4 sonuçlar
Arama Sonuçları
Listeleniyor 1 - 4 / 4
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 Monitoring diffusion of reptating polymer chains by a direct energy transfer method: A Monte Carlo simulation(Wiley-Blackwell, 2002-07-29) Tüzel, Erkan; Kısacıkoğlu, Kemal Batuhan; Pekcan, Mehmet ÖnderA kinetic Monte Carlo method was used to simulate the diffusion of reptating polymer chains across an interface. A time-resolved fluorescence technique in conjunction with a direct energy transfer method was used to measure the extent of diffusion of dye-labeled reptating polymer chains. The diffusion of donor- and acceptor-labeled polymer chains between adjacent compartments was randomly generated. The fluorescence decay profiles of donor molecules were simulated at several diffusion steps to produce mixing of the polymer chains. Mixing ratios of donor- and acceptor-labeled polymer chains in compartments were measured at various stages (snap-shots) of diffusion. It was observed that for a given molecular weight, the average interpenetration contour length was found to be proportional to the mixing ratio. Monte Carlo analysis showed that the curvilinear diffusion coefficient is inversely proportional to the weight of polymer chains during diffusion.Yayın Particle size and shell thickness dependence of the light intensity enhancement in the cap layers of Ag, Au, Al and SiO2@TiO2 core-shell nanostructures(Wiley-V C H Verlag GMBH, 2018-03-22) Başcura, Erdem Berkay; Karakurt, İsmailWe present a systematic study of the light intensity enhancement in the shell layers of half burrried Ag, Au, Al and SiO2 spherical nanoparticles capped with TiO2. We calculated the light intensity profiles near these structures when they are illuminated by a UV light at 380 nm. The calculations cover the particle-size range between 20 and 180 nm, and the cap thickness range between 6 and 80 nm. Our data is the first report on the intensity enhancement in the shell layers of TiO2-capped Al nanoparticles and Al@TiO2 core-shell nanostructures. We obtain, in the cap layers, an average intensity enhancement of similar to 3.7, similar to 6.1, similar to 2.4 and similar to 2.7 for a cap thickness of similar to 30nm above Ag, Al, Au and SiO2 particles. Taking into account the increase in the active surface area, these numbers can be multiplied by a factor of two, for each capped-nanoparticle system. The optimal Ag, Au, Al and SiO2-particle sizes for a 30-nm cap-thickness are found to be 120 nm, 80 nm, 140 nm, and 80 nm. While half-buried and capped-nanoparticle systems resemble the typical core-shell nanoparticles, the intensity enhancements are not equivalent. We compare the intensity increases in these two systems at the optimal sizes for Ag and Al particles for a 30-nm shell thickness.
