Cellulose nanocrystal/graphene oxide composite film as humidity sensor

Sensors and Actuators A 247 (2016) 221–226

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Cellulose nanocrystal/graphene oxide composite film as humidity sensor Abdullahil Kafy, Asma Akther, Md. I.R. Shishir, Hyun Chan Kim, Youngmin Yun, Jaehwan Kim ∗ Creative Research Center for Nanocellulose Future Composites, Dept. of Mechanical Engineering, Inha University, 100 Inha-Ro, Nam-Ku, Incheon 22212, South Korea

a r t i c l e

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Article history: Received 11 February 2016 Received in revised form 31 May 2016 Accepted 31 May 2016 Available online 2 June 2016 Keywords: Cellulose nanocrystal Graphene oxide Humidity sensor Relative capacitance

a b s t r a c t Cellulose nanocrystal/graphene oxide composite was reported as a humidity sensor in this study. The composite film was fabricated using simple blending the materials followed by oven drying. The composite film offers a unique advantages of cellulose combined with functionality of GO. It was capitalized to design renewable, flexible and cheap humidity sensor. Performance of the composite film as a humidity sensor was evaluated on the basis of relative capacitance change at different humidity level. Synthesized composite film was characterized using scanning electron microscope, Fourier transform infrared spectroscope, and X-ray diffraction. Environmental effect such as temperature was taken into account on the sensor performance. The sensing mechanism is explained on the basis of presence of hydrophilic functional groups in the composite. The linear and fast response of the developed sensor is advantageous. © 2016 Elsevier B.V. All rights reserved.

1. Introduction Monitoring and controlling humidity play a very important role in many industries. Controlling living environment, intelligent control for laundry, smart control for cooking in microwave ovens are some examples of humidity sensors. Humidity sensors are being used in automobile industries for window defogger and motor assembly line; in medical field respiratory equipment, incubators, medicine processing; in agricultural sectors to control greenhouse air, monitoring soil condition. Researchers are working hard to improve the performance of humidity sensor such as fast response, good sensitivity and small hysteresis. There are several transduction techniques for designing humidity sensors: for example, resistive, capacitive, optical, mechanical and acoustic techniques [1–10]. Generally, there are two types of humidity sensors: resistive type [11,12], and capacitive type [11,13]. A number of materials such as porous ceramic, electrolytes, polymers are being used for humidity sensors [14–16]. Humidity sensing ceramics include TiO2 , Al2 O3 as sensing materials to develop the sensors [17,18]. Ceramics show high mechanical strength as well as high resistance to temperature. On the other hand polymers are more compatible with IC

∗ Corresponding author. E-mail address: [email protected] (J. Kim). http://dx.doi.org/10.1016/j.sna.2016.05.045 0924-4247/© 2016 Elsevier B.V. All rights reserved.

production process. Some examples of humidity responsive polymer are cellulose acetate, poly methyl methacrylate, etc. [19,20]. Also, porous silicon has been reported as humidity sensing material [21]. Cellulose, the most abundant source of raw material on earth, is renewable material that can maintain our resources from the environment so as to overcome degradation of natural environmental services and diminished productivity. It is a kind of solid polymer which colorless, odorless and nontoxic. Some promising properties are also possessed, such as high mechanical strength, hydrophilicity, relative thermo-stabilization, biocompatibility, piezoelectricity, light weight, low material price and eco-friendly [22]. Composites based on cellulose are being used for coatings, pharmaceuticals, laminates, textile, optical films, etc. Recently, cellulose has been reported as a smart material [23]. Nowadays, cellulose became a very promising material for the development of flexible devices because of its light weight, low cost, environment friendly, good optical properties [24,25]. Recently, nanocrystalline form of cellulose is reported as high dielectric material which makes it a very good choice for development of many devices. To improve its properties, functional groups should be incorporated with it. Graphene, tightly packed carbon atoms in two dimensional honey comb structure, is a nanomaterial of the day. It provides many opportunities for sensor development [26]. Graphene has a high surface area, good mechanical strength, high carrier mobility

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at room temperature, quantum hall effect, increased electrical and thermal conductivity, optical transparency and excellent thermal conductivity [27]. Graphene Oxide (GO), a functional derivative of graphene, contains hydroxyl, ether, carboxyl and carbonyl functional groups. Presence of these functional groups make it easy to blend GO in other polymer matrix. Inclusion of GO in cellulose matrix can improve its mechanical, electrical as well as dielectric properties [28]. Many GO based sensors like solvent sensors, temperature sensors have already been reported [29,30]. Present work reports a simple fabrication process of cellulose nanocrystal (CNC) − GO composite film and its humidity sensor application. The CNC-GO composite film can offer a unique advantages of cellulose combined with functionality of GO. These synergistic advantages of CNC-GO composite film can be capitalized to design renewable, flexible and cheap humidity sensor. The morphology and structure of the composite film are studied using a scanning electron microscope (SEM), Fourier transform infrared spectroscope (FTIR) and X-ray diffraction (XRD). The humidity sensing capacity of the composite film is tested by measuring the capacitance change with different relative humidity and environmental effect on the sensor performance was also studied by considering the temperature change.

CNC suspension at a desired ratio (5 wt% and 10 wt%) followed by homogenization. To make a CNC-GO composite film, the suspension was poured in a plastic petri dish and dried in an oven at 60 ◦ C to evaporate the water and turn into a solid film. After 8 h of drying, GO blended CNC composite film (CGO) was obtained. The number after abbreviation, CGO, represents the weight percentage of GO present in the composite film. Finally, the film was collected and stored in a dried box. To compare the results, a pure CNC composite film was also fabricated following the same method.

2. Experimental details

The morphology of CNC was investigated using atomic force microscope (Veeco AFM). JEOLJSM −6400 F microscope was used to capture SEM images of the samples to investigate the morphology. The SEM samples were prepared by coating a platinum layer using ion sputter (EMITECH, K575X). The FTIR spectra was taken using a FTIR spectroscope (Bruker Optics, Billerica, MA) in the range of 500–4000 cm−1 by averaging 16 scans (resolution was 4 cm−1 ) at 1 min intervals to demonstrate the grafting of GOs to CNC. XRD patterns of the samples were checked with an X-ray diffractometer (DMAX-2500) using CuK␣ target radiation at 50 mA and 45 kV, at scanning rate of 0.0151 min−1 . The diffraction angle was varied from 10◦ to 40◦ . The variation in dielectric constant of the CNC matrix and its composites was measured within the frequency range of 20 Hz to 10 kHz using the LCR meter. The measurement was performed at 25 ◦ C and 25% relative humidity (RH) at 1 V. To evaluate the humidity sensor performance of the composite film, relative capacitance change was measured with the change of relative humidity using the LCR meter at 1 kHz and 1 V. Humidity was changed using an environmental chamber (Kwang-Myung Science, South Korea) that can control its inside temperature and humidity. To check the response of the sensor, relative humidity was increased step by step with 5% increment. To justify the

2.1. Materials Natural flake graphite, Avicel (cellulose microcrystalline from cotton linter with a size ∼50 ␮m), potassium permanganate (KMnO4 ), phosphoric acid (H3 PO4 ), hydrochloric acid (HCl) and 30% hydrogen peroxide (H2 O2 ) solution were procured from Sigma-Aldrich. Sulfuric acid (H2 SO4 ), ethanol was purchased from Daejung, South Korea. 2.2. Material preparation The CNC base matrix in this study was prepared by H2 SO4 (175 mL of 30% (v/v) aqueous) hydrolysis of Avicel powder (20.0 g) under mechanical stirring (200 rpm, 6 h) at 60 ◦ C [31]. Alkaline treatment of Avicel powder was done before acid hydrolysis to remove the non-cellulosic components. The resulted suspension of CNC was washed with deionized (DI) water several times to ensure a neutral pH suspension. Then the suspension was homogenized using a homogenizer and dialyzed overnight. Besides, GO was synthesized by the improved graphene oxide synthesis method [32] and dispersed in DI water. Then GO suspension was mixed with

2.3. Humidity sensor fabrication To fabricate the humidity sensor, an interdigital transducer (IDT) patterned electrode was deposited on a PET substrate using traditional lift off process. After that CNC/GO solution was poured drop wise on the pattered electrode and dried in the oven at 60 ◦ C. Then two end of the IDT patterned electrode was wired and connected to an LCR meter (HP 4284A). Fig. 1 shows the schematic of the fabricated sample. The comb distance of IDT electrode was 27 ␮m. 3. Characterization

Fig. 1. Schematic diagram of the fabricated sensor and its performance measurement.

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Fig. 2. SEM Cross section images: a) CNC b) CGO5 c) CGO10.

response time, humidity was increased continuously from 25% to 80% and decreased thereafter to 25%. For references, inside (very close to the fabricated sensor) humidity and temperature of the chamber were also measured using a commercial thermohygrometer (Sato, SK-110TRH type 4). Relative capacitance change measurement at different temperature was also taken place to justify the performance with the change of environment. Other than effect of temperature change, all other experiments were done at 25 ◦ C. The schematic diagram of the measurement procedure is shown in Fig. 1.

4. Result and discussion 4.1. Morphology and structure relationship The morphology of CNCs was investigated using the atomic force microscope (AFM) on drop casted sample on a silicon wafer and illustrated in Supplementary Information (Fig. S1). The shape of the CNC was rigid needle like structure with a dimeter of 30–40 nm and length of 100–300 nm. The synthesized GO from the improved

synthesis method has a thickness about–1.5 nm which was shown in our previous study [28]. To explain the properties of the composite it is very important to study the morphology and structure. Fig. 2 shows cross sectional image of FE-SEM and explains the morphological changes took place by the introduction of GOs in CNC matrix. Agglomeration of GO is not shown in the composite as illustrated in the images. CNC shows a rough cross sectional morphology which is reduced upon the introduction of GOs. This smoothness increases with the increased amount of GOs. This well bound surface and smoothness are associated with the indication of good reinforcement and well dispersion of GOs in cellulose matrix [28]. Agglomeration is not observed even with high concentration (10 wt.%) of GOs in the composite. FTIR and XRD were used to study the structural composition of the composite. The FTIR spectra of CNC and CGO composites are shown in Fig. 3a. All of the composites show same peaks. The broad band at 3410 cm−1 corresponds to O H stretching (intermolecular hydrogen bond) vibration. The peaks at 2901 cm−1 can be assigned to C H stretching and 1065 cm−1 arise due to the C O C pyranose ring skeleton vibrations. The band around 1730 cm−1 corresponds

Fig. 3. a) FTIR Spectra b) XRD analysis of CNC and CGO composites.

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Fig. 4. Variation of a) dielectric constant (␧’) and b) dielectric loss (tan ␦) of CNC and CGO composites.

to the C O stretching vibration of carboxyl of ester groups. Similar peaks in CNC and CGO composites denote the absence of any chemical interactions concerning CNC and GO when blended together. The proposed structure of CGO composite is associated with sort of intercalated weak intermolecular interactions which make a weak connection between filler and polymer molecules [33–35]. XRD is a very useful tool for graphene based materials as it can identify the extent of filler dispersion in the matrix. The XRD spectra of CNC and CGO composites are shown in Fig. 3b. CNC shows three well defined diffraction peaks at 14.7◦ , 16.5◦ and 22.7◦ which correspond to cellulose Iˇ [36]. Any peak related to GO is not observed in CGO composites as GO was completely exfoliated in the matrix.

4.2. Dielectric behavior To evaluate the dielectric characteristics of the composite, dielectric constant (␧’) and dielectric loss (tan ␦) was measured at ambient condition (25 ◦ C, 25% RH) within the frequency range of 20 Hz to 10000 Hz under 1 V. The results are shown in Fig. 4. Dielectric constant depends on the presence of polarizable electrical charge in the composite [37,38]. The ␧’ value of CGO10 (␧’ = 3857) is almost five times higher than the pure CNC film (␧’ = 792) at 20 Hz. It can be seen easily that under low frequency, increment of filler material, GO, in CNC increases the dielectric constant. Milan et al. as well as in our previous study exhibited similar results [28,39]. High dielectric constant and low dielectric loss were observed in the results because of dipoles in CNC due to spatial polarization structure [40,41]. Dielectric constants for all of the composites decrease with the frequency increase. At higher frequency above1 kHz, the dielectric constant of CGO10 is 652, which is almost six times higher than that of CNC, 106. The Maxwell–Wagner–Sillars (MWS) process states that polymer-filler interfacial interaction induces dielectric property changes of the composites. Large interfacial area of composites is responsible for providing numerous sites for the reinforced MWS effect [42]. When current flows across the interface of two dielectric materials, charges mount up at the interface with various relaxation times (t = ε/, where ‘ε’ is the dielectric permittivity and ‘’ is the conductivity). Presence of a reasonable number of oxide functionalities and conjugation on the GO sheet surface make it possible [43]. The dielectric measurement results also show similar result.

Relative capacitance change was measured using the following equation and plotted with RH in Fig. 5a. CR = (C − C0 ) /C0

(1)

Here, ‘C’ is the sensor capacitance in the presence of stimulus (humidity) and ‘C0 ’ is the initial capacitance. From the figure we can see the CR increases to 130 for CNC, 303 for CGO5 and 547 for CGO10. From the results, we see that relative capacitance, CR , changes exponentially with the humidity change for CNC, CGO5 and CGO10 composites. So this CR change can be calibrated as a linear relation with log of CR of humidity. Linearity is an important characteristic of sensors. As CGO10 shows higher response than the CNC composite under humidity change, for rest of the characterization, CGO10 was used. Besides, humidity hysteresis characteristics of CGO10 composite was also investigated by increasing the humidity from 25% to 90% and then decreasing back to 25% for adsorption and desorption of water molecules, respectively. As the results shown in Fig. 5b, the desorption curve of the sensor lagged behind its adsorption curve slightly. The reason of this lag is the removal time of humidity from its surface. The composite shows good humidity sensing behavior with very good reversibility. To develop sensors for practical application, the reliability of the sensors at different environmental condition is also important. For this purpose, the humidity sensor response was investigated at three different temperature levels (25 ◦ C, 35 ◦ C, 45 ◦ C), shown in Fig. 5c. With the increment of temperature, the slope lines of the humidity response shift up with the slope remains same. Thus, it can be said that temperature does not have much effect on the developed humidity sensor sensitivity. Fig. 5d shows the relative humidity change (%RH) as well as relative capacitance change with time. Relative humidity change was measured from a commercial hygrometer. Humidity change from commercial hygrometer and logarithm of relative capacitance changes shows similar trend with time. As the time response from commercial hygrometer and CGO10 shows similar behavior, we can say that CGO10 has a quick response time like commercial hygrometers. The novelty of this material is flexibility, environmentally friendly and cheap. To justify repeatability relative capacitance change with different humidity level was repeated 4 times. The results showed a highest deviation of about 4%. Measurement error is responsible for this deviation. 4.4. Working mechanism of the sensor

4.3. Humidity sensing Humidity sensing was explored by the measurement of relative capacitance change with the relative humidity (RH) change.

The sensitivity of the CGO composite is considerably higher than that of CNC film as shown in Fig. 5. In general, sensing ability of CNC film to detect water molecules depends on its hydrophilic

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Fig. 5. a) Relative capacitance change (CR) with relative humidity change for pristine CNC, CGO5 and CGO10 composite b) Humidity hysteresis curve of the sensor for CGO10 composite c) Relative capacitance change with humidity at different temperature d) Relative humidity change (%RH) and relative capacitance change with time.

functional groups such as hydroxyl group on its surface. Presence of the hydrophilic functional groups attracts water molecules and increases the capacitance. GOs have lots of hydroxyl groups as well as carboxyl groups in their structure [44]. The incorporation of GO in CNC matrix increases number of hydrophilic functional groups like hydroxyl groups and carboxyl groups in the composite. This increment in hydrophilic groups attracts more water molecules and causes higher sensitivity of CGO composites than CNC film. This can be furthermore confirmed by measuring water uptake percentage of CGO10 in 90% relative humidity which is almost twice higher than the pristine CNC film (Supplementary Information Table S1). 5. Conclusions Homogenous CNC/GO composite films were fabricated successfully using simple blend method followed by drying process. Structure and morphology of the composite films were studied using FTIR, XRD and SEM, ensuring very good dispersion of GO in CNC matrix. The dielectric property measurement exhibited high dielectric constant and low dielectric loss of the composites, which are associated with spatial polarization dipoles in CNC. The humidity sensing of the composite was evaluated by measurement of capacitance change with the humidity change. The linear response of the proposed sensor in log scale and fast response are advantageous in humidity sensing. Under different temperature levels, the proposed sensor exhibited the same sensitivity. With the advantages of CNC/GO composites, renewable, flexible and cheap humidity sensor can be developed. It is believed that this kind of flexible and environment friendly humidity sensor can be used in flexible and wearable electronics. Acknowledgement This research was supported by Creative Research Initiatives Program through the National Research Foundation of Korea (NRF)

funded by the Ministry of Science, ICT and Future Planning (NRF2015R1A3A2066301). Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.sna.2016.05.045. References [1] Y. Zhang, K. Yu, D. Jiang, Z. Zhu, H. Geng, L. Luo, Zinc oxide nanorod and nanowire for humidity sensor, Appl. Surf. Sci. 242 (2005) 212–217. [2] P.J. Schubert, J.H. Nevin, A polyimide-based capacitive humidity sensor, IEEE Trans. Electron. Devices 32 (1985) 1220–1223. [3] G. Sberveglieria, G. Rinchettia, S. Groppellia, G. Faglia, Capacitive humidity sensor with controlled performances based on porous Al2 O3 thin film grown on SiO2 -Si substrate, Sens. Actuators B: Chem. 19 (1994) 551–553. [4] Y.T. Kim, J.H. Kim, D.K. Kim, Y.H. Kwon, Force sensing model of capacitive hybrid touch sensor using thin-film force sensor and its evaluation, Int. J. Precis. Eng. Man. 16 (2015) 981–988. [5] F. Arregui, Y.J. Liu, I. Matias, R. Claus, Optical fiber humidity sensor using a nano fabry–perot cavity formed by the ionic self-assembly method, Sens. Actuators B: Chem. 59 (1999) 54–59. [6] G. Gerlach, K. Sager, A piezoresistive humidity sensor, Sens. Actuators A: Phys. 43 (1994) 181–184. [7] D.R. Southworth, L.M. Bellan, Y. Linzon, H.G. Craighead, J.M. Parpia, Stressbased vapor sensing using resonant microbridges, Appl. Phys. Lett. 96 (2010) 163503. [8] X.F. Wang, B. Ding, J.Y. Yu, M. Wang, F. Pan, A highly sensitive humidity sensor based on a nanofibrous membrane coated quartz crystal microbalance, Nanotechnology 21 (2010) 055502. [9] M. Penza, V.I. Anisimkin, Surface acoustic wave humidity sensor using polyvinyl-alcohol film, Sens. Actuators A: Phys. 76 (1999) 162–166. [10] S.K. Kwon, H.C. Cho, S.H. Yi, Analysis of the capacitive pressure sensor with ring mesa structure, Int. J. Precis. Eng. Man. 15 (2014) 1023–1028. [11] Y. Sakai, M. Matsuguchi, Y. Sadaoka, Humidity sensors based on polymer thin films, Sens. Actuators B: Chem. 35 (1996) 85–90. [12] Y. Sakai, M. Matsuguchi, N. Yonesato, Humidity sensor based on alkali salts of poly(2-acrylamido-2-methylpropane sulfonic acid), Electrochim. Acta 46 (2001) 1509–1514. [13] U. Kang, K.D. Wise, A high-speed capacitive humidity sensor with on-chip thermal reset, IEEE Trans. Electron. Devices 47 (2000) 702–710.

226

A. Kafy et al. / Sensors and Actuators A 247 (2016) 221–226

[14] T. Seiyama, N. Yamazoe, H. Arai, Ceramic humidity sensors, Sens. Actuators 4 (1983) 85–96. [15] G. Harsanyi, Polymeric sensing films: new horizons in sensorics? Sens Actuators A: Phys. 46–47 (1995) 85–88. [16] F.W. Dunmore, An improved electric hygrometer, J. Res. Nat. Bureau Stand. 23 (1939) 701–714. [17] K. Katayama, K. Hasegawa, Y. Takahashi, T. Akiba, H. Yanagida, Humidity sensitivity of Nb2 O5 −doped TiO2 ceramics, Sens. Actuators A: Phys. 24 (1990) 55–60. [18] R.K. Nahar, V.K. Khanna, A study of capacitance and resistance chracteristics of an Al O humidity sensor, Int. J. Electron. 52 (1982) 557–567. [19] G. Delapierre, H. Grange, B. Chambaz, L. Destames, Polymer based capacitive humidity sensor: characteristics and experimental results, Sens. Actuators 4 (1983) 97–104. [20] M. Matsuguchi, Y. Sadaoka, Y. Sakai, A capacitive-type humidity sensor using cross-linked poly (methyl methacrylate) thin films, J. Electrochem. Soc. 138 (1991) 1862–1865. [21] R.C. Anderson, R.S. Muller, C.W. Tobias, Investigation of porous silicon for vapor sensing, Sens. Actuators A: Phys. 21–23 (1990) 835–839. [22] K.K. Sadasivuni, D. Ponnamma, B. Kumar, M. Strankowskie, R. Cardinaels, P. Moldenaers, S. Thomas, Y. Grohens, Dielectric properties of modified graphene oxide filled polyurethane nanocomposites and its correlation with rheology, Compos. Sci. Technol. 104 (2014) 18–25. [23] J. Kim, S. Yun, Z. Ounaies, Discovery of cellulose as a smart material, Macromolecules 39 (2006) 4202–4206. [24] P. Lian, X. Zhu, S. Liang, Z. Li, W. Yang, H. Wang, Large reversible capacity of high quality graphene sheets as an anode material for lithium-ion batteries, Electrochim. Acta 55 (2010) 3909–3914. [25] S.K. Mahadeva, S. Yun, J. Kim, Flexible humidity and temperature sensor based on cellulose–polypyrrole nanocomposite, Sens. Actuators A: Phys. 165 (2011) 194–199. [26] Y. Zhu, S. Murali, W. Cai, X. Li, J.W. Suk, J.R. Potts, R.S. Ruoff, Graphene and graphene oxide: synthesis, properties, and applications, Adv. Mater. 22 (2010) 3906–3924. [27] E. Fortunato, P. Barquinha, R. Martins, Oxide semiconductor thin-Film transistors: a review of recent advances, Adv. Mater. 24 (2012) 2945–2986. [28] A. Kafy, K.K. Sadasivuni, H.C. Kim, A. Akther, J. Kim, Designing flexible energy and memory storage materials using cellulose modified graphene oxide nanocomposites, Phys. Chem. Chem. Phys. 17 (2015) 5923–5931. [29] A. Kafy, K.K. Sadasivuni, A. Akther, S. Min, J. Kim, Cellulose/graphene nanocomposite as multifunctional electronic and solvent sensor material, Mater. Lett. 159 (2015) 20–23. [30] K.K. Sadasivuni, A. Kafy, H.C. Kim, H. Ko, S. Mun, J. Kim, Reduced graphene oxide filled cellulose films for flexible temperature sensor application, Synthetic Met. 206 (2015) 154–161. [31] Y. Zhou, C. Fuentes-Hernandez, T.M. Khan, J.C. Liu, J. Hsu, J.W. Shim, A. Dindar, J.P. Youngblood, R.J. Moon, B. Kippelen, Recyclable organic solar cells on cellulose nanocrystal substrates, Sci. Rep. 3 (2013) 1536. [32] C.M. Daniela, V.K. Dmitry, M.B. Jacob, S. Alexander, S. Zhengzong, S. Alexander, B.A. Lawrence, L. Wei, M.T. James, Improved synthesis of graphene oxide, ACS Nano 4 (2010) 4806–4814. [33] T. Szabo, O. Berkesi, I. Dekany, DRIFT study of deuterium-exchanged graphite oxide, Carbon 43 (2005) 3186–3189. [34] L. Shen, H.S. Shen, C.L. Zhang, Temperature-dependent elastic properties of single layer graphene sheets, Mater. Des. 31 (2010) 4445–4449. [35] P. Pokharel, Q.T. Truong, D.S. Lee, Multi-step microwave reduction of graphite oxide and its use in the formation of electrically conductive graphene/epoxy composites, Compos. B: Eng. 64 (2014) 187–193. [36] K.K. Sadasivuni, A. Kafy, L. Zhai, H. Ko, S. Mun, J. Kim, Transparent and flexible cellulose Nanocrystal/reduced graphene oxide film for proximity sensing, Small 11 (2015) 994–1002. [37] K.K. Sadasivuni, D. Ponnamma, B. Kumar, M. Strankowskie, R. Cardinaels, P. Moldenaers, S. Thomas, Y. Grohens, Dielectric properties of modified graphene oxide filled polyurethane nanocomposites and its correlation with rheology, Composites. Sci. Technol. 104 (2014) 18–25. [38] Q. Du, M. Zheng, L. Zhang, Y. Wang, J. Chen, L. Xue, W. Dai, G. Ji, J. Cao, Preparation of functionalized graphene sheets by a low-temperature thermal exfoliation approach and their electrochemical supercapacitive behaviors, Electrochim. Acta 55 (2010) 3897–3903. [39] M. Jana, P. Khanra, N.C. Murmu, P. Samanta, J.H. Lee, T. Kuila, Covalent surface modification of chemically derived graphene and its application as supercapacitor electrode material, Phys. Chem. Chem. Phys. 16 (2014) 7618–7626. [40] S.C. Ray, S.K. Bhunia, A. Saha, N.R. Jana, Electric and ferroelectric behaviour of polymer-coated graphene-oxide thin film, Phys. Procedia 46 (2013) 62–70. [41] D.K. Pradhan, R. Choudhary, B. Samantaray, N. Karan, R. Katiyar, Effect of plasticizer on structural and electrical properties of polymer nanocomposite electrolytes, Int. J. Electrochem. Sci. 2 (2007) 861–871. [42] J.K. Yuan, S.H. Yao, Z.M. Dong, A. Sylvestre, M. Genestoux, J. Bai, Giant dielectric permittivity nanocomposites: realizing true potential of pristine carbon nanotubes in polyvinylidene fluoride matrix through an enhanced interfacial interaction, J. Phys. Chem. C 115 (2011) 5515–5521. [43] W. Ouyang, J. Sun, J. Memon, C. Wang, J. Geng, Y. Huang, Scalable preparation of three-dimensional porous structures of reduced graphene oxide/cellulose composites and their application in supercapacitors, Carbon 62 (2013) 501–509.

[44] M. Nasrollahzadeh, F. Babaei, P. Fakhri, B. Jaleh, Synthesis characterization, structural, optical properties and catalytic activity of reduced graphene oxide/copper nanocomposites, RSC Adv. 5 (2015) 10782–10789.

Biographies Abdullahil Kafy received BSc in Industrial and Production Engineering from Bangladesh University of Engineering and Technology, Bangladesh in 2009. He is now pursuing Ph. D at Inha University. His research interest includes Nanocellulose Long Fiber, Cellulose EAPap, Sensors and actuators, and Microfabrication.

Asma Akther received BSc in Industrial and Production Engineering from Shahjalal University of Science and Technology, Bangladesh in 2003. She is now pursuing M.Eng. in Mechanical Engineering at Inha University. Her research interest includes Design, Simulation of actuators, Cellulose EAPap, Bionsensor, Haptics and Microfabrication.

MD I.R. Shishir received BSc in Mechanical Engineering from Bangladesh University of Engineering and Technology, Bangladesh in 2012. He is now pursuing M. Eng. in Mechanical Engineering at Inha University. His research interest is molecular dynamics, sensors and actuators, microfabrication etc.

Hyun Chan Kim received B. E (Mechanical Engineering) from INHA University, Korea in 2014. He is now pursuing M. S (Mechanical Engineering) at INHA University. His research interest includes alignment of nanocellulose, sensor, haptic actuator, MEMs.

Youngmin Yun received B. E (Mechanical Engineering) from Inha University, Korea in 2010 and M.S. (Mechanical Engineering) from Inha University, Korea in 2012. He is now pursuing Ph. D at Inha University. His research interest includes Cellulose EAPap, haptic actuator.

Jaehwan Kim is Inha Fellow Professor of Department of Mechanical Engineering at Inha University, South Korea. Prof. Kim is director of Creative Research Center for Nanocellulose Future Composites, sponsored by National Research Foundation of Korea. He is an associate editor of Smart Materials and Structure, and Smart Nanosystems in Engineering and Medicine; an editor of International Journal of Precision engineering and Manufacturing, Frontier Materials − Smart Materials; editorial board member of International Journal of Precision Engineering and Manufacturing-Green Technology, Journal of Materials Science and Engineering, Actuators. His research interests are smart materials, cellulose, electroactive polymers, smart sensors, polymer based MEMS and biomimetic devices.