Development of Humidity Sensors using Layer-by-Layer nanoAssembly of Polypyrrole
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J16.4.1
Development of Humidity Sensors using Layer-by-Layer nanoAssembly of Polypyrrole R.Nohria, Y. Su*, R.K.Khillan, R. Dikshit,Y. Lvov and K. Varahramyan Institute for Micromanufacturing, Louisiana Tech University, Ruston, LA 71272 *[email protected]
Abstract In this paper we demonstrate high sensitive and fast response humidity sensors using layer-by-layer (LbL) nano-assembled films of Polypyrrole (PPY). Spin coated PPY films were used for sensitivity and response time comparisons. The change in electrical sheet resistance of the sensing films was monitored as the device was exposed to humidity. For 5% change in relative humidity sensitivity measured from layer-by-layer based devices was 10% and 8% for the spin coated devices. The response time for LbL based and spin coated device was measured as 25 seconds and 57 seconds respectively. The LbL nanoassembled films of PPY showed the better response in terms of sensitivity, response time, linearity and degradation. An intended application for these LbL nano-assembled devices is in disposable handheld instruments to monitor the presence of humidity in humidity sensitive environments. Key Words: - Polypyrrole, humidity sensor, layer-by-layer nano-assembly, spin coating. Introduction The importance of humidity sensing has been well understood and much research has been focused on the development of humidity sensitive materials. In recent years the influence of humidity has been given top priority in moisture sensitive areas such as high voltage engineering systems, storage areas, computer rooms etc. [1,2]. Different types of humidity sensors are available in market such as catalytic and tin oxide sensors which are not specific and consume significant amount of power. There has been a considerable interest in exploiting organic substances and doped conducting polymers [3-5] for humidity and gas sensing. Advantages with polymers as sensing materials are light weight, flexible, low cost, simple process for fabrication of sensor arrays and their properties can be tailored for sensing of a particular gas or humidity[6]. A number of different techniques such as electrochemical polymerization, chemical and electrochemical deposition and spin coating have been explored for the fabrication of polymer sensors [7-8]. The main issue of polymer sensors is senstivity of the deposited polymer, which is determined by the thickness of the sensing layer, sensing area and surface roughness. LbL is a unique method for the deposition of composite and polymeric films with controlled thickness at a nanometer range. In this paper, LbL nano-assembly is used for deposition of ultrathin Polypyrrole (PPY) film for humidity sensing application. Response time, sensitivity and degradation of LbL nano-assembled films are compared those obtained using spin coating of PPY films.
J16.4.2
Experimental Details PPY was purchased from Sigma-Aldrich. Before the nano-assembly of the PPY on the PYREX® glass substrate, the substrate was cleaned with acetone for 2 minutes and then rinsed in de-ionized water
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