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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 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 Effects of annealing on morphology of polymer/polymer (PS/PMMA) blend; a fluorescence study(John Wiley& Sons Inc, 2006-05-05) Uğur, Şaziye; Pekcan, Mehmet ÖnderSteady state fluorescence (SSF) technique conjunction with optical microscopy were used to study the morphology of polystyrene (PS)/poly(methyl methacrylate) (PMMA) blend upon annealing above glass transition in elevated time intervals. The PS/PMMA blends were prepared from dissolution of pyrene (P) and naphthalene (N) labeled PS and PMMA particles, respectively. Monte Carlo Simulations were performed to model the N and P fluorescence intensities (I-N and I-P), Using photon diffusion theory. Number of N and P photons (N-N and N-P) emerging from the front surface of the blend are calculated when only N is excited, where N-P photons are combined of photons from radiative (N-PR) and nonradiative (N-PNR) energy transfer processes. Optical microscopy images were taken at each annealing step to Support Our findings from fluorescence measurements.Yayın Poly (styrene) latex/modified na-activated bentonite nanocomposite films: a fluorescence study(Elsevier Science BV, 2008-12) Uğur, Şaziye; Yargı, Önder; Günister, Ebru; Pekcan, Mehmet ÖnderWe studied film formation of composites of surfactant-free polystyrene (PS) nanoparticles and modified Na-activated bentonite (MLB), by steady state fluorescence (SSF) technique. The films were prepared from a mixture of pyrene (P)-labeled PS particles and MLB at various compositions at room temperature. These films were annealed at elevated temperatures above the glass transition (T(g)) temperature of polystyrene for 10 min. Scattered light (I(S)) and fluorescence intensities (I(P)) from P were measured after each annealing step to monitor the stages of film formation. Evolution of transparency of the composite films was monitored by using photon transmission intensity, I(tr) Atomic force microscopy (AFM) was used to detect the variation in physical structure of annealed composite films. The nanocomposite films exhibited a percolation threshold at 20 wt.% MLB content. Below this fraction two distinct film formation stages were observed which are known as void closure and interdiffusion and above this fraction no film formation was detected. At 0-20 wt.% MLB, minimum film formation, T(0), void closure, T(v) and healing, T(h) temperatures were determined. Void closure and interdiffusion stages were modeled and related activation energies were determined. Void closure activation energies decreased as the percent of MLB increased, no variation was observed in backbone activation energies.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 The effect of clay particles on film formation from polystyrene latex(Wiley, 2006-06) Uğur, Şaziye; Alemdar, Ayşe; Pekcan, Mehmet ÖnderFilm formation from surfactant-free polystyrene (PS) latex was performed in the presence of 5% Na-montmorillonite (NaMMT). The composite films were prepared from pyrene (P)-labeled PS particles at room temperature and annealed at elevated temperatures above the glass-transition (T-g) temperature of polystyrene. Scattered light (I-s) and fluorescence intensity (I-p) from P were measured after each annealing step to monitor the stages of composite film formation. Minimum film formation temperature, T-o, and healing temperatures, T-h, were determined. Void closure and interdiffusion stages were modeled and related activation energies were measured. From these results, it was found that the presence of NaMMT in the PS latex film only affects the minimum film formation, but does not affect the void closure and backbone motion activities.Yayın 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 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.
