Browsing by Subject "Organically Modified Silica"

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Open Access
Formation of pyrene excimers in mesoporous ormosil thin films for visual detection of nitro-explosives
(American Chemical Society, 2014-04-01) Beyazkilic, P.; Yildirim, A.; Bayındır, Mehmet
We report the preparation of mesoporous thin films with bright pyrene excimer emission and their application in visual and rapid detection of nitroaromatic explosive vapors. The fluorescent films were produced by physically encapsulating pyrene molecules in the organically modified silica (ormosil) networks which were prepared via a facile template-free sol-gel method. Formation and stability of pyrene excimer emission were investigated in both porous and nonporous ormosil thin films. Excimer emission was significantly brighter and excimer formation ability was more stable in porous films compared to nonporous films. Rapid and selective quenching was observed in the excimer emission against vapors of nitroaromatic molecules; trinitrotoluene (TNT), dinitrotoluene (DNT), and nitrobenzene (NB). Fluorescence quenching of the films can be easily observed under UV light, enabling the naked-eye detection of nitro-explosives. Furthermore, excimer emission signal can be recovered after quenching and the films can be reused at least five times.
Open Access
Robust cassie state of wetting in transparent superhydrophobic coatings
(American Chemical Society, 2014) Tuvshindorj, U.; Yildirim, A.; Ozturk, F. E.; Bayındır, Mehmet
This paper investigates the stability of the Cassie state of wetting in transparent superhydrophobic coatings by comparing a single-layer microporous coating with a double-layer micro/nanoporous coating. Increasing pressure resistance of superhydrophobic coatings is of interest for practical use because high external pressures may be exerted on surfaces during operation. The Cassie state stability against the external pressure of coatings was investigated by squeezing droplets sitting on surfaces with a hydrophobic plate. Droplets on the single-layer coating transformed to the Wenzel state and pinned to the surface after squeezing, whereas droplets on the double-layer micro/nanoporous coating preserved the Cassie state and rolled off the surface easily. In addition, the contact angle and contact-line diameter of water droplets during evaporation from surfaces were in situ investigated to further understand the stability of coatings against Wenzel transition. A droplet on a microporous coating gradually transformed to the Wenzel state and lost its spherical shape as the droplet volume decreased (i.e., the internal pressure of the droplet increased). The contact line of the droplet during evaporation remained almost unchanged. In contrast, a water droplet on a double-layer surface preserved its spherical shape even at the last stages of the evaporation process, where pressure differences as high as a few thousand pascals were generated. For this case, the droplet contact line retracted during evaporation and the droplet recovered the initial water contact angle. The demonstrated method for the preparation of robust transparent superhydrophobic coatings is promising for outdoor applications such as self-cleaning cover glasses for solar cells and nonwetting windows.