Browsing by Author "Torun, İ."
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Item Open Access Chemical funneling of colloidal gold nanoparticles on printed arrays of end-grafted polymers for plasmonic applications(American Chemical Society, 2020-06) Pekdemir, S.; Torun, İ.; Şakir, M.; Ruzi, M.; Rogers, J. A.; Önses, M. SerdarSpatially defined assembly of colloidal metallic nanoparticles is necessary for fabrication of plasmonic devices. In this study, we demonstrate high-resolution additive jet printing of end-functional polymers to serve as templates for directed self-assembly of nanoparticles into architectures with substantial plasmonic activity. The intriguing aspect of this work is the ability to form patterns of end-grafted poly(ethylene glycol) through printing on a hydrophobic layer that consists of fluoroalkylsilanes. The simultaneous dewetting of the underlying hydrophobic layer together with grafting of the printed polymer during thermal annealing enables fabrication of spatially defined binding sites for assembly of nanoparticles. The employment of electrohydrodynamic jet printing and aqueous inks together with reduction of the feature size during thermal annealing are critically important in achieving high chemical contrast patterns as small as ∼250 nm. Gold nanospheres of varying diameters selectively bind and assemble into nanostructures with reduced interparticle distances on the hydrophilic patterns of poly(ethylene glycol) surrounded with a hydrophobic background. The resulting plasmonic arrays exhibit intense and pattern-specific signals in surface-enhanced Raman scattering (SERS) spectroscopy. The localized seed-mediated growth of metallic nanostructures over the patterned gold nanospheres presents further routes for expanding the composition of the plasmonic arrays. A representative application in SERS-based surface encoding is demonstrated through large-area patterning of plasmonic structures and multiplex deposition of taggant molecules, all enabled by printing.Item Embargo Fully transparent and superhydrophobic electrodes enabled by soft interfaces(Elsevier BV, 2022-12-16) Torun, İ.; Çelik, N.; Kiremitler, N. B.; Huang, X.; Önses, Mustafa SerdarThe simultaneous achievement of transparency, electrical conductivity and superhydrophobicity is a highly challenging and rewarding task for a range of technological applications. This manuscript reports a practical and fluorine-free approach for fully transparent and superhydrophobic coatings on a transparent electrode. The first step consists of the formation of a grafted film of poly(ethylene glycol) on an indium oxide coated glass substrate. The superhydrophobicity is then achieved by spray-coating a film of alkylsilane functionalized nanoparticles. The self-assembly of the hydrophobic nanoparticles on end-grafted poly(ethylene glycol) allows for controlled formation of roughness without sacrificing the transparency and electrical conductivity. The result is a multi-functional substrate with a static contact angle of 172°, sliding angle of 1°, 90.4% transparency at a wavelength of 550 nm, and a sheet resistance of 13.05 Ω/sq. The surface has high water impact-resistance and thermal stability provided by the soft-interface composed of end-grafted poly(ethylene glycol). The reported substrate exhibits outstanding figures of merit in terms of the water repellency, optoelectronic performance, and stability. Application in transparent heaters demonstrates the promise of the presented multi-functional coatings.Item Open Access Multiplexed patterning of cesium lead halide perovskite nanocrystals by additive jet printing for efficient white light generation(Elsevier, 2020-08-12) Altıntaş, Y.; Torun, İ.; Yazıcı, A. F.; Beşkazak, E.; Erdem, T.; Önses, M. SerdarInorganic perovskite nanocrystals (PNCs) offer the ability to precisely but also flexibly control the peak emission wavelength while also possessing narrow-band emission spectra and high quantum yields. Owing to these features, PNCs have been already employed as color converters on LEDs. Nevertheless, the anion exchange reactions that prevent the blending of perovskites of different colors remain as an important bottleneck. As a remedy to this issue, here we employ additive jet printing to form separated stripes of these nanocrystals. Within this framework, we first present the synthesis of CsPbBr3 and CsPbBrxI3−x nanocrystals spanning the whole visible regime and optimize the cleaning procedure to obtain PNCs possessing photoluminescence quantum yields as high as 91% and emission linewidths as narrow as 15 nm, making them suitable for high quality white light generation. Next, we employ electrohydrodynamic jet printing to form closely spaced stripes of PNCs of various colors and integrated these films with a blue LED to create a white LED. Our proof-of-concept LED achieves high photometric performance as it possesses a color rendering index of 91.3, luminous efficacy of optical radiation > 300 lm/Wopt, and correlated color temperature of ca. 7000 K. We believe that additive jet printing technique will pave the way for a ubiquitous use of these PNCs in light-emitting devices in the near future.Item Open Access One-step deposition of hydrophobic coatings on paper for printed-electronics applications(Springer, 2019) Gözütok, Z.; Kinj, Ö.; Torun, İ.; Özdemir, A. T.; Önses, Mustafa SerdarThe ability to pattern highly conductive features on paper substrates is critically important for applications in radio frequency identification (RFID) tags, displays, sensors, printed electronics, and diagnostics. Ink-jet printing particle-free reactive silver inks is an additive, material efficient and versatile strategy for fabrication of highly conductive patterns; however, the intrinsic wetting properties of cellulose based papers are not suitable to serve as substrates for this process. This study reports one-step and practical modification of the surface of paper substrates using industrially available materials. The paper substrates were dip-coated with films of hydrocarbon and fluorocarbon based polymeric resins. Ink-jet printing particle-free reactive silver inks on the modified paper substrates followed by fast thermal annealing resulted in highly conductive patterns. The coatings improved the conductivity of the patterns and reduced the number of printing layers required to obtain conductivity. We finally demonstrated fabrication of a printed RFID tag on the coated paper substrates operating at the frequency range of 865–870 MHz.Item Open Access Physically unclonable surfaces via dewetting of polymer thin films(American Chemical Society, 2021-03-10) Torun, N.; Torun, İ.; Şakir, M.; Kalay, M.; Önses, Mustafa SerdarFrom anti-counterfeiting to biotechnology applications, there is a strong demand for encoded surfaces with multiple security layers that are prepared by stochastic processes and are adaptable to deterministic fabrication approaches. Here, we present dewetting instabilities in nanoscopic (thickness <100 nm) polymer films as a form of physically unclonable function (PUF). The inherent randomness involved in the dewetting process presents a highly suitable platform for fabricating unclonable surfaces. The thermal annealing-induced dewetting of poly(2-vinyl pyridine) (P2VP) on polystyrene-grafted substrates enables fabrication of randomly positioned functional features that are separated at a microscopic length scale, a requirement set by optical authentication systems. At a first level, PUFs can be simply and readily verified via reflection of visible light. Area-specific electrostatic interactions between P2VP and citrate-stabilized gold nanoparticles allow for fabrication of plasmonic PUFs. The strong surface-enhanced Raman scattering by plasmonic nanoparticles together with incorporation of taggants facilitates a molecular vibration-based security layer. The patterning of P2VP films presents opportunities for fabricating hybrid security labels, which can be resolved through both stochastic and deterministic pathways. The adaptability to a broad range of nanoscale materials, simplicity, versatility, compatibility with conventional fabrication approaches, and high levels of stability offer key opportunities in encoding applications.Item Open Access Sponge-derived natural bioactive glass microspheres with self-assembled surface channel arrays opening into a hollow core for bone tissue and controlled drug release applications(Elsevier, 2020) Kaya, M.; Bilican, İ.; Mujtaba, M.; Sargın, İ.; Erginer-Hasköylü, M.; Toksoy-Öner, E.; Zheng, İ.; Boccaccini, A. R.; Cansaran-Duman, D.; Önses, M. S.; Torun, İ.; Akyüz, L.; Elbüken, ÇağlarPorous, bioactive microspheres have always been a dream material to biomedical scientists for bone regeneration and drug delivery applications due to their interconnectivity, unique pore geometry, encapsulation ability and porosity spanning macroscopic, microscopic and nanoscopic length scales. Extensive efforts have been made to produce such materials synthetically at a great cost of money, time and labor. Herein, naturally-assembled multifunctional, open-channeled and hollow bioactive micro silica spheres (diameter 209.4 ± 38.5 µm) were discovered in a marine sponge (Geodia macandrewii), by peeling the outer surface of the sterrasters using hydrogen fluoride. The obtained micro silica spheres exhibited valuable characteristics such as homogeneously distributed pores, a cavity in the center of the sphere, and channels (approx. 3000) opening from each pore into the central cavity. Simulated body fluid analysis demonstrated the bioactivity of the micro silica spheres; whereas, no bioactivity was recorded for the original untreated sterrasters. The non-cytotoxicity and osteogenic ability of the isolated microspheres were confirmed through osteoblast cell culture. Finally, these silica based porous microspheres were tested for controlled drug release capacity. The spheres showed excellent loading and release abilities for an anti-cancer drug, carboplatin, in simulated solutions and in human cancer cell culture, HeLa, through a real time cell analyzer system. The drug loading capacity of the porous beads was determined as 10.59%. Considering the unique biological and physicochemical properties, these novel bioactive silica spheres, which we name as giant macroporous silica (GMS), are promising materials for a range of applications including bone tissue engineering and drug delivery.Item Open Access Transferring the structure of paper for mechanically durable superhydrophobic surfaces(Elsevier, 2020-10-24) Torun, İ.; Celik, N.; Ruzi, M.; Önses, Mustafa SerdarSolution-phase deposition of nanomaterials represents a highly promising technology with strong industrial application potential for the fabrication of superhydrophobic surfaces. An important barrier towards the adaptation of such materials and processes in a broad range of applications is the limited mechanical durability of the nanostructures. Herein, we present a universal solution to this challenge by benefiting from the unique micro-structure of paper. Our approach is based on transferring the structure of paper into a target material, to form a mechanical protection layer for nanomaterials that were deposited from solution-phase, i.e. spray-coating. We demonstrate this concept through the transfer of the structure of paper to a free-standing PDMS film using a simple molding process. Spraying a dispersion of alkyl-silane functionalized silica nanoparticles on the structured free-standing film results in a hierarchically structured superhydrophobic surface with a water contact angle of 175° ± 2° and a sliding angle <2° ± 1°. The fabricated superhydrophobic surface displays high levels of mechanical, chemical and thermal stability. The robust, inexpensive, scalable, flexible, and environmentally friendly nature of the presented approach may be a key enabler in superhydrophobic coating applications.Item Open Access Writing chemical patterns using electrospun fibers as nanoscale inkpots for directed assembly of colloidal nanocrystals(Royal Society of Chemistry, 2020) Kiremitler, N. B.; Torun, İ.; Altıntaş, Y.; Patarroyo, J.; Demir, Hilmi Volkan; Puntes, V. F.; Mutlugün, Evren; Önses, Mustafa SerdarApplications that range from electronics to biotechnology will greatly benefit from low-cost, scalable and multiplex fabrication of spatially defined arrays of colloidal inorganic nanocrystals. In this work, we present a novel additive patterning approach based on the use of electrospun nanofibers (NFs) as inkpots for end-functional polymers. The localized grafting of end-functional polymers from spatially defined nanofibers results in covalently bound chemical patterns. The main factors that determine the width of the nanopatterns are the diameter of the NF and the extent of spreading during the thermal annealing process. Lowering the surface energy of the substrates via silanization and a proper choice of the grafting conditions enable the fabrication of nanoscale patterns over centimeter length scales. The fabricated patterns of end-grafted polymers serve as the templates for spatially defined assembly of colloidal metal and metal oxide nanocrystals of varying sizes (15 to 100 nm), shapes (spherical, cube, rod), and compositions (Au, Ag, Pt, TiO2), as well as semiconductor quantum dots, including the assembly of semiconductor nanoplatelets.