Carbon Nanotube (CNT) Adhesives
Members:
Rong-Shiuan (Renea) Chu
and Yang Zhao
![Mechanical Dry Adhesives
Carbon nanotubes are known for their extraordinary mechanical, electronic, and optical properties. When grown on a surface in an array, they provide an extremely large surface-to-volume ratio. CNTs bind to each other and to surfaces through van der Waals interactions. This is also the mechanisms used by geckos to create adhesion, whose feet are covered with hair that are about 100 nm in size. In contrast, CNTs can be 1-10 nm in size, which could potentially increase the surface area. Our group has measured the adhesive properties of CNT hair and found the strength (~12 N/cm2) to be comparable or sometimes better than that of geckos (~10 N/cm2). Furthermore, in contrast to geckos, CNT based dry adhesives are electrically and thermally conducting, which could be used to produce thermal and electrical interface materials for packaging applications.

Fig. 1. Vertically aligned dense multiwalled carbon nanotube arrays: (a-c) top view, (d) side view, (e-f) oxygen plasma treated top surface.

Fig. 2. (a) A toy bear with a space shuttle model in its right hand (total ~40 gram) was clung to a glass slide through dry adhesion between the glass surface and a patch of MWCNT array surface (2 x 3 mm2) grown on Si substrate. A string was used to connect the bear’s left hand and the backside of the Si substrate. (b) A lit light-emitting diode (LED) suspended by the electrically conducting dry adhesive CNT pads.
Thermal Interface Materials
Due to high thermal conductivity of carbon nanotubes along the tube direction, it is hoped that a dense layer of aligned carbon nanotubes could serve well as thermal interface materials in thermal management such as electronics cooling. While the thermal resistance through the CNTs is very small, the interface thermal resistance formed between the free CNT tips and the target surface was found to dominate the overall thermal resistance, usually > 0.1 oC∙cm2/W. Our measurement indicates that the bonded interface [by chemical vapor deposition (CVD)] between the bottom of the CNTs and the substrate has a much smaller thermal resistance ~ 0.01 oC∙cm2/W compared with the top surface. Following the similar idea, we improved the top interface by thermally welding the CNTs onto the target surface by a thin layer of indium and measured a much improved thermal interface with resistance comparable with that of the CVD interface at the bottom.
(a)

(b)

Fig. 3. (a) Schematic of the thermal characterization of the CNT interface by laser thermoreflectance method. The CNT array was grown onto the Si substrate and dry attached to a glass target surface. (b) Schematic of thermal measurement setup.](CNT_files/shapeimage_2.png)
