Abstract
Vapor-phase synthesis techniques of polymeric nanostructures offer unique advantages over conventional, solution-based techniques because of their solventless nature. In this work, we report the fabrication of coaxial polymer nanotubes using two different chemical vapor deposition methods. The fabrication process involves the deposition of an outer layer of the conductive polyaniline (PANI) by oxidative chemical vapor deposition, followed by the deposition of the inner layer of poly(2-hydroxyethyl methacrylate) (pHEMA) hydrogel by initiated chemical vapor deposition. The vapor-phase techniques allowed for fine-tuning of the thickness of the individual layers, keeping the functionalities of the polymers intact. The response of the single components and the coaxial nanotubes to changes in humidity was investigated for potential humidity sensor applications. For single-component conductive PANI nanotubes, the resistance changed parabolically with relative humidity because of competing effects of doping and swelling of the PANI polymer under humid conditions. Introducing a hydrogel inner layer increased the overall resistance, and enhanced swelling, which caused the resistance to continuously increase with relative humidity.
Highlights
In recent years, with the advances in nanotechnology, the use of nanostructured materials has become widespread in various applications, such as biotechnology [1,2], food industry [3,4], sensors [5] or photovoltaics [6]
The fabrication of PANI nanotubes and PANI/poly(2-hydroxyethyl methacrylate) (pHEMA) coaxial nanotubes were done via oxidative chemical vapor deposition and initiated chemical vapor deposition to enhance the control and sensitivity level of humidity sensors
Ability to control the thickness during deposition via these vapor-phase methods allowed depositing two layers of different polymers inside the pores of anodized aluminium oxide (AAO) track-etch membranes
Summary
With the advances in nanotechnology, the use of nanostructured materials has become widespread in various applications, such as biotechnology [1,2], food industry [3,4], sensors [5] or photovoltaics [6]. The fabrication of PANI nanotubes and PANI/pHEMA coaxial nanotubes were done via oxidative chemical vapor deposition (oCVD) and initiated chemical vapor deposition (iCVD) to enhance the control and sensitivity level of humidity sensors. Annealing at temperatures above 100 °C initiates deformation and causes damage in the crystalline structure of PANI polymer chains resulting in the increase of the band gap energy.
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