Browsing by Subject "Superhydrophilic"

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Open Access
Organically modified silica nanostructures based functional coatings for practical applications
(2015) Tuvshindorj, Urandelger
In the past decades, the fabrication of superhydrophobic surfaces have received considerable attention due to the variety of potential applications ranging from biology to industry. Although significant progress has been made in their fabrication and design, there is still need to solve some problems in real-life use of these coatings, such as low stability against external pressure, lack of long term robustness, challenges in presice control over the degree of wettability and the need for facile fabrication methods. In this context, this thesis seeks simple solutions for mentioned problems based on organically modified silica superhyrophobic coatings. First, we investigate the stability of the Cassie state of wetting in transparent superhydrophobic coatings by comparing a single-layer micro-porous coating with a double-layer micro/nanoporous coating. The stability of the Cassie state in coatings were investigated with droplet compression and evaporation experiments, where external pressures as high as a few thousand Pa are generated at the interface. A droplet on a microporous coating gradually transformed to the Wenzel state with increasing pressure. The resistance of the micro/nano-porous surfaces against Wenzel transition during the experiments were higher than microporous single-layer coating and even higher than leaves of Lotus; prevalent natural superhydrophobic surface. Then, we reported a facile method for the preparation hydrophilic patterns on the superhydrophobic ormosil surfaces. On the defined areas of the superhydrophobic ormosil coatings, wetted micropatterns were produced using Ultraviolet/Ozone (UV/O) treatment which modifies the surface chemistry from hydrophobic to hydrophilic without changing the surface morphology. The degree of wettability of the patterns can be precisely controlled depending on the UV/O exposure duration and extremely wetted spots with water contact angle (WCA) of nearly 0º can be obtained. The ormosil coatings and modified surfaces preserve their wettability for months at room conditions. Furthermore, we demonstrated selective and controlled adsorption of protein and adhesion of bacteria on the superhydrophilic patterns which could be potentially used for biological applications.
Open Access
Synthesis of silica-based nanomaterials and their applications in fluorescent, biological and chemical sensing
(2018-06) Beyazkılıç, Pınar
This thesis describes development of nanoparticle-based liquid sensors and coatings for droplet-based bioassays. Liquid sensors were produced from mesostructured (2-50 nm) hybrid silica nanoparticles. Detection of trace trinitrotoluene (TNT) and dopamine in aqueous phase was shown based on uorescence of nanoparticles. Silica nanoparticles were synthesized using a facile one-pot solgel method. Pyrene molecules were hybridized with hydrophobic parts of cetyltrimethylammonium micelles followed by silica growth around micelles. Nanoparticles showed good dispersibility and colloidal stability in water. Pyrene exhibited bright and highly stable emission. Pyrene emission exhibited a rapid, sensitive and visual uorescence quenching against TNT and dopamine. For droplet-based assays, robust superhydrophilic patterned superhydrophobic coatings were developed. Biomolecular adsorption and droplet mixing were shown on coatings which were prepared using sol-gel method followed by ultraviolet/ ozone (UV/O) treatment. Droplet-based biomolecular detection platforms were developed using superhydrophilic patterned superhydrophobic surfaces. Bene tting from con nement and evaporation-induced shrinkage of droplets on wetted patterns, sensitive glucose and DNA detection was demonstrated. Glucose was detected based on enhancement of polydopamine (PDA) emission by hydrogen peroxide (H2O2) produced in glucose oxidation reaction. Detection in evaporating droplets resulted with bright uorescence and high sensitivity for analyte molecules. This was due to droplet evaporation which concentrated molecules and increased reaction rates. Surfaces and nanoparticles developed in this thesis hold great potential for biological and chemical analysis with low sample volumes owing to their simple production, sensitive detection responses and versatility.