PEDOT:PSS humidity sensor was fabricated using a drop-casting method between thermally evaporated gold electrodes with 30 μm separation and 300 μm channel width on a glass substrate. AC, DC resistivity, and AFM techniques were used to characterize the PEDOT:PSS humidity sensor in the same environmental conditions. The change of resistivity was monitored with increasing relative humidity (RH) up to 90%. The resistivity increases linearly up to a maximum value, and then it starts to decrease abruptly above 80% relative humidity (RH) after saturation of water uptake. The decrease in resistivity above 80% RH seems to be due to the water meniscus layer formed on the saturated PEDOT:PSS film. Below 80% RH, the device works like a humidity sensor.TÜBİTAK project number of TBAG-108T718 and DPT2003K12039

ZnO nanoparticles have been synthesized by the sol-gel method with approximately 10 nm diameter and the humidity adsorption and desorption kinetics of ZnO nanoparticles were investigated by quartz crystal microbalance (QCM) technique. The morphology and crystal structure of the ZnO nanoparticles have been characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The roughness of the surface has been investigated using atomic force microscope (AFM). The dynamic Langmuir adsorption model was used to determine the kinetic parameters such as adsorption and desorption rates and Gibbs free energy under relative humidity between 45% and 88%. The relative sensitivity of the ZnO nanoparticles-based humidity sensor was determined by electrical resistance measurements. Our reproducible experimental results show that ZnO nanoparticles have a great potential for humidity sensing applications at room temperature operations. © 2009 Elsevier B.V. All rights reserved.Istanbul University Project number: 2526 and Project number: UDP 367

The humidity-sensing properties of ZnO nanowires synthesized by carbothermal catalyst-free vapor solid (VS) technique were studied. The morphology and the crystal structure were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The humidity adsorption and desorption kinetics of the synthesized ZnO nanowires were investigated via quartz crystal microbalance (QCM) measurements. The observed positive frequency shift of ZnO nanowires when loaded on the QCM crystal under varying relative humidity conditions can be explained in terms of visco-elastic variations in their mechanical stiffness.Istanbul University (2526 and UDP 6728); State Planning Organization of Turkey (DPT2003K120390); Scientific and Technological Research Council of Turkey (TBAG 109T240

Zinc oxide (ZnO) based fibers with a diameter of 80-100 nm were prepared by electrospinning. Polyvinyl alcohol (PVA) and zinc acetate dihydrate were dissolved in water and the polymer/salt solution was electrospun at 2.5 kV cm(-1). The resulting electrospun fibers were subjected to calcination at 500°C for 2h to obtain ZnO-based fibers. Humidity sensing properties of the fiber mats were investigated by quartz crystal microbalance (QCM) method and electrical measurements. The adsorption kinetics under constant relative humidity (RH) between 10% and 90% were explained using Langmuir adsorption model. Results of the measurements showed that ZnO-based fibers were found to be promising candidate for humidity sensing applications at room temperature.

The preparation of calcium stearate (CaSt₂) using precipitation and Langmuir−Blodgett techniques was investigated in this study. While sodium stearate and calcium chloride were used in the precipitation process, calcium stearate nanofilms were produced from stearic acid and calcium chloride in sodium borate buffer with the Langmuir−Blodgett technique. Fourier transform infrared (FTIR) spectroscopy indicated carboxylate bands at 1577 and 1543 cm⁻¹ in equal intensity in the powder form, but the films had a higher intensity 1577 cm⁻¹ band than the 1543 cm⁻¹ band. This showed the calcium ions associated with the COO⁻ ions in the monodendate and bidendate structures in powders, and it was mainly in the bidendate structure in films. While characteristic peaks of CaSt₂ at 2θ values of 6.40° and 19.58° were obtained in the X-ray diffraction (XRD) pattern of the dried powdered product, no sharp peaks were present in the 13 layer CaSt₂ film. From scanning electron microscopy (SEM) micrographs, it was seen that calcium stearate powder had lamellar structure and the average particle size was 600 nm. The AFM picture of the CaSt₂ film indicated the surface was not smooth with a peak to valley distance of 6 nm.