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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 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 Molecular alignment during gel formation from methyl methacrylate: An excimer fluorescence study(Taylor & Francis Ltd, 2005-05) Kaya Aktaş, Demet; Erdoğan, Matem; Pekcan, Mehmet ÖnderGlass transition during bulk polymerization was studied in free-radical cross-linking copolymerization (FCC) of methyl methacrylate (MMA) using the steady-state fluorescence (SSF) technique. Naphthalene (N) was used as a monomer and excimer forming probe. Changes in the viscosity of the pregel solutions due to gel formation dramatically enhance both monomer and excimer fluorescent yield of N molecules. The reaction time at which the monomer and excimer intensities exhibit a sudden increase corresponds to the reaction time at which the rate of polymerization becomes maximum resulting from the gel effect. This effect was used to study the gelation of MMA, as a function of time, in various N concentrations. The results were interpreted in the view of percolation theory. The gel fraction, beta, and weight average degree of polymerization, gamma, exponents beta=0.40 +/- 0.02 and gamma=1.70 +/- 0.07 were found in agreement with percolation results for both monomer and excimer measurements, 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 Universal behaviour of glass transition exponents in various polymeric systems(VSP BV, Brill Academic Publishers, 2005) Pekcan, Mehmet Önder; Kaya Aktaş, DemetThe fast transient fluorescence (FTRF) technique was used to study the critical exponents during glass transition in free-radical cross-linking copolymerization (FCC). Methyl methacrylate (MMA), ethyl methacrylate (EMA) and various combinations of MMA with EMA were used during FCC experiments. Pyrene (Py) was used as a fluorescence probe and its fluorescence lifetimes from its decay traces were measured during glass transition. Changes in the viscosity of the pre-gel solutions due to glass formation dramatically increased the Py fluorescent lifetimes, which were used to study the glass transition of MMA, EMA and their mixtures as a function of time, at various temperatures and monomer concentrations. The results were interpreted in the view of percolation theory. The critical exponents, beta and gamma, were measured near the glass transition point and found to be around 0.37 +/- 0.015 and 1.69 +/- 0.05, respectively, in all systems studied, which are in good agreement with the static percolation results.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.
