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Publication Metadata only A novel mold design for one-continuous permeability measurement of fiber preforms(Sage Publications Ltd, 2015) N/A; N/A; Department of Mechanical Engineering; Yalçınkaya, Mehmet Akif; Sarıoğlu, Ayşen; Sözer, Murat; PhD Student; Master Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; 110357One-continuous permeability measurement experiments allow measuring permeability of a fiber preform within a range of fiber volume fractions by conducting a single unsaturated (a.k.a. transient) flow experiment on a dry specimen at an initial thickness, and a set of saturated flow experiments on the wetted specimen by varying the thickness of the mold cavity. This approach allows quicker database construction and reduces the effect of inherent variation of fabric structure caused by inconsistent labor on permeability. In this study, the drawbacks of previous mold designs are eliminated by using appropriate sealing, gap thickness adjustment mechanism and features that allow straightforward and reliable manual operation. Experiments for three different fabric types are conducted and the results are discussed. It is mainly observed that the unsaturated permeability is higher than the saturated permeability.Publication Metadata only Dynamic pressure control in vartm: rapid fabrication of laminates with high fiber volume fraction and improved dimensional uniformity(Wiley, 2019) Altan, M. Cengiz; Department of Mechanical Engineering; Department of Mechanical Engineering; Yalçınkaya, Mehmet Akif; Sözer, Murat; Master Student; Faculty Member; Department of Mechanical Engineering; College of Engineering; College of Engineering; N/A; 110357The compaction pressure on the fibrous preform is one of the most critical parameters in vacuum assisted resin transfer molding (VARTM), which significantly affects the preform permeability, mold filling time, and final thickness of the fabricated composite. In this study, the compaction pressure on the vacuum bag was controlled during and after the mold filling to achieve rapid impregnation and improve the fiber volume fraction of the laminate. It was shown that the dynamic pressure control (1) enabled the manipulation of the fabric permeability and faster distribution of the resin to decrease the mold filling time, (2) improved the dimensional uniformity of the laminate by reducing the thickness variation, and (3) increased the fiber volume fraction by further consolidating the preform and removing the excess resin. One of the most essential and prominent features of the process was shown to be the resin removal from the inlet by applying external pressure, which reduced the thickness variation in laminates from 15 to 1%. The mold filling time was reduced by 48% compared with conventional VARTM, while achieving a high fiber volume fraction up to 64% and a low void content of below 1%. POLYM. COMPOS., 40:2482-2494, 2019.Publication Metadata only Effect of part thickness variation on the mold filling time in vacuum infusion process(Sage Publications Ltd, 2014) N/A; Department of Mechanical Engineering; Yalçınkaya, Mehmet Akif; Sözer, Murat; PhD Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 110357An experimental setup was used to fairly compare mold filling times in vacuum infusion and resin transfer molding, and a 9.5% shorter mold filling time in vacuum infusion was observed than in resin transfer molding. The setup was also used to conduct compaction and permeability characterization experiments, and the results were used in a simplified vacuum infusion model, which is more straightforward to solve than the conventional full and coupled models in the literature. Simulated filling time in vacuum infusion was 31% shorter than in resin transfer molding. The faster resin flow in vacuum infusion is explained by the fact that the thickness in the wetted upstream region increases with time, and thus the effective permeability in that region increases.Publication Metadata only Effect of permeability characterization at different boundary and flow conditions on vacuum infusion process modeling(Sage Publications Ltd, 2017) N/A; N/A; Department of Mechanical Engineering; Yalçınkaya, Mehmet Akif; Çağlar, Barış; Sözer, Murat; PhD Student; PhD Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; 110357Permeability characterization of a fabric preform is a key factor that affects the accuracy of process modeling of vacuum infusion. There are various flow types and boundary conditions (such as one-dimensional or radial flow under constant injection pressure or constant injection flow rate during unsaturated or saturated flow regimes) used in permeability measurement experiments in the literature. This study investigates the effect of using different flow and injection boundary conditions in permeability characterization on the results of coupled one-dimensional mold-filling and compaction model. The results of the model are compared with vacuum infusion mold-filling experiments. It is shown that using the permeability measured at constant injection pressure and unsaturated flow results in the closest fill time compared to the experiments for all three types of fabrics investigated in this study.Publication Metadata only Electro-conductive silica nanoparticles-incorporated hydrogel based on alginate as a biomimetic scaffold for bone tissue engineering application(Taylor and Francis Ltd., 2023) Derakhshankhah, Hossein; Eskandani, Morteza; Vandghanooni, Somayeh; Jaymand, Mehdi; Department of Mechanical Engineering; N/A; Taşoğlu, Savaş; Nakhjavani, Sattar Akbar; Faculty Member; Researcher; Department of Mechanical Engineering; Koç University Research Center for Translational Medicine (KUTTAM) / Koç Üniversitesi Translasyonel Tıp Araştırma Merkezi (KUTTAM); College of Engineering; N/A; 291971; N/AAn innovative electrically conductive hydrogel was fabricated through the incorporation of silica nanoparticles (SiO2 NPs) and poly(aniline-co-dopamine) (PANI-co-PDA) into oxidized alginate (OAlg) as a biomimetic scaffold for bone tissue engineering application. The developed self-healing chemical hydrogel was characterized by FTIR, SEM, TEM, XRD, and TGA. The electrical conductivity and swelling ratio of the hydrogel were obtained as 1.7 × 10−3 S cm−1 and 130%, respectively. Cytocompatibility and cell proliferation potential of the developed scaffold were approved by MTT assay using MG-63 cells. FE-SEM imaging approved the potential of the fabricated scaffold for hydroxyapatite (HA) formation and bioactivity induction through immersing in SBF solution.Publication Metadata only Micro-phase separation via spinodal-like decomposition in hexamethylynediisocyanate (HDI)-polyurea(Springer, 2012) Kulkarni, Amit S.; Beaucage, Gregory; Wilkes, Garth L.; Das, Sudipto; Department of Chemistry; Yılgör, İskender; Faculty Member; Department of Chemistry; College of Sciences; 24181Micro-phase separation in hexamethylynediisocyanate-polyurea was studied using small-angle X-ray scattering and infrared absorption. It was found that phase separation in this system followed spinodal-like decomposition on a 3-4 nm size scale with phase separation occuring on a time scale of days.Publication Metadata only Modification of polyolefins with silicone copolymers. I. processing behavior and surface characterization of PP and HDPE blended with silicone copolymers(John Wiley & Sons Inc, 2002) Süzer, Şefik; Department of Chemistry; Department of Chemistry; Yılgör, İskender; Yılgör, Emel; Faculty Member; Researcher; Department of Chemistry; College of Sciences; College of SciencesPermanent surface modification of polypropylene and high-density polyethylene was obtained by blending with small (0.1 to 5.0% by weight) amounts of silicone copolymers. A triblock polycaprolactone-b-polydimethylsiloxane copolymer and a multiblock polydimethylsiloxane-urea copolymer were used as modifiers. Blends were prepared in a twin-screw extruder. Influences of the type and amount of the additive on the processing behavior and surface and bulk properties of the resulting systems were investigated. During processing, the additives also acted as very efficient processing aids, increasing the extruder output dramatically, up to 200%. Surface characterization by water-contact angle measurements and X-ray photoelectron spectroscopy clearly showed the formation of silicone-rich surfaces even with very small amounts of additives, such as 0.1% by weight.Publication Metadata only Modification of polyolefins with silicone copolymers. II. Thermal, mechanical, and tribological behavior of pp and hdpe blended with silicone copolymers(Wiley, 2002) Sınmazçelik, Tamer; Department of Chemistry; Department of Chemistry; Yılgör, Emel; Yılgör, İskender; Researcher; Faculty Member; Department of Chemistry; College of Sciences; College of Sciences; 40527; 24181Thermoplastic polyolefin (TPO) films with permanent, silicone-rich, low-friction, low-abrasion surfaces were obtained by melt blending of high-density polyethylene (HDPE) and polypropylene (PP) with polydimethylsiloxane (PDMS)-containing block copolymers. Two different block copolymers, a siloxane-urea segmented copolymer and a polycaprolactone-b-PDMS triblock copolymer were used as modifiers at levels between 0.1 and 5.0% by weight. Blends were prepared in a twin-screw extruder. Modified films displayed surfaces with very low friction coefficients and high abrasion resistance, which depended on the type and the level of additive incorporated into the system. Bulk properties of these modified systems, such as crystallization and melting behavior or tensile properties, were not affected.Publication Metadata only Multiscale modeling of the morphology and properties of segmented silicone-urea copolymers(Springer, 2012) Yıldırım, Erol; Yurtsever, Mine; Department of Chemistry; Department of Chemistry; Yurtsever, İsmail Ersin; Yılgör, İskender; Yılgör, Emel; Faculty Member; Researcher; Department of Chemistry; College of Sciences; College of SciencesMolecular dynamics and mesoscale dynamics simulation techniques were used to investigate the effect of hydrogen bonding on the microphase separation, morphology and various physicochemical properties of segmented silicone-urea copolymers. Model silicone-urea copolymers investigated were based on the stoichiometric combinations of alpha,omega-aminopropyl terminated polydimethylsiloxane (PDMS) oligÖmers with number average molecular weights ranging from 700 to 15,000 g/mole and bis(4-isocyanatocyclohexyl)methane (HMDI). Urea hard segment contents of the copolymers, which were determined by the PDMS molecular weight, were in 1.7-34% by weight range. Since no chain extenders were used, urea hard segments in all copolymers were of uniform length. Simulation results clearly demonstrated the presence of very good microphase separation in all silicone-urea copolymers, even for the copolymer with 1.7% by weight hard segment content. Experimentally reported enhanced properties of these materials were shown to stem from strong hydrogen bond interactions which leads to the aggregation of urea hard segments and reinforcement of the PDMS.Publication Metadata only Thermal stabilities of end groups in hydroxyalkyl terminated polydimethylsiloxane oligomers(Springer, 1998) Department of Chemistry; Department of Chemistry; Yılgör, İskender; Yılgör, Emel; Faculty Member; Researcher; Department of Chemistry; Collage of Sciences; Collage of Sciences; 24181; N/AThermal stabilities of alpha,omega-hydroxypropyl, alpha,omega-hydroxybutyl, alpha,omega-2-hydroxypentyl and alpha,omega-hydroxyhexyl terminated polydimethylsiloxane (PDMS) oligomers were studied Hydroxypropyl and hydroxybutyl terminated polydimethylsiloxane oligomers showed degradation upon heating, through the loss of functional end groups as determined by FT-IR spectroscopy and gel permeation chromatography, alpha,omega-Hydroxyhexyl and alpha,omega-2-hydroxypentyl terminated polydimethylsiloxane oligomers were stable under similar conditions. Instability of the end groups is due to the back biting of the terminal silicon in the PDMS by the primary hydroxyl oxygen, leading to the formation of 5 and 6 membered, stable, heterocylic compounds. Loss of end groups also resulted in a dramatic increase in the molecular weights of the oligomers produced, as determined by gel permeation chromatography.