Title : Effect of surface texture on self organization of titania nanotubes
Abstract:
The ordered development of TiO2 nanotubes has been of special interest in various biomedical applications such as their usage in drug delivery systems, anti-microbial medicines, and enhancing osseointegration in implants [1–4]. Previous works have also explored the effect of surface roughness on the length, growth rate and degree of self-organization of the obtained NT arrays [5]. The surface profile of the titanium sample also influences the growth characteristics of nanotubes. Surface defects and features such as micro valleys and peaks can significantly impact the growth behavior of titania nanotubes. These sites can act as preferential locations of nucleation for the initiation and growth of nanotubes [6]. This study investigates the effects of the lay and textures of various surface machining methods on nanotube growth and
organization. Various machining processes were used to modify the surface i.e. polishing, grinding, facing and lapping. Their surface characterization was done using white light interferometry to understand the surface profile. Various surface parameters such as surface roughness (Ra) and texture aspect ratio (Str) were derived. Anodization experiments were conducted on samples after surface modification. The experimental setup which consisted of a two-electrode system with platinum mesh as the cathode, and titanium as the anode had ethylene glycol + 2.5% v/v H20 + 0.5% w/w NH4F as an electrolyte with an aging of 5 hours. The experiments were conducted at room temperature at 45V for 15 minutes. The current transients were analyzed for all the samples. The nanotube morphology was analyzed and quantified using FE-SEM. Table. 1 summarises the findings of this study. It links the typical surface topographies, FE-SEM images and schematic diagrams of nanotube distribution to the machining operations. The Ra values for four surfaces i.e. polishing, grinding, facing and lapping were 22 nm, 525 nm, 4330 nm and 63 nm respectively while the texture aspect ratio (Str) were 0.621, 0.14, 0.245 and 0.572 respectively. Surface roughness dictates the nucleation time and growth of TNTs. It was observed that nanotubes were formed on polished and lapped surfaces while nanopores were formed on ground and faced samples. The directionality in the growth of nanotubes was governed by Str ratio. It was observed that a low Str ratio in the case of ground and faced samples favored an organized growth of nanopores while a high Str ratio in polished and lapped samples generated dense growth of nanotubes with no organization. SEM images show the formation of nanotubes in the case of polished and lapped samples, while the formation of ordered nanotubes in the case of ground and faced samples. This is in line with the proposed hypothesis. The pores/tubes had a mean diameter of 63 nm which is dependent on the input conditions i.e. applied anodization voltage, time and choice of electrolyte which were kept constant for all the samples. It was found that the nanotubes grew in circular grooves on faced samples and in linear grooves on ground samples. While a dense development of nanotubes was seen on samples that had been mechanically polished and lapped.
