Rigorous electromagnetic modeling

This chapter provides the general theories and discussions of optical sfruc-tures and characteristics of OLEDs. To start with, it presents a simple and analytical formulation of microcavity effects in OLEDs based on the concepts of the Fabry-Perot cavity this provides a clearer physical insight but is more limited in its description of the effects of microcavity. Subsequently, this chapter provides a brief description of rigorous electromagnetic modeling of optical characteristics of OLEDs. These notions are then used as the... 

The theory for the van der Waals interactions presented in the previous section applies to macroscopic media only in a qualitative sense. This is because (i) the additivity of the interactions is assumed — i.e., the energies are written as sums of the separate interactions between every pair of molecules (ii) the relationship of the Hamaker constant to the dielectric constant is based on a very oversimplified quantum-mechanical model of a two-level system (iii) finite temperature effects on the interaction are not taken into account since it is a zero-temperature description. Here, we present a simplified derivation of the van der Waals interaction in continuous media, based upon arguments first presented by Ninham et al a more rigorous treatment can be found in Ref. 4. The van der Waals interactions arise from the free energy of the fluctuating electromagnetic field in the system. For bodies whose separations... 

In this respect the approach by Ninham and Yaminsky is much easier to use. In principle the influence of solvent structure can be taken into account within the DLVO model by using a convenient Lifshitz-like ansatz. There, all non-electrostatic interactions are taken into account via frequency summations over all electromagnetic interactions that take place in the solutions. If done rigorously, the result should be more or less exact. As a proof of principle, Bostrom and Ninham made a first attempt in this direction. The classical DLVO ansatz was replaced by a modified Poisson-Boitzmann (PB) equation, in which a simplified so-called dispersion term was added to the electrostatic interaction. In this way ion specificity came in quite naturally via the polarisability and the ionisation potential of the ions. However, it turned out that this first-order approximation of the non-electrostatic interactions was not sufficient to predict the Hofineister series of surface tension. Heavier ions such as iodide had to be supposed to have smaller polarisabilities compared to smaller ions such as chloride. Although the exact polarisabilities of ions in water are still under debate, this is not physical. 

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