Non-interacting rigid gas

In order to understand the overall orientation of the chromophores within guest-host systems under differing external electric fields, we examine the orientational alignment of the dipole moment of the chromophores with respect to the direction of the external electric field. In the non-interacting rigid gas model, the intermolecular electrostatic interactions are ignored and one can describe a general order parameter of... 

We chose the temperature of 600 K for our simulations and initially choose a density of 0.9g/cm so that we were performing the simulations in the rubbery region of the polymer. Examination of the poling results (Figure 8) reveals that at this density and temperature, and a dilute concentration (5% by weight), the system does not behave as the non-interacting rigid gas model predicts. The predicted order for this system has a value of 0.60. The system s calculated order parameter... 

Since the uniform electron density is perfectly neutralized by a rigid uniform positive background, the total energy per electron of the uniform gas is just + xe, where the non-interacting kinetic energy is... 

In many production routes, and also during processing, polymer systems have to undergo pressure. Changes in the volume of a system by compression or expansion, however, cannot be dealt with in rigid-lattice-type models. Thus, non-combinatorial free volume ( equation of state ) contributions to AG have been advanced [23 - 29]. Detailed interaction functions have been suggested (but all of them are based on adjustable parameters, for blends, e.g., Mean-field lattice gas [30], SAFT [31], specific interactions [32]), and have been succesfully applied, for example, by Kennis et al. [33]. 

The reason we prefer to use 1 M for the standard state in both the gas phase and in liquid solution is that using the same concentration in the gas phase and solution eliminates an entropic term in the statistical mechanical free energy and allows us to focus on the interaction terms coupling the solute to the solvent. In particular, using the standard state of Equation 67, we can write the free energy of solvation of a rigid, non-rotating solute as... 

In summary, there are two main factors one must consider in gas phase non-cova-lent interactions of molecules the first is the energy of the interaction, which, provided the molecules are oriented favorably and are not like charged, is attractive (favors associations). On the other hand, the entropy of association is quite negative and disfavors association. The two terms are often correlated, i.e., the stronger and more favorable the AE, the more rigid the complex and the larger and more negative the AS. 

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