Sacrificial bonds in stacked-cup carbon nanofibers: biomimetic toughening mechanisms for composite systems.

Many natural composites, such as nacre or bone, achieve exceptional toughening enhancements through the rupture of noncovalent secondary bonds between chain segments in the organic phase. This "sacrificial bond" rupture dissipates enormous amounts of energy and reveals significant hidden lengths due to unraveling of the highly coiled macromolecules, leaving the structural integrity of their covalent backbones intact to large extensions. In this work, we present the first evidence of similar sacrificial bond mechanisms in the inorganic phase of composites using inexpensive stacked-cup carbon nanofibers (CNF), which are composed of helically coiled graphene sheets with graphitic spacing between adjacent layers. These CNFs are dispersed in a series of high-performance epoxy systems containing trifunctional and tetrafunctional resins, which are traditionally difficult to toughen in light of their highly cross-linked networks. Nonetheless, the addition of only 0.68 wt % CNF yields toughness enhancements of 43-112% for the various blends. Analysis of the relevant toughening mechanisms reveals two heretofore unseen mechanisms using sacrificial bonds that complement the observed crack deflection, rupture, and debonding/pullout that are common to many composite systems. First, embedded nanofibers can splay discretely between adjacent graphitic layers in the side walls; second, crack-bridging nanofibers can unravel continuously. Both of these mechanisms entail the dissipation of the pi-pi interactions between layers in the side walls without compromising the structural integrity of the graphene sheets. Moreover, increases in electrical conductivity of approximately 7-10 orders of magnitude were found, highlighting the multifunctionality of CNFs as reinforcements for the design of tough, inexpensive nanocomposites with improved electrical properties.

[1]  Anthony G. Evans,et al.  Crack deflection processes—I. Theory , 1983 .

[2]  G. P. Tandon,et al.  Average stress in the matrix and effective moduli of randomly oriented composites , 1986 .

[3]  Y. Benveniste,et al.  A new approach to the application of Mori-Tanaka's theory in composite materials , 1987 .

[4]  Reshef Tenne,et al.  Stress-induced fragmentation of multiwall carbon nanotubes in a polymer matrix , 1998 .

[5]  A. Lesser,et al.  The effect of network architecture on the thermal and mechanical behavior of epoxy resins , 1998 .

[6]  Elizabeth C. Dickey,et al.  Load transfer and deformation mechanisms in carbon nanotube-polystyrene composites , 2000 .

[7]  K. Lozano,et al.  Nanofiber‐reinforced thermoplastic composites. I. Thermoanalytical and mechanical analyses , 2001 .

[8]  Paul K. Hansma,et al.  Bone indentation recovery time correlates with bond reforming time , 2001, Nature.

[9]  G. Hwang,et al.  Efficient Load Transfer to Polymer‐Grafted Multiwalled Carbon Nanotubes in Polymer Composites , 2004 .

[10]  Peter F. Green,et al.  Elastic modulus of single‐walled carbon nanotube/poly(methyl methacrylate) nanocomposites , 2004 .

[11]  Sung-Moo Song,et al.  Mechanical and physical properties of epoxy composites reinforced by vapor grown carbon nanofibers , 2005 .

[12]  Jacqueline A. Cutroni,et al.  Sacrificial bonds and hidden length dissipate energy as mineralized fibrils separate during bone fracture , 2005, Nature materials.

[13]  L. Schadler,et al.  Quantitative equivalence between polymer nanocomposites and thin polymer films , 2005, Nature materials.

[14]  Bodo Fiedler,et al.  Influence of different carbon nanotubes on the mechanical properties of epoxy matrix composites – A comparative study , 2005 .

[15]  L. Brinson,et al.  Functionalized SWNT/polymer nanocomposites for dramatic property improvement , 2005 .

[16]  Bodo Fiedler,et al.  FUNDAMENTAL ASPECTS OF NANO-REINFORCED COMPOSITES , 2006 .

[17]  Georg Schitter,et al.  Sacrificial bonds and hidden length: unraveling molecular mesostructures in tough materials. , 2006, Biophysical journal.

[18]  Juan A. Conesa,et al.  Differences between carbon nanofibers produced using Fe and Ni catalysts in a floating catalyst reactor , 2006 .

[19]  Linda S. Schadler,et al.  Fracture Transitions at a Carbon‐Nanotube/Polymer Interface , 2006 .

[20]  J. A. Conesa,et al.  Evidence for growth mechanism and helix-spiral cone structure of stacked-cup carbon nanofibers , 2007 .

[21]  N. Kotov,et al.  Fusion of Seashell Nacre and Marine Bioadhesive Analogs: High‐Strength Nanocomposite by Layer‐by‐Layer Assembly of Clay and L‐3,4‐Dihydroxyphenylalanine Polymer , 2007 .

[22]  Gary G. Tibbetts,et al.  A review of the fabrication and properties of vapor-grown carbon nanofiber/polymer composites , 2007 .

[23]  S. Jeelani,et al.  Effect vapor grown carbon nanofiber on thermal and mechanical properties of epoxy , 2007 .

[24]  A. Waas,et al.  Ultrastrong and Stiff Layered Polymer Nanocomposites , 2007, Science.

[25]  R. Krishnamoorti,et al.  The role of interfacial interactions in the dynamic mechanical response of functionalized SWNT-PS nanocomposites , 2007 .

[26]  L. Brinson,et al.  Effect of Cross-Link Density on Interphase Creation in Polymer Nanocomposites , 2008 .

[27]  K. Winey,et al.  Cellular structures of carbon nanotubes in a polymer matrix improve properties relative to composites with dispersed nanotubes , 2008 .

[28]  L. Brinson,et al.  Functionalized graphene sheets for polymer nanocomposites. , 2008, Nature nanotechnology.

[29]  A. Nadarajah,et al.  Elastic properties and morphology of individual carbon nanofibers. , 2008, ACS nano.

[30]  L. Brinson,et al.  Preparation and characterization of multiwalled carbon nanotube dispersions in polypropylene: Melt mixing versus solid‐state shear pulverization , 2009 .

[31]  Faramarz Gordaninejad,et al.  Energy absorption capability of nanocomposites: A review , 2009 .

[32]  L. Brinson,et al.  Effects of dispersion and interfacial modification on the macroscale properties of TiO(2) polymer matrix nanocomposites. , 2009, Composites science and technology.

[33]  R. Ritchie,et al.  On the Fracture Toughness of Advanced Materials , 2009 .

[34]  Yi Cui,et al.  Carbon-silicon core-shell nanowires as high capacity electrode for lithium ion batteries. , 2009, Nano letters.

[35]  Uttandaraman Sundararaj,et al.  A review of vapor grown carbon nanofiber/polymer conductive composites , 2009 .

[36]  L. Brinson,et al.  Curved-fiber pull-out model for nanocomposites. Part 2: Interfacial debonding and sliding , 2009 .

[37]  Hyoung-Sug Kim,et al.  LBL assembled laminates with hierarchical organization from nano- to microscale: high-toughness nanomaterials and deformation imaging. , 2009, ACS nano.

[38]  Jun Li,et al.  Characterization of carbon nanofiber electrode arrays using electrochemical impedance spectroscopy: effect of scaling down electrode size. , 2010, ACS nano.

[39]  L. Brinson,et al.  Viscoelastic behavior of nanotube-filled polycarbonate: Effect of aspect ratio and interface chemistry , 2010 .

[40]  A. Skordos,et al.  Percolation threshold of carbon nanotubes filled unsaturated polyesters , 2010 .

[41]  L. Brinson,et al.  Measurement of the critical aspect ratio and interfacial shear strength in MWNT/polymer composites , 2010 .

[42]  Zhongwei Chen,et al.  Platinum nanopaticles supported on stacked-cup carbon nanofibers as electrocatalysts for proton exchange membrane fuel cell , 2010 .

[43]  M. Naraghi,et al.  Mechanical properties of vapor grown carbon nanofibers , 2010 .