Inherent-opening-controlled pattern formation in carbon nanotube arrays

Abstract

We have introduced inherent openings into densely packed carbon nanotube arrays to study self-organized pattern formation when the arrays undergo a wetting-dewetting treatment from nanotube tips. These inherent openings, made of circular or elongated hollows in nanotube mats, serve as dewetting centres, from where liquid recedes from. As the dewetting centres initiate dry zones and the dry zones expand, surrounding nanotubes are pulled away from the dewetting centres by liquid surface tension. Among short nanotubes, the self-organized patterns are consistent with the shape of the inherent openings, i.e. slender openings lead to elongated trench-like structures, and circular holes result in relatively round nest-like arrangements. Nanotubes in a relatively high mat are more connected, like in an elastic body, than those in a short mat. Small cracks often initialize themselves in a relatively high mat, along two or more adjacent round openings; each of the cracks evolves into a trench as liquid dries up. Self-organized pattern control with inherent openings needs to initiate the dewetting process above the nanotube tips. If there is no liquid on top, inherent openings barely enlarge themselves after the wetting-dewetting treatment.

Fabrication and multifunctional properties of a hybrid laminate with aligned carbon nanotubes grown In Situ

“…Given the difficulty of dispersing and wetting CNTs in epoxy, capillaritydriven wetting of the aligned CNT forests is postulated as the underlying mechanism. Previous work with solvents has demonstrated a strong capillary effect of aligned CNT forests [24][25][26][27]. Our previous work with complex thermosets, including epoxies with similar viscosities as those used here, has demonstrated that long (exceeding 0.5 mm) aligned CNT forests are readily and effectively (i.e., no micron-scale voids) wet [14].…”

Three-dimensional elastic constitutive relations of aligned carbon nanotube architectures

“…Another problem of polymer nanocomposites formed using unaligned CNTs is that a uniform dispersion of CNTs leads to isotropic nanocomposite properties, which cannot be optimized for any single operating direction. These two shortcomings can be remedied by using aligned networks of CNTs, known as forests, where capillary forces can be used to aid with the polymer infusion, 19,[32][33][34] and where A-PNCs with anisotropic properties can be formed. Here the anisotropy in stiffness of variable V f A-PNCs formed via capillary-induced wetting is quantified, and their full three dimensional elastic constitutive relations are developed.…”

Fabrication and Characterization of Ultrahigh‐Volume‐ Fraction Aligned Carbon Nanotube–Polymer Composites

“…The matrix infuses into the CNT forest via capillary-induced wetting, at rates that depend on properties of the CNT forest (e.g., volume fraction) and the polymer (e.g., viscosity, contact angle). [32,33] The epoxy is cured following the recommended process for each polymer, yielding the desired nanocomposites (Fig. 1B).…”

“…Several groups have investigated capillarity-induced wetting of CNT forests, focused on increasing the volume fraction of a dry CNT forest using solvent-induced densification, or creating controlled CNT micropatterns. [32,33,38,39] Low-viscosity and low-boiling-point solvents (e.g., isopropyl alcohol) are introduced into the ends of a CNT forest and because of capillary forces, the solvent is pulled into the forest and at the same time densifies it, creating a higher-volume-fraction A-CNT forest. The solvent-induced densification approach does not provide control over volume fraction, and the final densified forest is a function of the solvent and forest.…”

“…In other cases, CNT forest microfeatures (e.g., a pillar of square cross-section) having aspect ratios close to 1 are densified by the solvent to create higher-volume-fraction microfeatures. [31,40] Capillarity-driven patterning is well reviewed [32,41,42] and the degree of wetting and densification are noted to be a function of the contact (or wetting) angle of the liquid with the CNTs, the liquid's viscosity, and CNT characteristics (diameter, volume fraction). Solvent-induced densification was also explored in this work using isopropyl alcohol, and the resulting forests were highly contracted, irregular, and contained micrometer-scale cells as observed by others.…”