Viscoelasticity and high buckling stress of dense carbon nanotube brushes

Abstract

We report on the mechanical behavior of a dense brush of small-diameter (1-3 nm) noncatalytic multiwall (2-4 walls) carbon nanotubes (CNTs), with ~10 times higher density than CNT brushes produced by other methods. Under compression with spherical indenters of different radii, these highly dense CNT brushes exhibit a higher modulus (~17-20 GPa) and orders of magnitude higher resistance to buckling than vapor phase deposited CNT brushes or carbon walls. We also demonstrate the viscoelastic behavior, caused by the increased influence of the van der Waals' forces in these highly dense CNT brushes, showing their promise for energy-absorbing coatings.

Biomimetic superelastic graphene-based cellular monoliths

“…The compression experiments at different strain rates (10-3,000% per minute) revealed that the stress-strain curve was almost independent on the strain rate. Similar to other dense carbon viscoelastic materials 16,42 , the high-energy loss coefficient could be attributed to the intersheet van der Waals adhesion and frictions during bending/buckling in the compression and the unloading process, as well as de-binding of the contacted cell walls when unloaded. The face-to-face oriented stacking configuration of graphene sheets in the cell wall maximizes the contact area between graphene sheets, which can generate frictions that are comparable to or even higher than that of dense carbon nanotube structures 15 .…”

A microstructurally motivated description of the deformation of vertically aligned carbon nanotube structures

“…The collective properties of carbon nanotubes in the form of vertically aligned carbon nanotubes (VACNTs) have been explored for applications ranging from micro-electromechanical system (MEMS) [1][2][3] to low temperature energy dissipating materials. [4][5][6] This has led to growing interest in developing an understanding of VACNT's mechanical response which is key for rational design and life cycle analysis. [1][2][3]5,[7][8][9][10][11][12][13] VACNT materials are complex, hierarchical, and largely disordered assemblies of carbon nanotubes (CNTs) aligned nominally vertically with respect to the growth substrate.…”

“…[4][5][6] This has led to growing interest in developing an understanding of VACNT's mechanical response which is key for rational design and life cycle analysis. [1][2][3]5,[7][8][9][10][11][12][13] VACNT materials are complex, hierarchical, and largely disordered assemblies of carbon nanotubes (CNTs) aligned nominally vertically with respect to the growth substrate. Experimental investigations have found that VACNTs have mechanical energy dissipative properties, 4,5,7,10 can exhibit high recoverability after large strains, 8,14,15 and deform via a sequential periodic buckling mechanism under uniaxial compression.…”

“…[1][2][3]5,[7][8][9][10][11][12][13] VACNT materials are complex, hierarchical, and largely disordered assemblies of carbon nanotubes (CNTs) aligned nominally vertically with respect to the growth substrate. Experimental investigations have found that VACNTs have mechanical energy dissipative properties, 4,5,7,10 can exhibit high recoverability after large strains, 8,14,15 and deform via a sequential periodic buckling mechanism under uniaxial compression. 1,2,7,8,11 While observations of these behaviors are numerous, the physical mechanisms governing them remain poorly understood.…”

Nonlinear viscoelasticity of freestanding and polymer-anchored vertically aligned carbon nanotube foams

“…23 The micro-and nano-scale time-dependent mechanical response of freestanding VACNTs has been characterized using indentation techniques. [24][25][26] Under a spherical indenter, VACNT forests have been shown to undergo timedependent creep deformation 26 and viscoelastic relaxation due to the thermally activated change in nanotube contacts. 24 Dense CNT brushes have been shown to exhibit a viscoelastic response under dynamic indentation with loads below the critical CNT buckling load.…”