Thermomechanical properties of chemically modified graphene/poly(methyl methacrylate) composites made by in situ polymerization Jeffrey R. Potts a , Sun Hwa Lee b , Todd M. Alam c , Jinho An a , Meryl D. Stoller a , Richard D. Piner a , Rodney S. Ruoff a, * a Department of Mechanical Engineering and the Texas Materials Institute, University of Texas at Austin, One University Station C2200, Austin, TX 78712-0292, USA b Department of Materials Science and Engineering KAIST, Daejeon 305-701, Republic of Korea c Department of Electronic and Nanostructured Materials, MS 0886, Sandia National Laboratories, Albuquerque, NM 87185-0886, USA ARTICLE INFO Article history: Received 13 December 2010 Accepted 3 February 2011 Available online 22 February 2011 ABSTRACT The morphology and thermomechanical properties of composites of poly(methyl methac- rylate) (PMMA) and chemically modified graphene (CMG) fillers were investigated. For com- posites made by in situ polymerization, large shifts in the glass transition temperature were observed with loadings as low as 0.05 wt.% for both chemically-reduced graphene oxide (RG-O) and graphene oxide (G-O)-filled composites. The elastic modulus of the composites improved by as much as 28% at just 1 wt.% loading. Mori–Tanaka theory was used to quan- tify dispersion, suggesting platelet aspect ratios greater than 100 at low loadings and a lower quality of dispersion at higher loadings. Fracture strength increased for G-O/PMMA composites but decreased for RG-O/PMMA composites. Wide angle X-ray scattering sug- gested an exfoliated morphology of both types of CMG fillers dispersed in the PMMA matrix, while transmission electron microscopy revealed that the platelets adopt a wrin- kled morphology when dispersed in the matrix. Both techniques suggested similar exfoli- ation and dispersion of both types of CMG filler. Structural characterization of the resulting composites using gel permeation chromatography and solid state nuclear magnetic reso- nance showed no change in the polymer structure with increased loading of CMG filler. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Graphene, a two-dimensional layer of sp 2 -bonded carbon atoms, exhibits exceptional physical properties and is being explored for use in a variety of applications [1]. Chemically modified graphene (CMG) platelets, which can be made in bulk quantities from graphite oxide (GO), have been investi- gated as a composite filler [2,3]. There are three primary methods for producing GO [4], all of which generate a product with a larger interlayer spacing than graphite (0.6–1.2 nm depending on humidity versus 0.34 nm, respectively) and has several oxygen-based functional groups decorating the surface (e.g., carboxylic acids, epoxides, alcohols) [4,5]. This larger interlayer spacing and presence of hydrophilic surface functionalities are both thought to facilitate the exfoliation of layered GO particles into single- or few-layer graphene oxide (G-O) platelets in water and in polar organic solvents [6] via sonication or stirring. GO can also be exfoliated via ‘thermal shocking’ [7] (i.e., rapid heating including under inert gas) or microwave irradiation [8] to create loosely-stacked, 0008-6223/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbon.2011.02.023 * Corresponding author. E-mail address: [email protected](R.S. Ruoff). CARBON 49 (2011) 2615 – 2623 available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/carbon
9
Embed
Thermomechanical properties of chemically modified ...utw10193.utweb.utexas.edu/Archive/RuoffsPDFs/253.pdfThermomechanical properties of chemically modified graphene/poly(methyl methacrylate)
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Thermomechanical properties of chemically modifiedgraphene/poly(methyl methacrylate) composites madeby in situ polymerization
Jeffrey R. Potts a, Sun Hwa Lee b, Todd M. Alam c, Jinho An a, Meryl D. Stoller a,Richard D. Piner a, Rodney S. Ruoff a,*
a Department of Mechanical Engineering and the Texas Materials Institute, University of Texas at Austin, One University Station C2200,
Austin, TX 78712-0292, USAb Department of Materials Science and Engineering KAIST, Daejeon 305-701, Republic of Koreac Department of Electronic and Nanostructured Materials, MS 0886, Sandia National Laboratories, Albuquerque, NM 87185-0886, USA
A R T I C L E I N F O
Article history:
Received 13 December 2010
Accepted 3 February 2011
Available online 22 February 2011
0008-6223/$ - see front matter � 2011 Elsevidoi:10.1016/j.carbon.2011.02.023
ments in the non-oxidative thermal stability compared with
neat PMMA.
Attempts were made to characterize any change in poly-
mer structure with CMG loading to investigate whether the
property improvements of the composites were influenced
by possible changes in polymer structure, due to the presence
of G-O platelets during polymerization. As shown in Fig. 7, no
change in the NMR spectrum was observed between neat
PMMA and the composites. GPC measurements indicated that
the molecular weight of the composites increased slightly
with higher loadings of CMG filler (Table 2). Both 1H and 13C
solution NMR revealed that the dominant triad tacticity of
Fig. 6 – TGA curves for the RG-O composites versus neat
PMMA, showing increased thermal stability with loading of
RG-O. Similar trends were observed for G-O/PMMA
composites.
Table 3 – Tacticity ratios for neat, 8 wt.% G-O/PMMA and8 wt.% RG-O/PMMA samples based on integration of thecarbonyl region in the 13C NMR solution spectra.
2622 C A R B O N 4 9 ( 2 0 1 1 ) 2 6 1 5 – 2 6 2 3
4. Conclusions
We prepared composites of PMMA with two types of CMG
materials as filler: graphene oxide (G-O) and reduced graph-
ene oxide (RG-O). The composites were prepared using an
in situ polymerization method and processed using micro-
compounding/injection molding or hot pressing. Injection
molded samples were subjected to standard tensile testing
and showed increases in modulus for both CMG/PMMA com-
posites, but only increases in strength for G-O in PMMA. In-
creases in the dynamic modulus were observed by DMA,
where we also observed shifts of over 15 �C in Tg versus neat
PMMA. Spectroscopic studies using FT-IR and NMR along with
GPC revealed no evidence of variation in the structure of the
polymer with increased CMG loading. The results indicate
that both RG-O and G-O fillers provide substantial property
improvements relative to neat PMMA, although this study
suggests that G-O platelets offer the advantage of increased
tensile strength whereas RG-O platelets do not. Mori–Tanaka
theory suggests a good dispersion of filler at lower loadings
(up to 1 wt.%), which progressively worsens at higher load-
ings. Based on TEM observations and solid state NMR studies,
we believe this is due to agglomeration of the platelets
(whether due to incomplete exfoliation and/or platelet
restacking) at higher loadings.
Acknowledgements
The authors would like to thank Prof. Don Paul for use of the
melt compounding and injection molding equipment, Prof.
Ken Liechti for use of mechanical testing equipment, and
Prof. Chris Bielawski for use of the GPC and IR spectrometer.
This work was supported (in part) by the Laboratory Directed
Research and Development (LDRD) program and the National
Institute for Nano-Engineering at Sandia National Laborato-
ries. Sandia National Laboratories is a multi-program labora-
tory operated by Sandia Corporation, a wholly owned
subsidiary of Lockheed Martin company, for the US Depart-
ment of Energy’s National Nuclear Security Administration.
Appendix A. Supplementary data
Supplementary data associated with this article can be found,
in the online version, at doi:10.1016/j.carbon.2011.02.023.
R E F E R E N C E S
[1] Zhu Y, Murali S, Cai W, Li X, Suk JW, Potts JR, et al. Grapheneand graphene oxide: synthesis, properties, and applications.Adv Mater (Weinheim, Germany) 2010;22:3906–24.
[3] Kim H, Abdala AA, Macosko CW. Graphene/polymernanocomposites. Macromolecules 2010;43:6515–30.
[4] Dreyer DR, Park S, Bielawski CW, Ruoff RS. The chemistry ofgraphene oxide. Chem Soc Rev 2010;39(1):228–40.
[5] Park S, Ruoff RS. Chemical methods for the production ofgraphenes. Nat Nanotechnol 2009;5(4):217–24.
[6] Park S, An JH, Jung IW, Piner RD, An SJ, Li XS, et al.Colloidal suspensions of highly reduced graphene oxidein a wide variety of organic solvents. Nano Lett2009;9(4):1593–7.
[7] Schniepp HC, Li JL, McAllister MJ, Sai H, Herrera-Alonso M,Adamson DH, et al. Functionalized single graphene sheetsderived from splitting graphite oxide. J Phys Chem B2006;110(17):8535–9.
[8] Zhu YW, Murali S, Stoller MD, Velamakanni A, Piner RD, RuoffRS. Microwave assisted exfoliation and reduction of graphiteoxide for ultracapacitors. Carbon 2010;48(7):2118–22.
[9] Kim H, Macosko CW. Morphology and properties of polyester/exfoliated graphite nanocomposites. Macromolecules2008;41(9):3317–27.
[10] Kim H, Macosko CW. Processing-property relationships ofpolycarbonate/graphene composites. Polymer2009;50(15):3797–809.
[11] Kim H, Miura Y, Macosko CW. Graphene/polyurethanenanocomposites for improved gas barrier and electricalconductivity. Chem Mater 2010;22(11):3441–50.
[12] Moon IK, Lee J, Ruoff RS, Lee H. Reduced graphene oxide bychemical graphitization. Nat Commun. doi: 10.1038/ncomms1067.
[13] Stankovich S, Piner RD, Chen X, Wu N, Nguyen SBT, Ruoff RS.Stable aqueous dispersions of graphitic nanoplatelets via thereduction of exfoliated graphite oxide in the presence ofpoly(sodium 4-styrenesulfonate). J Mater Chem2006;16:155–8.
[14] Stankovich S, Dikin DA, Piner RD, Kohlhaas KA,Kleinhammes A, Jia Y, et al. Synthesis of graphene-basednanosheets via chemical reduction of exfoliated graphiteoxide. Carbon 2007;45(7):1558–65.
[15] Li D, Muller MB, Gilje S, Kaner RB, Wallace GG. Processableaqueous dispersions of graphene nanosheets. NatNanotechnol 2008 Feb;3(2):101–5.
[16] Stankovich S, Dikin DA, Dommett GHB, Kohlhaas KM,Zimney EJ, Stach EA, et al. Graphene-based compositematerials. Nature 2006;442(7100):282–6.
[17] Jang JY, Kim MS, Jeong HM, Shin CM. Graphite oxide/poly(methyl methacrylate) nanocomposites prepared by anovel method utilizing macroazoinitiator. Compos SciTechnol 2009;69(2):186–91.
[18] Paul DR, Robeson LM. Polymer nanotechnology:nanocomposites. Polymer 2008;49(15):3187–204.
[19] Hummers WS, Offeman RE. Preparation of graphitic oxide.J Am Chem Soc 1958;80(6):1339.
[20] Paredes JI, Villar-Rodil S, Martinez-Alonso A, Tascon JMD.Graphene oxide dispersions in organic solvents. Langmuir2008;24(19):10560–4.
[21] Ramanathan T, Abdala AA, Stankovich S, Dikin DA, Herrera-Alonso M, Piner RD, et al. Functionalized graphene sheets forpolymer nanocomposites. Nat Nanotechnol 2008Jun;3(6):327–31.
[22] Bansal A, Yang H, Li C, Cho K, Benicewicz BC, Kumar SK,et al. Quantitative equivalence between polymernanocomposites and thin polymer films. Nat Mater2005;4(9):693–8.
[23] Ellison CJ, Torkelson JM. The distribution of glass-transitiontemperatures in nanoscopically confined glass formers. NatMater 2003;2(10):695–700.
[24] Priestley RD, Ellison CJ, Broadbelt LJ, Torkelson JM. Structuralrelaxation of polymer glasses at surfaces, interfaces, and inbetween. Science 2005;309(5733):456.
[25] Qiao R, Brinson LC. Simulation of interphase percolation andgradients in polymer nanocomposites. Compos Sci Technol2009;69(3–4):491–9.
[26] Rittigstein P, Priestley RD, Broadbelt LJ, Torkelson JM. Modelpolymer nanocomposites provide an understanding of
C A R B O N 4 9 ( 2 0 1 1 ) 2 6 1 5 – 2 6 2 3 2623
confinement effects in real nanocomposites. Nat Mater2007;6(4):278–82.
[27] Mori T, Tanaka K. Average stress in matrix and average elasticenergy of materials with misfitting inclusions. Acta Metall1973;21:571–4.
[28] Tandon GP, Weng GJ. The effect of aspect ratio of inclusionson the elastic properties of unidirectionally alignedcomposites. Polym Compos 1984;5:327–33.
[29] Fornes TD, Paul DR. Modeling properties of nylon 6/claynanocomposites using composite theories. Polymer2003;44(17):4993–5013.