干黏附碳纳米管垂直阵列的转移及其黏附性能评价

Abstract

Vertically aligned carbon nanotube arrays(VACNTs) exhibit high aspect-ratios and excellent mechanical strength, and have attracted attention in the field of gecko-inspired dry adhesives. However, the poor interfacial bonding between the silicon substrate and the VACNTs, the hard and brittle silicon substrate which is suitable for the growth of VACNTs in chemical vapor deposition(CVD) technique limit the development and application of VACNTs as the gecko-inspired dry adhesive. To overcome these limitations we present a simple and cost-effective heating transfer method without other media-assisted. We combine this with thermal oxidation detachment to transfer the grown VACNTs onto flexible polycarbonate(PC) substrates. The transfer process provides two different VACNTs morphologies; a curly entangled segment in the bottom and an aligning end segment in the top. The bottom transfer maintains the top morphology of the pristine VACNTs, which differs from the flip-over process known as top transfer. This transfer process results in a double transferred VACNTs structure which is a new type of dry adhesive. By optimizing the transfer process, the interfacial bonding force between the VACNTs and PC substrates is nearly three times stronger than that of grown VACNTs on silicon substrates at 250°C. The shear adhesion strengths of the bottom- and top-transferred VACNTs were tested and analyzed. Then, the shear adhesion strength of the transferred VACNTs were tested and analyzed according to the difference between the morphology and the degree of graphitization on the top of VACNTs after the top/bottom transfer methods. The shear adhesion strength of the transferred VACNTs increased with the normal preload. The adhesion strength of the bottom-transferred VACNTs was approximately 5 N/cm2, whereas that of the top-transferred VACNTs was 2.8 N/cm2 under a 16 N/cm2 normal preload force. The bottom-transferred VACNTs showed better adhesion because of the increasing contact area and higher degree of graphitization on the top of the structure according to scanning electron microscope and Raman spectra. Our transfer method is nondestructive, fast and suitable for VACNTs with a height greater than 200 um. Moreover, this method is not restricted by the area of the VACNTs, and thus can improve their integrity and flexibility, and increase their application as gecko-inspired dry adhesives.