Observation of chemicals evaporation (ethanol, methanol and 2-propanol) using vibrated microcantilever

Abstract

Microcantilever is a device of MEMS (microelectro-mechanical system) which can be used as a bio-chemical sensor, such as to determine the characteristics of chemical liquids. In this work, an investigation of evaporation rate of chemical liquids, i.e., ethanol, methanol, and propanol, was carried out using resonant frequency change of vibrated microcantilever. We used two types of microcantilever, namely uncoated-microcantilever (reference) and ZnO-coated microcantilever. A growth of ZnO nanorods on microcantilever was carried out by hydrothermal method through 2 stages, i.e., a coating of seed (seeding) and growth of ZnO rods. The seed layer was deposited by dip-coating method from the solution of zinc nitrate tetrahydrate (ZNT) and dietanolamine (DEA) in ethanol. ZnO nanorods were then grown by hydrothermal method from the solution of zinc nitrate tetrahydrate (ZNT) and hexamethylenetetramine (HMTA) in demineralized water at 80°C for 2 hours. The experimental results show that, the resonant frequency of uncoated-microcantilever before dropping ethanol was measured of 36.80 kHz. After dropping ethanol on the microcantilever, the resonant frequency raised to 36.84 kHz. From the resonant frequency data, the evaporation rate of ethanol can be calculated to be 0.150 picogram/minute. Moreover, the evaporation rate of methanol and propanol was obtained 0.149 picogram/minute and 0.149 picogram/minute, respectively. For ZnO-coated microcantilever, the resonant frequencies before and after dropping propanol reveal the value of 13.98 kHz and 12.33 kHz, respectively. However, the resonant frequency did not return to the initial value after ethanol dropping, indicating that the propanol molecule reacts with the ZnO surface and remains on the surface.