AIP Conference Proceedings 1972, 030010 (2018); https://doi.org/10.1063/1.5041231 1972, 030010
© 2018 Author(s).
Conductivity, dielectric and modulus study of chitosan-methyl cellulose – BMIMTFSI polymer electrolyte doped with cellulose nano crystal
Cite as: AIP Conference Proceedings 1972, 030010 (2018); https://doi.org/10.1063/1.5041231 Published Online: 05 June 2018
Muhammad Syukri Mohamad Misenan, Ernie Suzana Ali, and Azwani Sofia Ahmad Khiar
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Conductivity, Dielectric and Modulus study of Chitosan- Methyl Cellulose – BMIMTFSI Polymer Electrolyte Doped
with Cellulose Nano Crystal
Muhammad Syukri Mohamad Misenan
1,a), Ernie Suzana Ali
1,b), Azwani Sofia Ahmad Khiar
1,c)1Faculty of Science and Technology, Universiti Sains Islam Malaysia, Bandar Baru Nilai, 71800 Nilai, Negeri Sembilan, Malaysia
a)Corresponding author: [email protected]
Abstract. In this study, the effect of adding cellulose nanocrystal (CNC) on the conductivity of biopolymer electrolyte (BPE) based on chitosan-methylcellulose-BMIMTFSI has been studied. The samples were prepared via solution casting technique. The film was characterized by impedance spectroscopy HIOKI 3531- 01 LCR Hi-Tester to measure its ionic conductivity at room temperatures over a wide range of frequency between 50Hz-5MHz. Sample with 15 wt% of CNC shows the highest conductivity of 4.82 x 10-6 Scm-1 at room temperature. Dielectric and modulus studies were carried out to further understands the conductivity behavior of the samples. The increase in conductivity is mainly due to the increase in number of charge carriers.
INTRODUCTION
Polymer is a chemical compound where the molecules are bonded together in a long repeating chain with a unique property where it can be tailored depending on their intended purposes. In industries, the applications of polymer extend in many applications, from adhesives to precursors for high technology ceramics. In 1970s, Wright and Armand who were the first to show the potential of polymer as an electrolyte material which finally bring the new area of research called “Polymer electrolyte‟. Therefore, polymer electrolytes are generally those materials where a supramolecular system is doped with ions and presents a significant conductivity [1].
Unlike the usual solid ionic materials based on ceramics, glasses or the other inorganic compounds which is usually depends on the mode of charge transport and the value of ionic conductivity, polymer electrolyte can be conducted well above their glass transition temperatures and have ionic conductivity in the order of 100 to 1000 times lower than those of inorganic materials. The usage of polymer electrolyte could help to overcome the disadvantages of liquid electrolyte such as leakage or evaporation which would give difficulties in large scale production and is dangerous to living organism and environment.
Polymer electrolytes possess several advantage including shape versatility, flexibility, light weight and process ability which made them more attractive as compared to other materials especially for device applications. However, one drawback is the low ionic conductivity of polymer electrolytes that has hindered their applications. Therefore, many approaches have been studied such as formation of cross-linked networks, blending of polymers, addition of inorganic fillers and plasticization in order to achieve higher conductivity of polymer electrolyte [2].
Recently the attention has been drawn on the use of natural polymers because of their biodegradability, low production cost, good physical and chemical properties which promises good performance as polymer electrolyte
chitosan could produce efficient thin film of polymer electrolyte [4]. Ariffin and Khiar [5] has improved the conductivity of the blended polymer salt system by adding ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMITFSI) as plasticizer to a maximum of 3.98 x 10-4 cm-1.
Unfortunately, many host polymer loss their mechanical strength when doped with plasticizers thus lead to poor compatibility with the electrode [6]. Studies have shown that, addition of composite to polymer electrolyte can enhanced electrolyte/electrode compatibility and safety hazard [7].
In this work, BPE based on chitosan/methylcellulose/BMIMTFSI has been doped with CNC. The objective of this work is to investigate the conductivity of the BPE with addition of CNC at room temperature. CNC are distinctive nano materials derived from cellulose which is the most abundant and limitless natural polymer. These nano materials have established significant attention because of their mechanical, optical, chemical and rheological properties. CNCs are mainly obtained from naturally occurring cellulose fibers which are biodegradable and renewable in nature. Hence, they serve as a sustainable and environmental friendly material for most application.
Due to its advantages, many works on CNC have been found in literature mainly in food packaging and drug delivery application [8]. However, only few studies on CNC composited polymer electrolyte is found in literature [9].
MATERIAL AND METHODS Sample Preparation
A mixture of chitosan – methyl cellulose containing different weight percentage of BMITFSI was prepared by using solution casting technique. Methylcellulose and chitosan were dissolved separately in 60:40 ratio in which 0.6g chitosan was dissolved in 50ml in 1% diluted acetic acid while 0.4g methyl cellulose in 50ml distilled water.
BMITFSI fixed at 45 wt.% was then added into the chitosan and methyl cellulose blend mixture. An amount of 5wt.
%, 10wt. %, 15wt. %, 20wt. %, 25wt. % of CNC was added into the polymer solution. The solution was then further stirred to obtain homogenous solution and then casted onto plastic petri dish and left to dry at room temperature before further analysis.
Conductivity Measurement
The conductivity of the sample was measured by using Impedance Spectroscopy via HIOKI 3532 LCR Hi Tester Bridge interfaced to a computer. The impedance values were measured within the frequency of 50Hz to 1MHz. A negative imaginary impedance, Zi versus real impedance, Zr with same scale of horizontal and vertical axes were then plotted where the bulk resistance, Rb could be obtained. Hence, the conductivity of the sample in room temperature can be calculated by using:
𝜎 = 𝑡 𝑅%𝐴 (1) where R( is bulk resistance, t is the thickness of the thin film and A is the surface area of contact. In order to measure the thickness of the thin film, a digital micro meter screw gauge was used.
RESULT AND DISCUSSION
The conductivity graph of chitosan – methyl cellulose – BMIMTFSI – CNC electrolyte (Fig. 1) shows that the
conductivity of the system has increases upon addition of CNC. It increases from 2.55 × 10-6 S cm−1 to 4.82 × 10−6 S cm−1. From the cole – cole plot (Fig. 2), the increase in conductivity in the composite system is due to
the decrease of bulk resistance in the system similarly found by other workers [10-11].
However, the increase in conductivity is not that significant. Previous study have shown that, chitosan – methyl cellulose – BMIMTFSI system demonstrated an optimum conductivity of 1.51 × 10-6 S cm-1 without any additional of nano composite.
Many works from literature found that, the increase in conductivity with addition of filler could be due to have an acid or base surfaces [12-13]. This is quite opposite to the present observation. According to Samir et al., [14]
this phenomena could be due to two factors namely cellulosic filler having low dielectric constant or the occurrence of interaction between the filler and host has occurred.
FIGURE 1. Ionic Conductivity against the Cellulose Nano
Crystal concentration FIGURE 2. Cole-cole plots of the composite polymer electrolyte system
In this work, dielectric study was carried out to understand the conductive behavior of polymer electrolyte.
Dielectric constant, 𝜀* is identified as storage energy component while dielectric loss, 𝜀+ is known as factor to measure the energy loss for each cycle when electric field has been applied [15]. Both dielectric constant and dielectric loss can be represented by using equations (2) and (3):
𝜀*= 𝑍- 𝜔𝐶0(𝑍23+ 𝑍-3) (2) 𝜀+= 𝑍2 𝜔𝐶0(𝑍23+ 𝑍-3) (3)
where from the equation, 𝐶0= 𝜀0 𝐴 𝑡 in which 𝜀0 is the permittivity of the free space, t the thickness of the sample, A is the area of contact and 𝜔 = 2𝜋𝑓, where f represents the frequency in Hz respectively.
FIGURE 3. Variations of dielectric constant (a) and dielectric loss (b) as a function of frequency for CS/MC/BMIMTFSI/CNC
(a) (b)
Figure 3(a) and (b) shows the variations of dielectric constant and dielectric loss as a function of frequency for Chitosan/ Methyl Cellulose /BMIMTFSI/ CNC complexes. No appreciable relaxation peaks in the frequency from range 4 to 6 Hz was observed. Hence, the dielectric constant in this present study act as an indicator to show that the increase in conductivity is due to an increase in the number of mobile ion.
To further understand the dielectric behavior, dielectric modulus study needs to done in which this study will suppress the effects of electrode polarization. The equation for the real modulus, 𝑀*and the imaginary modulus 𝑀+ can be expressed as follows.
𝑀*= 𝜀* (𝜀+3+ 𝜀*3) (4) 𝑀+= 𝜀+ (𝜀+3+ 𝜀*3) (5)
Figure 4(a) and (b) depicts the variation of real part, 𝑀* and imaginary part, 𝑀+ of electric modulus respectively.
As the frequencies increases, both of 𝑀* and 𝑀+ also increases. At low frequencies regions, both 𝑀* and 𝑀+ tends towards zero values. The appearance of this long tail at low frequencies is highly attributed to the large capacitance associated with electrodes, confirming the non-Debye behavior [16].
FIGURE 4. Variations of real (a) and imaginary (b) part of dielectric modulus as a function of frequency for Chitosan/ Methyl Cellulose /BMIMTFSI/ CNC complexes
CONCLUSION
BPE with different weightage of CNC had been prepared by solution cast technique. The highest conductivity achieved by chitosan – methyl cellulose – BMIMTFSI – CNC electrolyte at ambient temperature (303 K) is 4.82 × 10-6 Scm-1. The optimum weightage of composite CNC is 15 w.t%. From the dielectric study, the conductivity was mainly due to the increase in mobile ions. Modulus study confirm that samples were non-Debye.
ACKNOWLEDGEMENTS
This work was funded by FRGS under vote USIM/FRGS-FST-32-51312. The authors would like to thank Faculty of Science and Technology, USIM for the facilities provided.
(a) (b)
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