Researcher:
Topçu, Gökhan

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Gökhan

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Topçu

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Topçu, Gökhan

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2020 - 20234

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Researcher Of Publications: search.filters.isAuthorOfPublication.88797855-2d05-48b0-8347-75a7a0752211

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    A novel photoinduced ligation approach for cross-linking polymerization, polymer chain-end functionalization, and surface modification using benzoyl azides
    (Wiley-V C H Verlag Gmbh, 2021) Kocaarslan, Azra; YIlmaz, Görkem; Yağcı, Yusuf; Department of Chemistry; Department of Chemistry; Department of Chemistry; Demirel, Adem Levent; Topçu, Gökhan; Faculty Member; Researcher; College of Sciences; College of Sciences; 6568; N/A
    Various ligation processes have recently become a powerful tool in synthetic polymer chemistry. Herein, the use of a new photochemical ligation process as a versatile approach for the cross-linking polymerization, functionalization of polymer chain ends, and surface modification of various materials such as silica and graphene oxide, is demonstrated. The process is based on the formation of urethane linkages by the reaction of photochemically in situ generated isocyanates from benzoyl azides with hydroxyl moieties in the presence of organobase, bicyclo[2.2.2]-1,4-diazaoctane (DABCO) under ambient conditions. The intermediates and obtained materials are characterized by NMR, FTIR, TGA, and TEM analyses. It is believed that this simple and efficient ligation process will expand future applications to fabricate complex macromolecular structures, biomaterials, and gels.
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    Refillable anti-icing SBS composite films
    (Elsevier, 2021) N/A; N/A; Department of Chemistry; Department of Chemistry; Department of Chemistry; Department of Chemistry; Department of Chemistry; Ijaz, Aatif; Topçu, Gökhan; Qureshi, Mohammad Haroon; Miko, Annamaria; Demirel, Adem Levent; Researcher; Researcher; PhD Student; Teaching Faculty; Faculty Member; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Koç University Research Center for Translational Medicine (KUTTAM) / Koç Üniversitesi Translasyonel Tıp Araştırma Merkezi (KUTTAM); N/A; College of Sciences; Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; N/A; N/A; N/A; 163509; 6568
    The lifetime of release-based anti-icing systems can be improved by refilling after the complete release of active agents. A novel swelling mediated consecutive filling of Diatomaceous Earth (DE) loaded Styrene-Butadiene-Styrene (SBS) composite films with PEG for anti-icing applications is reported. The degree of swelling and the diffusion of active agents into the composite was controlled by adjusting the composition of a binary mixture consisting of a non-solvent (acetone) and a good solvent (diethyl ether (DiEt)). Rhodamine 6G was used as a probe to show the extent of diffusion of dissolved molecules into SBS. The reversible loading of PEG-600 as anti-icing agent up to 19% by weight into DE/SBS composites and the complete release in the binary mixture having 30 vol. % DiEt was successfully achieved in consecutive cycles. After the 5th loading cycle, these composite films exhibited similar water contact angles (∼ 64°) and freezing delay times within error bars as those of the 1st loading cycle. At −15 °C, the average freezing delay time of the water droplets on DE/SBS composites filled with PEG in 30 vol. % DiEt was increased by a factor of three to 120 s. The successful refilling of the composites with reversible loading/release cycles and without any deterioration in the anti-icing properties at least up to 5 cycles is a significant contribution to the lifetime of release based functional coatings.
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    Oxide glass formers extending persistent luminescence in Eu and Dy co-doped strontium aluminates
    (Elsevier, 2023) Ergene, Arzu Cosgun; Abkenar, Sirous Khabbaz; Gungor, Ayca Senol; Gunay, Ece; Kurt, Hasan; Ow-Yang, Cleva W.; Department of Chemistry; Department of Chemistry; Topçu, Gökhan; Researcher; College of Sciences; N/A
    Recent work has shown that the incorporation of electrically charged, non-bridging oxygen (NBO) species into Eu and Dy co-doped Sr4Al14O25 (S4A7ED) crystal structure, in the form of Bo2O-, induces the clustering of divalent Eu and trivalent Dy, which is manifested as persistent luminescence (PersiL). Because other ceramic compounds exhibiting persistent luminescence also contain Si, P, and Zr, we evaluated other oxide glass forming cations-Si, P, Zr and V-for extending PersiL in S4A7ED. To understand the structural changes that these cations imparted to the atomic arrangements inside the S4A7ED crystal structure, we applied FTIR and micro-Raman spectroscopy to analyze the impact of charged NBOs. Raman shifts were revealed in Si-doped S4A7ED exhibiting PersiL at 1077 cm-1, corresponding to vibrations involving SiO4 tetrahedra with 2 bridging oxygens (BOs) and 2 NBOs and at 1107 cm-1, corresponding to vibrations involving SiO4 tetrahedra with 3 BOs and 1 NBOs. Raman shifts were also observed in P-doped S4A7ED exhibiting PersiL at 1070 cm-1, corresponding to PO4 tetrahedra with 1 BO and 3 NBOs, and at 700 cm-1, corresponding to PO4 tetrahedra with 2 BOs and 2 NBOs. These results suggest that PersiL extension in S4A7ED compounds, Pechini-processed with oxides of Si, P, Zr, and V, is correlated to structural changes from the incorporation of polyanions with NBOs, although the presence of a BO in the cation polyhedra is also essential.
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    Recent developments of colorimetric mechanical sensors based on polymer composites
    (Royal Soc Chemistry, 2020) Inci, Ezgi; Güner, Tuğrul; Demirkurt, Merve; Demir, Mustafa M.; N/A; Topçu, Gökhan; N/A; N/A; N/A
    Colorimetric mechanical (force, pressure, strain, and impact) sensors allow naked-eye visualization of existing structural deformations of a system occurring upon application of a mechanical action. The combination of mechanochromic materials with polymers offers a practical approach to designing and fabricating these sensors. Polymers as matrices can tolerate a wide range of forces and permits reusability of the sensors. On the other hand, mechanochromic materials provide unique colour properties depending on the type of mechanical action. They have also been frequently employed for the quantification of mechanical forces. As an example, non-centrosymmetric crystals are combined with polymers for sensing impact forces. Structures with photoluminescence and scattering and plasmonic resonances can be used to fabricate strain and pressure responsive composite materials, respectively. This study reviews recent advances in colorimetric mechanical sensor systems prepared using polymers and inorganic and organic mechanochromic materials working under a wide range of forces.