Comments(0) | Mulai hari ini, secara rasminya blog saya akan berpindah ke :
http://syukcurz-ii.blogspot.com/
This is my New Hope, New Life and a New Start of My journey.
Terima Kasih keatas sokongan kawan2 selama ini.. jumpa anda di sana!!!
Comments(0) | hurmm… currently ramai lak yg da berhijrah wat blog baru. xkisahlah sama ada blog tu da xmampu nak menanggung kapasiti atau penulis nak bertukar selera. mungkin juga masing2 ada masalah dan alasan tersendiri. Dr. Mahathir pon da bukak blog yg baru. http://chedet.co.cc/chedetblog/ . Yasmin ahmad lak da buat sambungan blog part 2 lak . http://www.yasminthefilmmaker.blogspot.com/
aku pon rasa macam nak ber hijrah gakla. memamndangkan kapasiti ” media library” blog friendster da hampir mencapai had maksimum da.. apa pun tgu jer la announcement dari aku kemudian.
Comments(7) | Salam…. ni aku nak cerita pasal pengalaman g holiday kat phuket lak kat hangpa suma.
ok. trip ni aku da plan sejak dari february 2008. time tu airasia offer tiket 1 sen. setelah bertanya kepada beberapa org dan tersebar ke beberapa orng akhirnya 10 person tanpa pikir panjang have decide nak pegi. aku igt lagi time aku tgh survey tiket tu da kul 3pg n juz beberapa org jer yg da bg nama penuh n no ic kat aku. nak tgu dapat suma detail tu pon da satu prob. nak punch kredit kad pon satu lagi prob. tawla airasia. klu lambat skit pon da sold out. n bertambah mahal harga nya dan hasilnya, hanya 6 org dari pada kami sahaja yg dapat tiket 1 sen sehala (exclude surcaj) manakala lagi 4 dapat tiket 1 sen sehala gak tapi flight yang berbeza. nakwat cmna kan nak tiket murah. Thanx alot to abg che faizah coz sudi bagi guna kredit kad dia. setelah dapat booking dengan senang hati selepas bersusah payah aku pon wat la meeting ng 10 org yg berminat nak p ni. then baru find out yg most of them ni xda pasport. kecuali aku, marina n lat. minimum nak wat pasport group ni 5 org pada harga Rm300. manakala pasport individu pun RM300 gak seorng. memikirkan semua nya masih belajar. aku tak rasa depa akan buat pasport international individu. so jalan terbaik adalah tukar flight memandangkan pada hari yg aku booking tu, kos untuk tukar flight cuma RM300. so setelah mendapat kebenaran suma org yg nak ambik masa sehari gak bersama2 top up yg xberenti2 nak arrange 10 org ni aku pon dapat la tukar flight tp yg terkejutnya da meningkat menjadi RM600, 2x ganda dan kena tambah tiket flight rm 15 sehala. tula lembap lagik. rugi betul. xcaya buleh tgk kat ilternary kat bawah ni nnt. tp xpa org ckp berat sama di pikul ringan sama di jinjing. duit flight ni aku bahagi sama rata. sbb kita p sama2 kan. duit pasport lak ley share gak nnt.
in da mean time aku da wat la beberapa research pasal phuket ni. berkaitan pengainapan, pengangkutan, n of coz tempat2 menarik untuk dilawati. setelah menilai beberapa faktor da kreteria seperti kemudahan asas, jarak dari pantai, harga, dan kemdahan internet. aku telah pilih sebuah GuestHouse yg agak menarik pada pandangan aku. dat is Jochen’s Residence. dengan jarak 200 meter dari pantai, pada harga yg agak murah la.
ok. ni jer dpt p setelah sekian lama merancang. bak kata org kita hanya mampu merancang, tuhan yang menentukanya… apapun thnx tu all of u guys coz masih utuh untuk g trip ni… (from left Me!, Che Faizah, Marina, Jamsari and Irfan Raimi)
AKU ketika berenang2 (hehee… tu ketika berendam2 jer) dan dikelilingin ikan2. hehee… pastu aku memberanikan diri untuk snorkeling dikawasan yg lebih dalam. thnx to irfan for give me dat strenght!. huhuu…
KAMI!
Comments(0) | somebody post dis
“i’v already SPOKEN our LOVE is BROKEN i don’t want to do this any LONGER…“
Y do we need to broke the LOVE? god help us…
My life is brilliant.
My love is pure.
I saw an angel.
Of that I’m sure….
Comments(1) | sejak balik phuket ari2, banyak lak tawaran yg dtg kat aku, doc aku minta aku isi job application kat website UKM untuk jawatan Research Officer (RO). wow! dat my dreaming job ever. doc suh aku isi n antar salinan kat Prof. uhuhuu.. terharu la ng doc coz sudi rekemen aku tuk job tu. and ari2 gak aku taw akak se-Lab dapat National Fellowship (NSF), alhamdullilah. setelah 2x g intervw akhirnya dapat gak biasiswa tu, igt xdpt dah ari2. tawakal jer la..
Then the next day, ari selasa lak Doc carik lagi, dis time doc suh jumpa Assoc. Prof program Kimia. my godness, dis time doc nominate aku tuk g germany. tuk menghadiri 59th Meeting of Nobel laureates in chemistry. nomination jerla, then intervw jap ng assoc. prof. n aku diberi borang nomination untuk di isi. huhuu… bayak lak bende kena isi huhuu… plus nak kena wat “Letter of Interest n Letter of Support lak” leceh2, but nak xnak aku kena la mengarang gak, tgh wat la ni
Hari rabu lak terus ade intervw tuk jawatan RO huhuu.. everything goin smoothly but time last skali diorg bukak skrol tgk nama ” MOHD FAIZ JALAJALHU SARJANA MUDA SENIBINA” yallah aku silap bawk skrol huhuuu…aku g bwk skrol housemate aku lak celakakak tul huhuu….
nak wat cmne dah, pasrah jerla tawakal jerla
ni lak list yang sepatutnya g interview but juz 5org jer yg hadir, kak wahida, anuar, azmi, fairuz and me. harap2 adala peluang
Comments(0) | welll…dis is wat actually happen during, afta n be4 da conference,
penat gak r, coz sblumni baru jer balik dari penang n dpt la rest kejap sehari 2. then continue wif this conference lak. actually hari ahad 30NOV tu kami dah ke TIara Beach untuk registration tapi disebabkan kelupaan tahap dewa aku tak bawa dokumen yang diperlukan untuk registration. so kak aminah jerla yang dpt register n membawa pulang beg labtop pemberian seketriat RCSSST2008 manakala shwu peng ng aku hanyalah menjadi peneman sahajo hahaa.. buang masa dan tenaga sahaja. yang bagusnya kami dpt la booking hotel kat Eagle Ranch Resort dulu.
Comments(0) | This paper was presented at 24th REGIONAL CONFERENCE ON SOLID STATE SCIENCE AND TECHNOLOGY 2008 (RCSSST 2008) at Tiara Beach Resort, Port Dickson, Negeri Sembilan, Malaysia.
49% Poly(Methyl Methacrylate)-Grafted Natural Rubber Based Solid Polymer Electrolytes.
1M.S. Su’ait, 1*A. Ahmad, 1H. Hamzah and 2M.Y.A. Rahman
1 School of Chemical Sciences and Food Technology, Faculty of Sciences and Technology, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia.
2 College of Engineering, Universiti Tenaga Nasional, 43009 Kajang, Selangor, Malaysia.
*Corresponding Author : (azizan@ukm.my)
Abstract: The potential of 49% poly(methyl methacrylate)–grafted natural rubber (MG49) as a solid polymer electrolyte (SPE) film in rechargeable batteries system has been investigated. The flat, thin and flexible films were prepared by solution casting technique. The ionic conductivity was investigated by alternating current impedance spectroscopy (AC EIS). The highest conductivity was given by 20 wt. % of LiBF4 salt loading with 2.26×10-7 S.cm-1 whereas 4.00×10-8 S.cm-1 by 15 wt. % LiClO4 salt loading. The observation on structural studies done by X-ray diffraction (XRD) showed the amorphous phase to be appearing at the highest conductivity.
Keywords: Ionic conductivity, 49% poly(methyl methacrylate)–grafted natural rubber, Solid polymer electrolyte
1. Introduction
Research on polymer electrolyte was first conducted by Fenton et al. (1973). They found that the non conducting polymer, polyethylene oxide (PEO) became conducting when lithium salt was added into the polymer matrix. The finding of ionic conductivity in these polymer material complexes with salt has led to the development of electrochemical devices such as rechargeable batteries, electrocromic windows and sensing device for chemicals/gases usage [1].
Recently, modified natural rubber (NR) based SPE had grab draw the attention for many researchers. This is due to its attractive attributes such as low glass transition temperature (Tg), soft elastomer characterization at room temperature, and good elasticity. Suitable elasticity can result in flat, thin, and flexible film. Furthermore, modified NR gives excellent contact between an electrolytic layer and an electrode in battery system. It could also act as a polymeric solvent and the ionic conductivity is higher compared to glassy or crystalline state of polymer [2]. On the other hand, certain of modified NR such as epoxidized natural rubber (ENR) and poly(methyl methacrylate)–grafted natural rubber (MG) both possess oxygen atoms, which can act as electron donor atoms in the structure of the polymer host. The oxygen atoms with lone pair of electron formed a coordinate bond with Li+. Fig. 1 shows the structure of MG monomer. ion from perchlorate salt, producing a polymer-complex [8]. However, ENR based SPE shows a drawback to its mechanical properties such as slightly sticky and difficult to peel off from substrate [4,5] as compared to MG film which is more free standing, elastic and flexible. Previous studies on various MG were conducted elsewhere [2,3,6-9]
Fig. 1. Structure of MG monomer
In this work, MG49 is doped with lithium salts such as LiClO4 and LiBF4 to prepare SPE by solution casting technique [2,3,6,8,9]. All samples were characterized by using AC impedence spectroscopy (EIS) and X-ray diffraction (XRD). It is expected that LiClO4 and LiBF4 salt to acquire different optimum ionic conductivity due to the differences in the anion size and lattice energy of appropriate salt.
2.Experimental and characterization
2.1 Materials.
MG49 was commercially obtained. Lithium perchlorate (LiClO4) salt was supplied by Fluka, while lithium tetrafluoroborate (LiBF4) salt by Aldrich. All the materials were used without further purification.
2.2 Sample preparation.
All the polymer electrolyte samples were prepared by solution casting technique. MG49 rubber was sliced into a grain size. The quantity of MG49 was dissolved in stopped flasks containing toluene. After 24 hours, the solution is stirred with efficient magnetic stirring for the next 24 hours until complete dissolution of MG49 into clear viscous solution. LiClO4 salt solution was prepared separately in THF solution and stirred for 12 hours. These two solutions were then mixed together for 24 hours to obtain a homogenous solution. The electrolyte solutions were then casted onto a glass Petri dish and the solvent were allowed to slowly evaporate in a fume hood at room temperature. A free standing film was obtained when the solvent completely evaporated. Residual solvents were then removed in vacuum oven for 48 hours at 50C. The samples were then stored in a desiccator until further use. The same experimental procedure is repeated for LiBF4 salt.
2.3 Characterization.
The ionic conductivity measurements were carried out by AC impedance spectroscopy using high frequency resonance analyzer (HFRA) model 1255 with applied frequency from 6500 Hz to 0.1 Hz at perturbation voltage of 2500 mV. The disc shaped sample of 16 mm in diameter was sandwiched between two stainless steel block electrodes. The measurements were conducted at room temperature.The ionic conductivity (σ) was calculated from the bulk resistance (Rb) obtained from the intercept on real impedance axis, the film thickness (l), and the product of effective contact area (A) according to the equationσ= [ l/(A Rb) ]. X-ray diffraction model D5000 Siemens is used to observe on the appearance and disappearance of crystalline or amorphous phase as a function of salts content. The data were collected from the range of diffraction angle 2θ from 20° to 80° at rate 0.05° s-1.The analysis was conducted at room temperature.
3. Results and Discussion
3.1. Ionic conductivity
Typical impedance plots are shown in Fig. 2. Ionic conductivity and O/Li ratio of solid polymer electrolyte MG49-LiClO4 and MG49-LiBF4 are shown in Table 1 and had been expressed into a graph in Fig. 3. The graph shows the ionic conductivity increases with the increasing of salt loading up until the optimum level in polymer host due to the increasing of the number of conducting species in the electrolyte. Ionic conductivity without salt content (0 wt. % salt) is 1.03×10-12 S.cm-1. The highest conductivity, given by 20 wt. % of LiBF4 salt loading in MG49 is 2.26×10-7 S.cm-1 while 15 wt. % LiClO4 salt loading is 4.00×10-8 S.cm-1. This optimum value shows the maximum and an effective interaction between oxygen atoms and lithium ion in the electrolyte. However, our finding of LiClO4 salt is slightly lower than the finding by Alias et al. [6]. In contrast, our finding of LiBF4 salt is slightly higher. They founded that the ionic conductivity of MG49 with 30 wt. % of LiCF3SO3 is 1.76 x 10-7 S.cm-1.
(a)
(b)
Fig. 2 Typical impedance plot for (a) MG49-LiClO4 and (b) MG49- LiBF4
|
wt. % salt loading |
Conductivity, σ (S.cm⁻¹) |
O/Li Ratio |
||
|
MG49 + LiClO₄ |
MG49 + LiBF4 |
MG49 + LiClO₄ |
MG49 + LiBF4 |
|
|
0 |
1.03E-12 |
1.03E-12 |
- |
- |
|
5 |
4.42E-10 |
3.35E-12 |
51/1 |
45/1 |
|
10 |
2.72E-09 |
7.77E-12 |
26/1 |
23/1 |
|
15 |
4.00E-08 |
3.01E-11 |
17/1 |
15/1 |
|
20 |
1.25E-09 |
2.26E-07 |
13/1 |
11/1 |
|
25 |
4.23E-10 |
9.63E-10 |
9/1 |
8/1 |
Table 1 The ionic conductivity and O/Li ratio of SPE MG49-LiClO4 and MG49-LiBF4
Fig. 3 The ionic conductivity of SPE MG49-LiClO4 and MG49-LiBF4
The interaction was explained by FTIR investigated by Kamuta et al. [12] shows that a coordinate bond was formed in the complexes between lithium ion and oxygen atoms. The O/Li ratio for the optimum LiBF4 salt loading is 11 of oxygen atoms to 1 lithium ion or simply wrote 11/1 compared to the optimum LiClO4 salt loading which is 17/1. The different value in O/Li is due to the differences in the molar mass and weight percent of the lithium salt. The main reason LiBF4 salt has a higher ionic conductivity as compared to LiClO4 salt due to the differences in anion size and lattice energy of appropriate salt. LiBF4 salt has low lattice energy due to the delocalization of large anion’s charge as compared to LiClO4 salt [1]. Nevertheless, the ionic conductivity decrease rapidly after the optimum salt loading because of the ion association or ion aggregation [9]. However these findings are slightly lower than the finding by Idris et al. [2] and Ali et al. [9]. This is because in this research, there is no plasticizer such as polypropylene carbonate (PC) and ethylene carbonate (EC) added into the SPE. The presence of PC and EC in polymer electrolyte can easily corrode the lithium metal electrode in electrochemical cell [5].
3.2. Structural studies
The XRD analysis is used to determine the structure and crystallization of polymer host by observing the appearance and disappearance of crystalline or amorphous region. Fig. 4 (a) and (b) shows the XRD diffractograms for SPE MG49-LiClO4 and LiClO4 salt. While, Fig. 5 (a) and (b) shows the XRD diffractograms for SPE MG49-LiBF4 and LiBF4 salt respectively. The intense peak shows the crystalline region occurs in the polymer host. The amorphous region occurs when the intensity of the peak became broader [10]. Fig. 4 (b) illustrated that the intense peak of LiClO4 showed at 21.1°, 23.3°, 31.7°, 33.1°, 35.7°, 39.5° and 47.3°. Moreover, Fig. 5 (b) shows an intense peak of LiBF4 at 21.4°, 23.6°, 26.8°, 28.2°, 32.0°, 32.8°, 39.9°, 44.6° and 54.9°. Pure MG49 in Fig. 4 (b) and 5 (b) showed a single peak at 26.6° that belongs to MMA monomer in rubber chain. With addition of salt content from 5 wt. % to 25 wt. %, the MMA single peak at 26.6° disappear and it only appears after the addition of 25 wt. % of LiClO4 salt.
As mentioned earlier, the highest ionic conductivity doped with 15 wt. % of LiClO4 salt and 20 wt. % of LiBF4salt loading respectively. From the XRD patterns in Fig. 4 (a) and 5 (a), the highest ionic conductivity are located at 15 wt. % of LiClO4 salt and 20 wt. % of LiBF4salt loading which have a broadening intensity. In other word, amorphous region appears in polymer host. This finding approved the suggestion from elsewhere [1,2,4,6,9-11] that amorphous region provides high ionic conductivity compared to the crystalline or semi-crystalline region. The different of the crystallization in both salts can also be observed via the intense peak. The presence of LiClO4 peaks at angle around 23°, 35° and 47° in Fig. 4 (a) and LiBF4 peaks at angle 28° in Fig. 5 (a) showed that the crystalline phase occurred after the maximum conductivity in SPE MG49 doped with lithium salts due to the ion association between cation and anion, respectively in the electrolyte at the high salt concentration. The salt affects the overall conductivity through crystalline complexes formation, intramolecular crosslinking of the polymer chains and the degree of salt dissociation-number of charge carriers [1].
(a)
(b)
Fig. 4. XRD diffractograms for (a) MG49-LiClO4 and (b) LiClO4 salt
(a)
(b)
Fig. 5. XRD diffractograms for (a) MG49-LiBF4 and (b) LiBF4 salt
4. Conclusion
The film of SPE MG49 doped with lithium salts (LiClO4 and LiBF4) have been successfully prepared by solution casting technique.The highest conductivity for LiBF4 salt was 20 wt. %, and for LiClO4 salt was 15 wt. %. The ionic conductivities obtained are within the range of ~10-8-10-7 S.cm-1 at room temperature. The observation on structural studies done by X-ray diffraction (XRD) showed the amorphous phase to be appearing at the highest conductivity.
5. Acknowledgements:
The authors would like to extend their gratitude towards Polymer Research Center (PORCE), Universiti Kebangsaan Malaysia for allowing this research to be carried out. This work is supported by the MOSTI grant 03-01-02-SF0423.
6. References
[1]F.M. Gary (1997). Polymer electrolytes, London: RCS Monographs, The Royal Society of Chemistry.
[2]R. Idris, M.D. Glasse, R.J. Latham, R.G. Linford And W.S. Schlindwein (2001). Polymer electrolytes based on modified natural rubber for use in rechargeable lithium batteries. Journal of Power Sources 94, 206-211.
[3]K. Kamuta and Y. Alias (2006). FTIR spectra of plasticized grafted natural rubber-LiCF3SO3 electrolytes. Journal of Spectrochimica Acta Part A 64, 442-447.
[4]M.D. Glasse, R. Idris , R.J. Latham, R.G. Linford and W.S. Schlindwein (2002). Polymer electrolytes based on modified natural rubber PEO-ENR25/ENR50-LiCF3SO3. Journal of Solid State Ionics 147, 289–294.
[5]G. Lu, Z-F. Li, S-D. Li and J. Xie (2001). Blends of natural rubber latex and methyl methacrylate-grafted rubber latex. J. Applied Polymer Sciences 85, 1736–1741.
[6]Y. Alias, I. Ling and K. Kumutha (2005). Structural and electrochemical characteristics of 49% PMMA grafted polyisoprene-LiCF3SO3-PC based polymer electrolytes. J. Ionics 11, 414.
[7]P.C. de Oliveira, A.M. de Oliveira, A. Garcia, J.C. de Souza Barboza, C.A. de Carvalho Zavaglia and A.M. dos Santos (2005). Modification of natural rubber: A study by H NMR to asses the degree of graphitization of PolyDMAEMA or PolyMMA onto rubber particles under latex form in the presence of redox couple initiator. European Polymer Journal 41, 183-1892.
[8]K. Kamuta, Y. Alias and R. Said (2005).FTIR and thermal studies of modified natural rubber based solid polymer electrolytes. Journal of Ionics 11: 472-476.
[9]A.M.M. Ali, M.Z.A. Yahya, H. Bahron, & R.H.Y. Subban (2006). Electrochemical studies on polymer electrolytes based on PMMA-grafted natural rubber for lithium polymer battery. Journal of Ionics 12, 303–307.
[10]Y-J. Wang, Y. Pan, and D. Kim (2006). Conductivity studies on ceramic Li1.3Al0.3Ti1.7(PO4)3-filled PEO-based solid composite polymer electrolytes. Journal of Power Sources 159, 690-710.
[11]S.R. Mohapatra, A.K. Thakur and R.N.P. Choudhary (2008).Studies on PEO-based sodium ion conducting composite polymer films. Journal of Ionics 14, 255-262.
Comments(2) | 26 hb Nov 2008
My 1st conference yang aku jadi oral presenter. cuak gak r. seram sejuk dibuatnya. aku antara yang group 1st yang kena present dulo. 2nd speaker taw. mana x cuak.hampir sebulan gak aku siapkan paper untuk present ni. n dah banyak kali dah aku kena ubah macam2. Dr. Azmi dari USM kejuruteraan memulakan soalan2 yang membunuh aku. aku apa lagi mencurahkan sambil menggoreng segala ilmu yg aku ada la kat c2. budak2 aku ckp aku nampak confident time melalut sini sana tu. ahaaahaa..anyway i think my Q-A session is suck bila ada sorng budak ni tanya soklan berkaitan FTIR yang aku wat. actually time 4 Q-A dah abis dah tyme 2. tp aku lak dengan confident nya nak jawap soklan 2. klu aku taw sklan pasal FTIR mmg aku x tanya dah. wat xnmpak ja..about presentaion i think ok. cuma mic tu wat sleck skit cilakak la. pas abis 2 aku rasa lega sgt2. puas. tapi pasni ada lagi 1 conference lagi kat Port Dickson, RCSSST2008. Tiara Beach resort. ni 3hari 2mlm lak. manala… aku nak tdo. dinner mlm ni di Naza Hotel, menu adalah BBQ. tahap kesedapannya hanyalah biasa2 saja. tp yg menariknya ke”hevoc”kan geng kami yang melalak2 sesuka hati mengikot alunan lagu2 selepas habis dinner tu hahaaa….ari2 berakhir dgn kepenatan yang teramat sangat. kul 1230mlm baru sampai umah sejak kluar dari kul 530 pagi td.
27hb Nov 2008
pagi ni len skit, mak aku yang drive sbb nnt ptg kami aku trus balik ke UKM nek bus. sementara tgu conference stat aku jalan2 bersama2 adik2 ku di tepian pantai lu menghabiskan masa2 terluang aku. lagpon dah nak balik ukm sat g.
arini turn kak mina, ieda n jamilah lak present hehee… aku dah lega dah. ieda punya ketaq samapi xlalu nak lunch tghari2 hahaa…. ni muka2 takot orng2 yg nak present
kul 3 lebey cm2 kami nek bus nak balik dah…tp sempat lagi nak begambar tu ehehee… pic kat bawah tu semua deligasi UKm bersama Dr. Azizan
xabis lagiii…. seblum balik tu sempat lagi round2 penang taw. yerla bukan sume penah g penang ni.. dalam kul 12mlm 2 khamis elamat sampai kat ukm…
Comments(0) | This paper was presented at VIIIth National Symposium On Polymeric Materials 2008 (NSPM 2008), Naza Hotel. Penang.
Preparation and Characterization of Solid Polymer Electrolytes
49% Poly(Methyl Methacrylate)-Grafted Natural Rubber - Poly(Methyl Methacrylate) - Lithium Perchlorate Salts.
1M.S. Su’ait, 1*A. Ahmad, 1H. Hamzah and 2M.Y.A. Rahman
1 School of Chemical Sciences and Food Technology, Faculty of Sciences and Technology, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia.
2 College of Engineering, Universiti Tenaga Nasional, 43009 Kajang, Selangor, Malaysia.
*Corresponding Author : azizan@ukm.my
Abstract: The potential of hybrid polymer 49% poly(methyl methacrylate)–grafted natural rubber (MG49) and poly(methyl methacrylate) (PMMA) as a polymer host in solid polymer electrolyte (SPE) film for rechargeable batteries system has been investigated. The hybrid films were prepared by solution casting technique. The ionic conductivity was investigated by alternating current electrochemical impedances spectroscopy (EIS). The highest conductivity is 1.47×10-8 S.cm-1 at 20 wt. % of LiClO4. The observation on structural studies done by X-ray diffraction (XRD) showed that the crystallinity phase is reduced at the highest conductivity. The Fourier transform infrared spectroscopy (FTIR) analysis showed that the interaction between lithium ion and oxygen atoms occurred at carbonyl (C=O) and ether (C-O-C) groups.
Keywords: Ionic conductivity, MG49, PMMA, Lithium perchlorate, Solid polymer electrolyte
1. Introduction
Research on polymer electrolyte was firstly conducted by Fenton et al. [1]. They found that the non-conducting polymer, polyethylene oxide (PEO) become conductive when lithium salt was added into the polymer matrix. However, research on PMMA based SPE was only conducted in 1985 by Iijima and co-workers [2]. The finding of ionic conductivity in these polymer material complexes with salts has led to the development of electrochemical devices such as rechargeable batteries, electrochromic windows and sensing devices for chemicals/gases [3].
PMMA has been used as a polymer host due to its high transparency in the visible region as preferred solid electrolytes in electrochromic window [4], high stability at lithium-electrolyte surface [5] and able to be diluted in various organic solvents [6]. PMMA based electrolyte is also less reactive towards the lithium electrode. It induces more favourable passivation film on the electrode surface. Therefore, it is expected that a higher cyclibility of lithium electrode in PMMA based electrolyte [7]. PMMA also acts as a stiffener that fast ion transport occurs through a continuous conduction path which does not affect the electrochemical stability of the electrolyte [8]. The increasing in surface exposure of PMMA could increase the mechanical properties and increase the melting level of lithium salts due to the high dielectric properties of lithium salts. In addition, PMMA has a polar functional group in their main polymer chain that shows high affinity for lithium ions to transport. Oxygen atom from carbonyl group (C=O) will form a coordinate bond with lithium ion from doping salts [7]. The main drawback of plasticized gel-based PMMA system is its poor mechanical properties. Its mechanical properties can only be improved by modifying the ratio between polymer host and plasticizer/solvent. However, this will adversely affect the ionic conductivity and easily corrode the lithium metal anode in an electrochemical cell [9]. Polymer electrolyte must have enough mechanical strength to hold the pressure between anode and cathode, as gel polymer electrolyte (GPE) is unable to do so as compared to solid polymer electrolyte.
To overcome the drawback of GPE and mechanical properties of PMMA film, PMMA was hybrided with elastomer material such as modifier natural rubber to improve the segmental motion in polymer hybrid systems and hence a more flexible and elastic material. Natural rubber and synthetic rubber like poly(styrene-co-butadiene) (SBR) and poly(acrylonitrie-co-butadiene) (NBR) rubber were not suitable because natural rubber has sticky properties and not compatible with PMMA [10]. Besides, natural rubber does not has polar group to enhance the ion mobility in the SPE system. Whereas, synthetic rubber gives a poor mechanical properties at low polymer concentrations [11]. Recently, modified natural rubber such as epoxidized natural rubber (ENR) and PMMA–grafted natural rubber (MG) based SPE had drawn the attention of many researchers [9,11-13,15,17-19]. This is due to the attractive attributes such as low glass transition temperature (Tg), soft elastomer characterization at room temperature, and good elasticity. Suitable elasticity can result in flat, thin, and flexible film. Furthermore, modified NR gives excellent contact between an electrolytic layer and an electrode in batteries system. It can also act as a polymeric solvent and the ionic conductivity is higher as compared to glassy or crystalline state of polymer [3]. On the other hand, modified NR has oxygen atoms, which can act as electron donor atoms in the structure of the polymer host. Research conducted by Kamuta et al. [12], Alias et al. [15] and Ali et al. [19] found that the oxygen atoms with lone pair of electron formed a coordinate bond with lithium ion from perchlorate salt and hence a polymer-complex. However ENR based SPE shows a drawback to its mechanical properties such as slightly sticky and difficult to peel off from substrate [9,13,14] as compared to MG film which is more free standing, elastic and flexible. Previous studies on various MG was conducted elsewhere [3,12,15-18]. Fig. 1 shows the structure of MG monomer [16].
Fig. 1. Structure of MG monomer
In this work, polymer hybrid MG49-PMMA with ratio 30:70 is doped with LiClO4 salt to prepare SPE by solution casting technique. All the sample were characterized by using AC electrochemical impedences spectroscopy (EIS), X-ray diffraction (XRD) and Fourier transform spectroscopy (FTIR). It is expected that LiClO4 salt gives an optimum value for ionic conductivity studies in polymer hybrid (30:70) MG49-PMMA.
2. materials and methods
2.1 Materials.
MG49 was commercially obtained. PMMA low molecular weight and LiClO4 salt were supplied by Fluka. All the materials were used without further purification.
2.2 Sample preparation.
All the polymer electrolyte samples were prepared by solution casting technique. MG49 rubber was sliced into a grain size. The quantity of MG49 was dissolved in stopped flasks containing toluene. After 24 hours, the solution was stirred with efficient magnetic stirring for the next 24 hours until complete dissolution of MG49 into clear viscous solution. PMMA solution was prepared in another stopped flask containing toluene and stirring for 24 hours. These two solutions were then mixed together for 24 hours to obtain a homogenous solution. LiClO4 salt was dissolved in THF solution for 12 hours and doped to the solutions for the next 24 hours with continue stirring to obtain a homogenous solution. The electrolyte solutions were casted onto a glass Petri dish and the solvent were allowed to slowly evaporate in a fume hood at room temperature. A free standing film was obtained when the solvent completely evaporated. Residual solvents were then removed in vacuum oven for 48 hours at 50C. The samples were then stored in a desiccator until further use. The same experimental procedure was repeated for different weight percent salts loading.
2.3 Characterization.
The ionic conductivity measurements were carried out by AC EIS using High Frequency Resonance Analyzer (HFRA) model 1255 with applied frequency from 6500 Hz to 0.1 Hz at perturbation voltage of 2500 mV. The disc shaped sample of 16 mm in diameter was sandwiched between two stainless steel block electrodes. XRD model D-5000 Siemen was used to observe on the appearance and disappearance of crystalline or amorphous phase as a function of salt content. The data was collected from the range of diffraction angle 2θ from 2° to 80° at rate 0.04° s-1. FTIR spectrum was recorded by computer interfaced Perkin Elmer GX Spectrometer. The electrolyte was casted onto NaCl windows and was analyze in the frequency range of 4000 cm-1 to 400 cm-1 with scan resolution of 4 cm-1. All the analysis was conducted at room temperature.
3. Results and Discussion
3.1. Ionic conductivity
Typical impedance plots are shown in Fig. 2. According to Rajendran et al. [7] and Kim et al. [29], the complex impedance plots showed two well-defined regions, there is a semicircle in the high frequency range which is related to conduction process in the bulk of complex and the linear region in the low frequency range that is attributed to the effect of blocking electrodes. At low frequency, the complex impedance plot shows a straight line parallel to the imaginary axis, but the double layer at blocking electrodes causes the curvature.
Fig. 2. Typical impedence plot of 30/70 MG49-PMMA 20 wt. % LiClO4
The bulk resistance (Rb) was obtained from the intercept on real impedance axis (Z’ axis). The ionic conductivity (σ) was calculated from the Rb, the film thickness (l) and contact area of the thin film (A=2πr), according to the equation σ= [l/(A.Rb)]. Ionic conductivity and O/Li ratio of SPE MG49-PMMA-LiClO4 is showed in Table 1. Ionic conductivity at 0 wt. % of LiClO4 salt content is 4.07×10-12 S.cm-1 and the highest ionic conductivity is 1.47×10-8 S.cm-1 at 20 wt. % LiClO4 salt. The ionic conductivity increased as the salt loading increases up to its optimum level in polymer host. This is due to the increase of the number in conducting species in the electrolyte. This optimum value indicates the maximum and an effective interaction between oxygen atoms and Li+ ion in the electrolyte.
The interaction that occurs was explained by FTIR investigation from elsewhere [7,9,12,15,17,19,20,24]. It was founded that a coordinate bond was formed in the polymer-salt complexes between Li+ and oxygen atoms. The O/Li ratio for the optimum LiClO4 salt loading is 7 of oxygen atoms to 1 lithium ion or can be simply written as 7/1. The different value in O/Li is due to the difference of weight percent (wt. %) of the lithium salt. The higher ionic conductivity in addition of 20 wt. % LiClO4 salt was caused by the large anion size and low lattice energy of LiClO4 salt generally expected to promote greater dissociation of salts, thereby providing higher concentration of ions [21]. Nevertheless, the ionic conductivity decreases after the optimum salt loading due to the ions association or ions aggregation [18] and the effect of lithium salt’s crystallization in the polymer host as shown in the XRD diffractograms in Fig. 3.
However these findings are slightly lower than the finding by Latif et al. [9], Idris et al. [11] and Ali et al. [18] because in this research, there is no plasticizer such as polypropylene carbonate (PC) and ethylene carbonate (EC) added into SPE and a different type of lithium salt used. The presence of PC and EC in polymer electrolyte can easily corrode the lithium metal electrode in electrochemical cell [14].
Table 1. The ionic conductivity and [O/Li] ratio of SPE MG49-PMMA-LiClO4
|
wt. % salt loading |
Conductivity, σ (S.cm⁻¹) |
O/Li Ratio |
|
0 |
4.07E-12 |
- |
|
5 |
1.34E-11 |
29/1 |
|
10 |
2.32E-09 |
14/1 |
|
15 |
4.10E-09 |
10/1 |
|
20 |
1.47E-08 |
7/1 |
|
25 |
7.18E-09 |
5/1 |
3.2. Structural studies
The XRD analysis is used to determine the structure and crystallization of polymer-salts complex by observing the appearance and disappearance of crystalline or amorphous region. Fig. 3 shows the XRD diffractograms of SPE MG49-PMMA-LiClO4 in the angle range 2 to 80°. The bell shaped intense curve in Fig. 3 shows the semi-crystalline region occurs in the polymer host (PMMA) while the amorphous region occurs when the intensity of the peak became broader at 20 wt. % LiClO4 salt loading [25].
However, the system is not fully amorphous based on the presence of LiClO4 peak at 23.0° and PMMA single peak at 13.2°. In addition, a high ionic conductivity level do still occurs due to the reduction in the intensity of the PMMA crystallization peak from bell shaped curve to a broadening shape. This finding approved the suggestion from elsewhere [1,13,18,20-26] that either the amorphous region or the reduction of crystalline region gives high ionic conductivity as compared to the crystalline or semi-crystalline region. The presence of LiClO4 peaks at angle 23.0°, 31.4° and 35.3° in Fig. 3 showed that the crystalline phase occurred in SPE MG49-PMMA doped with 25 wt. % LiClO4 salt. This is because of the recrystallization of LiClO4 salt due to the ion association between Li+ and ClO4- in the electrolyte at the high salt concentration. There are no significant changes from 5 wt. % to 15 wt. % salt loading in SPE MG49-PMMA. The salt affect the overall ionic conductivity through crystalline complexes formation, intramolecular crosslinking of the polymer chains and degree of salts dissociation-number of charge carriers [1].
Fig. 3. XRD diffractograms of 30/70 MG49-PMMA-LiClO4 from 2 to 80°
3.3. FTIR Spectrum studies
FTIR spectroscopy is used to observe the vibration energy of covalent bond in the polymer host and the interaction occurs in the polymer-salt complexes. Since each type of bonds has a different natural frequency of vibration, so the identification of absorption peak in the vibration portion of infrared region will give a specific type of bonding [27,28]. In this research, the main interests are shown on the oxygen atoms of the carbonyl (C=O) (1750 cm-1-1730 cm-1) and ether group (C-O-C) (1300 cm-1-1000 cm-1) from PMMA and MG49 [27]. According to the literature [5,7,12,17-20,22,24], the oxygen atoms acted as electron donor atoms in the structure of polymer host and form a coordinate bond with lithium ion from doping salts to form polymer-salt complexes. Carbonyl from ester group shows a very strong peak appearing in the range of 1750 cm-1 to 1735 cm-1 for simple aliphatic esters and shift to lower wavenumbers by about 15 cm-1 to 25 cm-1 in the polymer salt complexes [18,27].
From the experiment conducted, the C=O symmetrical stretching frequency of PMMA and MG49 in polymer-salt complexes gives rise to an intense, very strong and sharp peak at 1733 cm-1 and 1734 cm-1 respectively. With addition of lithium salt loading, the intensity of C=O symmetric stretching of MMA peak reduced and shifted to the lower wave number from 1732 cm-1 to 1735 cm-1. The shifting of C=O symmetric stretching of MMA peak are demonstrated in Fig. 4(a). The shifting of the intensity peaks confirmed the interaction between lithium ion from doping salt and oxygen atoms in the structure of polymer host to form a coordinate bond and subsequently forming polymer-salt complexes. Previous study reported that the shifting of the intensity peaks still occur even though in insignificant range. Kamuta et. al [17] reported that the C=O stretching of MMA at 1729 cm-1 is shifted to 1728 cm-1 in the MG30-EC with LiCF3SO3 salt complex. The inconsistent changes in wavenumbers are observed in O-CH3 asymmetric deformation of MMA and C-O symmetric stretching of MMA. However, in term of peak intensities illustrated in Fig. 4(b), the intense, strong and sharp peak became weak and broader with addition of lithium salt. This is due to the weak interaction between oxygen atoms and lithium ion from doping salt. This change has not been reported before. It was also observed, that there is no significant changes at C=C stretching of polyisoprene and CH3 asymmetric stretching of MMA/rubber structure.
(a)
(b)
Fig. 4. FTIR spectrum for (a) carbonyl group and (b) ether group
4. Conclusion
SPE MG49-PMMA doped with LiClO4films have been successfully prepared by solution casting technique. The highest conductivity is 1.47×10-8 S.cm-1 at 20 wt. % of LiClO4 salt loading. The observation on structural studies done by XRD showed that the crystallinity phase is reduced at the highest conductivity and FTIR analysis showed that the interaction between lithium ion and oxygen atoms occurred at carbonyl (C=O) and ether (C-O-C) groups.
5. ACKNOWLEDGEMENTS
The authors would like to extend their gratitude towards Universiti Kebangsaan Malaysia for allowing this research to be carried out. This work is supported by the MOSTI grant 03-01-02-SF0423.
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