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Dead-end filtration is a facile method to globally align single wall carbon nanotubes (SWCNTs) in large area films with a 2D order parameter, S2D, approaching unity. Uniaxial alignment has been achieved using pristine and hot-embossed membranes but more sophisticated geometries have yet to be investigated. In this work, three different patterns with radial symmetry and an area of 3.8 cm2 are created. Two of these patterns are replicated by the filtered SWCNTs and S2D values of ≈0.85 are obtained. Each of the radially aligned SWCNT films is characterized by scanning cross-polarized microscopy in reflectance and laser imaging in transmittance with linear, radial, and azimuthal polarized light fields. The former is used to define a novel indicator akin to the 2D order parameter using Malu's law, yielding 0.82 for the respective film. The films are then transferred to a flexible printed circuit board and terminal two-probe electrical measurements are conducted to explore the potential of those new alignment geometries. more...

Dead-end filtration has proven to effectively prepare macroscopically (3.8 cm$^2$) aligned thin films from solutionbased single-wall carbon nanotubes (SWCNTs). However, to make this technique broadly applicable, the role of SWCNT length and diameter must be understood. To date, most groups report the alignment of unsorted, large diameter (≈1.4 nm) SWCNTs, but systematic studies on their small diameter are rare (≈0.78 nm). In this work, films with an area of A = 3.81 cm$^2$ and a thickness of ≈40 nm are prepared from length-sorted fractions comprising of small and large diameter SWCNTs, respectively. The alignment is characterized by cross-polarized microscopy, scanning electron microscopy, absorption and Raman spectroscopy. For the longest fractions (L$_{avg}$ = 952 nm ± 431 nm, Δ = 1.58 and L$_{avg}$ = 667 nm ± 246 nm, Δ = 1.55), the 2D order parameter, S2D, values of ≈0.6 and ≈0.76 are reported for the small and large diameter SWCNTs over an area of A = 625 µm$^2$, respectively. A comparison of Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory calculations with the aligned domain size is then used to propose a law identifying the required length of a carbon nanotube with a given diameter and zeta potential. more...

Single wall carbon nanotubes (SWCNTs) dispersed by negatively charged sodium deoxycholate (DOC) or positively charged cetrimonium bromide (CTAB) are shown to assemble into aligned films (3.8 cm$^{2}$) on polycarbonate membranes by slow flow dead-end filtration. Global alignment (S$_{2D max}$≈ 0.85) is obtained on both pristine polyvinylpyrrolidone (PVP) coated membranes and those with an intentional 150–600 nm groove pattern from hot embossing. In all cases, a custom microfluidic setup capable of precise control and measurement of the volume rate, transmembrane pressure, and the filtration resistance is used to follow SWCNT film formation. Conditions associated with the formation of SWCNT crystallites or their global alignment are identified and these are discussed in terms of membrane fouling and the interaction potential between the surface of the membrane and nanotubes. SWCNT alignment is characterized by cross-polarized microscopy, atomic force microscopy, scanning electron microscopy (SEM), and Raman spectroscopy. more...