Sensing Capacitors Based on Thin Films of Unsaturated Polyester Resin/Carbon Nano-Tubes Nano-Composites

VOCs (volatile organic compounds) are associated with emissions from industrial processes, transportation and the use of organic solvents that are partially toxic or carcinogenic. They tend to evaporate easily at room temperature. When exposed to volatile analytes, absorption of the chemical into the polymer film may alter its permittivity and effective volume, resulting in changes in the capacitance and resistance respectively of the sensor elements. Since the discovery of carbon nano-tubes (CNTs) numerous studies have focused on the development of novel futuristic materials by combining CNTs with polymers to achieve their complimentary properties. The lack of published information regarding systems comprising un saturated polyester resin (UPR) and CNTs composite materials, especially UPR/CNTs based chemo-capacity sensors, promotes the development of novel hybrid nano-material thin film sensing units. CNTs high aspect ratio provides the composites with better electric and mechanical performance than the other candidates such as carbon black. Although highly selective sensors do exist for a limited number of analytes, such gas sensors are highly affected by contaminants and humidity. In addition, these sensors contain a high weight percentage of conducting filler and the use spectra of amorphous polymers is limited. In the present study, chemical capacity sensors based on nano-composite thin films of unsaturated polyester resin (UPR in 40wt% of styrene)/carbon nano-tubes (only 0.05wt% of Multi Wall-CNTs) are developed and investigated under AC voltage and standard environment conditions (ambient air, at room temperature and atmospheric pressure). The purpose is to detect and quantify THF under these conditions for the first time. The change in both resistance and capacitance at low and high frequencies (between 500Hz to10KHz), due to different volumes of the exposed THF (10µl, 20µl and 30µl) and THF droplet (source) - sensing unit height variations (1mm,2mm and 3mm) were studied.