Journal of Molecular Structure 1044 (2013) 328–330

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Journal of Molecular Structure

journal homepage: www.elsevier .com/locate /molstruc

Spectroscopic investigation of PVA-TIO2 membranes gamma irradiated

Mihai Todica ⇑, Luciana Udrescu, Grigore Damian, Simion Astilean‘‘Babes-Bolyai’’ University, Faculty of Physics, Cluj-Napoca, Romania

h i g h l i g h t s

" PVA membranes doped with different concentrations of TiO2 were investigated by ESR and XRD methods." ESR signals corresponding to free electrons appear after gamma irradiation." The effect of radiation on the local ordering of polymeric chains depends on the concentration of TiO2." The modifications induced by gamma irradiation involve mainly the polymeric matrix." Recombination of free electrons appears after 21 days of relaxation.

a r t i c l e i n f o

Article history:Available online 13 December 2012

Keywords:Polyvinyl alcoholESRTiO2

Gamma irradiation

0022-2860/$ - see front matter � 2012 Elsevier B.V. Ahttp://dx.doi.org/10.1016/j.molstruc.2012.12.006

⇑ Corresponding author. Address: No. 1, M. Koga400084, Romania. Tel.: +40 264 405300; fax: +40 264

E-mail address: mihai.todica@phys.ubbcluj.ro (M.

a b s t r a c t

The modifications of the PVA-TiO2 membranes exposed to gamma radiations were investigated by ESRand XRD methods. The ESR spectra show the appearance of a strong signal associated with the breakingof the polymeric chain and the appearance of the unpaired electrons. The mechanism is influenced by theconcentration of TiO2. The modification of local order of the polymeric chains after irradiation is con-firmed by XRD method.

� 2012 Elsevier B.V. All rights reserved.

1. Introduction

The polyvinyl alcohol (PVA) is one of the most used polymers inthe pharmaceutical industry as support for many medical drugsdue to its high biocompatibility and good chemical stability. Manystudies show that clotrimazole or other active substances, used fre-quently for the treatment of the skin diseases, can be easy intro-duced in the polymeric matrix of PVA and then delivered atcontrolled rate only in the desired area of the skin. Usually thesepharmaceutical products are displayed on the skin, and frequentlyare exposed accidentally or during the therapy, to the UV or gam-ma radiations. Such radiations can induce modifications of thestructure of the polymeric matrix or of the active substance, andfor this reason some researches were conducted in the directionof reducing the effect of such radiations [1–3]. The absorbance inthe UV domain can be modified by addition of TiO2 nanoparticlesand was already studied [4–6], but the behavior of such systemsunder gamma irradiation will offer complementary informationconcerning the applications of this polymer in medicine and phar-

ll rights reserved.

lniceanu Street, Cluj-Napoca591906.

Todica).

macy. The goal of this work is the observation of the behavior ofsuch systems under gamma irradiation.

2. Experimental

For our studies we used pure PVA membranes, and PVA mem-branes doped with different amount of TiO2, obtained from aque-ous gel of PVA. The gel is obtained from PVA in powder state anddistilled water. The weight concentration of polymer in water is20%. The mixture was stirred 4 h at constant temperature 25 �C,until a homogeneous dispersion of the polymer is obtained. Thenthe gel was displayed on a glass plate and kept 24 h in dark, atroom temperature, until the water evaporates. The doped mem-branes were obtained from this gel, before draying, by additionof different amounts of TiO2. The composition was stirred 4 hand then was dried 24 h in dark at room temperature. The concen-trations of TiO2, refereed to the weight of aqueous gel, were 10%and 20%.

The gamma exposure was realized using 60Co source with theflux of radiation 5.6 Gy/h, different time intervals correspondingto 24 KGy and 36 KGy. The X-ray diffraction (XRD) was performedwith Brucker X-ray diffractometer with Cr Ka (k = 0.228 nm) at45 kV and 40 mA. The 2h range of 20–120� was recorded. ESR spec-

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M. Todica et al. / Journal of Molecular Structure 1044 (2013) 328–330 329

tra were recorded at room temperature with Brucker-Biospin EMXspectrometer operating at X-band (9–10 GHz).

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Fig. 2. The ESR spectra of pure PVA and PVA doped with different concentrations ofTiO2 irradiated at D2 = 36 KGy. Pure PVA (curve A); PVA with 10% TiO2 (curve B);and PVA with 20% TiO2 (curve C).

3. Results and discussions

The interaction of high energy radiations with the substance,particularly gamma radiation, can induce electronic excitations,breaking of chemical bonds, or scission of the polymeric chains.UV–VIS investigation of PVA membranes submitted to high dosesof gamma radiation indicates the breaking of some chemical bondsfollowed by the delivery of free water and modification of the localconformation of the polymeric chain [5]. The breaking of chemicalbonds is frequently followed by the apparition of unpaired elec-trons of the atoms involved in the broken chemical bond, andcan be easy investigated by ESR technique [7,8]. Modifications in-duced by gamma radiations were observed also for other systems,polyvinyl alcohol/polyethylene glycol polymer blends, polyvinylalcohol/humic acids blends [9,10].

The ESR spectra were recorded for pure PVA membrane beforeand after exposure at D1 = 24 KGy and D2 = 36 KGy doses of gammaradiation. The spectrum of the unirradiated sample do not showany signal, (Fig. 1 curve A). After irradiation a strong signal, with-out hyperfine structure, is observed at B0 = 3365 G, (Fig. 1 curveB). The value of g factor is g = 2 that corresponds to free unpairedelectron, [11,12]. As suggested by Bhat et al. two mechanism arepossible: (i) the interaction of gamma photon with the hydrogenof OH bending group and the delivery of the H+ ion from this bond;and (ii) the interaction with the bond between the carbon and OHgroup followed by the breaking of this bond and the apparition ofOH� group [13]. Both mechanisms are accompanied by the appari-tion of unpaired electrons. The concentration of unpaired electronsincreases with the dose of radiation, that is shown by the increaseof the amplitude of the ESR signal, (Fig. 1 curve C).

Similar behavior was observed for the samples doped with TiO2.Before irradiation the ESR spectrum do not contains any signal, butafter irradiation a signal appears at the same value of B0 = 3365 Gas for the pure PVA; (g = 2). The effect was observed for both dosesof radiation. The similitude between the ESR spectra of doped andpure PVA membranes suggests that the unpaired electrons are pro-vided only by the PVA and not for the TiO2. On the other hand, at agiven dose of radiation, the amplitude of the absorption signal de-creases with the concentration of TiO2, (Fig. 2). The TiO2 nanopar-

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Fig. 1. The ESR spectrum of pure PVA before irradiation (curve A), and the spectraafter gamma irradiation at two doses; D1 = 24 KGy (curve B) and D2 = 36 KGy (curveC).

ticles behave like a shield against gamma radiation, reducing thenumber of gamma photons that interact with the PVA molecules.The screening effect of TiO2 increases with the concentration ofdopant that explains the decreases of the amplitude of the absorp-tion ESR signal with the increase of concentration of TiO2. These re-sults suggest a dispersion of TiO2 in the PVA matrix withoutchemical interaction [14–17]. This supposition is confirmed by Ra-man investigations of PVA-TiO2 systems reported in previous work[5], where the similitude between the spectra of pure PVA anddoped membranes, and the apparition of vibration bands at thesame wavenumbers for both kinds of sample, indicates no chemi-cal interaction between the TiO2 and PVA, without apparition ofnew chemical bonds.

An interesting effect of relaxation was observed after irradia-tion. The samples were kept 21 days in dark, at room temperature,and the ESR signal was recorded again. The amplitude of the signalof pure PVA decreases significantly after 21 days. Similar effect wasobserved for the doped membranes, (Fig. 3). The decrease of the

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Fig. 3. The ESR spectra of pure PVA and PVA with 10% TiO2 in irradiated state andafter 21 days of relaxation. Pure PVA irradiated (curve A); pure PVA after relaxation(curve B); PVA with 10% TiO2 irradiated (curve C); PVA with 10% TiO2 afterrelaxation (curve D).

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20 40 60 80 1002θ (deg)

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Fig. 4. The X-ray difractograms of pure PVA membrane gamma irradiated (curve A),and before irradiation (curve B). PVA with 20% TiO2 before irradiation (curve C), andirradiated (curve D).

330 M. Todica et al. / Journal of Molecular Structure 1044 (2013) 328–330

amplitude of the signal is determined by the decrease of the num-ber of unpaired spins of the systems. This behavior leads to theconclusion that a process of recombination of the unpaired elec-trons appears after irradiation.

Verification of the hypothesis of breaking chains by gammaradiation can be done by XRD technique. Every scission of thechains or breaking of chemical bonds increases the mobility ofpolymeric segments, having as effect the modification of local or-der of polymeric chains. Generally the polymeric membranes ob-tained from the aqueous gels are known as amorphous systems,but at high polymeric concentration the polymeric chains canadopt a local ordered arrangement, behaving like a crystallinestructure [18–20]. The lattice parameter of such structure has a va-lue close to the wavelength of X radiation. The structure of suchsystems may be investigated by XRD method. The difractogramof pure PVA membranes before gamma irradiation shows a broadpeak at 2h = 29� assigned to diffraction from the planes (101),(Fig. 4). The shape of the peak, broad with a maximum, showsthe existence of an important amount of the polymer in the amor-phous state, and also in the ordered state, [21,22]. The local orderin PVA is determined by hydrogen bonds between the hydrogenatoms and OH bending groups of the same chain or of the neigh-boring chains, [13,22]. The unit cell associated to this structure ismonoclinic with the parameters a = 7.81 Å, b = 2.5 Å andc = 5.51 Å [23]. The hydrogen bonds reduce the mobility of thechain and give some rigidity to the polymeric lattice. The ampli-tude of the peak of PVA decreases after irradiation. During the irra-diation, some hydrogen bonds are broken, the mobility of thechains increases, and some local ordered structures are destroyed[13]. The crystalline character of the sample decreases after irradi-ation, effect that explains the decrease of the amplitude of the dif-fraction peak (Fig. 4).

The samples containing TiO2 exhibit the characteristic peak ofPVA at the same angle 2h = 29� and supplementary peaks at2h = 38.2�, 2h = 56.4�, 2h = 74.5� and 2h = 86.4�, associated to TiO2

dopant [13,14]. After irradiation the amplitude of the peak ofPVA decreases, like in the case of pure membrane, but still remains

at the same angle. The gamma radiation produces scission of thepolymeric chains and increases theirs mobility, but the TiO2 nano-particles prevent the local reorganization of the chains in new crys-talline structures. The effect is the decrease of the local order of thepolymeric matrix that explains the modification of the intensity ofthe diffraction peak of PVA after irradiation. On the other hand theamplitude and the position of the TiO2 peaks remain almost un-changed. This behavior suggests that the TiO2 nanoparticles arenot affected by irradiation, only the polymeric matrix being subjectto modifications.

4. Conclusions

The gamma irradiation of pure PVA membranes producesbreaking of the chemical bonds and scission of the polymericchains followed by the apparition of unpaired electrons. The effectis more intense when the dose of radiation increases. After irradi-ation an effect of recombination of unpaired electrons appearsafter 21 days of relaxation. The PVA-TiO2 system behaves like a dis-persion of nanoparticles in the polymeric matrix without chemicalinteraction. The presence of TiO2 nanoparticles diminishes the ef-fect of the gamma radiation on the polymeric matrix, havingshielding effect against the gamma rays. However the structureof those nanoparticles is not affected by the irradiation.

Acknowledgments

This work was supported by CNCSIS-UEFISCDI, project PNII –ID_PCCE_101/2008 and PNII – ID_PCCE_129/2008.

References

[1] Viorica Simon, Fizica Biomaterialelor, Presa Universitara Clujeana, Cluj-Napoca, 2002.

[2] C.D. Nechifor, D.O. Dorohoi, C. Ciobanu, Rom. J. Phys. 54 (3–4) (2009) 349.[3] H. Kaczmarek, A. Podgorski, J. Photochem. A: Chem. 191 (2007) 209.[4] M. Todica, L. Udrescu, C.V. Pop, M. Pop, T. Stefan, S. Simon, Stud. UBB Chem. 3

(LVI) (2011) 165.[5] M. Todica, L. Udrescu, Cent. Eur. J. Phys. 9 (6) (2011) 1536.[6] L. Udrescu, E. Dinte, C.V. Pop, T. Stefan, M. Todica, Stud. UBB Phys. 2 (LVI)

(2011) 167.[7] G. Damian, Talanta 60 (2003) 923.[8] O. Cozar, V. Chis, L. David, G. Damian, I. Barbur, J. Radioanal. Nucl. Chem. 220

(2) (1997) 241.[9] S.G. Abd Alla, H.M. Said, A.W.M. El-Naggar, J. Appl. Sci. 94 (2004) 167.

[10] M. Ilcin, O. Hola, B. Bakajova, J. Kucerik, J. Radioanal. Nucl. Chem. 283 (2010) 9.[11] Al. Nicula, Rezonant�a magnetica, Editura didactica s�i pedagogica, Bucures�ti,

1980.[12] G.E. Pake, Paramagnetic Resonance, Benjamin Inc, New York, 1962.[13] N.V. Bhat, M.M. Nate, M.B. Kurup, V.A. Bambole, S. Sabharwal, Nucl. Instrum.

Meth. B 237 (2005) 585.[14] C.C. Yang, J. Membr. Sci. 288 (2007) 51.[15] S. Mallakpour, A. Barati, Prog. Org. Coat. 71 (2011) 391.[16] X. Chen, J. Mater. Sci. Lett. 21 (2002) 1637.[17] H.M. Nizam El-Din, A.M. El-Naggar, I.A. Faten, Polym. Int. 52 (2002) 225.[18] M. Rubinstein, R. Colby, Polymer Physics, Oxford University Press, Oxford,

2002.[19] P.G. De Gennes, Scaling Concepts in Polymer Physics, Cornell University Press,

Ithaca, 1979.[20] J.P. Cohen, Addad NMR and Fractal Properties of Polymeric Liquids and Gels,

Pergamon Press, London, 1992.[21] W.H. Eisa, Y.K. Abdel-Moneam, Y. Shaaban, A.A. Abdel-Fattah, A.M. Abou Zeid,

Mater. Chem. Phys. 128 (2011) 109.[22] K.A. Bogle, S.D. Dhole, V.N. Bhoraskar, Appl. Phys. Lett. 88 (2006) 263105.[23] C.W. Bunn, Nature 161 (1948) 929.