Self‐Assembly of Single‐Walled Carbon Nanotubes into a Sheet by Drop Drying

Abstract

Single-walled carbon nanotubes (SWNTs) are currently the focus of extensive interdisciplinary studies because of their unique physical and chemical properties and potential electronic applications, for example, in making sensors and fieldemission devices.[1] Processing of SWNT-based materials into engineered macroscopic materials is still in its infancy; the most successful methods so far have been based on adapting techniques that had been developed in other areas of material science such as colloids and polymers. Recent successes include preparing fibers and ribbons of SWNTs; [2] films of pure SWNTs, [3,4] polymers doped with SWNTs, [5,6] and growth in situ of SWNT arrays. [7] Evaporation of drops on substrates has been used for patterned deposition of solutes onto non-porous substrates, such as in DNA microarrays, [8] nanolithography, [9] protein crystallization, [10] and stretching DNA for hybridization studies. [11,12] Shimoda et al. [13] prepared continuous selfassembled films of SWNT bundles on glass near a receding contact line by solvent evaporation. The moving contact line of a drying drop could be similarly used to form aligned patterns of SWNTs on substrates for making films or for nanofabrication. Drops of a solution on a substrate follow one of two drying mechanisms: either the drop maintains a constant contact angle by de-pinning the contact line (e.g., water on non-wetting substrates [14] ), or the contact line gets pinned and the drop maintains a fixed contact area (e.g., colloidal dispersions [15] ).Deegan and co-workers [15][16][17] have studied the drying of drops of colloidal dispersions and found that the particles deposit in a ring at the periphery of the drop due to capillary flow in which the pinned contact line causes the solvent to flow towards the edge. Recent investigations have also shown the formation of a skin or crust at the free surface of drops of polymers and colloidal suspensions. [18,19] Pauchard and Allain [19] found that the crust may collapse and evolve into different shapes as the surface area remains constant while the drop volume decreases due to solvent evaporation. "Crusting" on the surface of spin-cast films [20,21] is a well-known phenomenon.De Gennes [22] suggested a transport model for crust formation in spin-cast films. Because the glass-transition or gelation temperature of a pure polymer/colloid is higher than that in solution, [19] at any temperature below the glass transition there is a critical particle concentration at which the system transitions from fluid to glassy or gel-like. Evaporation of solvent from the free surface leads to a local increase in concentration of the polymer/suspension at the free surface, and a very thin glassy or gelled crust is formed at the free surface. Here, we investigated drying of a sessile drop of individually suspended SWNTs in an aqueous solution of F68 Pluronic. We found that, instead of assembling on the substrate, the SWNTs selfassemble into a crust at the free surface. This entangled meshlike crust was characterized b...

Lipid-Modulated Assembly of Magnetized Iron-Filled Carbon Nanotubes in Millimeter-Scale Structures

“…These patterns, consisting of primarily end-to-end oriented individual nanotubes, have to our knowledge not previously been observed: flow-induced patterns of acidtreated and/or detergent-solubilized carbon nanotubes gave rise to a side-to-side packing of nanotubes at high CNT concentration or to isolated nanotubes at low CNT density. [14][15][16][17] Lipid bilayer functionalization and end-to-end nanotube pattern formation are relevant for the development of bioelectronic devices, potentially enabling networks of carbon nanotubes that are electrically insulated from a biological electrolyte solution to transmit highly specific binding events from bilayer-embedded receptor proteins.…”

“…When the perimeter of an evaporating droplet becomes pinned to the surface, further evaporation results in height but not in area reduction of the droplet, and the resulting radial capillary flow within droplets of concentrated CNT suspensions has been shown to induce side-to-side alignment of nanotubes. [13][14][15][16][17] In this paper, we compare the patterns that are formed by evaporation of droplets of dilute aqueous suspensions of uncoated iron-filled multi-walled CNTs (Fe-filled MWNTs) with the patterns that are formed by Fe-filled MWNTs that are coated with lipid bilayers. Fe-filled MWNTs were employed because their relatively large diameter is favorable for lipid bilayer attachment while the iron core renders these CNTs ferromagnetic, enabling manipulation by external magnetic fields.…”

Control of the Morphology and Structural Development of Solution‐Processed Functionalized Acenes for High‐Performance Organic Transistors

“…[8] In particular, the drying behavior during solution processing has a critical role in the selforganization of organic semiconductor molecules. The recently reported drying-mediated self-assembly of nanoparticles, [81] diblock copolymers, [82] and carbon nanotubes [83] indicates that control of the evaporation-induced flows of solvent during a drying process is important to the self-assembly of organic semiconductor molecules during solution processing because solvent flows can easily transport the molecules.…”

Fabrication of Directionally Aligned Carbon Nanotube Thin Films on Solid Surfaces Using Chemical Patterns

“…In addition, directionally aligned CNTs are required in the applications to electrically conducting films, such as interconnects in the electric packaging. To form well-ordered CNT thin films, several approaches have been intensively studied, such as Langmuir-Brodgett method [16][17][18], dropping the CNT suspension [19][20][21], self-assembly method [22,23], trapping by chemical combination [24,25], using liquidliquid interface [26], and laminar flow in microfluidic channel [27].…”