFM using scanning probe microscope from Digital Instrument USA with Nanoscope IV controller. The tapping mode was employed in air at the
Fig. 2. X-ray diffraction pattern of virgin and irradiated PES films.
cantilever’s resonant frequency (1–5 kHz) using a probe and cantilever unit composed of silicon tip with a tip radius of 20 nm. The scan rate and scan lines per image are 1.969 Hz and 512, respectively. Small square pieces of approximately 0.5 cm 0.5 cm in area were cut from each sample. 3. Results and discussion 3.1. XRD measurements The typical XRD patterns of virgin and irradiated PES membrane for different ion fluence are given in Fig. 2. The diffraction pattern of virgin polymer clearly indicates that this polymer is amorphous in nature. Diffraction pattern of virgin PES sample shows prominent X-ray peak at 2u = 17.98 however, in case of irradiated
Fig. 1. Repeating unit of bisphenol-A poly(ethersulfone).
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Table 1 X-ray diffraction results on particle size and reduction in particle size, for virgin and irradiated PES films. S. no.
PES (fluence ion/cm2)
Particle size (A˚)
Loss in particle size (%)
1 2 3 4
Pristine 81010 21011 41011
9.39 9.25 8.63 8.24
– 1.56 8.12 12.29
Table 2 Dynamic characterization by DMA. S. no.
PES (fluence ion/cm2)
tan d
Ttan d
1 2 3
Pristine 1 109 8 1010
1.17 1.586 1.06
225 235 228
3.3. FTIR analysis
samples the observed changes in the diffraction pattern have been shown in Table 1. It is evident from the XRD results that the pattern of the irradiated PES is broader than the virgin, which indicates the more disordered state in irradiated polymer films and also a change crystallite size. In the case of virgin sample, the average crystallite size is estimated to 9.39 A˚. But in case of 4 1011 ion/cm2 irradiated film, the average value of crystallite size is found to be 8.24 A˚, it shows that the particle size L reduces by 12.29% compared to the virgin sample due to heavy ion irradiation. 3.2. Dynamic mechanical analysis Dynamic mechanical analysis of poly(ethersulfone) (PES) membrane with different ion fluence is shown in Fig. 3 as dynamic loss tangent (tan d) vs. temperature. Table 2 shows the tan d value of virgin and irradiated poly(ethersulfone) films. To increase in Tg of a polymer can be accounted for crosslinking of chain. The peak width also has increased with ion fluence. As the ion fluence increases, the glass transition temperature (Tg) increases, but after fluence 1 109 ion/cm2 the Tg again gets to decreases, due to overlapping of tracks [13]. Increase of tan d was confirmed and showed a crosslinking structure induced by the ion irradiation [14]. The tan d of Cl ion irradiated membrane increases with increasing ion fluence of 1 109 ion/cm2, but at the fluence of 8 1010 ion/cm2 it decreases shows the increment in the amorphization state [15,22], due to the chain scissioning.
Fig. 3. Temperature versus dynamic loss (tan d) curve for PES films.
Fig. 4 shows the FTIR spectra of virgin and ion irradiated poly(ethersulfone) (PES) membrane. The FTIR spectra do not show any changes up to ion fluence of 1011 ion /cm2. The only change in the spectra of the irradiated sample that the new peaks at 2375 and 3305 cm1 appears after the irradiation at fluence 4 1011 ion / cm2, it may be due to C–H stretching due to alkyne formation [16], the peak at 3745 cm1 also disappear in all the spectra of irradiated samples. 3.4. UV–vis measurement Ultraviolet–visible (UV–vis) spectroscopy is an important tool for investigation as it gives an idea about the value of optical band gap energy (Eg). The absorption of light energy by polymeric materials in UV and visible regions involves promotion of electrons in s, p and h orbital from the ground state to higher energy states which are described by molecular orbitals [17]. Ion beam interaction with polymer generates damage which leads to the formation of new defects and new charge states. The change in the surface roughness due to the ion irradiation is shown in Fig. 6. After irradiation the roughness of the polymer surface increases at higher fluence. The results of absorption studies with UV–vis spectrophotometer carried out on virgin and irradiated samples at higher fluences
Fig. 4. FTIR spectra of (A) virgin, (B) irradiated with 8 1010 ion/cm2, (C) irradiated with 2 1011 ion/cm2 and (D) irradiated with 4 1011 ion/cm2 PES films.
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Table 3 Variation of absorption edge (lg) and energy gap (Eg) in pristine and irradiated samples of PES at different fluences. S. no.
Fluence (ions/cm2)
Absorption edge (lg) (nm)
Band gap energy (eV)
1 2 3 4
Pristine 8 1010 2 1011 4 1011
312 9 321 11 402 16 580 19
3.95 0.06 3.80 0.06 3.62 0.06 3.18 0.05
The optical absorption method can be used for the investigation of the optically induced transitions and can provide information about the bond structure and energy gap in crystalline and noncrystalline materials [19]. The shift in absorption edge was correlated with the optical band gap Eg given by Fig. 5. Optical absorption spectra of poly(ethersulphone) (PES) irradiated with Cl9+ ions of 100 MeV.
are illustrated in Fig. 5. The optical absorption spectrum of the virgin sample (Fig. 5 (curve a)) shows a sharp decrease with increasing wavelength up to 310 nm, followed by a plateau region. Fig. 5 (curve b–d) shows the optical spectra for PES polymer samples after irradiation to the fluences of 8 1010, 2 1011 and 4 1011 ion/ cm2, respectively. It is evident that optical absorption increases with increasing fluence and this absorption shifts from UV–vis towards the visible region for irradiated samples. The increase in absorption may be attributed to the formation of a conjugated system of bonds due to bond cleavage and reconstruction [18].
Eg ¼
hc
lg
where, h is the Planck constant and c is the velocity of light. The wavelength lg is determined using Tauc’s expression [20] from the intersection with abscissa of the plot of (e1/2/l) versus (1/l), where e is the optical absorbance and k is the wavelength. The values of lg and the corresponding results of energy gap (Eg) for pristine as well as irradiated samples are reported in Table 3. It is observed that energy gap decreases with the increase in ion fluence. Optical band gap decreases by almost 20% at highest fluence 4 1011 ions/cm2. Studies shows that the carbon enriched domains created in polymers during irradiation are responsible for the decrease in band gap [21].
Fig. 6. AFM image of (A) virgin, (B) irradiated with 8 1010 ion/cm2 and (C) irradiated with 4 1011 ion/cm2.
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4. Conclusion Techniques like X-ray diffractometer, Fourier transform infrared spectroscopy, Dynamic mechanical analysis and UV–vis measurements, show change in crystallinity and chemical structures of polymer films after irradiation by the chlorine ions. The heavy ion irradiated polymer films exhibited significant change to their crosslinking. XRD measurements show the decrease of the peak intensity with increased ion fluence. Increasing in amorphous nature in polymer is observed with increasing fluence traced by XRD measurements. An increase in the dynamic loss tangent (tan d) was also confirmed and suggested an enhanced absorption capacity of impact. FTIR and DMA results strong support the increase of the amorphization and reduced the density of irradiated polymers, chain scissions and structure degradations. Acknowledgments The author is thankful to DST, New Delhi for financial assistance under Fast Track scheme (PS-17/2007). Financial assistance provided by DST, New Delhi and Max Planck, Germany under Max Planck-India Fellowship to Dr. Vaibhav Kulshrestha is gratefully acknowledged. One of the authors (VK) is grateful to ICTP, Italy to providing the Junior Associate ship to write this paper. The author is also thankful to IUAC, New Delhi for providing irradiation facility. References Fleisher, R.L., Price, P.B., Walker, R.M., 1975. Nuclear Tracks in Solids: Principles and Applications. University of California Press.
Hama, Y., Hamanaka, K., Matsumoto, H., Takano, T., Kudoh, H., Sugimoto, M., Seguchi Radiat, T., 1996. Phys. Chem. 48 (5) 549. Seguchi, T., Kudoh, H., Sugimoto, M., Hama, Y., 1999. Nucl. Instrum. Methods B 151, 154. Mehta, G.K., 1996. Nucl. Instrum. Methods Phys. Res. A 382, 335. Rajesh Kumar, Prasad Rajendra, Vijay, Y.K., Acharya, N.K., Verma, K.C., De, U., 2003. Nucl. Instrum. Methods Phys. Res. B 212, 221. Changlong, L., Zhiyong, Z., Youmeri, S., Mingdong, H., Zhiguang, W., Yanbin, W., Chonghong, Z., Xiaoxi, C., Jia, L., Baoquan, L., 2000. Nucl. Instrum. Methods Phys. Res. B 169, 78. Ferain, E., Legras, R., 1993. Nucl. Instrum. Methods B 82, 539. Steckenreiter, T., Balanzat, E., Fuess, H., Trautmann, C., 1999. Nucl. Instrum. Methods B 151, 161. Chipara, M.I., Reyes-Romero, J., 2001. Nucl. Instrum. Methods B 185, 77. Kulshrestha, V., Awasthi, K., Acharya, N.K., Singh, M., Avasthi, D.K., Vijay, Y.K., 2006. Desalination 195, 273–280. Kulshrestha, V., Awasthi, K., Acharya, N.K., Singh, M., Avasthi, D.K., Vijay, Y.K., 2006. J. Appl. Polym. Sci. 102, 2386–2390. Kulshrestha, V., Awasthi, K., Vijay, Y.K., 2007. Int. J. Hydrogen Energy 32, 3105– 3108. Kulshrestha, V., Awasthi, K., Acharya, N.K., Singh, M., Bhagwat, P.V., Vijay, Y.K., 2006. Polym. Bull. 56, 427–435. Perera, M.C.S., Rowen, C.C., 2000. Polymer 41, 323–334. Takahashi, S., Yoshida, M., Asano, M., Notomi, M., Nakagawa, T., 2004. Nucl. Instrum. Methods Phys. Res. B 217, 435–441. Dehaye, F., Balanzat, E., Ferain, E., Legras, R., 2003. Nucl. Instrum. Methods Phys. Res. B 209, 103–112. Dyer, J.R., 1994. Application of Absorption Spectroscopy of Organic Compounds. Prentice-Hall, NJ. Farenza, L.S., Papaleo, R.M., Hallen, A., Araujo, M.A., Livi, R.P., Sundqvist, B.U.R., 1995. Nucl. Instrum. Methods B 105, 134. Mishra, R., Tripathy, S.P., Sinha, D., Dwivedi, K.K., Ghosh, S., Khating, D.T., Muller, M., Fink, D., Chung, W.H., 2000. Nucl. Instrum. Methods B 168, 59. Tauc, J., Grigorovici, R., Vaneu, A., 1996. Phys. Stat. Solids 15, 627. Fink, D., Chug, W.H., Klett, R., Schmoidt, A., Cardosa, J., Montiel, R., Vazquez, M.H., Wang, L., Hosoi, F., Omichi, H., Oppelt-Langer, P., 1995. Radiat. Eff. Defects Solids 133, 193. Kulshrestha, V., 2009. Int. J. Hydrogen Energy 34, 9274.
Contents lists available at ScienceDirect
Micron journal homepage: www.elsevier.com/locate/micron
Short communication
Microstructure change in poly(ethersulfone) films by swift heavy ions Vaibhav Kulshrestha a,*, Garima Agarwal a, Kamlendra Awasthi b,c, Balram Tripathi b, N.K. Acharya e, Devendra Vyas a, Vibhav K. Saraswat d, Y.K. Vijay b, I.P. Jain a a
Centre for Non-Conventional Energy Resources, University of Rajasthan, Jaipur 302004, India Department of Physics, University of Rajasthan, Jaipur 302004, India c DST Unit on Nanoscience, Department of Chemical Eng., Indian Institute of Technology, Kanpur 208016, India d Department of Physics, Banasthali University, Banasthali, Tonk, India e Applied Physics Department, Faculty of Technology & Engineering, The M.S. University of Baroda, Vadodara-390 001, India b
A R T I C L E I N F O
A B S T R A C T
Article history: Received 28 October 2009 Received in revised form 8 December 2009 Accepted 8 December 2009
PES membrane of thickness 25 mm was irradiated by Cl9+ ions of energy 100 MeV at IUAC, New Delhi. Microstructure changes due to exposure to high-energy ions were investigated by Fourier transform infrared (FTIR) and ultraviolet/visible (UV/vis) absorption spectroscopies, X-ray diffraction technique and by dynamic mechanical analysis (DMA). A significant loss of crystallinity is observed by the XRD data. Particle size or grain size calculated using Scherrer formula indicates measurable change in particle size of irradiated samples. The polymer chain scissions and structure degradations are expected to occur for irradiated samples. Optical properties of the films were changed due to irradiation that could be clearly seen in the absorption spectra. FTIR does not show the remarkable change in the irradiated samples, but there is some change in the surface roughness observed by AFM. ß 2009 Elsevier Ltd. All rights reserved.
Keywords: PES FTIR XRD DMA UV–vis AFM
1. Introduction High-energy ion bombardment induced modifications in polymeric materials have been attracting much attention, nowadays. The interaction between high-energy ions and the polymeric chain entanglements is described mostly in terms of primary excitation and ionization of the matrix leading to scissioning of original bonds, production of radicals and excited atoms (C), energetically feasible excimers (C–C), bond rearrangements and crosslinking of oligomeric fragments. These processes are responsible for polymer structural modification and the changes in fundamental properties changes. The ionization and electronic excitation processes are considered to lead chain scissioning and crosslinking in polymers [1]. Their ratio depends however on the system. Chain scissioning leads to decrease in molecular weight and crosslinking to increase it. Both effects change the polymer phase, chemical structure, crystallinity and the molecular weight. The breaking of atomic bonds and the rearrangements of polymer structure around the ion path result in a heavily modified cylindrical area, which is called latent track [2]. In such a small cylinder, the energy deposited along the ion path is extremely high and can approach up to several hundred eV/A˚. Taking into account
* Corresponding author. Tel.: +91 141 2711049. E-mail address: [email protected] (V. Kulshrestha). 0968-4328/$ – see front matter ß 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.micron.2009.12.003
that the energy of carbon bonds is only few eV, this high-energy deposition is sufficient to break all bonds in the track core. At lower distances, the ionization and excitations are caused by energetic electrons. The maximum range of the electron cascade depends on the ion velocity and may be up to 1000 nm. It has been observed that the irradiation effect depend not only on target properties but also on ion beam parameters such as ion current, fluence, energy, etc. Experiments showed that semicrystalline polymers become amorphous after irradiation by suitable ions [3,4], resulting from scission process of the main chains of the trans configuration of the ethylene glycol residue. In this case amorphization does not mean that an atom leaves the lattice site and moves to other neighbours, in this process the long molecular chains are damaged partially but not completely destroyed by the ion impacts. The localized energy deposition activates the movement of molecular chain and thus the atoms leave their position in the crystalline lattice, although the close neighbours in the chain are partially reserved [5,6]. The glass transition (Tg) is one of the most important properties exhibited by a polymer, determining its physical state and influencing other properties such as mechanical stiffness and toughness. Dynamic mechanical analysis is a good technique to study the variation in the transition regions due to the high-energy radiation treatment of the polymers. To the best of our knowledge, Ferain and Legras [7], Steckenreiter et al. [8] and Chipara and Reyes-Romero [9] have analyzed the swift heavy ion induced degradation in PC. Ferain
V. Kulshrestha et al. / Micron 41 (2010) 390–394
391
studied the chemical modifications induced by SHI irradiations (Ar 4.5 MeV/amu) in a model compound, the diphenyl carbonate. Steckenreiter studied degradation processes in various polymers (PC, polyethyleneterephthalate, polyimide, polysulfone) induced by SHI irradiations. In situ Fourier transform infrared (FTIR) spectroscopy points out alkyne formation in all irradiated polymers. Chipara reported electron spin resonance (ESR) investigations on SHI irradiated PC. In present work chemical modifications induced by Cl9+ ions of 100 MeV energy at the ion fluences of 8 1010, 2 1011 and 4 1011 ion/cm2, have been studied using optical spectroscopy, XRD, thermomechanical and FTIR measurements. The choice of Cl9+ ion of 100 MeV due to its lower mass number but corresponding higher electronic energy loss, which is essential for track formation and the range of Cl9+ ion of 100 MeV is also much higher than the thickness of the films. The study of the detailed structure of ion track and its dependence on irradiation parameters is still on focus. 2. Experimental The poly(ethersulfone) PES material was procured in granular form from National Chemical laboratory, Pune, India (Fig. 1). The PES films of thickness 25 mm were prepared by the solution-cast method [10–12]. The films were dried under a low vacuum of 103 Torr at 60 8C (below the glass-transition temperature (Tg = 210 8C) for 10 h to complete removal of the solvent. These films were irradiated at fluence of 8 1010, 2 1011 and 4 1011 ion/cm2 by Cl9+ ion of 100 MeV. The range of the Cl9+ ion of 100 MeV in PES is 38 mm calculated by the SRIM 2007. The irradiation was performed under high vacuum of order 106 Torr at IUAC, New Delhi. The films were irradiated by the scanned beam of dimension, 1 1.5 cm2 [13]. X-ray diffraction patterns were obtained by means of a standard PW 1840 diffractometer, working at 40 kV and 25 mA, and equipped with a scintillation counter with single channel pulse height discriminator associated counting circuitry. The FeKa radiation (l = 1.93604 A˚) was collimated with soller slits. The Xray diffraction patterns were collected in a step-scanning mode with D2u = 0.0208 steps. Chemical modifications have also been analysed by Fourier transform infrared (FTIR) spectroscopy. FTIR spectroscopy was performed in transmission mode using NICOLET-550 FTIR spectrometer. The spectra were recorded in the wave number range of 1750–4000 cm1. Dynamic mechanical properties were studied using a rheometric dynamic mechanical thermal analyzer. Sample were cutted into strips of 15 mm 8 mm, and their dynamic loss tangent (tan d) was measured with in the range of 40–250 8C at heating rate of 3 8C/min. The spectra were recorded in the tensile mode, obtaining the dynamic loss tangent (tan d), at a frequency of 1 Hz, as a function of time. The UV/vis measurements were carried out on a HITACHI-U2900 spectrophotometer in absorption mode in the wavelength range of 800–190 nm. Topographical and roughness values of pristine and irradiated samples surface have been characterized by AFM using scanning probe microscope from Digital Instrument USA with Nanoscope IV controller. The tapping mode was employed in air at the
Fig. 2. X-ray diffraction pattern of virgin and irradiated PES films.
cantilever’s resonant frequency (1–5 kHz) using a probe and cantilever unit composed of silicon tip with a tip radius of 20 nm. The scan rate and scan lines per image are 1.969 Hz and 512, respectively. Small square pieces of approximately 0.5 cm 0.5 cm in area were cut from each sample. 3. Results and discussion 3.1. XRD measurements The typical XRD patterns of virgin and irradiated PES membrane for different ion fluence are given in Fig. 2. The diffraction pattern of virgin polymer clearly indicates that this polymer is amorphous in nature. Diffraction pattern of virgin PES sample shows prominent X-ray peak at 2u = 17.98 however, in case of irradiated
Fig. 1. Repeating unit of bisphenol-A poly(ethersulfone).
V. Kulshrestha et al. / Micron 41 (2010) 390–394
392
Table 1 X-ray diffraction results on particle size and reduction in particle size, for virgin and irradiated PES films. S. no.
PES (fluence ion/cm2)
Particle size (A˚)
Loss in particle size (%)
1 2 3 4
Pristine 81010 21011 41011
9.39 9.25 8.63 8.24
– 1.56 8.12 12.29
Table 2 Dynamic characterization by DMA. S. no.
PES (fluence ion/cm2)
tan d
Ttan d
1 2 3
Pristine 1 109 8 1010
1.17 1.586 1.06
225 235 228
3.3. FTIR analysis
samples the observed changes in the diffraction pattern have been shown in Table 1. It is evident from the XRD results that the pattern of the irradiated PES is broader than the virgin, which indicates the more disordered state in irradiated polymer films and also a change crystallite size. In the case of virgin sample, the average crystallite size is estimated to 9.39 A˚. But in case of 4 1011 ion/cm2 irradiated film, the average value of crystallite size is found to be 8.24 A˚, it shows that the particle size L reduces by 12.29% compared to the virgin sample due to heavy ion irradiation. 3.2. Dynamic mechanical analysis Dynamic mechanical analysis of poly(ethersulfone) (PES) membrane with different ion fluence is shown in Fig. 3 as dynamic loss tangent (tan d) vs. temperature. Table 2 shows the tan d value of virgin and irradiated poly(ethersulfone) films. To increase in Tg of a polymer can be accounted for crosslinking of chain. The peak width also has increased with ion fluence. As the ion fluence increases, the glass transition temperature (Tg) increases, but after fluence 1 109 ion/cm2 the Tg again gets to decreases, due to overlapping of tracks [13]. Increase of tan d was confirmed and showed a crosslinking structure induced by the ion irradiation [14]. The tan d of Cl ion irradiated membrane increases with increasing ion fluence of 1 109 ion/cm2, but at the fluence of 8 1010 ion/cm2 it decreases shows the increment in the amorphization state [15,22], due to the chain scissioning.
Fig. 3. Temperature versus dynamic loss (tan d) curve for PES films.
Fig. 4 shows the FTIR spectra of virgin and ion irradiated poly(ethersulfone) (PES) membrane. The FTIR spectra do not show any changes up to ion fluence of 1011 ion /cm2. The only change in the spectra of the irradiated sample that the new peaks at 2375 and 3305 cm1 appears after the irradiation at fluence 4 1011 ion / cm2, it may be due to C–H stretching due to alkyne formation [16], the peak at 3745 cm1 also disappear in all the spectra of irradiated samples. 3.4. UV–vis measurement Ultraviolet–visible (UV–vis) spectroscopy is an important tool for investigation as it gives an idea about the value of optical band gap energy (Eg). The absorption of light energy by polymeric materials in UV and visible regions involves promotion of electrons in s, p and h orbital from the ground state to higher energy states which are described by molecular orbitals [17]. Ion beam interaction with polymer generates damage which leads to the formation of new defects and new charge states. The change in the surface roughness due to the ion irradiation is shown in Fig. 6. After irradiation the roughness of the polymer surface increases at higher fluence. The results of absorption studies with UV–vis spectrophotometer carried out on virgin and irradiated samples at higher fluences
Fig. 4. FTIR spectra of (A) virgin, (B) irradiated with 8 1010 ion/cm2, (C) irradiated with 2 1011 ion/cm2 and (D) irradiated with 4 1011 ion/cm2 PES films.
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Table 3 Variation of absorption edge (lg) and energy gap (Eg) in pristine and irradiated samples of PES at different fluences. S. no.
Fluence (ions/cm2)
Absorption edge (lg) (nm)
Band gap energy (eV)
1 2 3 4
Pristine 8 1010 2 1011 4 1011
312 9 321 11 402 16 580 19
3.95 0.06 3.80 0.06 3.62 0.06 3.18 0.05
The optical absorption method can be used for the investigation of the optically induced transitions and can provide information about the bond structure and energy gap in crystalline and noncrystalline materials [19]. The shift in absorption edge was correlated with the optical band gap Eg given by Fig. 5. Optical absorption spectra of poly(ethersulphone) (PES) irradiated with Cl9+ ions of 100 MeV.
are illustrated in Fig. 5. The optical absorption spectrum of the virgin sample (Fig. 5 (curve a)) shows a sharp decrease with increasing wavelength up to 310 nm, followed by a plateau region. Fig. 5 (curve b–d) shows the optical spectra for PES polymer samples after irradiation to the fluences of 8 1010, 2 1011 and 4 1011 ion/ cm2, respectively. It is evident that optical absorption increases with increasing fluence and this absorption shifts from UV–vis towards the visible region for irradiated samples. The increase in absorption may be attributed to the formation of a conjugated system of bonds due to bond cleavage and reconstruction [18].
Eg ¼
hc
lg
where, h is the Planck constant and c is the velocity of light. The wavelength lg is determined using Tauc’s expression [20] from the intersection with abscissa of the plot of (e1/2/l) versus (1/l), where e is the optical absorbance and k is the wavelength. The values of lg and the corresponding results of energy gap (Eg) for pristine as well as irradiated samples are reported in Table 3. It is observed that energy gap decreases with the increase in ion fluence. Optical band gap decreases by almost 20% at highest fluence 4 1011 ions/cm2. Studies shows that the carbon enriched domains created in polymers during irradiation are responsible for the decrease in band gap [21].
Fig. 6. AFM image of (A) virgin, (B) irradiated with 8 1010 ion/cm2 and (C) irradiated with 4 1011 ion/cm2.
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4. Conclusion Techniques like X-ray diffractometer, Fourier transform infrared spectroscopy, Dynamic mechanical analysis and UV–vis measurements, show change in crystallinity and chemical structures of polymer films after irradiation by the chlorine ions. The heavy ion irradiated polymer films exhibited significant change to their crosslinking. XRD measurements show the decrease of the peak intensity with increased ion fluence. Increasing in amorphous nature in polymer is observed with increasing fluence traced by XRD measurements. An increase in the dynamic loss tangent (tan d) was also confirmed and suggested an enhanced absorption capacity of impact. FTIR and DMA results strong support the increase of the amorphization and reduced the density of irradiated polymers, chain scissions and structure degradations. Acknowledgments The author is thankful to DST, New Delhi for financial assistance under Fast Track scheme (PS-17/2007). Financial assistance provided by DST, New Delhi and Max Planck, Germany under Max Planck-India Fellowship to Dr. Vaibhav Kulshrestha is gratefully acknowledged. One of the authors (VK) is grateful to ICTP, Italy to providing the Junior Associate ship to write this paper. The author is also thankful to IUAC, New Delhi for providing irradiation facility. References Fleisher, R.L., Price, P.B., Walker, R.M., 1975. Nuclear Tracks in Solids: Principles and Applications. University of California Press.
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