İnşaat Mühendisliği Bölümü / Department of Civil Engineering

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Structural Characteristics of the Earthquake-Prone Building Stock in Istanbul and Prioritization of Existing Buildings in Terms of Seismic Risk-A Pilot Project Conducted in Istanbul
(Taylor and Francis Ltd., 2023) Aydoğdu, Hasan Hüseyin; Demir, Cem; CÖMERT, MUSTAFA; Kahraman, Tayfun; Ilki, Alper
Earthquakes have caused catastrophic results in cities since the beginning of settled life, and the cumulative experience of these events has indicated that the lack of seismic resilience brings enormous economic losses and threatens human life. Consequently, the importance of seismic risk mitigation of earthquake-prone structures has arisen to reduce the primary and secondary losses resulting from seismic events in the last decades as developments in the earthquake engineering field occur. The first step for ensuring seismic resilience is the identification of risky buildings, which is a difficult challenge for metropolises like Istanbul since the building stock consists of over a million buildings. Applying code-based detailed assessments to so many buildings is not practical in terms of time and cost. Moreover, the current code-based detailed assessment methodologies such as Provisions for the Seismic Risk Evaluation of Existing Buildings under Urban Renewal Law (2019) and Turkish Building Earthquake Code (2018) provide discrete predictions for existing buildings as either risky or non-risky or satisfying life safety/controlled damage or not. However, a ranking system based on a reliable and realistic risk classification to prioritize the buildings is needed. Therefore, as a pilot project, nearly 23,000 reinforced concrete buildings in 37 different districts of Istanbul have been investigated by Istanbul Metropolitan Municipality (IMM) through PERA2019 performance-based rapid assessment methodology by considering the Design Level and Scenario-Based Earthquake cases. This is the most up-to-date and comprehensive site survey and analysis conducted in Istanbul up to now. In this paper, the characteristics of the building stock in Istanbul based on the conducted site work and the outcomes of the rapid seismic safety assessment efforts are summarized. Then, a discussion on the seismic risk evaluation of the existing residential buildings based on the prioritization of the examined buildings is presented through the results obtained for the Design Level and Scenario-Based Earthquake cases.
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Seismic Retrofit of Substandard RC Columns Using Sprayed Glass Fiber-Reinforced Mortar and Basalt Textile Reinforcement
(Taylor & Francis Ltd., 2023) Ateş, Ali Osman; Hajihosseinlou, Saeid; Nasrinpour, Amin; Demir, Cem; CÖMERT, MUSTAFA; Maraşlı, Muhammed; İlki, Alper
This study investigates the seismic retrofit of substandard reinforced concrete (RC) columns through external jacketing of potential plastic hinge zones using sprayed glass fiber-reinforced mortar and basalt textile reinforcement. An innovative spraying method was used to apply the matrix material to the concrete surface. A total number of eight full-scale columns (four reference, four retrofitted) were tested under constant high axial load to capacity ratio and reversed cyclic lateral loading. Columns were constructed using low-strength concrete and transverse reinforcement with various spacing and inadequate hook detailing to mimic the columns in substandard structures. Test results are evaluated in terms of lateral load-drift ratio relationships, displacement ductility, stiffness degradation, energy dissipation, and residual displacements. Evaluation of the test results showed that the proposed technique is effective for seismic retrofit of substandard RC columns, particularly in terms of enhancement of displacement ductility, energy dissipation capacities, and reduction of residual displacements.
Open Access
Material Selection with Value Engineering Technique - A Case Study in Construction Industry
(University of Osijek, 2023) UĞURAL, MEHMET NURETTİN
As a result of the rising level of competition in the construction industry, businesses strive to stay one step ahead of their rivals and overcome the most fundamental optimization challenge of balancing quality, time, and cost parameters. This is not always possible, however. Occasionally, the project may be completed late, the budget may be exceeded, or the desired quality cannot be attained. Various strategies have been developed to address these issues. The value engineering method is among these techniques. Taking into account quality, time, and cost, value engineering executes cost-saving projects without disregarding customer expectations. Value engineering seeks to increase value by concentrating on functions other than cost management. By conducting value studies on the products, value engineering can introduce new designs, develop the existing product, or provide value to the customer. This study employed value engineering to determine the thermal insulation material to be used in a building. First, the functions to be worked on were determined by considering user expectations, and then three alternative products that provide these functions were identified among the most preferred products. By developing alternative products, the advantages and disadvantages of the original products were revealed. The most valuable product was determined by calculating the product's value in relation to its benefits and costs. Thus, the optimal product was selected by weighing the user's expectations, the product's benefits, and its price.
Open Access
Bulanık CPM ile Doğrusal Programlama: İnşaat Endüstrisinde Bir Vaka Çalışması
(Süleyman Demirel Üniversitesi Mühendislik Fakültesi, 2022) Değirmenci, Güllü; UĞURAL, MEHMET NURETTİN
İnşaat sektöründe karmaşık projelerin planlanması ve kontrolü için Kritik Yol Metodunun (KYM), yaygın olarak kullanılan yararlı bir araç olduğu kanıtlanmıştır. Ancak, faaliyetlerin süresi net sayılarla temsil edildiğinden, kritik yol analizinde faaliyet sürelerini kesin olarak tahmin etmek zorlaşır. Buna ek olarak, vakaların çoğu, görev sürelerinin sübjektif olarak hesaplanmasını gerektirir ve bu da faaliyetlerin süresi hakkında belirsizliğe neden olur. Bu makale, bulanık kümelere dayalı bir yaklaşım önererek bu sorunları ele almaktadır. Bu çalışmanın amacı, bir inşaat projesinin kritik yolunu ve tamamlanma süresini hesaplamak için bulanık sayıların nasıl kullanılacağını göstermektir. Çalışma kapsamında proje faaliyetlerine üçgen bulanık süreler verilerek iki ayrı çözüm algoritması oluşturulmuştur. Örnek bir inşaat projesinin kritik yolu ve proje süresi ilk çözüm algoritmasında proje faaliyetlerine üçgen bulanık süreler atanarak ve doğrusal programlama modeli kullanılarak hesaplanırken, ikinci çözüm algoritmasında bulanık proje süresi ve kritik yol Alfa kesme yöntemi (α -Kesme Yöntemi) kullanılarak hesaplanmış ve daha sonra Centroid yöntemi (Alanların Merkezi Yöntemi) kullanılarak netleştirilmiştir. Bu proje için kritik yol ve tamamlanma süresi önceden bilindiğinden, iki çözüm algoritması karşılaştırılmıştır. Kritik yol yöntemi yerine Bulanık kritik yol yönteminin kullanılmasının bu çalışmanın önemini vurgulayacağı umulmaktadır.
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Seismic Retrofitting Of the 19(TH) Century Hirka-i Serif Mosque Using Textile Reinforced Mortar
(Taylor & Francis Inc., 2022) Demir, C.; CÖMERT, MUSTAFA; KOÇAK, PINAR İNCİ; Dusak, S.; İlki, A.
In this study, a novel retrofitting intervention on the Hirka-i Serif Mosque (constructed in 1851), which has a significant importance for Muslims due to its historical relic preservation unit keeping the cloak of the Prophet Muhammad, was illustrated. For this purpose, first the seismic performance of the mosque was investigated through site investigations and structural analyses. A 3D finite element model of the Mosque was established, and the structural system was analyzed under the combined effects of the vertical loads and seismic actions. Additionally, the existing damages observed on the walls and vaults were investigated thoroughly. By taking the existing damages and the analyses results into consideration, a rehabilitation and seismic retrofit scheme was proposed and applied by making use of innovative materials. Throughout the study, recommendations of the guideline for earthquake risk management of historical structures in Turkey (2017) has been considered.
Open Access
Gömülü Betonarme Boruların Analitik ve Sayısal Yöntemler ile Tasarımı
(Turkish Chamber Civil Engineers, 2022) Demirci, Onur; Kılıç, Havvanur; YAZICI, GÖKHAN
Gömülü betonarme borular, kentsel altyapının kritik bileşenleridir. Tasarımlarında, boru özellikleri, boruyu çevreleyen dolgu zemin, yataklama koşulları ve etki eden dış yükler dikkate alınarak ampirik veya sayısal yöntemler kullanılır. Bu çalışmada, uygulamada yaygın olarak kabul gören ampirik ve sayısal analiz yöntemleri dikkate alınarak yapılan tasarım hesaplarındaki farklılıklar geri dolgu malzeme türü, dolgu yüksekliği ve boru çapı değişimi dikkate alınarak parametrik analizler ile incelenmiştir. Çalışma sonuçları, sayısal analizlerde zemin-boru etkileşiminin gerçekçi olarak dikkate alınması nedeniyle hesaplanan gerekli donatı alanlarının geleneksel tasarım yöntemlerinden elde edilen değerlere göre daha düşük olduğunu göstermektedir.
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Seismic Risk Assessment and Preliminary Intervention Cost-Benefit Analysis for the Building Stock of Istanbul
(Springer International Publishing, 2022) Demir, Cem; CÖMERT, MUSTAFA; Aydoğdu, Hasan Hüseyin; İlki, Alper
Past destructive earthquakes in highly seismic areas of the world have shown that the failure of earthquake-prone buildings endangers the lives of the inhabitants and may cause enormous financial losses. Management of the seismic risks through effective mitigation efforts requires the identification of risky buildings in our cities. However, this is a challenging task, since the building stock is generally too huge to be investigated by using detailed seismic assessment methods provided by current technical documents. On the other hand, available quick assessment methods such as street surveys may lead to remarkably erroneous estimations, particularly if the building stock is composed of substandard buildings constructed without proper engineering service and inspection. Thus, reliable rapid assessment methodologies are required for seismic risk identification and classification of buildings in big cities. In the scope of a recent campaign launched by the Istanbul Metropolitan Municipality (IMM), PERA2019 rapid assessment methodology has been employed on more than 20000 buildings from 33 different districts of Istanbul. In this study, firstly, the preliminary results obtained for those buildings by considering a Scenario-Based Earthquake case are summarized. Then, a preliminary cost-benefit analysis considering the pre-earthquake and post-earthquake intervention costs (such as retrofitting, reconstruction and structural and non-structural damage repairs) together with the secondary costs (such as interruptions on the use of damaged buildings) have been performed and discussed. The obtained results indicate that a synchronized effort orchestrating rapid assessment methodologies and intervention strategies may provide feasible and effective solutions for reduction of seismic risks in big cities like Istanbul.
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Assessment of Seismic Demand and Damping of a Reinforced Concrete Building After CFRP Jacketing of Columns
(Techno-Press, 2022) KOÇAK, PINAR İNCİ; Göksu, Çağier; Töre, Erkan; Binbir, Ergun; Ateş, Ali Osman; İlki, Alper
While the lateral confinement provided by an FRP jacket to a concrete column is passive in nature, confinement is activated when the concrete expands due to additional compression stresses or significant shear deformations. This characteristic of FRP jacketing theoretically leads to similar initial stiffness properties of FRP retrofitted buildings as the buildings without retrofit. In the current study, to validate this theoretical assumption, the initial stiffness characteristics, and thus, the potential seismic demands were investigated through forced vibration tests on two identical full-scale substandard reinforced concrete buildings with or without FRP retrofit. Power spectral density functions obtained using the acceleration response data captured through forced vibration tests were used to estimate the modal characteristics of these buildings. The test results clearly showed that the natural frequencies and the mode shapes of the buildings are quite similar. Since the seismic demand is controlled by the fundamental vibration modes, it is confirmed using vibration-based full-scale tests that the seismic demands of RC buildings remain unchanged after CFRP jacketing of columns. Furthermore, the damping characteristics were also found similar for both structures.
Open Access
Comparative Economic and Experimental Assessment of Air Source Heat Pump and Gas-Fired Boiler: A Case Study from Turkey
(MDPI, 2022) KUL, ÖNDER; UĞURAL, MEHMET NURETTİN
Since sustainability has become a major concern in the construction industry, making economically efficient investment decisions in energy conservation are needed to minimize energy consumption for space heating and cooling. Although Air-Source Heat Pump (ASHP) systems are used to meet buildings' heating and cooling demands worldwide, high initial setup costs limit the widespread use of these systems. This paper presents comparative assessment of ASHP system versus conventional gas-fired boiler system for a real commercial building with a floor area of 2500 m(2) in Istanbul, Turkey. The key performance variable, Coefficient of Performance (COP), of the ASHP system was experimentally evaluated. The experimental results revealed that the system's COP ranged from 3.22 to 4.32, while the outside temperature ranged from 4.8 to 18.6 degrees C and the supply water temperature ranged from 32.2 to 36.2 degrees C. Moreover, the economic analysis results showed that despite the high initial cost, ASHP systems are cost competitive against gas-fired boiler in Turkey. ASHP system could reduce the present value of total Life-Cycle Cost (LCC) by up to 26.4% (47,865 USD) compared to the conventional gas-fired boiler system because it can dramatically reduce the energy consumption per year.
Open Access
Zeminlerin Kıvam ve Kompaksiyon Özelliklerinin Tahmininde Rastgele Orman Regresyonu Yönteminin Uygulanabilirliği
(Süleyman Demirel Üniversitesi Mühendislik Fakültesi, 2021) Nuray, Said Enes; GENÇDAL, HAZAL BERRAK; Arama, Zülal Akbay
Bu makalede, yüksek plastisiteli kil zeminlerin kıvam limitleri ve kompaksiyon karakteristikleri arasındaki ilişki basit regresyon ve karar ağaçları tabanlı Rastgele Orman regresyon (RO) yöntemlerinin karşılaştırmalı olarak analiz edilmesi yoluyla irdelenmiştir. Zeminlerin kompaksiyon parametrelerini oluşturan maksimum kuru birim hacim ağırlık ve optimum su muhtevası değerlerinin doğrudan belirlenmesinde kullanılan standart laboratuvar deneylerin zorluğu ve uzun numune hazırlama-bekleme süreçleri içermesi nedeni ile göreceli olarak daha pratik deneyler kullanılarak bu parametrelerin tahmin edilmesi günümüzde sıklıkla uygulanılan bir yöntemdir. Ayrıca, kıvam limiti deneylerinden likit limit, tüm geoteknik mühendisliği tasarımlarında uygulanan ve tatminkar sonuçlar veren bir deneydir. Bu çalışmada, yüksek plastisiteli kil zeminlere ait literatürde sunulan 387 adet kıvam limiti ve 59 kompaksiyon-kıvam limiti test çiftinin kullanılması ile oluşturulan bir veri tabanı kullanılarak iki aşamalı bir tahmin süreci yürütülmüştür. Birinci aşamada plastisite indisinin doğrudan likit limit değerinden, ikinci aşamada ise kompaksiyon parametrelerinin plastisite indisinden tahmin olasılığı araştırılmıştır. Aynı zamanda, laboratuvar deneylerinden elde edilen gerçek verilerin tutarsızlık durumları ve bu verilerin belirli bir eğilim izlememesi sebebi ile genel regresyon çalışmalarında oluşan doğruluk oranı düşüklüğüne dikkat çekilerek, bu doğruluk oranlarının Rastgele Orman regresyonu yöntemi ile nasıl yükseltilebileceği de incelenmektedir. Sonuçlarda, Rastgele Orman regresyonu yönteminin yüksek plastisiteli kil zeminlerin kıvam ve kompaksiyon özelliklerinin tahmininde başarılı olduğu ve kullanılabilir nitelikte sonuçlar sunduğu gösterilmektedir.
Open Access
Düşük Plastisiteli Killi Zeminlerin Kıvam Özelliklerinin Tahmininde Rastgele Orman Yöntemi
(Afyon Kocatepe Üniversitesi, 2021) Akbay Arama Z.; Karakaş S.; Nuray S. E.; Alten O.; Akın M. S.; GENÇDAL, HAZAL BERRAK
Bu çalışma kapsamında, düşük plastisiteli killi zeminlerin kıvam özelliklerinin tahmininde Rastgele Orman yönteminin uygulanabilirliği değerlendirilmiştir. Bu amaçla, Birleştirilmiş Zemin Sınıflandırma Sistemi’ne göre düşük plastisiteli kil sınıfında yer alan 665 adet zeminin likit, plastik limit ve su muhtevasıdeney sonuçları derlenerek bir veri seti oluşturulmuştur. Python yazılımı kullanılarak yapılan tek ve çok değişkenli regresyon analizlerinde likit limit, derinlik, su muhtevası ve doğal birim hacim ağırlığı değerleri bireysel veya gruplar halinde girdi parametreleri olarak değerlendirilmiş ve plastisite indisi tahminindeki etkinlikleri araştırılmıştır. Aynı zamanda, laboratuvar verilerinin tutarsızlık durumları veya belirli bir eğilim izlememesi sebebi ile ortaya çıkan tahmin oranı azalmasına dikkat çekilerek, bu oranlarının Rastgele Orman yöntemi ile nasıl yükseltilebileceği konusu da incelenmiştir. Sonuçlar, Rastgele Orman yönteminin düşük plastisiteli kil zeminlerin plastisite indisi değerinin tahmininde kullanılabilir nitelikte olduğunu göstermektedir.
Open Access
Calculation of Pile Capacity in Cohesionless Soil by CPT Considering Spatial Variability
(Çukurova Üniversitesi Mühendislik Fakültesi, 2021) MERT, AHMET CAN; YAZICI, GÖKHAN
The study aims to construct a framework for CPT based ultimate pile capacity calculation for cohesionless soils with random field theory. Cone tip resistance (qc) was taken as the spatially varying parameter with a constant mean and changing coefficients of variation. CPT profiles were simulated with random field generations, and the ultimate capacity of a single pile (Qu) was calculated with these simulations. The influence of spatial variation of qc on the variation of Qu was investigated. The proposed framework was finally verified by comparing the results of an actual CPT database and the simulated CPT profiles in the study. The results showed that the critical vertical scale of fluctuation for CPT-based pile capacity calculations was equal to one diameter of pile (dv=1D), and that the method effectively predicted the ultimate pile capacity through simulated CPT profiles with random field. The proposed method is especially recommended for cases where the uncertainty consideration is necessary, yet the site-specific data is limited. The study aims to contribute a simple framework to the methods of CPTbased pile capacity with unceratinty consideration. The propesed method aims to facilitate the pile design framework with limited available data.
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The Applicability of Regression Analysis and Artificial Neural Networks to the Prediction Process of Consistency and Compaction Properties of High Plastic Clays
(Springer Science and Business Media Deutschland GmbH, 2021) Akbay Arama, Zülal; GENÇDAL, HAZAL BERRAK; Nuray, Said Enes; Yücel, Melda
In all kinds of site investigation reports prepared to acquire the current situation of the project site, it is a common fact to perform the consistency tests which are specialized as Atterberg limit tests. Consistency can be defined as an important term, especially for fine-grained soils, to appoint the current state of the water content of soil formation in the field. Based on the ease and cost-effectiveness of the Atterberg tests, it has become a traditional solution to determine the fundamental design properties such as the rigidity and strength of the soil formation with the use of empirical approaches that are developed according to them. In this context, “compaction” can be an interesting term to investigate the appropriateness of determination of special characteristics of the phenomenon such as the optimum water content and the maximum dry unit weight with the development of a new perspective based on a simplest experimental process formed with only the evaluation of water content. Because it is a complicated and time-consuming process to apply the compaction test beginning of the sample preparation step to the ultimate evaluation step. Hence, in this paper, an integrated study is performed for highly plastic clays to acquire the consistency and the compaction properties together with a direct relationship. A huge database was prepared according to the data’s given in the well-accepted literature sources by the transmission of liquid limit and plastic limit test results conducted for only the high plastic clays. Besides, simple equations are tried to be obtained to calculate the plasticity index and approximations are proposed to find the maximum dry unit weight and the optimum water content of the soil, respectively. As a result, the applicability of both the regression analysis and the artificial neural network studies to the attainment process of both consistency characteristics and compaction problem were compared with each other to procure a reliable determination process. © 2021, The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.
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Optimization and Modeling of Microwave-Assisted Extraction of Curcumin and Antioxidant Compounds From Turmeric by Using Natural Deep Eutectic Solvents
(Elsevier Sci Ltd., 2021) Doldolova, Khadija; Bener, Mustafa; Lalikoğlu, Melisa; Aşçı, Yavuz Selim; ARAT, REFİK; Apak, Reşat
Natural deep eutectic solvents (NADES) have recently come to the fore as new green solvents for foods, cosmetics and pharmaceuticals due to their unique solvation power and low toxicity. Turmeric extracts were prepared using the microwave assisted extraction method (MAE) using five NADES containing binary combinations of choline chloride, lactic acid, fructose, and sucrose. The MAE method was optimized and modeled by using response surface methodology to obtain maximum total antioxidant capacity (TAC) and curcumin contents (CC) in extracts for each NADES. All NADES extracts, except NADES-1 containing fructose and cholin chloride, exhibited higher TAC and CC than those in 80% methanol:water which was the preferred solvent in literature. NADES solvents did not interfere with subsequent antioxidant capacity measurements using the CUPRAC method. The proposed MAE is a potentially efficient and sustainable procedure in pharmaceutical and food industries for the extraction of antioxidants and curcumin from turmeric.
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Seismic Collapse Performance of a Full-Scale Concrete Building with Lightly Reinforced Columns
(Asce-Amer Soc Civil Engineers, 2021) Töre, Erkan; Demir, Cem; CÖMERT, MUSTAFA; İlki, Alper
Brittle failure of lightly reinforced concrete columns is one of the primary reasons for partial or total collapse of substandard existing buildings subjected to earthquake loading. This study presents collapse performance of a full-scale building that was performed to gain insight into the seismic behavior and the collapse mechanisms of nonductile buildings with lightly reinforced concrete columns. The three-story building was tested under displacement-controlled quasi-static reversed cyclic loading followed by a lateral pushover loading up to realization of the total collapse. In addition to the poor reinforcement details, columns had high axial load-to-axial capacity ratios as also observed in many existing substandard buildings. During the test, severe structural damage was observed at 0.9% first-story drift ratio in the cyclic part of the lateral loading and the brittle total collapse of the building took place during the pushover loading at 1.45% first-story drift ratio. In this paper, after the introduction of the test campaign, the formation of structural damage and collapse mechanisms are discussed. In addition, an attempt to predict the behavior and performance of the test building is made by using a column model that considers flexural, slip, and shear deformations. Finally, the obtained analytical results are compared with the experimental observations and results.
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Development of Textile Nanocomposites With Thermal Energy Storage Capability
(Natl Inst Science Communication-Niscair, 2021) Önder, Emel; SARIER, NİHAL
In this study, textile-based composites with dynamic heat storage capability have been designed and developed, in addition to their existing passive insulation capacity. First, poly(acrylonitrile) (PAN) shell and poly(ethylene glycol) (PEG1000 or PEG1500) cores are produced by coaxial electrospinning. Then, these are incorporated into felt based composite structures, which demonstrate enhanced thermal properties as well as buffering function against temperature changes in the environment. The thermal energy absorption and release capacities of the felt composites including PANPEG1000 or PAN-PEG1500 nanowebs are measured as high as 81 Jg(-1) between 33 degrees C and 46 degrees C, and 48 Jg(-1) between 46 degrees C and 54 degrees C respectively. Felt composites, combined with PAN-PEG nanowebs offer forthcoming production applications in the field of dynamic thermal management in various industries.
Open Access
One-Shot Preparation of Polybasic Ternary Hybrid Cryogels Consisting of Halloysite Nanotubes and Tertiary Amine Functional Groups: An Efficient and Convenient Way by Freezing-Induced Gelation
(MDPI, 2021) BEŞLİ, NUR SENA ÖKTEN; Orakdogen, Nermin
A convenient method for the preparation of polybasic ternary hybrid cryogels consisting of Halloysite nanotubes (HNTs) and tertiary amine functional groups by freezing-induced gelation is proposed. Ternary hybrid gels were produced via one-shot radical terpolymerization of 2-hydroxyethyl methacrylate (HEMA), 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS), and DEAEMA in the presence of HNTs. The equilibrium swelling in various swelling media and the mechanical properties of the produced ternary hybrid gels were analyzed to investigate their network structure and determine their final performance. The swelling ratio of HNT-free gels was significantly higher than the ternary hybrid gels composed of high amount of HNTs. The addition of HNTs to terpolymer network did not suppress pH- and temperature-sensitive behavior. While DEAEMA groups were effective for pH-sensitive swelling, it was determined that both HEMA and DEAEMA groups were effective in temperature-sensitive swelling. Ternary hybrid gels simultaneously demonstrated both negative and positive temperature-responsive swelling behavior. The swelling ratio changed considerably according to swelling temperature. Both DEAEMA and HEMA monomers in terpolymer structure were dominant in temperature-sensitive swelling. Mechanical tests in compression of both as-prepared and swollen-state demonstrated that strength and modulus of hybrid cryogels significantly increased with addition of HNTs without significant loss of mechanical strength. Ultimately, the results of the current system can benefit characterization with analysis tools for the application of innovative materials.
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Sepiolite-Embedded Binary Nanocomposites of (Alkyl)Methacrylate-Based Responsive Polymers: Role of Silanol Groups of Fibrillar Nanoclay on Functional and Thermomechanical Properties
(Elsevier, 2021) BEŞLİ, NUR SENA ÖKTEN; Orakdogen, Nermin
Binary nanocomposites filled with fibrillar nanoclay sepiolite (SP) was manufactured using a hydrophilic terpolymer matrix containing 2-(diethylamino)ethyl methacrylate, hydroxyethyl methacrylate and 2-acrylamido-2-methyl-1-propanesulfonic acid. A direct correlation between dispersion of nanofillers, matrix-filler local interaction and improvement of macroscopical mechanical properties was obtained. Mechanical testing revealed that incorporation of SP nanofillers impart to terpolymer matrix a higher degree of reinforcement. Besides fibrous structure of SP, the interactions between silanol (-SiOH) groups present along fibers and terpolymer chains are responsible of extent of reinforcement of nanocomposites. The increase in modulus imparted by incorporation of -SiOH groups reflected a continuous increase in crosslinking density created by terpolymer-nanofiller interactions. Effective crosslink density of nanocomposites was expressed by a cubic polynomial function of SP loading. Swelling ratio of SP nanofiller containing nanocomposites was found to highly decrease at CSP > 3.50%(w/v), with regard to clay-free terpolymers reflecting strong interactions between pendant hydroxyl, carbonly, tertiary amino groups of terpolymer matrix and silanol groups of SP. Excellent pHresponsive swelling was observed in the range of pH 2.1?10.7 and the nanocomposites swelled in acidic conditions depending on the amount of protonated diethyl amino groups. Sensitivity sequence of terpolymer nanocomposites to mono- and di-valent cations with a common anion (Cl-) on swelling was Na+ > K+ > Mg2+. The control of quantity of SP fibers and polymerization temperature allows to manage mechanical properties by just tuning chemical architecture of terpolymer/clay nanocomposites. SP reinforcement of terpolymers can enrich various further characteristics such as targeted delivery of biomolecules or drugs.
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Low Temperature Chemical Treatment of Graphene Films Made by Double Self-Assembly Process to Improve Sheet Resistance
(Elsevier Science, 2021) ARAT, REFİK; Jia, Guobin; Plentz, Jonathan
In this study, a low temperature hydro iodic acid (HI) vapor treatment of the self-assembled graphene films has been developed, and the electrical, optical, structural and morphological properties were investigated by four point probe, UV-Visible spectroscopy, Raman spectroscopy and scanning electron microscopy (SEM). Mono-, doubleand triple-layer of graphene flakes were deposited on glass substrates by using the Double Self-Assembly (DSA) process. The self-assembled graphene films were treated with HI vapors at 40 degrees C for different time intervals between 1 and 24 h. In addition, graphene deposition and HI-vapor treatment (at 40 degrees C for 1 h) was enforced three times to the same substrate. The optical transparency values of the self-assembled mono- (MGFs), double- (DGFs) and triple-layer graphene flakes (TGFs) were measured as 91, 85 and 80%, respectively (values at 550 nm). Due to the HI-vapor treatment, the sheet resistance of MGFs significantly reduced from 1.1 x 10(7) Omega omega square(-1) to 2.9 x 10(4) omega square(-1), the transparency of the graphene films slightly reduced by 2-5%, the I-D/I-G ratio of the DGFs decreased from 1.01 to 0.81, while the I-2D/I-G ratio increased from 0.43 to 0.48 in the Raman spectrum. Thanks to its impressive reducing effect on sheet resistance, HI-vapor treatment can be a suitable method to improve the conductivity of low-cost large area graphene films.
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Solution Processed Transparent Conductive Hybrid Thin Films Based on Silver Nanowires, Zinc Oxide and Graphene
(Elsevier, 2021) ARAT, REFİK; Jia, Guobin; Dellith, Jan; Dellith, Andrea; Plentz, Jonathan
Transparent conductive hybrid thin films based on silver nanowires (AgNW), zinc oxide (ZnO) and graphene were prepared using solution processing methods. For this study, the hexagonal (wurtzite) ZnO particles with a flower-like structure were synthesized by sol-gel reaction using zinc acetate dihydrate as a precursor at room temperature and pH value of 10. Ethanol dispersions of ZnO and commercial AgNW were deposited by spincoating method on glass substrates with fixed parameters to obtain AgNW-ZnO and ZnO-AgNW films, then their surfaces were covered with monolayer graphene flakes (MGFs) using a double self-assembly (DSA) process. The hybrid ZnO-AgNW-MGFs and AgNW-ZnO-MGFs films were characterized by XRD, SEM, UV?vis, four-point probe conductivity measurement, thermal (85 degrees C for 120 h) and long-term (ambient condition for 120 days) stability analyzes. The transmittances of AgNW-ZnO and ZnO-AgNW films were identical at 550 nm (80 %) and their sheet resistances (R-s) values were measured as 20.6 and 21.6 Omega/sq, respectively. After the MGFs deposition, the transmittances of hybrid films reduced to 72.5 and 76.8 %, while their R-s values decreased to 17.6 and 21.4 Omega/sq, respectively. Graphene flakes coating both enhanced the conductivity of hybrid films by improving the connection between silver nanowires and increased the thermal and long-term ambient stability of the films due to its barrier property against oxidation of silver nanowires.

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