WoS İndeksli Yayınlar Koleksiyonu / WoS Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7150
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Article Design and Performance of SiOC Foam-Silica Aerogel Composites for Hot and Cold Thermal Management Applications(Elsevier Ltd, 2025) Icin, Oyku; Vakifahmetoglu, CekdarThis study focuses on the fabrication of monolithic preceramic polymer-derived ceramic (SiOC) foam-silica aerogel composites by filling the open cells of ceramic foam with a silica aerogel solution using the sol-gel technique. The effects of different drying techniques (ambient pressure vs CO2 supercritical drying) and surface modification agents, including trimethylchlorosilane (TMCS) and hexamethyldisilazane (HMDZ), are comprehensively investigated. These factors are analyzed for their influence on the composites' morphology, porosity, chemical structure, and thermal insulation performance. The drying technique and surface modification agents are found to play a critical role in achieving a high filling ratio of silica aerogel within the composites. Pure silica aerogels exhibit specific surface areas (SSAs) reaching similar to 1120 m(2).g(-1), while the SiOC foam-silica aerogel composites demonstrate SSAs of 385-440 m(2).g(-1). Nearly all samples achieve a total porosity of similar to 93 vol%. Surface modification effectively tailors the surface properties, imparting hydrophobicity with a water contact angle of 133 degrees. Thermal conductivity at room temperature ranges between 38 and 43 mW<middle dot>m(-1)<middle dot>K-1. The potential applications of these SiOC foam-silica aerogel composites as thermal insulators are assessed under extreme thermal conditions. For instance, a 14 mm thick composite has a temperature of -27 degrees C when subjected to a cold source at -78 degrees C. Instead, when exposed directly to a butane flame (similar to 1200 degrees C), the backside of the composite recorded only similar to 57 degrees C.Article Citation - WoS: 11Citation - Scopus: 12Calf Thymus Dna Characterization and Its Adsorption on Different Silica Surfaces(Royal Society of Chemistry, 2015) Yetgin, Senem; Balköse, DevrimDNA adsorption is the initial stage of gene therapy for drug delivery systems and solid phase extraction methods of DNA purification. High pore volume and high adsorption capacity are simple requirements not only for producing 'smart' drug delivery systems but also the development of purification kits. Silica is the most used material for this purpose. The present study aimed at elucidating the calf thymus DNA biosorption process by the characterization of calf thymus DNA and silica to increase the efficiency of the currently used silica material. Mesoporous silica has long been used for DNA adsorption and silica aerogel is the new adsorbent investigated in the present study. When DNA solution was freeze dried on a silica wafer, self-assembled super helices formed as shown by atomic microscopy (AFM). Thus DNA existed not as single molecules but as large sized agglomerates in water. Thus it could be adsorbed in the macropores and on the external surface of adsorbents. Adsorption of calf thymus DNA to a silica aerogel, a mesoporous silica gel and a silica wafer was investigated in the present study. Silica aerogel was synthesized from TEOS by a supercritical ethanol drying process. The DNA adsorption capacity of the silica aerogel was nearly two times that of the mesoporous silica gel due to its macroporous structure and its higher silanol content. Silica aerogel was found to be a very promising material for DNA adsorption. Therefore silica aerogel can be considered as a good candidate for the delivery of DNA.Article Citation - WoS: 16Citation - Scopus: 16Synergistic Effect of Polymer-Surfactant Mixtures on the Stability of Aqueous Silica Suspensions(Elsevier Ltd., 2007) Şakar-Deliormanlı, AylinThe aim of the present work was to investigate the effect of cationic/nonionic surfactant mixtures on the dispersion and flocculation behavior of aqueous silica suspensions. In the study dodecylamine (DDA) was used as the cationic surfactant and polyethylene oxide-polypropylene oxide-polyethylene oxide (PEO-PPO-PEO) triblock copolymers were employed as the nonionic surfactant. The dispersion and flocculation behavior of aqueous silica suspensions were studied mainly by turbidity measurements at low solids loading (0.05 vol.%) to observe the stability of the system for a given time period. Rheological measurements were performed at higher solids loadings to determine the viscosity as a function of shear rate. Adsorption behavior of single and mixed surfactants onto silica surface was studied using a total organic carbon analyzer. Results of the study showed that dispersion and flocculation behavior of aqueous silica suspensions depends on the type and concentration of surfactant, cationic/nonionic surfactant ratio and surfactant addition sequence to the system.Article Citation - WoS: 47Effect of Filler Amount on Thermoelastic Properties of Poly (dimethylsiloxane) Networks(Elsevier Ltd., 2005) Demir, Mustafa Muammer; Menceloğlu, Yusuf Z.; Erman, BurakEnd-linked poly(dimethylsiloxane) (PDMS) networks were prepared in the presence of fumed silica particles with hydroxyl groups at their surfaces. The silica particles were introduced into the polymer solution prior to end-linking. Hydroxyl ended PDMS chains were end-linked via the tetra functional crosslinker, tetraethoxysilane. The filler content varied in the range 0-5 wt%. Atomic Force Microscopy was used to image and characterize the silica particles. Swelling, stress-strain and thermoelasticity experiments were performed. The temperature coefficient and the energetic part of the force in uniaxial extension are found to increase with increasing silica amount. This observation is ascribed to effects contributed possibly by the adsorption layer around the silica particles.