We have developed a synthetic gecko tape by transferring micropatterned carbon nanotube arrays onto flexible polymer tape based on the hierarchical structure found on the foot of a gecko lizard. The gecko tape can support a shear stress (36 N/cm 2 ) nearly four times higher than the gecko foot and sticks to a variety of surfaces, including Teflon. Both the micrometer-size setae (replicated by nanotube bundles) and nanometer-size spatulas (individual nanotubes) are necessary to achieve macroscopic shear adhesion and to translate the weak van der Waals interactions into high shear forces. We have demonstrated for the first time a macroscopic flexible patch that can be used repeatedly with peeling and adhesive properties better than the natural gecko foot. The carbon nanotube-based tape offers an excellent synthetic option as a dry conductive reversible adhesive in microelectronics, robotics, and space applications.adhesives ͉ nanomaterials ͉ hierarchical ͉ robotics F lexible adhesive tapes are indispensable in our daily lives, whether it is to leave a note to a friend or to seal packages. However, we rarely hang heavy objects on a wall using these tapes because the stickiness is time-and rate-dependent. The viscoelastic tapes do not work under vacuum, such as space applications, and where repeated attachment and detachment is required, such as wall-climbing robots. Nature has found an alternate solution to stick to surfaces without using sticky viscoelastic liquids. Natural selection has developed the wallclimbing lizard's foot (Fig. 1A) in a hierarchical structure, consisting of microscopic hairs called setae, which further split into hundreds of smaller structures called spatulas ( Fig. 1B) (1-4). On coming in contact with any surface, the spatulas deform, enabling molecular contact over large areas, thus translating weak van der Waals interactions into enormous attractive forces (4). There have been several theoretical models to elucidate the mechanism of gecko adhesion (5). However, it is not clear why nature has developed this intricate hierarchical structure of micrometer-size setae and nanometer-size spatulas on the gecko foot, instead of covering the whole feet with only setae or spatulas. Many synthetic structures using uniform polymer pillars and in some cases hierarchical structures (6, 7) have been constructed before, although the performance of these structures has not been as good as natural gecko (8, 9). One limitation of these polymer pillars with a high aspect ratio is that they are mechanically weak in comparison to keratin used in the natural foot-hairs.Here we have replicated the multiscale structure of setae and spatulas using microfabricated multiwalled carbon nanotubes and found that not only nanometer-length scales of spatulas (individual carbon nanotubes) but also micrometer-length scales of setae (patterns of carbon nanotubes) are important to support large shear forces. Our results show that a 1-cm 2 area of the carbon nanotube patterns transferred on a flexible tape (referred as a ''gec...

The design of reversible adhesives requires both stickiness and the ability to remain clean from dust and other contaminants. Inspired by gecko feet, we demonstrate the self-cleaning ability of carbon nanotube-based flexible gecko tapes.A gecko has the unique ability to reversibly stick and unstick to a variety of smooth and rough surfaces. The gecko's wall climbing ability, without the use of viscoelastic glue, has attracted significant attention. [1][2][3][4][5][6][7][8][9][10][11] Although the gecko does not groom its feet, its stickiness remains for months between molts. 12 The gecko's dirty feet can recover its ability to climb vertical walls only after a few steps. 12 Our daily experience with sticky tapes has been the opposite. The stickier the adhesive, the more difficult it is to keep it clean from dust and other contaminants. Synthetic self-cleaning adhesives, inspired by the gecko's feet, could be used for many applications including wall climbing robots and microelectronics.The secret of the gecko's adhesive properties lies in the microstructure of gecko feet. 1,[13][14][15] Microscopy shows that gecko feet are covered with millions of small hairs called setae, which further divide into hundreds of smaller spatulas ( Figure 1A). When such a structure is placed against any surface, hairs adapt and allow a very large area of contact with the surface. The van der Waals (vdW) interaction between the hairs and the substrate after contact is sufficient for the gecko to adhere. It has been suggested that this same hairy carpet on the gecko feet also plays an important role in self-cleaning. 12 Some of the other systems found in nature that exhibit self-cleaning properties are the leaves of lotus and lady's mantle plants. 18 The surface of lotus leaves have two levels of microscopic roughness ( Figure 1B). This hierarchical roughness along with a hydrophobic wax coating makes the lotus leaves superhydrophobic. 16,[19][20][21] A water droplet forms a large contact angle with low contact angle hysteresis. This results in the water droplets rolling off the surface, leaving the surface clean. Leaves of a lady's mantle plant have hairs of 10 µm diameter and length of 1 mm ( Figure 1C). It has been suggested that the individual hairs are hydrophilic. However, when acting together on the surface, they make the surface of the leaves superhydrophobic. 17 Even though the surface properties of the spatulas are not known, the hierarchical structure of gecko feet makes the macroscopic structure superhydrophobic. 12 Significant effort in developing synthetic materials inspired by gecko feet show comparable, and in some cases better, shear resistance than natural gecko feet. 2,[6][7][8][9]11 Still, these measurements were done in controlled environments and limited self-cleaning data of these synthetic materials were reported. 7 Recently, we have designed carbon nanotube-based

We report the synthesis of superhydrophobic coatings for steel using carbon nanotube (CNT)-mesh structures. The CNT coating maintains its structural integrity and superhydrophobicity even after exposure to extreme thermal stresses and has excellent thermal and electrical properties. The coating can also be reinforced by optimally impregnating the CNT-mesh structure with cross-linked polymers without significantly compromising on superhydrophobicity and electrical conductivity. These superhydrophobic conductive coatings on steel, which is an important structural material, open up possibilities for many new applications in the areas of heat transfer, solar panels, transport of fluids, nonwetting and nonfouling surfaces, temperature resilient coatings, composites, water-walking robots, and naval applications.

The wetting behavior of a surface under steam condensation depends on its intrinsic wettability and micrometer or nanoscale surface roughness. A typical superhydrophobic surface may not be suitable as a steamphobic surface because of the nucleation and growth of water inside the valleys and thus the failure to form an air-liquid-solid composite interface. Here, we present the results of steam condensation on chemically modified nanostructured carbon nanotube (CNT) mats. We used a plasma-enhanced chemical vapor deposition (PECVD) process to modify the intrinsic wettability of nanostructured CNT mats. The combination of low surface energy achieved by PECVD and the nanoroughness of the surface provides a mechanism to retain the superhydrophobicity of the CNT mats under steam condensation. The ability to withstand steam temperature and pressure for as long as 10 h implies the remarkably improved stability of the superhydrophobic state of the surface. The thermodynamic calculations carried out using a unit cell model clearly explain the steamphobic wetting behavior of the surface.