Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Article Citation - WoS: 27Citation - Scopus: 31Fluoroacrylate-Aromatic Acrylate Copolymers for Viscosity Enhancement of Carbon Dioxide(Elsevier Ltd., 2019) Kılıç, Sevgi; Enick, Robert M.; Beckman, Eric J.The effect of the structure of aromatic acrylate-fluoroacrylate copolymers on CO2 viscosity at elevated pressures was investigated. These copolymers were all found to be miscible with CO2 at pressures between 10-15 MPa (295 K) and induce an increase in the viscosity to some degree. It appears that stacking of aromatic rings is the key factor in viscosity enhancement. The results showed that viscosity of the solution increases with the increasing content of the aromatic acrylate unit in the copolymer, but a point is reached beyond which additional comonomer causes the relative viscosity to drop, suggesting that the aromatic rings associate through intramolecular rather than intermolecular interactions beyond the optimum value. The most effective CO2 thickener identified in this study was the 29% phenyl acrylate-71% fluoroacrylate copolymer. However, the presence of a spacer (methyl or ethyl) between the backbone and the aromatic group substantially diminished the viscosity enhancement.Article Effect of Temperature on Stability of Lipid Microbubbles(Turkish Chemical Society, 2019) Kılıç, SevgiThe effect of temperature on stability of lipid microbubble shell containing polyethyleneoxide-40-stearate (PEG40St) as emulsifier was investigated. Microbubbles at 4 °C were subjected to different temperatures up to 48 ºC (down-to-up) and it was found that both the number and the size of microbubbles remained unchanged in the population up to a certain time, so called “onset time”. The onset time was about 6 hours at 10 °C, 2 hours at 20 °C and shorter at elevated temperatures, exhibiting an exponential decrease with increasing temperature. Once the onset time was reached, the number of microbubbles started to decrease and the average size of the population started to increase. Observation of single microbubbles on a constant temperature heating stage exhibited that each microbubble had its own onset time, with the smaller microbubbles vanishing earlier than the larger ones. The Langmuir monolayer studies showed that hydration degree of the emulsifier PEG chains decreased with temperature, causing them go through conformational changes and subsequently destabilization of the shell. By subjecting the freshly produced microbubbles directly to the desired temperatures in up-to-down fashion, more stable microbubbles were able to be produced, with their onset time increased 40% at 10 °C to 500% at 38 °C. Overall, the results suggest that the new strategies need to be developed to control the collapse process in the microbubble shell resulting from the conformational changes in the PEG chains of the emulsifier for the design of more stable microbubbles. © 2019, Turkish Chemical Society. All rights reserved.Article Citation - WoS: 15Citation - Scopus: 13Phase Behavior of Dspc/Peg40st Mixtures at Higher Emulsifier Contents(Elsevier Ltd., 2018) Kılıç, Sevgi; Bölükçü, Elif ŞenizPhase behaviors of 1,2-Distearoyl-sn-glycero-3-phosphocholine (DSPC) and polyoxyethylene(40)stearate (PEG40St) were investigated with Langmuir monolayer isotherms and Brewster angle microscopy (BAM) imaging at DSPC/PEG40St molar ratios ranging from 9:1 to 5:5. Two plateaus were found in the Langmuir isotherms which were relatively shorter for the 9:1 mixture and extended significantly by increasing the PEG40St content, indicating that the PEG40St squeezed out whereas more emulsifier retained in the monolayer at higher PEG40St contents. A strong hysteresis was observed when the mixed monolayers were subjected to compression-expansion cycles. The degree of hysteresis for the first cycles also increased with increasing PEG40St content in the monolayer. Gray scale intensities in the Brewster angle microscopy images were determined for pure DSPC and pure PEG40St and a scale was established to better interpret the morphologies for the mixtures. Bud and vessels formed during the PEG40St squeezed out upon compression. Upon expansion, PEG40St and DSPC is reappeared on the monolayer. When considered BAM images together with the Langmuir isotherm, PEG40St molecules were found to be well distributed within the DSPC molecules at lower DSPC/PEG40St mole ratios and mostly phase separated at higher mole ratios. It was concluded that higher PEG40St content would be advantageous for the design of an efficient and cheaper ultrasound contrast agents.Article Citation - WoS: 4Citation - Scopus: 5Quantification of Peg40st Squeeze Out From Dspc/Peg40st Monolayers at Higher Molar Ratios(Elsevier Ltd., 2018) Kılıç, SevgiMixtures of 1,2 Distearoyl-sn-glycero-3-phosphocholine (DSPC) and polyoxyethylene-40-stearate (PEG40St) were prepared at different molar ratios and their miscibility were investigated using Langmuir isotherms. Pure DSPC monolayer exhibited a liquid-condensed (LC) phase whereas PEG40St monolayer exhibited liquid-expanded (LE) phase at the air-water interface at 22 ± 2 °C. At the collapse pressure of 33 mN/m, the PEG40St mean molecular area was calculated to be 28 Å2/molecule for 9:1 composition and 50 Å2/molecule for 5:5 composition, showing an increasing trend with the emulsifier content. A quantification method was developed to estimate the squeeze out amount of PEG40St from Langmuir isotherms of the DSPC/PEG40St mixtures at different molar ratios. Almost 93%, 82%, and 53% of PEG40St displaced for the 9:1, 7:3, and 5:5 mixtures, respectively, at the end of the first collapse plateau and showed a decreasing trend with the PEG40St content. Remaining PEG40St squeezed out at the end of the second collapse plateau, where 20% of PEG40St still contained within the 5:5 composition. It was concluded that increasing PEG40St content would be advantageous to design more stable lipid based microbubbles.Article Citation - Scopus: 1Synthesis of Stable Nano Calcite(Turkish Chemical Society, 2018) Kılıç, SevgiSynthesis of calcium carbonate (CaCO3) particles in the presence of a population of carbon dioxide (CO2) bubbles was investigated in the calcium hydroxide (Ca(OH)2) solution, which is a natural stabilizer for CaCO3. Possible chemical speciation reactions were presented for an inorganic synthesis of hollow nano-CaCO3 particles. In the progress of CaCO3 synthesis, some of the particles started to dissolve at their edges and turned into hollow nano-CaCO3 particles. Some of the pores closed at the end of crystallization as a result of dissolution-recrystallization mechanism. Hollow nano-CaCO3 particles with sizes of about 300 nm were synthesized with a narrow size distribution. It was concluded that the hollow nano-CaCO3 particles could be advantageous due to lower weights and higher surface areas.Article Citation - WoS: 23Citation - Scopus: 31Nano-Caco3 Synthesis by Jet Flow(Elsevier Ltd., 2017) Ülkeryıldız, Eda; Kılıç, Sevgi; Özdemir, EkremA new methodology was introduced to produce hollow nano calcite particles in homogenous size distribution without aggregation. The design consisted of a jet flow system in which the crystallization region was separated from the stabilization region. The newly produced nano CaCO3 particles of about 140 nm were removed from the crystallization region as quickly as possible into the stabilization region before aggregation or crystal growth. In the stages of crystallization, the particles started to dissolve from their edges which opened-up the pores inside the particles. At the late stages of crystallization, the open pores closed. These particles were stable in Ca(OH)2 solution and no aggregation was detected. Different particles with different morphologies can be produced by adjusting the stages in the crystallization.Article Citation - WoS: 48Citation - Scopus: 52Stability of Caco3 in Ca(oh)2 Solution(Elsevier Ltd., 2016) Kılıç, Sevgi; Toprak, Görkem; Özdemir, EkremThe effect of calcium hydroxide (Ca(OH)2) on the stability of calcium carbonate (CaCO3) particles was investigated with respect to the surface potential and particle size. Both CaCO3 and Ca(OH)2 were dissolved in ultrapure water at concentrations up to 100 mM. The solubility limits were about 18 mM for Ca(OH)2 and about 0.13 mM for CaCO3 at 23 °C in water. Dissolution of commercial CaCO3 in 10 mM of Ca(OH)2 solution and dissolution of Ca(OH)2 in 10 mM of CaCO3 slurry were also studied at similar conditions. Conductivity, pH, zeta potential, and average particle sizes were measured for each solution. The morphological characteristics of the particles were analyzed by the SEM images. It was found that the zeta potential of CaCO3 particles was greater than + 30 mV when they were placed in the Ca(OH)2 solution compared to a zeta potential value of - 10 mV in water. It was concluded that the Ca(OH)2 solution is a stabilizer for the CaCO3 particles.Article Citation - WoS: 20Citation - Scopus: 23Rice-Like Hollow Nano-Caco3 Synthesis(Elsevier Ltd., 2016) Ülkeryıldız, Eda; Kılıç, Sevgi; Özdemir, EkremWe have shown that Ca(OH)2 solution is a natural stabilizer for CaCO3 particles. We designed a CO2 bubbling crystallization reactor to produce nano-CaCO3 particles in homogenous size distribution without aggregation. In the experimental set-up, the crystallization region was separated from the stabilization region. The produced nanoparticles were removed from the crystallization region into the stabilization region before aggregation or crystal growth. It was shown that rice-like hollow nano-CaCO3 particles in about 250 nm in size were produced with almost monodispersed size distribution. The particles started to dissolve through their edges as CO2 bubbles were injected, which opened-up the pores inside the particles. At the late stages of crystallization, the open pores were closed as a result of dissolution-recrystallization of the newly synthesized CaCO3 particles. These particles were stable in Ca(OH)2 solution and no aggregation was detected. The present methodology can be used in drug encapsulation into inorganic CaCO3 particles for cancer treatment with some modifications.Article Citation - WoS: 14Citation - Scopus: 15Effect of Carbonic Anhydrase on Caco3 Crystallization in Alkaline Solution(American Chemical Society, 2016) Molva, Murat; Kılıç, Sevgi; Özdemir, EkremThe effect of bovine carbonic anhydrase (CA) on calcium carbonate (CaCO3) crystallization was investigated. A new method was developed to estimate the biocatalytic activity of CA in alkaline solution. The CA was immobilized within polyurethane (PU) foam, and compared its biocatalytic activity with the free-CA and bare-PU foam. A minireactor was created in a calcium hydroxide (Ca(OH)2) solution in order to control the CO2 transfer rate, and reproducible results were obtained. It was found that the free-CA lost its activity in less than 6 min at pH 12.5 in alkaline Ca(OH)2 solution. The CaCO3 crystallization rates for the immobilized-CA were found to be a U-shape, relatively lower at lower immobilized-CA amounts compared to those for the free-CA and bare-PU foam and higher when the amount of immobilized-CA increased. It was concluded that a higher immobilized-CA amount is required to accelerate the CaCO3 crystallization rates in Ca(OH)2 solution.Article Citation - WoS: 40Citation - Scopus: 46Influence of Tert-Amine Groups on the Solubility of Polymers in Co2(Elsevier Ltd., 2009) Kılıç, Sevgi; Wang, Yang; Johnson, J. Karl; Beckman, Eric J.; Enick, Robert M.There is a need to develop new, non-fluorous polymers that are highly soluble in CO2. Experimental evidence indicates that tertiary amine and pyridine groups may exhibit favorable Lewis acid-Lewis base type interactions with CO2. It is therefore reasonable to assume that incorporation of tertiary amines into the side chain or backbone of non-fluorous polymers may impart a degree of CO2-solubility to the polymer. We present experimental results for eight different tert-amine-containing polymers. Of these polymers, only propyl dimethylamine-functionalized poly(dimethylsiloxane) is soluble in CO2 at temperatures and pressures accessible in our experiments, but even this polymer is less soluble than non-functionalized poly(dimethylsiloxane) at the same chain length. We have performed ab initio calculations on tertiary amine-containing moieties representative of some of the polymers examined experimentally. Our calculations confirm that amine-CO2 interactions are indeed energetically favorable. However, we also find that the moiety self-interactions are typically more favorable than the CO2-moiety interactions. This indicates that the lack of solubility of amine-containing polymers in CO2 is a direct result of strong polymer-polymer interactions.