Orientation Distribution of Vertically Aligned Multiwalled Carbon Nanotubes

Abstract

Carbon nanotube "forests" show great promise in a variety of applications, from supercapacitors to fuel cells, but the realization of such materials for functional devices relies on a better control over processing routes such that targeted structures and associated properties can be reproducibly obtained. The orientation distribution of the nanotubes is a critical structural property affecting both electrical and mechanical response, yet it remains a challenging characteristic to quantify. Small-angle X-ray scattering (SAXS) is a technique well suited to investigate the vertical alignment of nanotubes.Here we show that the orientation distribution obtained from SAXS is not satisfactorily represented by the normal distribution or the Lorentzian, which have been used until now. Instead, an excellent agreement between model and data is found with the generalized normal distribution (GND). Such quantification of the carbon nanotube alignment can be used as direct input in simulations for optimizing structure−property relations.

Three-Dimensional Orientation of Nanofibrils in Axially Symmetric Systems Using Small-Angle X-ray Scattering

“…all the particles are in average aligned along a main direction, it is possible to obtain the 3D ODF without rotating the sample. Vainio et al 18 were able to recover the three-dimensional orientation of carbon nanotubes by tting the projected ODF using a general normal distribution (GND) function with two parameters.…”

“…The projected ODF Ψ χ was tted to a generalized normal distribution (GND) with two tting parameters describing the shape of the ODF and allowing the 3D-ODF Ψ φ to be recovered. There are however several advantages with the present Legendre-method compared to the GND tting method by Vainio et al 18 :…”

“…A method for comparing ODFs and taking into account the projected orientation was also proposed by Vainio et al 18 . The projected ODF Ψ χ was tted to a generalized normal distribution (GND) with two tting parameters describing the shape of the ODF and allowing the 3D-ODF Ψ φ to be recovered.…”

Nanostructured MWCNT/Polypyrrole Actuators with Anisotropic Strain Response

“…For a perfect vertical orientation f = 1, for random orientation f = 0, and for horizontal orientation f = −0.5. For an as‐grown MWCNT array, a typical value for the Hermans orientation parameter was 0.5 . For polymer‐infiltrated composites f varies for the different MWCNT volume fractions but by tendency is lowered due to the manufacturing process .…”

“…This global actuation strain of the hybrid thin film is calculated using the macroscopic thickness of the entire film, which includes porosity and the contribution of the MWCNTs. To calculate the local actuation strain of only the polypyrrole layer, the volume fraction of PPy in the MWCNT/PPy hybrid film was estimated using the density of the MWCNT array before and after the polymerization (pristine MWCNT array: 0.02 g cm −3 , volume fraction MWCNT array: 1%, MWCNT/PPy hybrid 0.25 g cm −3 ). The density of the pristine polypyrrole is 1.54 g cm −3 , leading to an approximately polypyrrole volume fraction of 15% for the MWCNT/PPy hybrids.…”