RESUMO
In this paper, we perform surface plasmon-coupled emission studies on Rhodamine 6G molecules embedded in a corrugated structure of a thin film composed of fluorinated silica particles, and a binding medium. Our results show enhancements of photoluminescence due to surface corrugation. By varying the size of the fluorinated silica nanoparticles we were able to control the surface correlation length scale of the corrugated surface structure. It was found that the coupling efficiency of the directional light emission is strongly correlated to the surface morphology, particularly the surface correlation length, of the corrugated dielectric structure. This substantial enhancement of signal could potentially be utilized in Organic Light Emitting Diode devices to enhance the light emission and transmission through a thin silver layer which can also serve as the cathode in Top-Emitting Organic Light Emitting Diodes.
RESUMO
A kinetic theory of glasses is developed using equilibrium theory as a foundation. After establishing basic criteria for glass formation and the capability of the equilibrium entropy theory to describe the equilibrium aspects of glass formation, a minimal model for the glass kinetics is proposed. Our kinetic model is based on a trapping description of particle motion in which escapes from deep wells provide the rate-determining steps for motion. The formula derived for the zero frequency viscosity η (0,T) is log η (0,T) = B - AF(T)kT where F is the free energy and T the temperature. Contrast this to the Vogel-Fulcher law log η (0,T) = B + A/(T - Tc). A notable feature of our description is that even though the location of the equilibrium second-order transition in temperature-pressure space is given by the break in the entropy or volume curves the viscosity and its derivative are continuous through the transition. The new expression for η (0,T) has no singularity at a critical temperature Tc as in the Vogel-Fulcher law and the behavior reduces to the Arrhenius form in the glass region. Our formula for η (0,T) is discussed in the context of the concepts of strong and fragile glasses, and the experimentally observed connection of specific heat to relaxation response in a homologous series of polydimethylsiloxane is explained. The frequency and temperature dependencies of the complex viscosity η (ω< T), the diffusion coefficient D(ω< T), and the dielectric response ε (ω< T) are also obtained for our kinetic model and found to be consistent with stretched exponential behavior.
RESUMO
Boehm and Martire have shown that the Flory-Huggins (FH) lattice model applied to mixtures of squares and rigid rods in solvent on a two dimensional lattice gives different results depending on whether rods or squares are placed first onto the lattice. This correct derivation places the validity of the FH model itself into question since the final result should be independent of the order of placement. An analysis of the FH model in terms of Poisson statistics suggests an alternative formula for the probability of successfully placing a rectangle into an area partially filled with other rectangles, which when incorporated into the FH counting procedure gives the exact thermodynamic result for the tiling of squares (i.e., no solvent and no rods). An attempt to solve the order of placement problem is made by solving the problem of one square plus any number of rods and then generalizing the statistics so that they are consistent with this result. Equations are given for squares plus rods plus solvent in both two and three dimensions. For plates plus solvent in three dimensions a purely entropy driven phase transition between an anisotropic layered phase and an isotropic phase is obtained. This transition is analogous to the isotropic to nematic liquid crystal phase transition in rigid rods. Our equations, when augmented by energy considerations, are useful for calculating the equilibrium properties of discotic systems, polymer-layered silicate composites, and the adsorption of plate like molecules onto surfaces.
