Researcher:
Şenses, Erkan

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Erkan

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Şenses

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Şenses, Erkan

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2018 - 201932020 - 202316

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Now showing 1 - 10 of 19
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    Influence of kosmotrope and chaotrope salts on water structural relaxation
    (American Chemical Society (ACS), 2020) Luo, Peng; Zhai, Yanqin; Mamontov, Eugene; Xu, Guangyong; Faraone, Antonio; Department of Chemical and Biological Engineering; Şenses, Erkan; Faculty Member; Department of Chemical and Biological Engineering; College of Engineering; 280298
    The structural relaxation in water solutions of kosmotrope (structure maker) and chaotrope (structure breaker) salts, namely sodium chloride, potassium chloride, and cesium chloride, were studied through quasielastic neutron scattering measurements. We found that the collective dynamics relaxation time at the structure factor peak obtained using heavy water solutions shows a distinctively different behavior in the kosmotrope as opposed to the chaotrope solutions, increasing with the salt concentration in the former and decreasing in the latter. In both cases the trends are proportional to the concentration dependence of the relative viscosity of the solutions. These results indicate that kosmotropes and chaotropes influence the solutions viscosity by impacting in opposite ways the hydrogen bond network of water, strengthening it in one case and softening it in the other.
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    Multiscale polymer dynamics in hierarchical carbon nanotube grafted glass fiber reinforced composites
    (American Chemical Society (ACS), 2019) Krishnamurthz, Ajay; Tao, Ran; Doshi, Sagar M.; Burni, Faraz Ahmed; Natarajan, Bharath; Hunston, Donald; Thostenson, Erik T.; Faraone, Antonio; Forster, Amanda L.; Forster, Aaron M.; Department of Chemical and Biological Engineering; Şenses, Erkan; Faculty Member; Department of Chemical and Biological Engineering; College of Engineering; 280298
    Carbon nanotube (CNT) grafted glass fiber reinforced epoxy nanocomposites (GFRP) present a range of stiffnesses (MPa to GPa) and length scales (mu m to nm) at the fiber-matrix interface. The contribution of functionalized CNT networks to the local and bulk polymer dynamics is studied here by using a combination of torsion dynamical mechanical thermal analysis (DMTA), positron annihilation lifetime spectroscopy (PALS), and neutron scattering (NS) measurements. DMTA measurements highlight a reduction in the storage modulus (G') in the rubbery region and an asymmetric broadening of the loss modulus (G '') peak in the alpha-transition region. NS measurements show a suppressed hydrogen mean-square displacement (MSD) in the presence of glass fibers but a higher hydrogen MSD after grafting functionalized CNTs onto fiber surfaces. PALS measurements show greater free volume characteristics in the presence of the functionalized CNT modified composites, supporting the view that these interface layers increase polymer mobility. While NS and DMTA are sensitive to different modes of chain dynamics, the localization of functionalized nanotubes at the fiber interface is found to affect the distribution of polymer relaxation modes without significantly altering the thermally activated relaxation processes.
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    Enteric coating of drug loaded aerogel particles in a wurster fluidized bed and its effect on release behaviour
    (Editions de Sante, 2023) Ulker, Zeynep; Demir, Enis; Işık, Murat; Ekmekçiyan, Nadin; Department of Chemical and Biological Engineering; Department of Chemical and Biological Engineering; N/A; N/A; N/A; Erkey, Can; Şenses, Erkan; Akgün, Işık Sena; Darvishi, Saeid; Karaz, Selcan; Faculty Member; Faculty Member; PhD Student; PhD Student; Master Student; Department of Chemical and Biological Engineering; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); College of Engineering; College of Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; 29633; 280298; N/A; N/A; N/A
    Ibuprofen loaded and unloaded alginate aerogel particles were successfully coated with methacrylic acid-ethyl acrylate copolymer in a Wurster fluidized bed. Pores of both aerogels were well-preserved during the coating process. Effects of drug loading, polymer rheology, and atomizing pressure on coating thickness and coating layer surface morphology were investigated. Coatings were conducted at circulatory particle motion regime. Due to low weight of unloaded aerogels, this regime was achieved at lower air flow rates than ibuprofen loaded aerogels. Coatings of ibuprofen loaded aerogels were conducted between 1.3 and 1.5 bar atomizing pressures and at 60 °C. Unloaded aerogels were coated at a constant and high atomizing pressure of 1.7 bar and at 60 °C. At this condition, coating thickness of unloaded aerogels increased linearly from 25.6 μm to 53.4 μm with increasing coating time from 10 to 50 min. For ibuprofen loaded aerogels, coating thickness increased non-linearly from 15.9 μm to 84.1 μm with increasing coating time from 10 to 180 min. Ibuprofen release from aerogels in acidic medium was prevented via coating. In the basic medium, the fastest release was obtained from uncoated aerogels and 57% of ibuprofen was released in 30 min while 44% of crystalline ibuprofen dissolved at the same time. The slowest release rate was achieved via coating and 13% of the drug was released from coated aerogels in 30 min. © 2023 Elsevier B.V.
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    Effect of polymeric viscoelastic environment on multiscale structural dynamics of lipid bilayers
    (Cell Press, 2022) N/A; N/A; Department of Chemical and Biological Engineering; Karaz, Selcan; Şenses, Erkan; Master Student; Faculty Member; Department of Chemical and Biological Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 280298
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    Entangled polymer dynamics in attractive nanocomposite melts
    (American Chemical Society (ACS), 2020) Şenses, Erkan; Tyagi, Madhu Sudan; Faraone, Antonio; Department of Chemical and Biological Engineering; N/A; Şenses, Erkan; Darvishi, Saeid; Faculty Member; PhD Student; Department of Chemical and Biological Engineering; College of Engineering; Graduate School of Sciences and Engineering; 280298; N/A
    We investigate single chain dynamics of an entangled linear poly(ethylene oxide) melt in the presence of well-dispersed attractive nanoparticles using high-resolution neutron spectroscopy at particle volume fractions as high as 0.53. The short-time dynamics shows a decrease of the Rouse rates with particle loading, yet the change remains within a factor of 2, with no evidence of segment immobilization as often hypothesized. The apparent reptation tube diameter shrinks by approximate to 10% from the bulk at a 0.28 particle volume fraction when the face-to-face interparticle distance approaches the single chain size. The tube diameter is remarkably concentration-independent at higher loadings where all chains are essentially bound to particle surfaces. These direct experimental observations on the microscopic chain dynamics in attractive nanocomposites are distinct from their nonattractive counterparts and account for some of the unusual dynamic behaviors of the nanoparticles as well as rheology in the composites.
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    Protective coating of highly porous alginate aerogel particles in a Wurster fluidized bed
    (Elsevier, 2022) Demir, Enis; Işık, Murat; Ekmekciyan, Nadin; N/A; Department of Chemical and Biological Engineering; Department of Chemical and Biological Engineering; Akgün, Işık Sena; Şenses, Erkan; Erkey, Can; PhD Student; Faculty Member; Faculty Member; Department of Chemical and Biological Engineering; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Graduate School of Sciences and Engineering; College of Engineering; College of Engineering; N/A; 280298; 29633
    Alginate aerogel particles were successfully coated with a copovidone and hydroxypropyl cellulose based polymer in a Wurster fluidized bed. The results indicate that the pores of aerogels were not damaged during the process. Several sets of experiments were conducted at three different temperatures and atomizing air pressures. Coating time for all the runs ranged from 5 min to 40 min and the coating thickness ranged from 12.4 +/- 4.6 mu m to 170.6 +/- 43.3 mu m.Changing bed temperature led to significant changes in coating thickness whereas both bed temperature and atomizing pressure affected coating layer surface morphology. The smoothest coating layer surface and the highest coating efficiency which was 69.2 +/- 0.4% were achieved at 50 degrees C with 1.7 bar atomizing pressure. At this condition, the coating layer thickness increased linearly with coating time.(c) 2022 Elsevier B.V. All rights reserved.
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    Surfactant driven liquid to soft solid transition of cellulose nanocrystal suspensions
    (Amer Chemical Soc, 2020) N/A; N/A; Department of Chemical and Biological Engineering; Department of Chemical and Biological Engineering; Kuşhan, Eren; Demir, Can; Şenses, Erkan; Master Student; Undergraduate Student; Faculty Member; Department of Chemical and Biological Engineering; Graduate School of Sciences and Engineering; College of Engineering; College of Engineering; N/A; N/A; 280298
    Cellulose nanocrystals (CNCs) have recently attracted wide interest due to their abundance, biocompatibility, and extraordinary physical properties. In particular, easy manipulation of their surface properties, hydrophilicity, and high aspect ratio make them ideal rheology modifiers; yet, the gelation mechanisms and microscopic origin of the complex rheological behavior in the presence of secondary components, such as polymers and surfactants, are far from well understood. In this work, we used light scattering, small-angle neutron scattering, and bulk rheology to study the phase behavior and mechanical behavior of aqueous CNC solutions in the presence of cationic 1-decyl trimethyl imidazolium chloride and 1-decyl trimethyl imidazolium ferric tetrachloride. The micelles of these surfactants form at similar cmc's (about 50 mM) and adopt identical hydrodynamic sizes (on the order of a few nanometers) and prolate-shaped ellipsoids but vary in their intermicelle interactions (charged vs neutral), thus allowing us to clarify the unprecedented effect of the surfactant micelle charge on the gel behavior of the aqueous CNC-surfactant complexes. Our results show that the positively charged micelles greatly strengthen the gel network while excessive free micelles weaken the gels due to repulsive micelle-micelle interaction. In the meantime, analysis of the transition from linear to nonlinear deformation regimes suggests that the gels gradually become more fragile with surfactant concentrations due to electrostatic repulsion of the charged micelles. Such a surfactant concentration-dependent gel fragility was not observed in the presence of the neutral micelles. These results provide a great step further in our understanding of the phase behavior and rheology of complex CNC-surfactant mixtures and obtaining biocompatible hydrogels with tunable mechanical properties.
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    Enhanced ionic conductivity and mechanical strength in nanocomposite electrolytes with nonlinear polymer architectures
    (TÜBİTAK, 2023) N/A; Department of Chemical and Biological Engineering; N/A; Bakar, Recep; Şenses, Erkan; Darvishi, Saeid; PhD Student; Faculty Member; PhD Student; Department of Chemical and Biological Engineering; Koç University Boron and Advanced Materials Application and Research Center (KUBAM) / Koç Üniversitesi Bor ve İleri Malzemeler Uygulama ve Araştırma Merkezi (KUBAM); Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; College of Engineering; Graduate School of Sciences and Engineering; N/A; 280298; N/A
    Solvent-free polymer-based electrolytes (SPEs) have gained significant attention to realize safer and flexible lithium-ion batteries. Among all polymers used for preparing SPEs electrolytes, poly(ethylene oxide), a biocompatible and biodegradable polymer, has been the most prevalent one mainly because of its high ionic conductivity in the molten state, the capability for the dissolution of a wide range of different lithium salts as well as its potential for the environmental health and safety. However, linear PEO is highly semicrystalline at room temperature and thus exhibits weak mechanical performance. Addition of nanoparticles enhances the mechanical strength and effectively decreases the crystallization of linear PEO, yet enhancement in mechanical performance often results in decreased ionic conductivity when compared to the neat linear PEO-based electrolytes; new strategies for decoupling ionic conductivity from mechanical reinforcement are urgently needed. Herein, we used lithium bis(trifluoromethane-sulfonyl)-imide (LiTFSI) salts dissolved in various nonlinear PEO architectures, including stars (4-arms and 8-arms) and hyperbranched matrices, and SiO2 nanoparticles (approximately equal to 50 nm diameter) as fillers. Compared to the linear PEO chains, the room temperature crystallinity was eliminated in the branched PEO architectures. The electrolytes with good dispersion of the nanoparticles in the nonlinear PEOs significantly enhanced ionic conductivity, specifically by approximately equal to 40% for 8-arm star, approximately equal to 28% for 4-arms star, and approximately equal to %16 for hyperbranched matrices, with respect to the composite electrolyte with the linear matrix. Additionally, the rheological results of the SPEs with branched architectures show more than three orders of magnitude enhancement in the low-frequency moduli compared to the neat linear PEO/Li systems. The obtained results demonstrate that the solvent-free composite electrolytes made of branched PEO architectures can be quite promising especially for irregularly shaped and environmentally benign battery applications suitable for medical implants, wearable devices, and stretchable electronics, which require biodegradability and biocompatibility. © TÜBİTAK.
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    Liposomes under shear: structure, dynamics, and drug delivery applications
    (Wiley-VCH, 2023) Department of Chemical and Biological Engineering; N/A; Şenses, Erkan; Karaz, Selcan; Faculty Member; Master Student; Department of Chemical and Biological Engineering; College of Engineering; Graduate School of Sciences and Engineering; 280298; N/A
    The targeted delivery to specific locations while not causing damage to healthy tissues efficiently remains a challenge in drug delivery systems. Through addressing this issue, stimuli-responsive materials have been under investigation. As one of the fundamental forces associated with blood flow, shear stress is taken as an advantage to design shear-sensitive drug carriers. Although blood flow is modeled as laminar flow under normal conditions, in case of constrictions caused by endothelial shear stress, cardiovascular diseases, or angiogenesis due to tumor formation, local shear stress can dramatically increase. To date, shear-sensitive materials have been investigated under two main categories: shear-disaggregated and shear-deformed nanoparticles based on their structural mechanism after exposure to high-shear stress. Among them, liposomes are promising materials with their soft and deformable structure, high biocompatibility, controlled-release properties, and sensitivity to shear stress. Herein, in this review, the effects of shear stress on liposomes in terms of their structural changes, flow regimes, rheological properties, and drug delivery applications are discussed. It is believed that this work provides a basis for designing more effective drug delivery systems considering the complexity of the human body.
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    Multiscale dynamics of lipid vesicles in polymeric microenvironment
    (Mdpi, 2022) N/A; N/A; N/A; N/A; N/A; Department of Electrical and Electronics Engineering; Department of Chemical and Biological Engineering; Department of Chemical and Biological Engineering; Karaz, Selcan; Han, Mertcan; Akay, Gizem; Önal, Asım; Nizamoğlu, Sedat; Kızılel, Seda; Şenses, Erkan; Master Student; Master Student; PhD Student; PhD Student; Faculty Member; Faculty Member; Faculty Member; Department of Electrical and Electronics Engineering; Department of Chemical and Biological Engineering; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; College of Engineering; College of Engineering; N/A; N/A; N/A; N/A; 130295; 28376; 280298
    Understanding dynamic and complex interaction of biological membranes with extracellular matrices plays a crucial role in controlling a variety of cell behavior and functions, from cell adhesion and growth to signaling and differentiation. Tremendous interest in tissue engineering has made it possible to design polymeric scaffolds mimicking the topology and mechanical properties of the native extracellular microenvironment; however, A fundamental question remains unanswered: that is, how the viscoelastic extracellular environment modifies the hierarchical dynamics of lipid membranes. in this work, we used aqueous solutions of poly(ethylene glycol) (PEG) with different molecular weights to mimic the viscous medium of cells and nearly monodisperse unilamellar DMPC/DMPG liposomes as a membrane model. Using small-angle X-ray scattering (SaXS), dynamic light scattering, temperature-modulated differential scanning calorimetry, bulk rheology, and fluorescence lifetime spectroscopy, we investigated the structural phase map and multiscale dynamics of the liposome-polymer mixtures. the results suggest an unprecedented dynamic coupling between polymer chains and phospholipid bilayers at different length/time scales. the microviscosity of the lipid bilayers is directly influenced by the relaxation of the whole chain, resulting in accelerated dynamics of lipids within the bilayers in the case of short chains compared to the polymer-free liposome case. at the macroscopic level, the gel-to-fluid transition of the bilayers results in a remarkable thermal-stiffening behavior of polymer-liposome solutions that can be modified by the concentration of the liposomes and the polymer chain length.