Scanning electron microscope (SEM) pictures of multiwalled carbon nanotube arrays. [(a)–(c)] Top view of a MWCNT array with increasing magnification showing entanglement of the nanotubes at surface. The diameters range from . (d) Side view of the MWCNT array where a patch of outer surface being peeled off, showing vertical alignment of the tubes. [(e)–(f)] Top view and side view of another MWCNT array of array height after oxygen plasma etching. Being etched off the entangling surface layer, the MWCNTs show good vertical alignment.
Maximum adhesive strengths measured between MWCNT arrays and various surfaces in the (a) normal direction and (b) shear direction. The target surfaces with apparent contact areas are (a) glass (microscope slide), (solid square); glass, (open square); gold (evaporated on Si), (solid circle); parylene (evaporated on Si), (solid diamond); gallium arsenide (GaAs), (open triangle); Si: (open circle), and (b) glass, (solid square); parylene, (solid diamond) and Si: (open circle). Each line represents an experiment run with several attachment-detachment cycles. The inset in (a) shows the inverse dependence of adhesive strength on contact area generalized with glass surfaces.
Measured work of adhesion between MWCNT array ( in height) surface and glass surface by JKR test (see Sec. II). The preload is in N rather than in because it is difficult to define the contact area at the spherical contact. At each preload value, the work of adhesion was measured for at least five repetitions with mean value and standard deviation shown. The solid line connecting the data points is a visual guide to the eyes.
(a) Toy bear with a space shuttle model in its right hand (total ) was clung to a glass slide through dry adhesion between the glass surface and a patch of MWCNT array surface grown on Si substrate. A string was used to connect the bear’s left hand and the backside of the Si substrate. (b) lit light-emitting diode (LED) suspended by the electrically conducting dry adhesive CNT pads.
Comparisons of adhesive strengths among various natural and synthetic materials.
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