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Yayın Vapor-induced film formation from low-T-g particles for different solvent compositions(Elsevier Inc, 2006-05-15) Arda, Ertan; Kara, Selim; Saraç, Ayfer; Pekcan, Mehmet ÖnderThe photon transmission method was used to study latex film formation from poly(vinyl acetate) (PVAc) particles induced by two different solvents. Films with the same latex content were prepared from PVAc particles and exposed to vapor of ethanol-water and acetone-water mixtures in various compositions. Transmitted photon intensities, I-tr, from these films increased with increasing vapor exposure time. The increase in I-tr is attributed to the increase in crossing density at the polymer-polymer junction. The Prager-Tirrell model was employed to obtain the back-and-forth frequency, v, of the reptating polymer chain during film formation induced by solvent vapor. It was observed that the produced v values increase as the solvent content is increased for both solvents. Abilities of both solvents to form films were interpreted with the solubility parameters of the solvents and the PVAc.Yayın A photon transmission study for film formation from poly(vinyl acetate) latex particles with different molecular weights(John Wiley & Sons Inc, 2007-10-15) Arda, Ertan; Kara, Selim; Pekcan, Mehmet ÖnderThe photon transmission technique was used to monitor the temperature evolution of film formation from poly(vinyl acetate) (PVAc) latex particles with two different molecular weights. Two sets of latex films were prepared below the glass transition temperature (T-g) of PVAc, which are named as low (LM) and high molecular weight (HM) films. These films were annealed at elevated temperatures above the Tg of PVAc for various time intervals. It is observed that transmitted photon intensity (I-tr) from these films increased as the annealing temperature was increased. Onset temperatures (T-H) at given times (tau H) for starting the optical clarity of LM and HM films were measured and used to calculate the healing activation energies (Delta H) for the PVAc minor chains, and found to be as 28.1 kcal/mol and 27.7 kcal/mol, respectively. The increase in the transmitted photon intensity, Itr above TH was attributed to the increase in the number of disappeared interfaces between the deformed latex particles. Prager-Tirrell (PT) model was employed to interpret the increase in the crossing density of chains at the junction surfaces. The interdiffusion (backbone) activation energies (Delta E) were measured and found to be 177.5 kcal/mol and 210.7 kcal/mol for a diffusing PVAc chains across the junction surface of LM and HM latex films, respectively.Yayın Time evolution of film formation from polystyrene particles: a percolation approach(Springer, 2005-12) Uğur, Şaziye; Pekcan, Mehmet ÖnderThis work reports the film formation process from surfactant-free polystyrene (PS) latex particles. Steady state fluorescence and photon transmission techniques were used to study the evolution of film formation. The films were prepared from fluorescein (F)-labeled PS latex particles at room temperature and annealed in 2.5-min-time intervals above the glass transition temperature (T-g) of PS. Fluorescence intensity (I-F) from F was measured after each annealing step to monitor the stages of film formation. Evolution of transparency of latex films was monitored by using the photon transmission intensity, I-tr. Drastic increase in I-tr and I-F above the critical annealing times t(r) and t(c) respectively, were attributed to the percolation behavior of the PS material. Critical exponents, beta, of percolation clusters were measured and found to be around 0.31 and 0.37 for Itr and IF measurement, respectively, which were attributed to the site percolation model.Yayın Film formation from TiO2-polystyrene latex composite: a fluorescence study(Taylor & Francis Group, 2007-03-01) Uğur, Şaziye; Sunay Yapışkan, Münüre Selin; Tepehan, Fatma Zehra; Pekcan, Mehmet ÖnderThis work reports the use of the steady state fluorescence (SSF) technique for studying film formation from TiO2 covered polystyrene (PS) latex particles. The composite films were prepared from pyrene (P)-labeled PS particles by covering them with TiO2 at room temperature and then annealed at elevated temperatures in 10 min time interval above glass transition (T-g) temperature of polystyrene. Five different composite films were studied in various TiO2 layer contents. Fluorescence intensities Ip from P were measured after each annealing step to monitor the stages of film formation. Films showed considerable increase in Ip above the certain onset temperature called minimum film forming temperature, T-0. Void closure and interdiffusion stages were modeled and related activation energies were determined and found to be 23.12 and 92.80 kJ mol(-1), respectively.Yayın Fluorescence study on Al2O3-polystyrene latex composite film formation(John Wiley & Sons Inc, 2005-06) Uğur, Şaziye; Salman, Oğuz Umut; Tepehan, Galip Gültekin; Tepehan, Fatma Zehra; Pekcan, Mehmet ÖnderThis work reports a steady state fluorescence (SSF) technique for studying film formation from mixture of Al2O3 and polystyrene (PS) latex particles. The composite films were prepared from dispersion of pyrene (P)labeled PS particles in Al2O3 solution at room temperature and annealed at elevated temperatures in 10-min time interval above glass transition (T-g) temperature of polystyrene. Nine different composites film were studied in various latex contents. Fluorescence intensities (I-P) from P were measured after each annealing step to monitor the stages of film formation. No variations in I-p were detected for the films prepared with higher than 33 wt% Al2O3 content. However films prepared below 33 wt% Al2O3 content show considerable increase in I-P above the certain onset temperature called minimum film forming temperature, To. Healing temperatures T., were determined from the maxima of I-P. Void closure and interdiffusion stages were modeled and related activation energies were determined and found to be 20 and 97 kJ.mol(-1), respectively.Yayın Film formation from nano-sized polystrene latex covered with various TiO2 layers(Wiley, 2006-12) Uğur, Şaziye; Sunay, Selin; Elaissari, Abdelhamid; Tepehan, Fatma Zehra; Pekcan, Mehmet ÖnderSteady-state fluorescence technique was used for studying film formation from TiO2 covered nano-sized polystyrene latex particles. The composite films were prepared from pyrene (P)-labeled PS particles by covering them with various layers of TiO2 at room temperature. These films then annealed at elevated temperatures in 10 min time interval above glass transition (T-g) temperature of polystyrene. Five different composite films were studied in various TiO2 layer contents. Fluorescence emission intensity, I-P from P was measured after each annealing step to monitor the stages of film formation. Films present significant increase in I-P above the certain onset temperature called minimum film forming temperature, To. However, at higher annealing temperatures, I-P showed a decrease. Increase and decrease in I-P were modeled by void closure and interdiffusion processes and related activation energies were determined, respectively. Dissolution of annealed PS film, with high TiO2 content presented a nice, ordered nanosized ceramic structure, which may predict the construction of nano-layer photonic crystals.Yayın Film formation from nano-sized polystyrene latex particles(John Wiley & Sons Ltd, 2005-05) Uğur, Şaziye; Elaissari, Abdelhamid; Pekcan, Mehmet ÖnderThis work reports on the steady state fluorescence (SSF) technique for studying film formation from surfactant-free, nano-sized polystyrene (PS) latex particles prepared via emulsion polymerization. The latex films were prepared from pyrene M-labeled PS particles at room temperature and annealed at elevated temperatures in 5, 10, 15, 20 and 30 min time intervals above the glass transition temperature (T-g) of PS. During the annealing processes, the transparency of the film was improved considerably. Monomer and excimer fluorescence intensities, I-p and I-E respectively, from P were measured after each annealing step to monitor the stages of film formation. Evolution of transparency of the latex films was monitored by using photon transmission intensity, It,. Void closure and interdiffusion stages were modeled and related activation energies were determined and found to be 10.3 and 50.3 kJ mol(-1). Void closure temperatures, T-v, were determined from the minima of I-tr value. CopyrightYayın Ceramic encapsulated latex composites(Elsevier Inc, 2006-04-15) Uğur, Şaziye; Pehlivan, Esat; Tepehan, Fatma Zehra; Pekcan, Mehmet ÖnderThis work reports the encapsulation of latex particles in Al(2)O(3)-polystyrene (PS) composite films. These films were prepared from PS particles in Al(2)O(3) dispersion at room temperature in various latex contents. Composite films were annealed at elevated temperatures in 10 min time interval above the glass transition temperature (T,,) of polystyrene. Transmitted photon intensities. I(tr) were monitored after each annealing step. AFM micrographs were also used to observe the physical changes of the composite films during annealing. It was observed that latex particles are encapsulated above a critical Al(2)O(3) content of 33 wt% which corresponds to the critical occupation probability of p(c) = 0.33 at which the film obey the site-percolation model with a critical exponent of 0.45. Below pc it was seen that complete latex film formation process took place, where transparency of the film was increased by annealing.Yayın Jet motorlarinda uygulanan efüzyon film soğutma akış karakteristiklerinin PIV yöntemiyle incelenmesi(Sürdürülebilir Havacılık Araştırma Derneği, 2018-12-01) Yalçın, Sinan Eren; Yakın, Evren Yılmaz; Kuşhan, Melih Cemal; Karakoç, Tahir HikmetEfüzyon soğutma tekniği, modern yanma odalarında kullanılan en gelişmiş soğutma teknolojisidir. Bu çalışmada 1/9 ölçekte boyutlandırılmış bir yanma odası cidarında, efüzyon film soğutmanın ana akım üzerine etkileri Parçacık Görüntülemeli Hız Ölçümü (PIV) yöntemi kullanılarak deneysel olarak incelenmiştir. Bu amaçla bu çalışmada, ana akım Reynols (Re) sayısı 15000 değerine sabitlenmiş, 2.25 mm delik çaplı efüzyon plakası için, delik açıları 30° ve 45° değişiyor iken, efüzyon plakasından 7 farklı üfleme debisi için testler gerçekleştirilmiş ve soğutma filmi oluşumu incelenmiştir. PIV deneylerinden elde edilen veriler incelenerek, çapraz akışta jet karışımlarında meydana gelen akış haritası çıkarılmıştır ve film oluşma karakteristiği belirlenmiştir. Akış haritası sonuçlarına göre, soğutucu deliklerden düşük debili üflemelerde jetler ana akıma yenik düşmekte, tam tersine yüksek debilerde jetler ana akımla eş baskın özellikte olduğu için, film oluşumu gözlemlenmiştir. Ayrıca soğutma deliklerinin açılarının artışının film oluşumuna olumsuz etkisi gösterilmiştir.Yayın Film formation stages for poly(vinyl acetate) latex particles: a photon transmission study(Springer-Verlag, 2006-07) Kara, Selim; Pekcan, Mehmet Önder; Saraç, Ayfer; Arda, ErtanPhoton transmission technique was used to monitor the evolution of transparency during film formation from poly(vinyl acetate) (PVAc) latex particles. The latex films were prepared below the glass transition temperature (T-g) of PVAc. These films were annealed at elevated temperatures in various time intervals above the T-g of PVAc. It is observed that transmitted photon intensity (I-tr) from these films increased as the annealing temperature is increased. It is seen from I (tr) curves that there are two film formation stages. These successive stages are named void closure (viscous flow) and interdiffusion. The activation energies for viscous flow (Delta H) and backbone motion (Delta E (b)) were obtained by using well-defined models. The averaged values of the backbone (Delta E (b)) and the viscous flow activation energies (Delta H) were found to be 188.6 and 5.6 kcal/mol, respectively. The minimum film formation (tau (M),T (M)) and healing points (tau (H),T (H)) were determined. Minimum film formation (Delta E (M)) and healing activation energies (Delta E (H)) were measured using these time-temperature pairs. Delta E (M) and Delta E (H) were found to be 32.5 and 28.3 kcal/mol, respectively.
