- Nano Express
- Open Access
Effects of the alkylamine functionalization of graphene oxide on the properties of polystyrene nanocomposites
© Jang et al.; licensee Springer. 2014
- Received: 7 March 2014
- Accepted: 19 May 2014
- Published: 28 May 2014
Alkylamine-functionalized graphene oxides (FGOs) have superior dispersibility in low-polar solvents and, as a result, they interact with low-polar polymers such as polystyrene. In this work, the functionalization of graphene oxide using three types of alkylamines, octylamine (OA), dodecylamine (DDA), and hexadecylamine (HDA), was performed, and nanocomposites of polystyrene (PS) and FGOs were prepared via solution blending. Different dispersions of FGOs over PS were obtained for the three alkylamines, and the properties of the PS composites were influenced by the length of the alkylamine. A better thermal stability was observed with a longer chain length of the alkylamine. On the other hand, functionalization with the shortest chain length alkylamine resulted in the highest increase in the storage modulus (3,640 MPa, 140%) at a 10 wt.% loading of FGO.
- Graphene oxide
Graphene has attracted intensive interest due to its extraordinary electrical, thermal, and mechanical properties [1, 2]. Among its wide range of applications, recent studies have demonstrated that polymer nanocomposites based on graphene have resulted in dramatic improvements in the mechanical, electrical, and gas barrier properties of pristine polymers [3–6]. Homogeneous dispersion of graphene in the polymer matrix is an essential requirement to obtain the desired properties. Graphene oxide (GO) with abundant oxygen-containing groups, such as epoxy, hydroxyl, and carboxyl, can be well dispersed in a polymer matrix due to its good interaction with polymer chains [7–9]. However, the agglomeration of graphene sheets due to van der Waals forces only allows for a successful colloidal suspension within a narrow range of organic solvents. Park et al. reported that highly reduced graphene oxide was dispersed in organic solvents with a sum of solubility parameters (δp and δH) in the range of 13 to 29 . Recently, it was reported that alkylamine-functionalized graphene oxide (FGO) exhibited good dispersion in solvents and a strong interfacial interaction with low-polar organic solvents and polymers [11–17]. GO modified with HDA showed superior dispersion up to 7 mg/mL in organic solvents with low Hansen solubility parameters, such as xylene and toluene . Thus, they could be effectively used as a nanofiller even in low-polar polymers such as polyethylene [19, 20].
In this work, three alkylamines, OA, DDA, and HDA, with different alkyl chain lengths were utilized to examine the effect of alkylamine functionalization of GO on the properties of FGO/PS composites. When the FGO/PS nanocomposites were prepared by solution blending, the FGOs were homogeneously dispersed over the PS matrix even at a high concentration in chloroform.
Preparation of FGO and FGO/PS nanocomposites
GO was prepared by a modified Hummers method using expanded graphite (Grade 1721, Asbury Carbons, Asbury, NJ, USA) which was heated for 10 s in a microwave oven. The ratio of GO to alkylamines (CH3(CH2)7NH2, CH3(CH2)11NH2, CH3(CH2)15NH2, Sigma Aldrich, St. Louis, MO, USA) was fixed at 1.0 g of GO to 0.01 mol of alkylamine. The alkylamine solutions were prepared by dissolving 0.010 mol of OA, DDA, or HDA in 30 mL of ethanol (SK Chemicals, Gyeonggi-do, Korea). The FGOs were produced by gradually adding the alkylamine solution into the GO solution (1.0 mg/mL) followed by stirring at 60°C for 12 h. During the alkylamine functionalization, the color of the GO solution gradually changed from yellow to black. This change was accompanied by an aggregation of graphene particles due to the hydrophobicity of the alkylamine-functionalized GO, indicating the simultaneous functionalization and slight reduction of GO [14, 19]. The suspensions were filtered and washed three times with methanol. The obtained products were denoted as FGO-OA, FGO-DDA, and FGO-HDA, respectively.
For solution blending of the FGOs and PS, we selected chloroform (OCI Chemical, Seoul, Korea), which is an effective media for both FGOs and PS. Based on the amount of PS (Mw approximately 192,000 g mol−1, Sigma Aldrich, St. Louis, MO, USA), the FGO loadings relative to PS were fixed at 0.5, 1.0, 2.0, 3.0, 5.0, and 10.0 wt.%. Solution blending was easily performed by adding 5 g of PS into the FGO in chloroform. The resulting FGO/PS solution was stirred for 2 h followed by sonication for 30 min. After that, the FGO/PS suspension was coaggregated by pouring the solution into 1.5 L of methanol (SK Chemicals, Gyeonggi-do, Korea) under vigorous stirring for 1 h. The products were filtered and washed three times with methanol and dried at 60°C for 12 h.
The compositions of the FGO/PSs were analyzed using an elemental analyzer (EA; Flash 2000, Thermo Scientific, Hudson, NH, USA). Fourier transform infrared (FT-IR) spectra were analyzed using an FT-IR spectrometer (Nicolet 380, Thermo Scientific, Madison, WI, USA). The morphologies of the freshly fractured surface of the neat PS and FGO/PS composites film were observed by scanning electron microscopy (SEM; JSM-6500FE, JEOL, Tokyo, Japan). A small amount of the FGO/PS nanocomposites was dispersed in ethanol in order to obtain meticulous field emission transmission electron microscope (FETEM; JEM-2100 F, JEOL, Tokyo, Japan) images. Thermogravimetric analysis (TGA) was performed under a nitrogen atmosphere at a heating rate of 10°C/min (Q50, TA Instruments, New Castle, DE, USA). The dynamic mechanical properties of the FGO/PS composites were measured using a dynamic mechanical analyzer (DMA-Q800, TA Instruments, New Castle, DE, USA) in the single cantilever deformation mode at a frequency of 1 Hz from 0°C to 180°C at a heating rate of 3°C/min.
The elemental analysis was further used to confirm the covalent functionalization of GO with DDA. The N contents were determined to be 3.07, 3.17, 3.21, and 3.21 wt.% for reaction times of 6, 12, 18, and 24 h, respectively, while the Cgraphene/O ratios were in the range of 2.01 to 2.43. After 12 h of reaction, the Cgraphene/N ratio tended to saturate around 12.5, corresponding to one DDA molecule per six aromatic rings on the GO sheet.
Glass transition temperatures obtained from the tan δ curves
FGO loading (wt.%)
Three types of FGO/PS composites were successfully prepared by solution blending. FGOs in the form of grafted alkylamines showed excellent dispersion over PS even at 10 wt.% loading. The dispersed FGOs formed different morphologies over the PS matrix due to the steric effects resulting from the different chain lengths of the alkylamines. All of the FGO/PS composites possessed improved thermal properties and storage moduli with FGO loading. FGO-HDA/PS, which has the longest chain length, showed the best thermal stability compared to other alkylamines. On the other hand, the storage modulus of the FGO-OA/PS composite achieved a maximum value of 3,640 MPa at 10 wt.% FGO-OA loading, which corresponded to 140% of the pristine PS. The functionalization of GO with alkylamines is thought to improve the compatibility of GO with various low-polar polymers due to their good interfacial interaction.
This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2011–0022485).
- Geim AK, Novoselov KS: The rise of graphene. Nat Mater 2007, 6: 183–191. 10.1038/nmat1849View ArticleGoogle Scholar
- Allen MJ, Tung VC, Kaner RB: Honeycomb carbon: a review of graphene. Chem Rev 2010, 110: 132–145. 10.1021/cr900070dView ArticleGoogle Scholar
- Stankovich S, Dikin DA, Dommett GHB, Kohlhaas KM, Zimney EJ, Stach EA, Piner RD, Nguyen ST, Ruoff RS: Graphene-based composite materials. Nature 2006, 442: 282–286. 10.1038/nature04969View ArticleGoogle Scholar
- Pham VH, Cuong TV, Dang TT, Hur SH, Kong B-S, Kim EJ, Shin EW, Chung JS: Superior conductive polystyrene-chemically converted graphene nanocomposite. J Mater Chem 2011, 21: 11312–11316. 10.1039/c1jm11146aView ArticleGoogle Scholar
- Ramanathan T, Abdala AA, Stankovich S, Dikin DA, Herrera-Alonso M, Piner RD, Adamson DH, Schniepp HC, Chen X, Ruoff RS, Nguyen ST, Aksay IA, Prud’Homme RK, Brinson LC: Functionalized graphene sheets for polymer nanocomposites. Nat Nanotechnol 2008, 3: 327–331. 10.1038/nnano.2008.96View ArticleGoogle Scholar
- Rajagopalan B, Pham VH, Jang J, Hur SH, Chung JS: A one pot solution blending method for highly conductive poly (methyl methacrylate)-highly reduced graphene nanocomposites. Electron Mater Lett 2013, 9: 837–839. 10.1007/s13391-013-6025-3View ArticleGoogle Scholar
- Dreyer DR, Park S, Bielawski CW, Ruoff RS: The chemistry of graphene oxide. Chem Soc Rev 2010, 39: 228–240. 10.1039/b917103gView ArticleGoogle Scholar
- Dang TT, Pham VH, Vu BK, Hur SH, Shin EW, Kim EJ, Chung JS: Clean and effective catalytic reduction of graphene oxide using atomic hydrogen spillover on Pt/γ-Al2O3 catalyst. Mater Lett 2012, 86: 161–164.View ArticleGoogle Scholar
- Pham VH, Cuong TV, Hur SH, Oh E, Kim EJ, Shin EW, Chung JS: Chemical functionalization of graphene sheets by solvothermal reduction of a graphene oxide suspension in N-methyl-2-pyrrolidone. J Mater Chem 2011, 21: 3371–3377. 10.1039/c0jm02790aView ArticleGoogle Scholar
- Park S, An J, Jung I, Piner RD, An SJ, Li X, Velamakanni A, Ruoff RS: Colloidal suspensions of highly reduced graphene oxide in a wide variety of organic solvents. Nano Lett 2009, 9: 1593–1597. 10.1021/nl803798yView ArticleGoogle Scholar
- Heo C, Moon H-G, Yoon CS, Chang J-H: ABS nanocomposite films based on functionalized-graphene sheets. J App Polym Sci 2012, 124: 4663–4670.Google Scholar
- Choudhary S, Mungse HP, Khatri OP: Dispersion of alkylated graphene in organic solvents and its potential for lubrication applications. J Mater Chem 2012, 22: 21032–21039. 10.1039/c2jm34741eView ArticleGoogle Scholar
- Niyogi S, Bekyarova E, Itkis ME, McWilliams JL, Hamon MA, Haddon RC: Solution properties of graphite and graphene. J Am Chem Soc 2006, 128: 7720–7721. 10.1021/ja060680rView ArticleGoogle Scholar
- Compton OC, Dikin DA, Putz KW, Brinson LC, Nguyen ST: Electrically conductive “alkylated” graphene paper via chemical reduction of amine-functionalized graphene oxide paper. Adv Mater 2010, 22: 892–896. 10.1002/adma.200902069View ArticleGoogle Scholar
- Liang Y, Wu D, Feng X, Müllen K: Dispersion of graphene sheets in organic solvent supported by ionic interactions. Adv Mater 2009, 21: 1679–1683. 10.1002/adma.200803160View ArticleGoogle Scholar
- Mei Q, Zhang K, Guan G, Liu B, Wang S, Zhang Z: Highly efficient photoluminescent graphene oxide with tunable surface properties. Chem Commun 2010, 46: 7319–7321. 10.1039/c0cc02374dView ArticleGoogle Scholar
- Tessonnier J-P, Barteau MA: Dispersion of alkyl-chain-functionalized reduced graphene oxide sheets in nonpolar solvents. Langmuir 2012, 28: 6691–6697. 10.1021/la2051614View ArticleGoogle Scholar
- Jang J, Pham VH, Hur SH, Chung JS: Dispersibility of reduced alkylamine-functionalized graphene oxides in organic solvents. J Colloid Interface Sci 2014, 424: 62–66.View ArticleGoogle Scholar
- Kuila T, Bose S, Mishra AK, Khanra P, Kim NH, Lee JH: Effect of functionalized graphene on the physical properties of linear low density polyethylene nanocomposites. Polym Test 2012, 31: 31–38. 10.1016/j.polymertesting.2011.09.007View ArticleGoogle Scholar
- Kim H, Kobayashi S, AbdurRahim MA, Zhang MJ, Khusainova A, Hillmyer MA, Abdala AA, Macosko CW: Graphene/polyethylene nanocomposites: effect of polyethylene functionalization and blending methods. Polymer 2011, 52: 1837–1846. 10.1016/j.polymer.2011.02.017View ArticleGoogle Scholar
- Liu J, Wang Y, Xu S, Sun DD: Synthesis of graphene soluble in organic solvents by simultaneous ether-functionalization with octadecane groups and reduction. Mater Lett 2010, 64: 2236–2239. 10.1016/j.matlet.2010.06.058View ArticleGoogle Scholar
- Jabbari E, Peppas NA: Use of ATR-FTIR to study interdiffusion in polystyrene and poly(vinyl methyl ether). Macromolecules 1993, 26: 2175–2186. 10.1021/ma00061a006View ArticleGoogle Scholar
- Rorabacher DB, Melendez-Cepeda CA: Steric effects on the kinetics and equilibria of nickel(ΙΙ)-alkylamine reactions in aqueous solution. J Am Chem Soc 1971, 93: 6071–6076. 10.1021/ja00752a018View ArticleGoogle Scholar
- Kuila T, Bose S, Hong CE, Uddin ME, Khanra P, Kim NH, Lee JH: Preparation of functionalized graphene/linear low density polyethylene composites by a solution mixing method. Carbon 2011, 49: 1033–1037. 10.1016/j.carbon.2010.10.031View ArticleGoogle Scholar
- Zhan Y, Yang X, Guo H, Yang J, Meng F, Liu X: Cross-linkable nitrile functionalized graphene oxide/poly(arylene ether nitrile) nanocomposite films with high mechanical strength and thermal stability. J Mater Chem 2012, 22: 5602–5608. 10.1039/c2jm15780bView ArticleGoogle Scholar
- Wang J, Qin S: Study on the thermal and mechanical properties of epoxy-nanoclay composites: the effect of ultrasonic stirring time. Mater Lett 2007, 61: 4222–4224. 10.1016/j.matlet.2007.01.058View ArticleGoogle Scholar
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