Şaziye Uğur

Void closure and interdiffusion processes during latex film formation from surfactant-free polystyrene particles: a fluorescence study.

This study reports a steady state fluorescence (SSF) technique for studying film formation from surfactant-free polystyrene (PS) latex particles. The latex films were prepared from pyrene (P)-labeled PS particles at room temperature and annealed at elevated temperatures for 5-, 10-, 20-, and 30-min time intervals above the glass transition (T(g)) temperature of polystyrene. During the annealing processes, the transparency of the film changed considerably. Scattered light (I(sc)) and fluorescence intensity (I(0P)) from P were measured after each annealing step to monitor the stages of film formation. Evolution of transparency of latex films were monitored using photon transmission intensity, I(tr). Scanning electron microscopy (SEM) was used to detect variation in the physical structure of annealed films. Onset temperature for film formation, T(0), void closure, T(v), and healing temperatures, T(h), were determined and corresponding activation energies were measured. Void closure and interdiffusion stages were modeled and related activation energies were determined.

Pyrene lifetimes for monitoring polymer dissolution: a fast transient fluorescence study

Fast transient fluorescence technique (FTRT) was used to measure pyrene (Py) lifetimes during dissolution of glassy polymer, which is formed by free radical polymerization of methyl methacrylate (MMA), and Py was introduced during polymerization as a fluorescence probe to monitor swelling and dissolution. The dissolution process of poly(methyl methacrylate) (PMMA) glass was performed in chloroform (80%)–heptane (20%) mixture. Fluorescence lifetimes of Py from its decay traces were used to monitor the dissolution process. A model was derived for low quenching efficiencies for measuring mean lifetimes, 〈τ〉, of Py and it was observed that 〈τ〉 values decreased as the dissolution process proceeded. Desorption, D and mutual diffusion, Dm coefficients of Py molecules were measured during dissolution of PMMA and found to be around 1.19×10−6 and 1.23×10−6 cm2 s−1, respectively.

Determination of relaxation and diffusion activation energies during dissolution of latex film using in situ fluorescence technique

Abstract In situ real-time steady state fluorescence measurements used for studying the dissolution of polymer films. These films were formed from pyrene labelled poly(methyl methacrylate) (PMMA) latex particles, sterically stabilized by polyisobutylene. Annealing was performed above the T g at 180°C during 1 h for film formation. Desorption of pyrene labelled PMMA chains was monitored in real time by the change in pyrene fluorescence intensity. Dissolution experiments were performed in toluene and a toluene/heptane mixture at elevated temperatures. Relaxation ( k 0 ) and diffusion ( D ) parameters were measured and found to be around 10 −2 mg cm −2 min −1 and 10 −11 cm 2 s −1 , respectively. Using these parameters, relaxation ( ΔE k O ) and diffusion ( ΔE D ) activation energies were calculated and found to be 11.36 and 24.38 kcal mol −1 and were attributed to the side-chain and backbone motions, respectively.

Molecular weight effect on polymer dissolution: a steady state fluorescence study

Abstract In situ steady state fluorescence (SSF) technique was used to study the dissolution of disc-shaped polymer glasses in various molecular weights, M W . The glass discs were formed by free-radical polymerization of methyl methacrylate (MMA). Pyrene (P) was introduced during polymerization as a fluorescence probe to monitor the dissolution process in chloroform. Desorption of poly(methyl methacrylate) (PMMA) chains from discs were monitored simultaneously by observing the change of P fluorescence intensity, I . Diffusion model with a moving boundary was employed to quantify the fluorescence data observed from dissolving PMMA discs made at various molecular weights. It is observed that desorption coefficient, D decreased by increasing molecular weight, M W by obeying D ≈ M −1 law.

Film formation from TiO2-polystyrene latex composite: a fluorescence study

This 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 I P from P were measured after each annealing step to monitor the stages of film formation. Films showed considerable increase in I P 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.

Film formation from PS latex doped PNIPAM hydrogels at various heating and cooling rates

Film formation from polystrene (PS) latex doped poly(N-isopropylacrylamide) (PNIPAM) hydrogels was studied by using photon transmission technique. The transmitted light intensity, I tr 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°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.

Polymer-Ceramic Nanocomposites

Steady state fluorescence (SSF) and photon transmission (PT) techniques were used for studying film formation from TiO2 and Al2O3 covered polystyrene (PS) latex particles. These films were annealed at elevated temperatures in 10 min time intervals above glass transition (Tg) temperature of polystyrene. Fluorescence emission, Ip and transmitted photon, Itr intensities were measured after each annealing step to monitor the stages of film formation. Films present dramatic increase in both Itr and Ip above the certain onset temperature called minimum film forming temperature, T0. Dissolution of annealed PS film, with high TiO2 content presented a nice, ordered nano-sized ceramic structure, which may predict the construction of nano-layer photonic crystals. It was observed that latex particles are encapsulated above a critical Al2O3 content of 33 wt% which corresponds to the critical occupation probability of pc=0.33 at which the film obey the site-percolation model with a critical exponent of 0.45.

Molecular weight effect on swelling and viscous flow of polymeric glass exposed to organic vapor: A steady state fluorescence study

Polymeric glasses formed from linear poly(methyl methacrylate) (PMMA) chains in various molecular weights were exposed to chloroform vapor to study swelling and viscous flow mechanisms. In situ steady state fluorescence (SSF) experiments were performed to monitor the vapor uptake and viscous flow processes. Direct illumination of the disc shape films were performed to excite the pyrene (P) molecules embedded inside the PMMA films. Variation in P intensity, I P, was monitored during swelling and viscous flow of the PMMA material exposed to chloroform vapor. It was observed that PMMA film swells like a crosslinked gel at early times by obeying the Li-Tanaka equation. At later times, i.e.longer than terminal relaxation times, τ t, swollen PMMA material flows linearly with time. Swelling time constant, τ c, terminal relaxation time, τ t, and viscosity η of PMMA films during vapor uptake were measured and found to be strongly correlated with the molecular weight (M) of PMMA. The exponent of M for τ t and η were measured and found to be around 3.

A Study on the Solvent Vapor Induced Film Formation of PS/AgNPs Composites

In this study, pyrene (P) tagged polystyrene (PS) latex dispersions and silver nanoparticles (AgNPs) were mixed at various weight fractions in the range between 0 and 50 wt%. The prepared mixtures were dropped on the glass substrates by considering drop casting method and were dried at the room temperature. The resultant powder films were then exposed to solvent vapor to monitor how film formation and morphological behaviors of PS/AgNPs composites are altered. Film formation behavior of composites was assessed via fast transient fluorescence (FTRF) which measures the fluorescence lifetimes of P from its decay traces during vapor exposure process. It was observed that pyrene lifetimes decreased as vapor exposure time, t increased. A Stern–Volmer kinetic analysis was used for low quenching efficiencies to interpret the decrease in pyrene lifetimes. UV-Vis (UVV) technique was employed to monitor optical transparency of the films. In the range of 0-20 wt% of AgNPs content, smooth and transparent films were obtained. However, above this range, the films were seen that they have low transparency and poor film formation since the increment in AgNPs content was lead to aggregations. The Prager–Tirrel model was employed to the FTRF data to obtain back-and-forth frequencies, ν, of the reptating PS chains during vapor induced film formation process. SEM images of the samples were taken after film formation process is completed and were found to be consistent with optical and fluorescence quenching data.

Investigation of Magnetic Properties of PS LATEX/MNPs Composite Films

In the work reported here the magnetic properties of nanocomposite system composed of polystyrene (PS) latex polymer and superparamagnetic nanoparticles (MNPs), is presented. A series of mixtures were prepared by mixing of PS latex dispersion with different amount of MNPs and drop casting on glass substrates at room temperature. After drying, film samples were annealed at 250 °C for 10 min. Morphological changes of the films were examined by scanning electron microscopy (SEM) and magnetic properties studied using vibrating sample magnetometer (VSM) as a function of MNPs content. The saturation magnetization (Ms) of composites increased as MNPs content increased. Ms showed two maxima at 50 wt% and 85 wt% MNPs contents with Ms values of 0.014 emu and 0.020 emu, respectively. The morphological changes of PS/MNPs composite films were also found consistent with these results indicating that magnetic properties these composites can be readily tuned by varying MNPs content.