Dry adhesives from carbon nanofibers grown in an open ethanol flame

Abstract

Based on magnetic-field-assisted growth of carbon nanofibers in an open ethanol flame we fabricated arrays of carbon nanofibers with different degrees of orientation. Inspired by the dry adhesive system of geckos we investigated the adhesive properties of such carbon nanofiber arrays with ordered and random orientation. AFM-based force spectroscopy revealed that adhesion force and energy rise linear with preload force. Carbon nanofibers oriented by a magnetic field show a 68% higher adhesion (0.66 N/cm2) than the randomly oriented fibers. Endurance tests revealed that the carbon nanofiber arrays withstand 50.000 attachment/detachment cycles without observable wear.

Locally Controlled Growth of Individual Lambda‐Shaped Carbon Nanofibers

“…Pan and Bao demonstrated growth of CNFs in an open ethanol flame in 2002 . Inspired by this and other studies, we grew CNFs from NiCl 2 ·6H 2 O on silicon substrate completely covered with a thin 60 nm copper layer in an open ethanol flame and studied the adhesion properties of the resulting CNF arrays . Considering the simplicity and cost‐effectiveness of this process, it is surprising that it works without the usual reduction step, where the catalyst gets reduced by hydrogen or ammonia gas .…”

“…Considering the simplicity and cost‐effectiveness of this process, it is surprising that it works without the usual reduction step, where the catalyst gets reduced by hydrogen or ammonia gas . In the described open flame process, this reduction step is performed through the thin copper layer . Analyzing this growth process in more detail, we observed that the thickness as well the geometry of the copper layer is important for the growth of CNTs/CNFs.…”

“…In general, the growth of CNTs/CNFs in an open flame is comparably facile. Exposing the silicon substrate, covered with a copper layer of right thickness and a suitable catalytic salt, to the ethanol flame by hand with tweezers is sufficient . For the current study, however, we built a setup allowing for a more controlled growth of lambda‐shaped CNFs.…”

“…Geckos, for example, have hierarchical nanostructures at their toes enabling them to stick and climb on nearly every surface . Nonbranched MW‐CNTs and CNFs are, due to their size and mechanical properties, already used to mimic nanostructures of geckos . Branched CNFs might lift the mimicry to the next hierarchy level improving the overall adhesion on rough surfaces.…”

“…Other approaches like welding of selected CNTs by electron beams are most likely beyond any commercial application . Alternative growth processes utilizing an open flame from a paraffin wax candle, a butane‐based Bunsen burner, or an ethanol burner are less demanding regarding machinery, process gases, and energy input. However, compared to conventional CVD or plasma‐enhanced CVD processes, which are widely described in textbooks, they are only sparsely examined up to now.…”