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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 Percolation approach to film formation from surfactant-free polystyrene particles(Taylor & Francis, 2005-09) Uğur, Şaziye; Pekcan, Mehmet ÖnderIn this study, a film formation process from surfactant-free polystyrene (PS) latex particles is reported. Steady state fluorescence (SSF) and photon transmission (UVV) techniques were used to study the evolution of film formation. The latex films were prepared from pyrene (P)-labeled PS particles at room temperature and annealed at time intervals of 2.5 min above the glass transition temperature (T-g) of PS. During the annealing processes, the transparency of the film changed considerably. Fluorescence intensity (I-0P) from P was measured after each annealing step to monitor the stages of film formation. Evolution of transparency of latex films were monitored by using photon transmission intensity, I-tr. A drastic increase in I-tr and I-0P above the critical annealing times, t(r) and t(c) were attributed, respectively to percolation behavior of PS material from one side to the other side of the latex film. Critical exponents, beta of percolation clusters were measured and found to be around 0.35 and 0.25 for I-tr and I-0P measurements, respectively.Yayın Films formed from polystyrene latex/clay composites: A fluorescence study(Springer New York, 2005-07) Uğur, Şaziye; Alemdar, Ayşe; Pekcan, Mehmet ÖnderThis study reports a steady-state fluorescence (SSF) technique for studying film formation from surractant-free polystyrene (PS) latex and Na-montmorillonite (SNaM) composites. The composite films were prepared from pyrene (P)-labeled PS particles and SNaM clay at room temperature and annealed at elevated temperatures in 10-min intervals above glass transition temperature (T-g) of polystyrene. During the annealing processes, the transparency of the fllm improved considerably. Scattered light (I-s) and fluorescence intensity (I-s) from P were measured after each annealing step to monitor the stages of film formation. Evolution of transparency of composite films was monitored by using photon transmission intensity, I-tr Scanning electron microscopy (SEM) was used to detect the variation in physical structure of annealed composite-films. Minimum flIm formation temperature, T-o, and healing temperatures, T-h, were determined. Void closure and interdiff-usion stages were modeled and related activation energies were determined. It was observed that both activation energies increased as the percent of SNaM was increased in composite films.Yayın Film formation from PS latex doped PNIPAM hydrogels at various heating and cooling rates(VSP BV, Brill Academic Publishers, 2008-05-01) Uğur, Şaziye; Yargı, Önder; Pekcan, Mehmet ÖnderFilm formation from polystrene (PS) latex doped poly(N-isopropylacrylamide) (PNIPAM) hydrogels was studied by using photon transmission technique. The transmitted light intensity, It, was monitored during film formation process. Films were prepared by annealing, 10 wt% PS doped PNIPAM particles at five different heating and cooling rates at temperatures ranging from 10 to 100 degrees C. I-tr presented a hysteresis loops during heating-cooling cycles, which were explained by void closure and void reconstruction processes. The corresponding activation energies were measured during reversible film formation process. Void closure and void reconstruction models were introduced to produce the activation energies.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.Yayın Effect of annealing rate on film formation from poly(vinyl acetate) latex particles(Taylor & Francis Ltd, 2008) Arda, Ertan; Kara, Selim; Pekcan, Mehmet ÖnderThe photon transmission technique was used to monitor the time and temperature evolution of 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 various annealing rates above the Tg of PVAc. It was observed that transmitted photon intensity (I-tr) from these films increased at all annealing rates as the annealing time and temperature are increased. The increase in the I-tr is attributed to the increase in crossing density at the junction surface. The healing points (tau(H), T-H) were determined for various annealing rates and the healing activation energy (Delta H) was measured and found to be 43.4 kcal/mol. The interdiffusion (backbone) activation energies (Delta E) and reptation frequencies (nu) of PVAc chains were measured. The averaged value of Delta E was found to be 226.6 kcal/mol. It is observed that Delta E is unchanged but nu is increased as increasing the annealing rates.
