ESR and XRD investigation of effects induced by gamma radiation on PVA-TiO2 membranes

Cent. Eur. J. Phys.DOI: 10.2478/s11534-013-0276-3

Central European Journal of Physics

ESR and XRD investigation of effects induced bygamma radiation on PVA -TiO2 membranes

Research Article

Mihai Todica∗, Traian Stefan, Diana Trandafir, Simion Simon

“Babes-Bolyai” University, Faculty of Physics, No. 1, M. Kogalniceanu, Cluj-Napoca 400084, Romania

Received 27 January 2013; accepted 28 June 2013

Abstract: The effects of gamma radiation on the local structure of PVA membranes containing TiO2 were investigatedby ESR and XRD methods. An intense ESR signal is observed after irradiation at 16 KGy dose. This signalappears only for irradiated samples and it is associated with the breaking of the polymeric chain, followedby local reorganization of the polymeric segments and the apparition of the unpaired electrons and freeradicals. The intensity of the signal decreases with the concentration of TiO2, indicating a shielding effect ofthe dopand. That the modification of local order of the polymeric chains has been modified after irradiationis confirmed by XRD method.

PACS (2008): 82.70.Dd; 82.70.Gg; 82.90.+j

Keywords: poly(vinyl alcohol) (PVA) • ESR • XRD • TiO2 • gamma irradiation© Versita sp. z o.o.

1. Introduction

The development of systems with controlled release ofmedical drugs is currently of interest to the pharmaceuti-cal industry. One of the solutions proposed for this pur-pose is the encapsulation or the introduction of the druginto a bio degradable or soluble matrix, [1, 2]. Polymersare preferred for this purpose because they have the ca-pacity to form an elastic network which can include themedical drug in theirs pores or holes. The poly(vinyl alco-hol) (PVA) is a hydrophilic polymer, with high bio compat-ibility, that can be easily crosslinked by different chemicalor physical methods in order to obtain hydro gels or mem-branes suitable for carrying medical drugs. For example,

∗E-mail: [email protected]

PVA crosslinked hydrogels obtained by repeated freez-ing/thawing methods were used for the controlled releaseof proteins charged in multilaminate membranes, [3, 4].Hydrogels obtained by freeze-thaw cycling are used tointroduce artificial cartilage for orthopedic implants, [5].Photo-crosslinked poly(vinyl alcohol) hydrogels contain-ing different medical agents were used as the releasevehicle for wound healing applications, [6]. PVA cryo-gels obtained by repeated freezing and melting were em-ployed as matrices for cell immobilization, [7, 8]. Somecrosslinked PVA gels have also been obtained by irra-diation with specific doses of gamma radiation, [9, 10].Furthermore, PVA gels offer the possibility of including intheir structure certain inorganic compounds that can en-hance the physical properties of the polymeric matrix, butwhich are biologically inert. For instance, the introductionof TiO2 in to polymeric matrices enhances the viscoelasticproperties of PVA hydrogels, [11]. The doped PVA mem-

ESR and XRD investigation of effects induced by gamma radiation on PVA -TiO2 membranes

branes with TiO2 are used in the photocatalytic degra-dation of ethanol, [12], and cross linked PVA containingTiO2 nanoparticles are used for humidity sensors, [13]. Inmedicine TiO2 is introduced into the polymeric matrix inorder to reduce the penetration of UV radiation, but alsofor its antimicrobial action, [14–17].During the sterilization process or during the therapythese pharmaceutical systems are frequently submitted togamma exposure. The effect of such high energy radia-tion on the polymeric support could be the breaking ofthe polymeric chains with the apparition of free radicals,and perturbation of the ordered domains of the polymericmatrix, [18]. The free radicals could have a negative effecton the health of the patient do to their capacity to interactwith DNA structures, leading to the apparition of cancercells. On the other hand, the modification of the crys-tallinity of the polymeric matrix affects the rigidity of thepolymer and the capacity of spreading of the pharmaceu-tical product on the skin surface. Moreover, the delivery ofthe drug from the matrix is influenced by the crystallinityof the polymer. Preliminary works focused on hydrogelsof PVA without dopants, and reported: the possibility ofcross-linking this polymer by irradiation; the modificationof the viscosity under irradiation; the effect of such radia-tion on polymers submerged in water; qualitatively mod-ification of certain physical properties [19]. However, thestructural modification of the system PVA – TiO2 undergamma irradiation has yet to be fully investigated, andthis represents the aim of our work. The most appropriatetechniques for this study are Electronic Spin Resonance(ESR) and X-Ray Diffraction (XRD). ESR measurementscan indicate the apparition of unpaired electrons and freeradicals, and XRD can detect all modification of the crys-tallinity of the system, [20].

2. Materials and methods

For our study we used pure PVA membranes, and PVAmembranes containing different amounts of TiO2, 1%, 20%and 30%. Both kinds of sample were obtained from aque-ous PVA gels. The gels were prepared by mixing the poly-mer with distilled water, at constant temperature 55◦C forthree hours, until a homogeneous dispersion of polymerwas obtained. Then the gel was displayed on glass platesand kept 24 hours in darkness at room temperature. Thepure membranes were obtained directly from this gel bysimple evaporation of water. The PVA-TiO2 membraneswere obtained from the aqueous gel in which the TiO2

was introduced at the desired concentration. The mixturewas stirred for four hours at room temperature and thendisplayed on glass plates and dried for 24 hours. The

samples were analyzed in their original state and aftergamma exposure. The gamma exposure was realized us-ing a 60Co source with radiation flux 5.6 Gy/h until the16 KGy dose was accumulated. The X-ray diffraction wasperformed with a Brucker X-ray diffractometer with CuKα λ = 1.54 Å at 45 KV and 40 mA. The 2θ range of 10–120◦ was recorded. ESR spectra were recorded at roomtemperature with a Brucker-Biospin EMX spectrometeroperating at X-band (9 – 10 GHz).

3. Results and discussion

PVA is one of the simplest polymers containing inits monomer only carbon, hydrogen and oxygen atoms(CH2CHOH). The connections between two adjacentmonomer is realized trough the carbon covalent bonds ofthe backbone chain. The oxygen and hydrogen atoms areincluded in OH bending groups and don’t participate tothe connections between the monomers, but these atomsparticipate in the hydrogen bonds established betweenthe bending groups OH of two neighboring chains, [21]. Adetailed description of the behavior of the hydrogen bondsin the excited state, caused by the interaction of matterwith radiation is presented in references [22, 23].Due to its high energy, the gamma radiation interactswith the electrons of the atoms inducing electronic exci-tation or even ionization of the atoms with the apparitionof unpaired electrons. Occasionally these processes areaccompanied by the breaking of chemical bonds and ap-parition of free radicals. For PVA molecules the mostsusceptible bonds that may be affected by gamma radia-tion are the connections between hydrogen and oxygen,and hydrogen and carbon. A possible mechanism for thisis the breaking of the bond between hydrogen and oxygenof OH bending group with the delivery of the H+ ion fromthis bond. The oxygen of this broken bond can form adouble bond with its neighboring carbon only if this car-bon breaks its covalent bond with the next monomers. Theeffect is the scission of the chain on the right side of themonomer, (Fig. 1a). Another possibility is the breakingof the bond between the backbone carbon and OH groupwith the delivery of OH− ion. The carbon atom has thetendency to form a double bond with its neighboring car-bon, but this is possible only if this carbon atom breaks itsbond with the previous monomer. The result is the scissionof the chain on the left side of the monomer, (Fig. 1b). Theions H+ and OH− can combine together to create watermolecules. The final effect is the breaking of the backbonechain with the creation of double bonds C=C and C=O inthe repeat unit and the apparition of water molecules [21].The possibility also exist of a gamma photon breaking the

Mihai Todica, Traian Stefan, Diana Trandafir, Simion Simon

PVA monomers

H

C C C C

H H H H

H O

H

O

+ H+

H

C C C C

H H H H

H O

H

O

H hν

a)

hν

H

C C C C

H H H H

H O

H

O

H

H

C C C C

H H H H

H O

H

+ OH-

b)

OH- H

+ H2O +

+ H+

C C

H

H O

H

H

C C

H H

O

H

hν c) *

Figure 1. The scission of backbone chain of PVA under gamma ir-radiation followed by the apparition of OH− and H+ ionsand free radicals.

14

Fig. 2

-2 108

-1 108

0

1 108

2 108

3200 3300 3400 3500

Am

pl [a

rb.

un

its]

B [gauss]

A

B

Figure 2. The ESR spectra of pure PVA membranes. A before irra-diation; B after irradiation.

bond between H and C atoms of H–C–OH group with-out other rearrangement of the chemical bonds inside themonomer, [24]. The effect in this case is the apparitionfree radical –(CH2–C–OH)– and H+ ion, (Fig. 1c). Theexistence of unpaired electrons and free radicals can bereadily observed by ESR technique, [25, 26].The effect of irradiation on pure PVA membranes is clearlyshown by ESR spectra recorded before and after irradia-tion, (Fig. 2). Before irradiation the sample gives a weakESR signal, indicating the existence of a small quantity

15

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300

400

3200 3300 3400 3500

PVA 30% TiO2

PVA 1% TiO2

PVA 20% TiO2

Am

pl [a

rb.

un

its]

B [gauss]

Figure 3. The ESR spectra of PVA membranes with different amountof TiO2 after irradiation.

of unpaired electrons. After irradiation a strong signalwithout hyperfine structure appears at 3365 G (g = 2.02),associated with the presence of a great number of un-paired electrons. This signal is determined by the un-paired electron on the substrate 2p of the oxygen of theOH− ion resulting from the breaking of –C–O–H bonds,or the unpaired electrons of the free radicals produced bythe mechanism presented above. Previous work reportedby the authors showed the increase of the amplitude ofthis signal with the dose of radiation [27]. Similar ESRinvestigations were made on samples with TiO2. For thesesamples the quantity of TiO2 is different but the quantityof PVA is the same, in order to have the same contributionof the polymer to the ESR signal for all the samples. Asin the case of pure PVA, the samples give very weak ESRsignals before irradiation. This means that the TiO2 doesnot contribute to the ESR signal. After irradiation a strongsignal appears at 3365 G with the same shape and char-acteristics as the signal of pure PVA, (Fig. 3). The similar-ity between the ESR spectra of irradiated pure PVA andPVA-TiO2 membranes suggests that the unpaired elec-trons appear only from the PVA monomers: the electronicstructure of TiO2 is not perturbed by irradiation. This be-havior is observed for all the samples whatever the con-centration of TiO2. At a given dose of radiation the ampli-tude of the ESR signal decreases progressively with theincrease of the concentration of TiO2, (Fig. 3). We can af-firm that the number of unpaired electrons produced by agiven dose of radiation is influenced by the concentrationof TiO2. These nanoparticles behave like a shield againstthe gamma photons.An important phenomenon observed is the relaxation ofthe ESR signal. After receiving the maximum dose


16

0

100

200

300

400

3200 3300 3400 3500

PVA 1% TiO2 irrad

PVA 1% TiO2 relax

PVA 30% TiO2 irrad

PVA 30% TiO2 relax

Am

pl [a

rb u

nits]

B [gauss]

Figure 4. The amplitude of the ESR spectra of PVA membranes con-taining 1% and 30% TiO2, before and after 7 days of re-laxation.

D = 16 KGy the irradiation was stopped, the sampleswere kept in dark at room temperature, and the ESR spec-tra were recorded after 7 days of relaxation. We observeda reduction of the amplitude of the ESR signal after thisperiod of time. For pure PVA this behavior has been re-ported previously, [27]. Similar behavior is observed forthe samples with TiO2, but the effect is less pronouncedespecially at high concentration of TiO2. For instance forthe sample with 1% TiO2 the amplitude of the remain-ing ESR signal after 7 days of relaxation represents 64% of its initial value, and for the sample with 30% TiO2

the amplitude remains almost constant, (Fig. 4). As pre-sented previously a possible effect of gamma radiation isthe breaking of the H-C- bonds with the formation of freeradicals, or the breaking of the bending OH groups ofPVA with the apparition of OH− and H+ ions. These pro-cesses cease when the irradiation is stopped. The OH−

and H+ ions have the tendency to recombine giving riseto water molecules, so called free water [21]. The freeradicals also have a tendency to recombine. This leadsto a reduction in the concentration of unpaired electronsand thus a reduction in the amplitude of the ESR signal.However, this effect of recombination is affected by thepresence of the TiO2, being less significant when the con-centration of TiO2 increases. A possible explanation forthis phenomenon may be the reduction of the local mobil-ity of the polymeric segments in the presence of TiO2, [28].The migration and the possibility of recombination of OH−

and H+ ions or of the free radicals are diminished, whichreduces the relaxation effect.The potential breaking of polymeric chains by gamma ra-diation, and the modification of the local arrangement of

17

Fig. 5.

0

100

200

300

400

500

10 20 30 40 50 60 70 80 90

Am

pl [a

rb. u

nits]

2 θ [deg]

A

B

C

Figure 5. The diffractograms of pure PVA membranes before irradi-ation (curve A), simulation of data before irradiation (curveB), and after irradiation (curve C).

polymeric segments, may be investigated by the XRDmethod. Usually the polymeric materials don’t presentany structural order, being known as amorphous mate-rials, [29]. However in some cases, the peculiarities ofthe monomer allow the apparition of some ordered forma-tions along the chain itself or between two neighboringchains, known as crystalline domains, [30]. For PVA theapparition of such structures is determined by the hy-drogen bonds that may appear between the H and OHbending groups, [21]. These links allow the arrangementof different segments of the same chain in parallel struc-tures, or the arrangement of entire regions of two differentchains in parallel domains, [31]. Such ordered domains be-have like the atomic planes of a rigid lattice of crystallinesolid producing the diffraction of X rays. The unit cell ofPVA is monoclinic with the parameters a = 7.81, b = 2.5,c = 5.51 Å, β=91.42◦ and comprises two monomer unitsof vinyl alcohol, [32].The XRD diffractograms of pure PVA, before irradiation,show a broad signal between 10◦ and 22◦, with threepeaks, (Fig. 5). From literature it is known that the crys-talline phase of PVA produces maximum diffraction at 2θ= 19◦, corresponding to a mixture of planes (101) and (10-1), [21]. The enlargement of this peak is determined by theincrease of the amorphous phase to the detriment of crys-talline phases [29, 33]. This peak can be observed in ourdiffractograms at 2θ = 19.6◦, and confirms the significantpresence of material in the crystalline phase. The othertwo peaks are observed at 2θ = 13.5◦ and 16.3◦. Thesepeaks have also been observed by other authors, [21, 34].They are determined by the diffraction from (100) and (00-


1) planes. Due to the broadening of the signal, the peaksat 2θ = 13.5◦ and 16.3◦ are superposed on the peak at 2θ= 19.6◦. They can be clearly separated by numerical sim-ulation, (Fig. 5). Here, each peak was represented by aGaussian function centered on the corresponding diffrac-tion angle, with the amplitude and the width as adjustableparameters. After simulation we obtained the amplitudeof each peak as 49, 115 and 102 arbitrary units (in oursystem of reference), and the area under each peak as 38,102 and 807 arbitrary units, corresponding to diffractionangles 2θ =13.5◦, 16.3◦ and 19.6◦. The total area of thesignal between 10◦ and 22◦ is 947 arbitrary units. Thearea under each peak is proportional with the concen-tration of the corresponding crystalline phase. The per-centages of these phases, relative to the total crystallinephase and for each diffraction angle, are 4%, 10.7% and85.3%. These parameters were used to monitor the evo-lution of the system during the irradiation and relaxationprocesses.

After irradiation at D = 16 KGy dose, the diffraction signalremains broad in the angular domain, 10◦ – 22◦, but mod-ifications of the amplitude of the three peaks appear. Thepeak amplitudes at 2θ =13.5◦ and 16.3◦ increase to 66and 150 arbitrary units respectively, and the amplitude ofthe peak at 19.6◦ decreases to 62 arbitrary units, (Fig. 5).The relative changes in peak amplitudes, before and af-ter irradiation, reveal that structural rearrangements takeplace. In the unit cell of PVA crystal the molecular chainsare held together by the hydrogen bonds. Under gammairradiation these bonds break and the polymeric segmentsare free to rotate. The rotation in the clockwise directionis more probable making the direction (001) richer in thenumber of atoms, [21]. Thus we can explain the modifica-tion of the intensity of these peaks. Quantitative evalua-tion of the crystallinity is given by the area of the peaks.The values of these areas, after irradiation, are 52, 133,490, and the total area of the signal between 10◦ and 22◦

is 675 arbitrary units. The percentages of the crystallinephases corresponding to each peak are 7.7%, 19.7% and72.6%. The proportion of crystalline phase correspond-ing to the first two peaks, compared with the unirradiatedsample, increases after irradiation to the detriment of thethird peak. On the other hand the total area under thecurves, between 10◦ and 22◦, after irradiation is smallerthan before irradiation. This fact indicates not only a mod-ification in the percentage of different crystalline phasesof PVA, but a general reduction of the crystalline phaseof the polymer.

The samples containing TiO2, before irradiation, exhibitthe characteristic broad signal of PVA with three peaksat 2θ =13.5◦, 16.3◦ and 19.6◦, and supplementary peakscharacteristic of TiO2. We can observe a modification of

the amplitude of the peaks of PVA when the concentrationof TiO2 increases, (Fig. 6a). The amplitude of the peaksat 2θ =13.5◦ and 16.3◦ is maximum for the sample with1% TiO2, and decreases progressively for the samples with20% and 30% TiO2. This evolution indicates a reductionof the diffraction on the planes (100) and (00-1) with theconcentration of TiO2. The peak at 19.6◦ is difficult toobserve in empirical data because it is broad and of lowamplitude relative to the two other peaks. For better ob-servation of this peak, we extracted from the experimentaldata the values corresponding to the other two peaks andwe represented only the remaining values. Now we canclearly see the peak at 19.6◦ and we can watch its evolu-tion with the concentration of TiO2, (Fig. 6b). Its ampli-tude decreases progressively as the concentration of TiO2

increases. That corresponds to a reduction in diffractionon the planes (101) and (10-1). Similar behavior was ob-served by Mallakpour et al. for PVA with 10% TiO2, [28].Not only the amplitude, but also the area under the exper-imental curves between 100 and 22◦ decreases progres-sively with the concentration of TiO2; A=1418; 758; 538arbitrary units for the concentrations 1%, 20% and 30%.The evolution of these parameters indicates a decrease ofthe crystallinity of the polymer when the concentration ofTiO2 increases.

Apart from the peaks of PVA these diffractograms con-tain distinctive peaks of TiO2. For instance at 1% TiO2

concentration we can observe peaks at 2θ=25.2◦ (corre-sponding to the 101 plane of anatase phase), 2θ = 27.4◦

(corresponding to the 110 plane of rutil phases), and otherpeaks at 38◦, 64◦, 77◦, (Fig. 6b), [35]. When the con-centration TiO2 increases, these peaks appear again, butsupplementary peaks appear at 2θ= 46◦, 48◦, 54◦, 55◦

and 63◦ for samples with 20% and 30% TiO2, (Fig. 6b).Analyzing the diffractograms of samples with TiO2 we re-mark notable modifications only of the peaks of PVA andminor modifications on the TiO2 spectrum. That means areduction of the ordered phase and the increase of amor-phous phase of the polymer when the concentration ofTiO2 increases, [33]. The TiO2 nanoparticles dispersedin the polymeric matrix reduce the mobility of polymericchains and prevent the organization of polymeric segmentsin local ordered structures. The amorphous phase of thepolymer is dominant in membranes with TiO2.

For the irradiated samples, (D = 16 KGy), we can ob-serve the characteristic peaks of TiO2 without modifica-tion. Their position, shape and amplitudes remain un-changed before and after irradiation, indicating low effectof gamma photons on the structure of the TiO2. For thePVA the situation is subtly different. The broad signalobserved before irradiation persists, but a modification ofits amplitude occurs. Although the signal contains the


18

Fig. 6 a

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200

400

600

800

1000

1200

10 20 30 40 50 60 70 80 90

PVA 30% TIO2

PVA 20% TIO2

PVA 1% TIO2

2 θ [deg]

Am

pl [a

rb. u

nits]

(a)

19

Fig. 6 b

50

100

150

200

250

300

10 20 30 40 50 60 70 80 90

C PVA 30% TIO2

B PVA 20% TIO2

A PVA 1% TIO2

2 θ [deg]

Am

pl [a

rb. u

nits]

A

B

C

(b)

Figure 6. (a) The diffractograms of PVA membranes with 1%, 20%and 30% TiO2 before irradiation.(b) Detailed representation of the peak at 19.6◦ of PVAmembranes with 1%, 20% and 30% TiO2 before irradia-tion.

three peaks at 2θ =13.5◦, 16.3◦ and 19.6◦, we retainedfor our observation only the peak at 19.6◦, this one beingrepresentative of the cristallinity of PVA. It was disclosedfrom the other three by the same method used previouslyfor unirradiated doped samples. However we mention thatthe other two peaks follow the same evolution of amplitudeas the third one. At low concentration of TiO2, i.e. 1%, theamplitude of the peak at 2θ =19.6◦ signal decreases sig-nificantly after irradiation (from A = 135 arbitrary unitsto A = 70 arbitrary units, representing a decreases of

20

Fig. 7

0

50

100

150

200

250

10 20 30 40 50 60 70 80 90

A PVA 1% TiO2 relax

B PVA 1% TiO2 irrad

C PVA 1% TIO2 unirrad

Am

pl [a

rb. u

nits]

2 θ [deg]

A

B

C

Figure 7. The diffractograms of PVA membranes with 1% TiO2, be-fore irradiation, irradiated and relaxed 7 days.

21

Fig. 8

0

50

100

150

200

10 20 30 40 50 60 70 80 90

A PVA 20% TiO2 relax

B PVA 20% TiO2 irrad

C PVA 20% TIO2 unirrad

Am

pl [a

rb. units]

2 θ [deg]

A

B

C

Figure 8. The diffractograms of PVA membranes with 20% TiO2,before irradiation, irradiated and relaxed 7 days.

about 48%), (Fig. 7). The behavior of this sample is closeto that of a pure membrane. The concentration of TiO2

is too small to prevent major migration and reorganiza-tion of polymeric segments in ordered structures after thebreaking of the chains induced by irradiation. The highdynamics of the polymeric chains facilitates the existenceof amorphous phase of PVA, an effect that induces thebroadening of the PVA signal. When the concentration ofTiO2 increases the amplitude of the diffraction signal ofirradiated PVA membranes decreases again, but less sig-nificantly compared with the sample 1%. For the samplewith the concentration 20% the amplitude of the signal of


irradiated sample represents about 95% of the amplitudeof the unirradiated one, (Fig. 8). At higher concentration,i.e. 30%, the amplitude remains almost constant. This be-havior accords with the ESR measurements and confirmsthe reduction of the probability of local organization of thepolymeric segments in ordered structures in the presenceof TiO2 nanoparticles.The XRD method was also used to observe the evolutionof the local organization of polymeric chains after irradi-ation, during the relaxation process. The diffractogramsof doped samples before and after relaxation are similarfor characteristics set by TiO2, but contains some mod-ifications in the domain of PVA’s peaks. The character-istic peaks of TiO2 are not affected by the irradiation orrelaxation process, indicating a stable structure, but theamplitude of the peak at 2θ=19.6◦ from PVA decreasesafter irradiation during the relaxation period. As demon-strated by ESR, the gamma irradiation produces break-ing of the polymeric chains, followed by an increase intheir mobility the system evolving into a less organizedstructure. This process continues during the relaxationperiod, leading the system towards more favorable ener-getic states and less structure. For example, after 7 daysof relaxation the amplitude of the 2θ=19.6◦ peak of PVAof the sample with 1% TiO2 is smaller than its amplitudebefore relaxation, (Fig. 7). Similar behavior is observedfor all the concentrations of TiO2. However the amplitudeof the 2θ=19.6◦ peak of PVA decreases less significantlyfor the sample with 20% TiO2 (Fig. 8), and remains almostconstant for the sample with 30%. Being hydrophilic andhaving high polarity the TiO2 nanoparticles interact withthe OH bending groups of PVA attracting them. Havinghigh surface area, the nanoparticles have the tendency tobe surrounded by many such groups belonging to differ-ent neighboring segments of the same chain or of differentneighboring chains, [28]. The situation that appears in thedoped polymeric system is in someway similar with thatin the case of cross linking of the polymer with S or Siatoms. However the links with TiO2 are weaker than thecovalent bonds that appear in the case of vulcanization,but enough to reduce the mobility of the polymeric seg-ments. In these conditions the migration and the localreorganization of the broken chains after irradiation andduring the relaxation period is less probable at high con-centrations of TiO2.

4. Conclusions

The behavior of pure PVA membranes and PVA mem-branes with TiO2 before and after gamma irradiation wasinvestigated by ESR and XRD techniques. ESR measure-

ments reveal the apparition of unpaired electrons after ir-radiation, an effect associated with the breaking of chemi-cal bonds, scission of the polymeric chains and apparitionof free radicals. The effect is more intense for pure PVAmembranes and decreases in intensity when the concen-tration of TiO2 increases. This behavior suggests an effectof shielding against gamma radiations played by TiO2.The breaking of chemical bond and scission of the chainsare accompanied by modifications to the local organizationof the polymeric segments. XRD measurements indicatethe increase in the amorphous phase to the detriment ofthe crystalline phase of the PVA matrix during irradiation,but no modifications to the structure of the TiO2. The TiO2

nanoparticles prevent the organization of polymeric chainsin local ordered structures.For the irradiated samples, a diminution of the amplitudeof the ESR signal is observed after 7 days of relaxation.This effect is associated with a recombination process ofunpaired electrons after irradiation. The effect is less sig-nificant for doped samples. However the recombination isfollowed only by a little modification of the crystallinityof the polymer during the relaxation process, as can beseen from XRD measurements.Our investigations show the modification of the localstructure of the polymeric matrix under gamma exposure,and the possibility of limiting this effect with the additionof TiO2 nanoparticles.

Acknowledgment

This work was developed on the framework: SEC-TORAL OPERATIONAL PROGRAM FOR HUMANRESOURCES DEVELOPMENT 2007 – 2013, POS-DRU/107/1.5/S/76841 – “Innovative doctoral studies ina Knowledge Based Society”, Babes-Bolyai University,Cluj-Napoca, Romania, Ph.D. scholarship granted to Tra-ian Stefan, and CNCSIS-UEFISCDI, project PNII –ID_PCCE_101/2008

References

[1] S. Freiberg, X. X. Zhu, Int. J. Pharm. 282, 1 (2004)[2] K. E. Uhrich, S. M. Cannizzaro, R. S. Langer, K. M.

Shakesheff, Chem. Rev. 99, 3181 (1999)[3] C. M. Hassan, N. A. Peppas, Adv. Polym. Sci. 153, 37

(2000)[4] C. M. Hassan, J. E. Stewart, N. A. Peppas, Eur. J.

Pharm. Biopharm. 49, 161 (2000)[5] M. Kobayashi, H. S. Hyu, Materials 3, 2753 (2010)


[6] S. L. Bourke, M. Al-Khalili, T. Briggs, B. B. Michniak,J. Kohn, L. A. Poole-Warren, AAPS PharmSci. 5, E33,1 (2003)

[7] F. Yokoyama, I. Masada, K. Shimamura, T. Ikawa, K.Monobe, Coll. Polym. Sci. 264, 595 (1986)

[8] V. I. Lozinsky, A. L. Zubov, E. F. Titova, Enzyme. Mi-crob. Tech. 20, 182 (1997)

[9] N. A. Peppas, E. W. Merrill, J. Polym. Sci. Polym.Chem. Ed. 14, 441 (1976)

[10] A. Danno, J. Phys. Soc. Jpn. 13, 722 (1958)[11] X. Lia, S. Dong, H. Yan, C. Wu, 2011 Chinese Ma-

terials Conference, Procedia Engineering 27, 1488(2012)

[12] H. Mossalayi, F. Oshal, J. Chem. Pharm. Res. 3, 743(2011)

[13] M. Joshi, R. P. Singh, Sensors & Transducers 110,105 (2009)

[14] H. Ruixia, W. Leigang, W. Jin, H. Nan, Appl. Surf. Sci.256, 5000 (2010)

[15] M. Todica, L. Udrescu, C.V. Pop, M. Pop, T. Stefan, S.Simon, Studia UBB Chemia, LVI 3, 165 (2011)

[16] G. Thilo et al., J. Am. Dermatology 55, 882 (2006)[17] R. Yanagisawa et al., Exp. Biol. M. 234, 314 (2009)[18] C. D. Nechifor, D. O. Dorohoi, C. Ciobanu, Rom. J.

Phys. 54, 349 (2009)[19] O. Saito, J. Phys. Soc. Jpn. 14, 792 (1959)[20] B. Stuart, Polymer Analysis (John Wiley & Sons,

Chichester, 2002)[21] N. V. Bhat, M. M. Nate, M. B. Kurup, V. A. Bambole,

S. Sabharwal, Nucl. Instrum. Meth. B 237, 585 (2005)[22] G.J. Zhao, K.L. Han, Acc. Chem. Res. 45, 404 (2012)[23] M.X. Zhang, G.J. Zhao, ChemSusChem 5, 879 (2012)[24] H. Zahr El-Deen, A.I. Hafez, Arab. J. Sci. Eng., 34, 13

(2009)[25] G. Damian, Talanta 60, 923 (2003)[26] O. Cozar, V. Chis, L. David, G. Damian, I. Barbur, J.

Radioanal. Nucl. Ch. 220, 241 (1997)[27] M. Todica, L. Udrescu, G. Damian, S. Astilean, J.

Molec. Struct. 1044, 328 (2013)[28] S. Mallakpour, A. Barati, Prog. Org. Coat. 71, 391

(2011)[29] M. Tamasan, V. Simon, Dig. J. Nanomater. Bios. 6,

1311 (2011)[30] J. P. Cohen, Addad, Physical properties of polymeric

gels (John Wiley & Sons, Chichester, 1996)[31] V. N. Kuleznev, V. A. Shershnev, The Chemistry and

Physics of Polymers, (Mir Publishers, Moscow, 1990)[32] C. W. Bunn, Nature 161, 929 (1948)[33] C.-C. Yang, Mat. Lett. 58, 33 (2003)[34] G. Nasar, M. S. Khan, U. Khalil, J. Pak. Mater. Soc.

3, 67 (2009)[35] M. Hamadanian, A. Reisi-Vanani, A. Majedi, J. Iran.

Chem. Soc. 7, S52 (2010)

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