Biyoinformatik ve Genetik Bölümü Koleksiyonu
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Browsing Biyoinformatik ve Genetik Bölümü Koleksiyonu by Subject "Acrylamide"
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Article Citation Count: 22Critical Exponents of Gelation and Conductivity in Polyacrylamide Gels Doped by Multiwalled Carbon Nanotubes(Taylor & Francis Ltd, 2010) Aktas, Demet Kaya; Evingür, Gülşen Akin; Pekcan, ÖnderPolyacrylamide (PAM) doped by multiwalled carbon nanotube (MWNT) gels were prepared with different amounts of MWNTs varying in the range between 0.1 and 15 wt%. The PAM-MWNT composite gels were characterized by the steady state fluorescence technique (SSF). The alternative electrical conductivity (AC) of PAM-MWNT composite gels was measured by the dielectric spectroscopy technique. Observations around the gel point t(gel) for PAM-MWNTs composite gels showed that the gel fraction exponent beta obeyed the percolation result. The critical exponent r of AC electrical conductivity for the composite PAM-MWNT gel was also measured and found to be about 2.0 which agrees with a random resistor network. (C) Koninklijke Brill NV Leiden 2010Article Citation Count: 6Drying of Polyacrylamide Composite Gels Formed with Various Kappa- Carrageenan Content(Springer/Plenum Publishers, 2011) Evingür, Gülşen Akın; Pekcan, ÖnderDrying of polyacrylamide (PAAm)-kappa-carrageenan (kappa C) composite gels were monitored by using steady-state fluorescence technique. Disc shaped gels were formed from acrylamide (AAm) and N N'- methylenebisacrylamide(Bis) with various kappa- carrageenan (kappa C) contents by free radical crosslinking copolymerization in water. Pyranine (P) was doped as a fluorescence probe and scattered light I (sc) and fluorescence intensities I were monitored during drying of these gels. It is observed that fluorescence intensity of pyranine increased as drying time is increased for all samples. The increase in I was modeled using Stern- Volmer equation and diffusion with moving boundary. It is found that desorption coefficient D decreased as kappa C contents were increased. Supporting gravimetrical and volumetric experiments were also carried out during drying of PAAm- kappa C composite gels.Article Citation Count: 4Drying of polyacrylamide-multiwalled carbon nanotube (MWNT) composites with various MWNTs contents: a fluorescence study(Walter De Gruyter Gmbh, 2013) Evingür, Gülşen Akin; Pekcan, ÖnderWe studied the drying of polyacrylamide (PAAm)-multiwalled carbon nanotube (MWNT) composites prepared by free radical crosslinking copolymerization in water with a steady state fluorescence technique. Composite gels were prepared at room temperature with pyranine (Py) doped as a fluorescence probe. Drying experiments were performed in air at various MWNT contents by real time monitoring of the Py fluorescence intensity (I) which increased as the drying proceeded. The Stern-Volmer equation combined with the moving boundary diffusion model was used to explain the behavior of I during drying. It was observed that the desorption coefficient (D) increased as the temperature increased. Drying energies (Delta E) were measured for the drying processes for each MWNT content gel by using fluorescence gravimetrical and volumetric methods. It is understood that Delta E values decrease by increasing MWNT content until 1 wt % MWNT and then increase above the level of this threshold value. The energy of drying is strongly correlated with the MWNT content in the composite. Delta E drops to its lowest value at which conducting cluster starts to appear.Book Part Citation Count: 0EFFECT OF CONTENT AND TEMPERATURE ON THE PHASE TRANSITIONS OF POLYMER COMPOSITES DOPED BY KAPPA CARRAGEENAN AND ALGINATE(Elsevier Academic Press Inc, 2016) Evingür, Gülşen Akın; Pekcan, Önder[Abstract Not Available]Article Citation Count: 12Elastic percolation of swollen polyacrylamide (PAAm)-multiwall carbon nanotubes composite(Taylor & Francis Ltd, 2012) Evingür, Gülşen Akin; Pekcan, ÖnderPolyacrylamide (PAAm)-multiwalled carbon nanotube (MWNT) composites were prepared via free radical cross-linking copolymerization with different amounts of MWNTs varying in the range between 0.1 and 50 wt%. The mechanical properties of swollen PAAm-MWNT composites were characterized by the tensile testing technique. A small content of embedded nanotubes dramatically changes the compressive elastic modulus of the composites. Compressive elastic modulus dramatically increases up to 1wt% MWNT on increasing nanotube content and then decreases presenting a critical MWNT value indicating that there is a sudden change in the material elasticity. The critical exponent y of elasticity below the critical MWNT content 1 wt% is found to be 0.58 which is consistent with the suggestions of percolation in the superelastic percolation network for PAAm-MWNT composite.Article Citation Count: 6Elastic Properties of a Swollen PAAm-NIPA Copolymer with Various NIPA Contents(Taylor & Francis, 2014) Evingür, Gülşen Akin; Pekcan, ÖnderCopolymer based on cross-linked polyacrylamide (PAAm) having N-isopropylacrylamide (NIPA) was prepared and their elastic properties were studied as a function of NIPA contents. NIPA content dependency of the shear modulus S of the PAAm-NIPA copolymers due to volume phase transition was measured using tensile testing technique at 30 degrees C. It was observed that its shear modulus and toughness were found to be strongly dependent on NIPA content. It is understood that the shear modulus was found to increase with NIPA contents keeping constant temperature at 30 degrees C. Elastic properties of the PAAm-NIPA copolymers show compositional dependence.Article Citation Count: 3Fractal dimension and phase transition of graphene oxide (GO) doped polyacrylamide(ELSEVIER SCI LTD, 2020) Evingür, Gülşen Akın; Pekcan, ÖnderGraphene Oxide (GO)- Polyacrylamide composites prepared between 5 and 50 mu l GO were performed by Fluorescence Spectroscopy. The phase transition performed on the composites was measured by calculating the critical exponents, beta and gamma, respectively. In addition, fractal analysis of the composites was calculated by a fluorescence intensity of 427 nm. The geometrical distribution of GO in the composites was calculated based on the power law exponent values using scaling models. While the gelation proceeded GO plates first organized themselves into a 3D percolation cluster with the fractal dimension (D-f) of the composite, D-f = 2.63, then After it goes to diffusion limited clusters with D-f = 1.4, its dimension lines up to a Von Koch curve with a random interval of D-f = 1.14.Article Citation Count: 2Gelation of PAAm-PVP composites: A fluorescence study(World Scientific, 2014) Evingür, Gülşen Akin; Kaygusuz, Hakan; Erim, F. Bedia; Pekcan, ÖnderHybrid hydrogels are a new class of composite materials. Polyacrylamide (PAAm) hydrogels are mainly produced by free radical crosslinking copolymerization (FCC) of AAm in the presence of N N'-methylene bis (acrylamide) (BIS) as the crosslinker. Pyranine doped PAAm-poly (N-vinyl pyrrolidone) (PVP) composite were prepared with different amounts of PVP varying in the range between 0.0015 and 0.1 gr. It was observed that pyranine molecules as a fluoroprobe bind to AAm and PVP chains upon the initiation of the polymerization causing the fluorescence spectra of the bonded pyranines shift to the shorter wavelengths. The sol-gel phase transition and its universality were monitored and tested as a function of PVP contents. Observations around the critical point show that the gel fraction exponent beta agreed with the percolation result for below 0.025 gr PVP contents. However classical result was observed above 0.0125 gr PVP content.Article Citation Count: 3Kinetic models for the dynamical behavior of polyacrylamide (PAAm)-kappa-carrageenan (kappa C) composite gels(Springer, 2015) Evingür, Gülşen Akın; Pekcan, ÖnderA fluorescence method was employed for studying the drying and swelling of PAAm-kappa C composite gels which were formed from acrylamide (AAm) and N N'- methylenebisacrylamide (BIS) with various kappa-carrageenan (kappa C) contents by free radical crosslinking copolymerization in water. Composite gels were prepared at 80 A degrees C with pyranine (Py) as a fluorescence probe. Scattered light I (sc) and fluorescence emission intensities I (em) were monitored during drying and swelling of these gels. The fluorescence intensity of pyranine increased and decreased as drying and swelling time are increased respectively for all gel samples. The Stern-Volmer equation combined with moving boundary and Li-Tanaka models were used to explain the behavior of I (em) during drying and swelling processes respectively. It is found that the desorption coefficient D (d) decreased as kappa C contents were increased for a given temperature during drying. However the cooperative diffusion coefficient D (s) presented exactly the opposite case. Conventional gravimetrical and volumetric experiments were also carried out during drying and swelling of PAAm-kappa C composite gels. It was observed that D (d) and D (s) values measured with the fluorescence method were found to be much larger than they were measured with the conventional methods.Article Citation Count: 14Mechanical properties of graphene oxide-polyacrylamide composites before and after swelling in water(Springer, 2018) Evingür, Gülşen Akin; Pekcan, ÖnderPolyacrylamide (PAAm) hydrogels have been proposed for use as promising biomaterials in biomedical and tissue engineering but their poor mechanical and water-retention properties have hindered their development. Graphene oxide (GO) an excellent nanofiller was added to PAAm to produce mechanically strong GO-PAAm composites. The free radical crosslinking copolymerization method was used with GO content varying in the range between 5 and 50 A mu l of GO. The mechanical properties of the GO-PAAm composites are measured by compressive test revealing a decrease in the shear modulus and toughness of the composites above 8 A mu l of GO by increasing GO content.Article Citation Count: 8Monitoring of dynamical processes in PAAm-MWNTs composites by fluorescence method(Taylor & Francis Ltd, 2012) Evingür, Gülşen Akın; Pekcan, ÖnderPolyacrylamide (PAAm)-multi walled carbon nanotube (MWNT) composites were prepared by free radical cross-linking copolymerization in water. Ammonium persulfate and NN'-methylenebis (acrylamide) (BIS) were used as a free radical initiator and a crosslinker respectively. The drying and swelling processes of disc shaped PAAm-MWNT composites were monitored by the steady-state fluorescence technique at various temperatures. Disc shaped composite gels were prepared with pyranine (P) doped as a fluorescence probe. Scattered I-sc and emission light I-em intensities were monitored during drying and swelling of these gels. Since the decrease and increase in I-sc corresponds to the decrease and increase in turbidity of the drying and swelling hydrogel respectively the corrected fluorescence intensity I was introduced to analyse the drying and swelling processes. The Stern-Volmer equation combined with moving boundary and Li-Tanaka models were used to explain the behavior of I during drying and swelling processes respectively. Results indicated that the desorption coefficient D-d decreased by increasing MWNT content until 1 weight percentage of MWNT is reached and then increased above 1 wt% MWNT for a given temperature during drying. However cooperative diffusion coefficient D-s behaved opposite to D-d during swelling at a given temperature. Supporting gravimetric and volumetric experiments were also carried out during drying and swelling of PAAm-MWNT composite gels.Article Citation Count: 16Monitoring the gelation of polyacrylamide-sodium alginate composite by fluorescence technique(Taylor & Francis Ltd, 2012) Evingür, Gülşen Akin; Tezcan, Filiz; Erim, F. Bedia; Pekcan, ÖnderPolyacrylamide (PAAm)-sodium alginate (SA) composite was prepared with different amounts of SA varying in the range between 0.06% and 2% (w/v). The PAAm-SA composite was characterized by the steady-state fluorescence technique. Pyranine was added as a fluoroprobe for monitoring the polymerization. It was observed that pyranine molecules bind to AAm and SA chains upon the initiation of the polymerization. Thus the fluorescence spectra of the bonded pyranines shift to the shorter wavelengths. Fluorescence spectra from the bonded pyranines allowed us to monitor the sol-gel phase transition and to test the universality of the sol-gel transition as a function of SA contents. Observations around the critical point show that the gel fraction exponent beta and the weight average degree of polymerization exponent gamma agreed with the percolation result for (<0.25% (w/v)) SA contents. However classical results were produced at (<2% (w/v)) SA contents.Article Citation Count: 12Superelastic percolation network of polyacrylamide (PAAm)-kappa carrageenan (kappa C) composite(Springer, 2013) Evingür, Gülşen Akin; Pekcan, ÖnderThe elasticity of the polyacrylamide (PAAm)-kappa carrageenan (kappa C) composite was determined as a function of (w/v-%) kappa C content at 40 A degrees C. The gel composites studied contained various percentages (w/v-%) of kappa C. The elasticity of the swollen PAAm-kappa C composite was characterized by using the tensile testing technique. This study investigated the elasticity and the percolation threshold of PAAm-kappa C composite as a function of kappa C content. It is understood that the compressive elastic modulus decreases up to 1 (w/v-%) of kappa C and then increases at contents above 1(w/v-%) of kappa C. The critical exponent of elasticity y was determined between 1 and 1.6 (w/v-%) of kappa C and found to be 0.68. The observed elastic percolation threshold is consistent with the suggested values of the superelastic percolation network.Article Citation Count: 3Temperature Effect on the Elasticity of Acrylamide-n-Isopropylacrylamide Copolymers(Taylor & Francis Inc, 2018) Evingür, Gülşen Akin; Pekcan, ÖnderAcrylamide (AAm) - N-isopropylacrylamide (NIPA) copolymers were prepared via free radical crosslinking copolymerization with various weight percentages (wt%) of AAm and NIPA. The temperature dependence of the compressive elastic modulus G and toughness U-TU- of the PAAm- NIPA copolymers due to a volume phase transition was found using a compressive testing technique. It was observed that the compressive elastic modulus increased comprehensively when the temperature was increased between 30 degrees C and 60 degrees C. The PAAm- NIPA copolymers presented higher values of the compressive elastic modulus than pure NIPA above the lower critical solution temperature (LCST) (NIPA exhibits a volume phase transition from hydrophilic to hydrophobic in water at 31 degrees C) and their compressive elastic modulus and toughness had a strong temperature dependence.
