Browsing by Subject "Silica--Surfaces."
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Item Open Access Fluorescent aerogel films for TNT sensing(Bilkent University, 2009) Yıldırım, AdemSilica aerogels are unique materials with extraordinary properties such as, high porosity, large surface area and low refractive indices. Due to these properties, they can be applied to a wide range of areas including, insulation, catalyst support, sensors and dielectric materials. However, until know because of their poor mechanical properties and costly production a few applications of aerogels were realized. Ambient pressure drying method is a promising way to produce low cost aerogels and thus expanding the realized application areas of aerogels. This method is based on lowering the surface tension on the gel network, in order to minimize the collapse of the gel during drying. For this purpose gel surface can be modified to make it hydrophobic. In the first part of this work, ambient pressure production of fluorescent aerogel thin films are described. The produced fluorescent films were characterized to identify their morphological, optical and surface properties. The gel was produced by using methlyltrimethoxysilane (MTMS) to produce hydrophobic gel. A porphyrin derivative (TCPPH2) was simply mixed with the sol before gelation for the fluorescence property. After gelation and aging the produced gels are homogenized and spin coated on glass substrates. The produced films were found to be highly porous (60.3-77.1%), fluorescent and transparent in visible region (82-89%). In the second part, sensing performances of the films were examined by using the common explosive trinitrotoluene (TNT). All films show fluorescence quenching based sensing against TNT exposure. The quenching efficiency of the films is highly thickness dependent. For the thinnest film (120 nm) the quenching efficiency was found to be 8.6% in 10 seconds and for the thickest film (1100 nm) film 2.1% in 10 seconds.Item Open Access Organically modified silica based nanomaterials for functional surfaces(Bilkent University, 2012) Budunoğlu, HülyaOrganically modified silicas (ormosils) are unique materials due to their combined properties achieved from organics and inorganics. Ormosils contain at least one non-hydrolysable organic groups which results in a decrease of rigid Si-O-Si bonds, introducing a flexible character. Therefore, ormosils exhibit both flexibility of organics and atmospheric stability of inorganics. Organic group determines the functionalities of ormosils, thus their properties can be adjusted by choice of appropriate organic modification. Ormosils can be easily prepared in mild conditions of sol-gel technique, and can be applied on different surfaces by low cost and simple techniques. In this thesis, we prepared superhydrophobic-superhydrophilic, antireflectiveantifogging, anticorrosion and antiicing (ice retarding) functional surfaces using organically modified silica and its nano-composites in thin film form. Methyltrimethoxysilane (MTMS) is used in the synthesis of all films due to its intrinsically hydrophobic nature. This monomer is found to enable porous film formation without any modifications at ambient temperature and pressure. Superhydrophobic ormosil aerogel films with water contact angles reaching 179.9 and porosity of 86 % have been prepared using phase separated colloidal suspensions of MTMS, which exhibited flexibility, thermal stability and superhydrophilic transition after annealing at 600 C. Antireflective films with high mechanical stability are prepared from co-condensation of MTMS with tetraethylorthosilicate monomer, which exhibited transmission as high as 99.6 % with flexibility and transition to antifogging after annealing at 600 C. Anticorrosion films for glass surfaces have been prepared by encapsulation of ZnO and ZrO2 nanoparticles to yield nano-composites of porous and nonporous ormosil films, which resulted in four times less corrosion compared to bare glass and acts as a barrier layer for corrosion of glass substrates against alkaline corrosion. In formation of antiicing coatings various combinations of ormosil films mentioned are used and correlation between contact angle, stability of contact angle against cooling, surface roughness and freezing times are investigated. Compared to bare glass, freezing times are increased two order of magnitudes.