Hierarchical Structure of Carbon Nanotube Networks

Abstract

The hierarchical structure of semidilute suspensions of single-walled carbon nanotubes in polymeric matrices, studied by the use of ultrasmall and small angle neutron scattering, indicates an aggregate size that is independent on both nanotube concentration and polymer matrix and a mesh within the floc that becomes slightly denser with increasing nanotube concentration. The number of clusters grows linearly with concentration of nanotubes. These structural parameters suggest that the interactions between the flocs dictate the concentration-dependent elastic strength scaling of the network, with the absolute values of the specific elastic strength being inversely related to the percolation threshold.

Tailored Nanocomposites of Polypropylene with Layered Silicates

“…In contrast, the MA-functionalized PP chains are able to form at most two contacts per chain with the silicate layers and further because of physical entanglements of such doubly tethered polymers leads to effective bridging interactions between the nanoparticles [25][26][27] (Scheme 1b), and to the development of an extended and possibly hierarchical superstructure which is manifested macroscopically in the solid-like behavior. Thus, even though the individual MA group interactions with the silicate are weaker than the corresponding ammonium cation interactions with the silicate layers, 28 the MA-treated PP can promote the formation of a filler network structure -and consequently result in a solid-like rheological response-because of their ability to effectively bridge silicate sheets.…”

Practical applications of small-angle neutron scattering

“…8, 109 alongside a schematic depiction of the structures detected. In the low Q region, I(Q) is typically found to scale in proportion with Q Àa , with a lying between 2 and 3, [106][107][108][109][110][111] indicative of a dense fractal network similar to those discussed for the P3HT gels. As before, a decreased value for the exponent indicates a less dense network, which is also reflected in the onset point of the fractal structure (approx.…”

Carbon Nanotube-Based Poly(ethylene oxide) Nanocomposites

“…The scattering vector q (¼4p/l sin(y/2), with l and y as the wavelength and scattering angle, respectively) dependence of the scattered intensity, I(q), is found to be roughly independent of nanotube loading over the entire q range (3 Â 10 À5 < q < 0.1 Å À1 ) studied. The scattered intensity, when scaled by the composition of the mixtures, pÂ(1 À p) (expected for disordered systems), forms a mastercurve [62]. This superposition which indicates that the structure of the network is over a length-scale (¼2p/q) range of 6 nm to 20 mm for a broad range of semi-dilute compositions (p/p c ) is self-similar.…”

“…As discussed before, for welldispersed CNTs, the entropic barrier to dispersion offers a limited concentration window between the percolation threshold and isotropic to nematic transition. For SWNT-PEO nanocomposites with the nanotube concentration window (2 p/p c 10), the network structure was systematically investigated using small-and ultrasmall-angle neutron-scattering methods [62]. These systems thus represent a semi-dilute dispersion of nanoparticles, a range of significant practical importance for technological applications.…”

“…These systems thus represent a semi-dilute dispersion of nanoparticles, a range of significant practical importance for technological applications. A three-dimensional network of anisotropic nanoparticles is expected to show multiple length scales, and small-and ultrasmall-angle neutron scattering (SANS and USANS, respectively [63,64]) are ideal techniques to probe the hierarchical structure [62,65] of such a network. The scattering vector q (¼4p/l sin(y/2), with l and y as the wavelength and scattering angle, respectively) dependence of the scattered intensity, I(q), is found to be roughly independent of nanotube loading over the entire q range (3 Â 10 À5 < q < 0.1 Å À1 ) studied.…”