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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 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.
