We report the growth and detailed structural investigation of a new morphological manifestation of carbon-based nanostructures in the form of tapered whiskers with uniform 1−3 nm hollowness. The base of the whiskers is in the submicron scale, tapering uniformly to form a pointed tip in the form of a pipette. These hollow nanopipettes have a shell containing helical graphitic sheets. We propose that these whiskers grow by competing phenomena of growth and etching that control their aspect ratio.
In this paper, the influence of single walled carbon nano tubes (SWCNTs) addition on the tribological properties of the polyimide (PI) films on silicon substrate was studied. PI films, with and without SWCNTs, were spin coated onto the Si surface. Coefficient of friction and wear durability were characterized using a ball-on-disk tribometer by employing a 4 mm diameter Si 3 N 4 ball sliding against the film, at a contact pressure of~370 MPa, and a sliding velocity of 0.042 ms -1 . Water contact angle, AFM topography, and nano-indentation tests were conducted to study the physical and mechanical properties of the films. SWCNTs marginally increased the water contact angle of PI film. The addition of SWCNTs to PI has increased the hardness and elastic modulus of pristine PI films by 60-70%. The coefficient of friction of PI films increased slightly (~20%) after the addition of SWCNTs, whereas, there was at least two-fold increase in the wear life of the film based on the film failure condition of coefficient of friction higher than 0.3. However, the film did not show any sign of wear even after 100,000 cycles of rotation indicating its robustness. This increase in the wear durability due to the addition of the SWCNTs is believed to be because of the improvement in the load-bearing capacity of the composite film and sliding induced microstructural changes of the composite film.
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