Colloidal graphene oxide/polyaniline nanocomposite ... - Inha DSpace

44 downloads 0 Views 1MB Size Report
This journal is c The Royal Society of Chemistry 2010. COMMUNICATION .... P. Ramesh, M. E. Itkis, E. Bekyarova and R. C. Haddon, J. Phys. Chem. C, 2007, 111, 7565. ... 14 M. Deka, A. K. Nath and A. Kumar, J. Membr. Sci., 2009, 327,. 188.
COMMUNICATION

www.rsc.org/chemcomm | ChemComm

Colloidal graphene oxide/polyaniline nanocomposite and its electrorheologyw Wen Ling Zhang, Bong Jun Park and Hyoung Jin Choi* Received 24th March 2010, Accepted 8th June 2010 First published as an Advance Article on the web 25th June 2010 DOI: 10.1039/c0cc00557f

Due to its excellent in-plane mechanical, structural, thermal and electrical properties, graphite has been widely used as an inexpensive and hydrophilic host in industry. In recent years, graphene, single-layer two-dimensional (2D) graphite, has attracted great attention in both academia and industry.1 It has been also adopted as an excellent inorganic host to enhance thermal and electrical properties of polymer materials.2 In addition, it is considered as the best alternative candidate of carbon nanotubes (CNTs) due to the low cost of its raw material (graphite) and its transparency. Similar to graphene, graphene oxide (GO) has a layer structure with phenolic, carboxyl and epoxide groups introduced by oxidation,3 which is strongly hydrophilic and dispersible in water. The polarity of GO provides compatibility with polymer matrices when used as a host material in composites. However, the GO requires procedure of reduction or thermal treatment prior to use, in order to improve its electrical conductivity. Conversely, the GO powder can be applied as an electrorheological (ER) fluid without further processing, due to its insulated conjugated structure. Note that ER fluids are an example of smart materials, whose rheological properties are accurately controllable in an applied electric field. When an external electric field is applied, the fluid shows rapid, dramatic changes of rheological properties and forms a chain-like structure.4 These properties disappear as soon as the external electric field is removed. Usually, an ER fluid is composed of electrically conducting particles dispersed in an insulating oil. As one of promising ER materials, a conducting polymer such as polyaniline (PANI) has been studied.5 Because of its ease of preparation and outstanding environment stability, the conducting PANI, its derivative and even PANI-based composites have been adopted to ER materials.6 However, PANI should be de-doped before usage to reduce its electrical conductivity. In order to rectify these problems of PANI, we applied GO as an inorganic host which plays a role

as a dopant in oxidation polymerization with PANI at a same time. Previously, either graphite or graphite oxide nanocomposites with PANI have been reported.7 Here, the nanocomposite of colloidal graphene oxide (CGO) and PANI was fabricated via in situ oxidation polymerization in the presence of CGO prepared via a modified Hummers method without any other dopant (detailed experimental procedure can be found in ESIw), in which the important property of CGO is its hydrophilic nature in aqueous media.8 In this work, it is found that after suitable ultrasonic treatment, the CGO readily forms a stable colloidal suspension in aqueous medium. A schematic diagram of hydrogenation reaction of aniline monomer by CGO is shown in Fig. 1, showing hydroxyl and carboxyl groups on the CGO surface by oxidation. The acidic functional groups on CGO can hydrogenate the aniline monomer more easily, improving both the electrical properties and thermal stability of the nanocomposite. Fig. 2 shows scanning electron microscopy (SEM) images of the surface morphology and shape of both CGO and CGO/PANI nanocomposites. The morphology of CGO in Fig. 2a is observed to be a flaky texture, reflecting its layered microstructure. As for the nanocomposite (Fig. 2b), it forms a coralline-like morphology which is obviously different from that of CGO. We attribute this to the surrounding of PANI particles on the CGO host. Note that the macro-morphology of PANI is generally irregular with flat microstructure. In addition, each flaky layer of the CGO uniformly piles up while layers of nanocomposite have individual directions due to the influence of PANI, indicating that the in situ polymerization affects the ordering structure of GO. Further evidence in the coexistence of the GO layer and PANI particles in the nanocomposite is provided by the Fourier-transform infrared spectroscopy (FT-IR) spectra shown in Fig. 3. The typical FT-IR spectrum of CGO in Fig. 3a is an agreement with previous work.9 The bands centered at 3426 and 1397 cm 1 are attributed to deformation of the –OH bond of CGO and CO–H groups, respectively. The band centered at 1054 cm 1 is associated with stretching of the C–O bond. The stretching vibration of the carbonyl or carboxyl groups is observed as a band at 1724 cm 1. The spectrum of PANI in Fig. 3c shows CQC stretching vibration

Department of Polymer Science and Engineering, Inha University, Incheon, 402-751, Korea. E-mail: [email protected] w Electronic supplementary information (ESI) available: Experimental procedure, Table 1 (electrical conductivity of samples), XRD results, FT-IR spectra and TGA data, and the reaction process. See DOI: 10.1039/c0cc00557f

Fig. 1 Schematic of reaction between CGO and aniline monomer.

A nanocomposite of colloidal graphene oxide (CGO) and polyaniline (PANI) was fabricated via in situ oxidation polymerization in the presence of CGO prepared via a modified Hummers method without a dopant, in which the graphene oxide was individually exfoliated. Its electrorheological properties and other physical characteristics were studied.

5596 | Chem. Commun., 2010, 46, 5596–5598

This journal is

c

The Royal Society of Chemistry 2010

Fig. 2 SEM images of (a) CGO and (b) CGO/PANI nanocomposite.

bands attributable to the quinonoid and benzenoid units at 1586 and 1498 cm 1, respectively. In addition, a stretching band assigned to C–N also appears at 1306 cm 1. The spectrum of the CGO/PANI nanocomposite is shown in Fig. 3b, showing peaks of both CGO and PANI with peaks of hydroxyl and carbonyl groups from CGO and strong peaks of functional groups from PANI. Therefore, we can conclude that the nanocomposite of CGO/PANI is successfully obtained based on both SEM and FT-IR data. Thermogravimetric analysis (TGA) was performed on both CGO and the CGO/PANI nanocomposite to determine their thermal stabilities under nitrogen atmosphere. The TGA curves are given in Fig. S1 (ESIw), where the initial weight loss up to 150 1C for each curve is ascribed to the removal of bound water molecules. In this stage, the weight loss of CGO/PANI nanocomposite is lower than that of CGO due to the formation of PANI on GO layers. A major weight loss at about 198 1C for CGO is attributed to the decomposition of the oxygen functional groups on its layer.10 In the case of the CGO/PANI nanocomposite, the degradation rate in this step is much lower than that of CGO. The last weight loss at about 280 1C for CGO can be assigned to the combustion of its carbon skeleton.11 Increased thermal stability of the CGO/PANI nanocomposite could be due to the deposited PANI on the CGO layers. Transmission electron microscopy (TEM) data of the products are shown in Fig. 4. TEM samples were prepared by pipetting a few drops of dispersion onto carbon-300 mesh grids. It is apparent that the nanocomposite has a different morphology from that of CGO. Fig. 4a shows a transparent lamellar structure for CGO which confirms that we have obtained a single-layer graphene. However, the presence of a few thick regions also indicates residual graphite oxide. By comparison, Fig. 4b displays distinct differences in morphology for CGO/PANI nanocomposites. PANI particles seem to fully cover the CGO layer and form a flossy structure, so that the layered structure of CGO can not be observed

Fig. 3 FT-IR spectra of (a) CGO, (b) CGO/PANI nanocomposite and (c) pure PANI.

This journal is

c

The Royal Society of Chemistry 2010

Fig. 4 TEM images of (a) CGO and (b) CGO/PANI nanocomposite.

clearly. From the two images, we can also see that the morphology of CGO shows an in-plane structure while that of the CGO/PANI nanocomposite is no longer flat, which may be due to the embedding of PANI. Fig. 5(a–d) provides X-ray diffraction patterns (XRD) of pristine graphite, CGO, pure PANI and the CGO/PANI nanocomposite, respectively. The strong peak at 26.541 in the pristine graphite pattern shown in Fig. 5a was not present in the CGO which showed a peak at 11.851 in Fig. 5b, indicating the presence of residual stacked layers of graphene oxide with functional groups containing oxygen, which was formed during oxidation. According to Bragg’s law, nl = 2d sin y, where n is an integer, y is the angle of incidence (or reflection) of the X-ray beam, and l is the X-ray wavelength (in the case of Cu-Ka1 radiation, l = 0.154 nm) the distance between CGO layers is 0.746 nm which is larger than that of pristine graphite (0.335 nm), implying the exfoliation of graphite.12 We observed that there is a weak and broad peak appearing at 2y = 11.421 as shown in Fig. 5d (d = 0.774 nm), which is lower than that of pristine CGO. This shows that the inter-planar spacing of the CGO/PANI nanocomposite was broadened due to the disturbance by PANI and that the pristine CGO was fully exfoliated by treatment with PANI. In addition, a diffraction peak at about 2y = 18.051 appeared in Fig. 5d, indicating that the rich functional groups on the GO layers might induce PANI to grow with a relatively ordered chain structure. As shown in Fig. 5c, pure PANI with HCl dopant showed broad two peaks at 19.62 and 25.61 which indicate the polaron form of the emeraldine salt state.13 For the composite, however, the peak at 25.61 almost disappeared while a new weak peak at 42.561 was evident. This indicates that the state of PANI in the CGO/PANI nanocomposite was basically the insulating emeraldine base form.14 The result indicates that the CGO can play a role as a proton provider during oxidation with conducting PANI. Nevertheless, the proportion of proton composite after polymerization is close to the de-doped state, which makes PANI a suitable candidate for ER application. The formation of the nanocomposite and doping state of PANI in the composite as inferred from the XRD data above should be reflected in the electrical conductivity. The electrical conductivity of the products were measured and results are given in Table S1 (ESIw). Obviously, graphite has excellent conductivity (6.7  102 S cm 1). However, after oxidation, the conductivity of CGO is found to be much reduced by many orders of magnitude (6  10 6 S cm 1). Also, the conductivity of the CGO/PANI nanocomposite (2  10 9 S cm 1) was much lower than that of CGO in accordance with the Chem. Commun., 2010, 46, 5596–5598 | 5597

nanocomposite provides adjustable electrical conductivity that can be used as a potential ER fluid. This work was supported by the Industrial Strategic Technology Development Program funded by the Ministry of Knowledge Economy, Korea (2009).

Notes and references

Fig. 5 XRD patterns of (a) graphite, (b) CGO, (c) pure PANI and (d) CGO/PANI nanocomposite.

Fig. 6 OM images of (a), (b) CGO/PANI nanocomposite without an electric field (left) and with an electric field (right).

de-doped PANI conductivity. This conductivity value of the CGO/PANI nanocomposite is thus suitable for an ER fluid.15 Fig. 6 shows fibrillation of CGO/PANI nanocomposite particles dispersed in silicone oil which is a characteristic ER phenomenon in an electric field. Here the ER fluids act as smart materials whose rheological properties are accurately controllable in an applied electric field.16 Most ER fluids are comprised of inorganic particles dispersed in an insulating liquid such as silicone oil. The changes in microstructure of the ER fluid were observed using an optical microscope (OM) under a DC applied electric field using a DC high voltage source. The gap distance between two parallel electrodes was fixed at 300 mm. When the electric field is absent, both of the nanocomposites were found to be randomly dispersed in silicon oil like a Newtonian fluid. However, when an electric field (0.2 kV mm 1) was applied, particles started to move and formed strong fibrillated-chain structures in the direction of the electric field.17 Note that such OM observation of the ER fluid has been reported for CNT systems. Bulk rheological characterization of the CGO/PANI nanocomposite based ER fluid using a rheometer under an applied electric field is the subject of current investigation.18 In conclusion, a CGO/PANI nanocomposite was synthesized via in situ oxidation polymerization in the presence of CGO. The thermal stability of the CGO/PANI nanocomposite was increased compared with that of the pristine CGO due to the deposited PANI on CGO layers with regular microstructure. Due to hydrophilic nature of CGO, the nanocomposite synthesized can be dispersed easily in aqueous media in spite of the water insolubility of the monomer aniline, which will increase its application potential. The CGO/PANI

5598 | Chem. Commun., 2010, 46, 5596–5598

1 (a) K. S. Novoselov, A. K. Geim, S. V. Morozov, D. Jiang, M. I. Katsnelson, I. V. Grigorieva, S. V. Dubonos and A. A. Firsov, Nature, 2005, 438, 197; (b) A. H. Castro Neto, F. Guinea, N. M. R. Peres, K. S. Novoselov and A. K. Geim, Rev. Mod. Phys., 2009, 81, 109. 2 (a) K. S. Novoselov, A. K. Geim, S. V. Morozov, D. Jiang, Y. Zhang, S. V. Dubonos, I. V. Grigorieva and A. A. Firsov, Science, 2004, 306, 666; (b) S. Stankovich, D. A. Dikin, G. H. B. Dommett, K. M. Kohlhaas, E. J. Zimney, E. A. Stach, R. D. Piner, S. T. Nguyen and R. S. Ruoff, Nature, 2006, 442, 282; (c) Z. F. Liu, Q. Liu, Y. Huang, Y. F. Ma, S. G. Yin, X. Y. Zhang, W. Sun and Y. S. Chen, Adv. Mater., 2008, 20, 3924; (d) A. P. Yu, P. Ramesh, M. E. Itkis, E. Bekyarova and R. C. Haddon, J. Phys. Chem. C, 2007, 111, 7565. 3 (a) N. I. Kovtyukhova, P. J. Ollivier, B. R. Martin, T. E. Mallouk, S. A. Chizhik, E. V. Buzaneva and A. D. Gorchinskiy, Chem. Mater., 1999, 11, 771; (b) N. A. Kotov, I. Dekany and J. H. Fendler, Adv. Mater., 1996, 8, 637; (c) T. Cassagneau, F. Guerin and J. H. Fendler, Langmuir, 2000, 16, 7318–7324. 4 (a) X. P. Zhao and J. B. Yin, Chem. Mater., 2002, 14, 2258; (b) X. Niu, M. Zhang, J. Wu, W. Wen and P. Sheng, Soft Matter, 2009, 5, 576. 5 (a) M. S. Cho, Y. H. Cho, H. J. Choi and M. S. Jhon, Langmuir, 2003, 19, 5875; (b) P. Hiamtup, A. Sirivat and A. M. Jamieson, J. Mater. Sci., 2010, 45, 1972. 6 (a) Q. Cheng, V. Pavlinek, Y. He, C. Li and P. Saha, Colloid Polym. Sci., 2009, 287, 435; (b) H. J. Choi and M. S. Jhon, Soft Matter, 2009, 5, 1562; (c) F. F. Fang, H. J. Choi and J. S. Joo, J. Nanosci. Nanotechnol., 2008, 8, 1559. 7 (a) S. Higashika, K. Kimura, Y. Matsuo and Y. Sugie, Carbon, 1999, 37, 354; (b) X. S. Du, M. Xiao and Y. Z. Meng, J. Polym. Sci., Part B: Polym. Phys., 2004, 42, 1972; (c) M. Seredych, R. Pietrzak and T. J. Bandosz, Ind. Eng. Chem. Res., 2007, 46, 6925. 8 (a) S. Stankovich, R. D. Piner, S. T. Nguyen and R. S. Ruoff, Carbon, 2006, 44, 3342; (b) S. Stankovich, R. D. Piner, X. Q. Chen, N. Q. Wu, S. T. Nguyen and R. S. Ruoff, J. Mater. Chem., 2006, 16, 155; (c) T. Szabo, E. Tombacz, E. Illes and I. Dekany, Carbon, 2006, 44, 537. 9 (a) G. I. Titelman, V. Gelman, S. Bron, R. L. Khalfin, Y. Cohen and H. Bianco-Peled, Carbon, 2005, 43, 641; (b) R. Bissessur, P. K. Y. Liu, W. White and S. F. Scully, Langmuir, 2006, 22, 1729–1734. 10 G. C. Wang, Z. Y. Yang, X. W. Li and C. Z. Li, Carbon, 2005, 43, 2564. 11 P. G. Liu, K. C. Gong, P. Xiao and M. Xiao, J. Mater. Chem., 2000, 10, 933. 12 T. Kyotani, H. Moriyama and A. Tomita, Carbon, 1997, 35, 1185. 13 J. P. Pouget, M. E. Jozefowicz, A. J. Epstein, X. Tang and A. G. MacDiarmid, Macromolecules, 1991, 24, 779. 14 M. Deka, A. K. Nath and A. Kumar, J. Membr. Sci., 2009, 327, 188. 15 F. F. Fang, B. M. Lee and H. J. Choi, Macromol. Res., 2010, 18, 99. 16 (a) J. B. Yin, X. P. Zhao, X. Xia, L. Q. Xiang and Y. P. Qiao, Polymer, 2008, 49, 4413; (b) F. F. Fang, J. H. Kim, H. J. Choi and C. A. Kim, Colloid Polym. Sci., 2009, 287, 745; (c) K. Oz, M. Yavuz, H. Yilmaz, H. I. Unal and B. Sari, J. Mater. Sci., 2008, 43, 1451. 17 (a) B. Wang, M. Zhou, Z. Rozynek and J. O. Fossum, J. Mater. Chem., 2009, 19, 1816; (b) S. J. Park, M. S. Cho, S. T. Lim, H. J. Choi and M. S. Jhon, Macromol. Rapid Commun., 2005, 26, 1563. 18 (a) H. J. Jin, H. J. Choi, S. H. Yoon, S. J. Myung and S. E. Shim, Chem. Mater., 2005, 17, 4034; (b) I. S. Lee, S. H. Yoon, H. J. Jin and H. J. Choi, Diamond Relat. Mater., 2006, 15, 1094.

This journal is

c

The Royal Society of Chemistry 2010