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Zhao, W.,Shan, C.,Elias, A.L.,Rajukumar, L.P.,O'Brien, D.J.,Terrones, M.,Wei, B.,Suhr, J.,Lu, X.L. Pergamon Press ; Elsevier Science Ltd 2015 Carbon Vol.95 No.-
To expand the applications of carbon nanotubes (CNTs) at macroscale, a heteroatom doping technique has been employed to fabricate isotropic 3-D CNT architectures by inducing elbow-like covalent junctions into multiwalled CNTs. As the junctions modify the topology of each CNT by favoring the stable bends in CNTs, junction stiffness and the consequence of junction-related morphology changes in sponge's hyperelasticity remain largely elusive. In this study, two types of 3-D multiwalled CNT sponges were fabricated by inducing boron-doped or nitrogen-doped covalent junctions into CNTs. Hyperelastic properties of the sponges were experimentally quantified as the functions of CNT morphology. A novel microstructure informed continuum constitutive law was developed specifically for such isotropic CNT sponges with junctions. Analyzing the experimental data with the new theory demonstrated that, for the first time, the effective modulus of boron-doped junctions (~100 GPa) is higher than that of nitrogen-doped junctions (~20 GPa), and the junction stiffness is a key factor in regulating the hyperelastic compressive modulus of the material. Theoretical analysis further revealed that increased number of junctions and shorter segments on each individual CNT chain would result in stronger hyperelastic 3-D CNT networks. This study has established a fundamental knowledge base to provide guidance for the future design and fabrication of 3-D CNT macrostructures.
Cruz-Silva, Rodolfo,Morelos-Gomez, Aaron,Kim, Hyung-ick,Jang, Hong-kyu,Tristan, Ferdinando,Vega-Diaz, Sofia,Rajukumar, Lakshmy P.,Elí,as, Ana Laura,Perea-Lopez, Nestor,Suhr, Jonghwan,Endo, Morin American Chemical Society 2014 ACS NANO Vol.8 No.6
<P>Graphene oxide (GO) has recently become an attractive building block for fabricating graphene-based functional materials. GO films and fibers have been prepared mainly by vacuum filtration and wet spinning. These materials exhibit relatively high Young’s moduli but low toughness and a high tendency to tear or break. Here, we report an alternative method, using bar coating and drying of water/GO dispersions, for preparing large-area GO thin films (<I>e.g.</I>, 800–1200 cm<SUP>2</SUP> or larger) with an outstanding mechanical behavior and excellent tear resistance. These dried films were subsequently scrolled to prepare GO fibers with extremely large elongation to fracture (up to 76%), high toughness (up to 17 J/m<SUP>3</SUP>), and attractive macroscopic properties, such as uniform circular cross section, smooth surface, and great knotability. This method is simple, and after thermal reduction of the GO material, it can render highly electrically conducting graphene-based fibers with values up to 416 S/cm at room temperature. In this context, GO fibers annealed at 2000 °C were also successfully used as electron field emitters operating at low turn on voltages of <I>ca.</I> 0.48 V/μm and high current densities (5.3 A/cm<SUP>2</SUP>). Robust GO fibers and large-area films with fascinating architectures and outstanding mechanical and electrical properties were prepared with bar coating followed by dry film scrolling.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2014/ancac3.2014.8.issue-6/nn501098d/production/images/medium/nn-2014-01098d_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn501098d'>ACS Electronic Supporting Info</A></P>