Silver nanocrystals were synthesized in natural rubber matrix via UV irradiation technique. A high intensity UV light with a wavelength below 300 nm was used to reduce the silver ions in the natural rubber matrix

Abu Bakar, M.

Abu Bakar, N. H. H.

Ismail, J.

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·iMicroSoM. Vol 7, No 1 (April 2004)SILVER NANOCLUSTERS AND NANOFRACTALS INNATURAL RUBBER MATRIXN. H. H. Abu Bakar, J. Ismail*, and M. Abu BakarSchool of Chemical Sciences, Universiti Sains Malaysia, 11800 Minden, Penang, Malaysiajamis@usm.myABSTRACTSilver nanocrystals were synthesized innatural rubber matrix via UV irradiationtechnique. A high intensity UV light with awavelength below 300 nm was used toreduce the silver ions in the natural rubbermatrix. Silver ions (AgN03) were reduced intwo different mitural rubber environments i.efilm and colloid. The resulting silvernanocrystals obtained were compared interms of the morphology and particle sizedistribution investigated using transmission. electron microscopy (TEM). Studies showedthat small silver nanoparticles were obtainedin natural rubber - silver (NR - Ag) filmswhile nanofractals were formed in the NR -Ag colloids. XRD analysis confIrmed theface centered cubic (fcc) structure of thesilver crystals.INTRODUCTIONMaterials manufactured from polymerscontaining noble metal nanoparticles havereceived tremendous attention in the pastfew years. Synthetic as well as natural"polymer$ such as PMMA1 and chitosan2have been used as stabilizers and matrices.Natural rubber latex or also known as cis - 1,4 - polyisoprene is a natural colloidobtained from the tree Hevea Brasiliensis.Due . to its excellent properties andrenewablity, it has been widely used inmanufacturing industries such as tyres andgloves3. In an effort to broaden the use ofthis polymer in other fields, the first stepwas taken in implanting nanosized metalparticles in films cast from the latex as wellas stabilizing them in natural rubber colloid.14Nanosize" noble metals display variousproperties compared to its bulk material.Different methods have been widelyinvestigat~d in order to control the size of"the nanocrystals formed. Among them are",chemical reduction4 - 5 and irradiationtechniques6• Here, we discuss the formation"of silver nanoclusters in natural rubbermatrix, synthesized by UV irradiation.MATERIALS AND METHODSNatural rubber latex, a gift from BARD(Malaysia) Sdn Bhd, was centrifuged at"5613g using a Kubota Model 5800centrifuge. The cream phase was separatedand diluted to 30% DRC. with doublydistilled water to obtain clean natural rubberlatex. Following this, 1 g of the clean latexwas weighed and diluted with 20 ml ofdistilled water. This colloid was then addedwith 2.94 x 10-5 mol of silver nitrate(AgN03) (Johnson Matthey, U.K.) andsubsequently, the mixture was homogenizedfor 30 minutes.Two samples were preparedfor lEM analyses. An aliquot of thehomogenized mixtures above was dilutedfive folds with water. A drop of the dilutedcolloid mixture was then placed onto acarbon coated copper grid and dried at 50°C.The grid was then irradiated with the UVlight followed by lEM analysis. To anotheraliquot, the homogenized mixtures were UVirradiated prior to the placement on thecopper grid. Upon drying, the sample wassubjected to TEM analysis.xRD analysiswas also carried out on the samples. Thepatterns were obtained using a SIEMENSD5000 X-ray Diffractometer in the 28 rangeof20-60°.MicroSoM. Vol 7, No 1 (April 2004)RESULTS AND DISCUSSIONSmall spherical silver particles weresynthesized when NR - silver (NR - Ag)films were irradiated with a UV light. Figure1a- b shows the TEM micrographs and sizedistribution histograms after 20 and 90minutes of irradiation. The average particlesize at both UV irradiation times is 7.39 ±3.50 and 4.79 ± 1.70 nm respectively. It canbe seen that a narrower size distribution wasobtained afte~ 90 minutes. This proves thatthe' silver particle size reduces withincr,easing irradiation time.d =3.39 +/-1.14 nmd =7.14 +/·1.74 nm'l- bo ~Diameter (nm)~ ~ ~ ~ ~ ~Diameter (nm)4035,~30:5 25:s 20.c'C 151iiis 105(}<:)(a)7060,~ 50co ':=40::J.:g 30..S20100()(b)Figure 1: TEM images of silver nanoparticles embedded in natural rubber films after.(a) 20 and (b) 90 minutes of UV irradiation.In contrast, when a mixture of NR - Ag "ioncolloid was irradiated, fractals wereobtained. These structures were the result ofsilver cluster aggregation, based on thefollowing reaction7,Ag+ irradiation Ag clusters aggregation fractal----+~ ~morphologiesThis growth phenomenon occurs due to non-equilibrium growth and molecularanisotropl. It has been reported that factorssuch as solvents9 and absorbates 10 play arole in fractal growth. However, that is notthe case here. Both systems contain the sameamount of rubber and silver. Due to this, wecan conclude that the fractals may be a resultof rapid hitting and sticking of the silvernanocrystals, which can occur in thecolloids, compared to the films. The fractal15"dimension D =1.67 is in agreement with thediffusion - limited aggregation model ll ,12,The TEM micrographs of the fractals areMicroSoM. Vol 7, No 1 (April 2004)shown in Figure 2 at two differentmagnifications.Figur~ 2: TEM Images of NR - Ag Colloids After 90 Minutes UV IrradiationFinally, XRD analysis was carried out toobserve the nature of the nanoparticles.XRD patterns of the samples exposed to UVmadiation in films as well as in colloidsystems are typical of the silver crystals aspresented in Figure 3a - b. Both~,fSl'- ~. ._--- ., .p'_ T -- --.- -"-~.'---'!O .'" :c ~£ :?~ ~! 1:\ is ': .,:. ~" .,; } -.;patterns clearly demonstrate that the peaksare assignable 'to the (111), (200), (311) and(222) planes of face centered cubic (fcc)silver crystals. These are similar to thosereported by Y6ngchun Zhu et al. [3.tlI~L__.,~~~-..-~_ .........r....-ro-_...--~.r- .. ~,- •.-.......-_10 ~ ~ ~ w ~ ~ ~ ~ ~ ~ t~ lC ~ ~.r-,...."r.(a) (b)Figure 3: XRD Patterns for (a) Natural-Rubber - Silver Film, (b) Natural Rubber - Silver Colloid.CONCLUSIONIn summary, it has been shown that it ispossible to synthesize silver nanocrystalswith different morphologies even with thesame materials. Spherical silvernanoparticles with an average size of 4.79 ±1.70 nm in fIlms after 90 minutes ofinadiation were able to be firmed. On theother hand, nanofractals with a fractal16dimension of 1.67 were obtained in NR -Ag colloids.ACKNOWLEDGEMENTThis work was supported by a USM-FRGSgrant no. 304/ PKIMIA / 670007.REFERENCES1. A. L. Stepanov, V. N. Popok, 1. B.Khaibullin and U. Kreibig, NuclearInstruments and Methods in Phys.Res. B, 191 (2002) 473 - 477.2. M. Adlirn and M. Abu Bakar,MicroSoM, 5 - 6 (2003) 6-103. M. P. Stevens, Polymer Chemistry:An Introduction, Oxford UniversityPress, New York, 3rd Edition, (1999)477 -478.4. N. E. Kotelnikova, G. Wagener, M.Stoll, V. N. Demidor, Russ. J. Appl.Chern. 76 (2003) 117.5. A. L. Rogoch, G. P. Shevchenko, Z.M. Afanaseva, V. V. Sviridov, J.Phys. Chern. B, 101 (1997) 8129.6. 's. Kapoor, T. Mukherjee, Chern.Phys. Lett. 370 (2003) 83.MicroSoM. Vol 7, No 1 (April 2004)7. Q. Yang, F. Wang, K. Tang, C.Wang~ Z. Chen and Y. Qian, Mater.Chern. Phys. 78 (2002) 495 - 500.8. X. Zbeng, L. Zhu, X. Wang, A. Yanand y. Xie, J. Cryst. Growth, 260·(2004) 255 - 262.9. R. He, X. Qian, J. Yin and Z. Zhu,Chern. Phys. Lett. 369 (2003) A54 -.458.10. G. Wei, Y. Deng and C. W. Nan,Chern. Phys. Lett. 367 (2003) 5i2 -515.'11. N. H. H. Abu Bakar, J. Ismail and M.Abu Bakar, Proceedings RegionalConference for Young Chemists(2004), April 13-14, USM, Penang.12. T. A. Witten and L. M. Sander, Phys.Rev. B; 27 (1983) 5686 - 5697.13. Y. Zhti, M. Ii, H. Zheng, Y. Li, Z.Yang and Y. Qian, Mater. Lett. 58(2004) 1121 - 1126.CONTRIBUTION FROM MEMBERSWe invite short scientific articles and short communication of interest to microscope users (light and electronmicroscopy), technical tips, announcements of new books, local microscopy related invents and 'positionavailable' for publication in this bulletin. Manuscripts should be typewritten in 'words' format and sent to theeditor via email or regular mail (with diskette). All materials received are subjected to inclusion and editing atthe discretion of the editorial board. .ADVERTISINGMicroSoM invites commercial advertisement of microscopes and microscopy related products. The rates are asfollows:Pa~es Per issue Three issuesOuarter page, B&W RM 100.00 RM 250.00Half page, B&W RM200.00 RM 500.00Full page, B&W RM400.00 RM 1000.00Colour (inside cover) RM 600.00 RM 1500.00Colour (back cover) RM900.00 RM2500.00We will attempt to place short 'new product announcements' in the MicroSoM on a space available basis, freeof charge for those advertisers who purchase ads in the same bulletin.All communications can be addressed to :Prof. Dr. Radzali Othman (Editor-in-Chief, MicroSoM)School of Materials & Mineral Resources Engineering,Engineering Campus, Universiti Sains Malaysia,14300 Nibong Tebal, Seberang Perai Selatan, Penang.Tel: 04 5937788 ext 6122 Fax: 04 5941011Email: microsom2003@yahoo.comorradzali@eng.usm.my17

Polymer Chemistry: An Introduction,

Silver Nanoclusters And Nanofractals In Natural Rubber Matrix.

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Silver Nanoclusters And Nanofractals In Natural Rubber Matrix.

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