Mixtures and Composite Materials

It is often possible to predict with accuracy many properties of ideal solutions, such as dilute gas mixtures, as well as liquid mixtures of closely related substances such as pentane and hexane. On the other hand, liquid mixtures of substances with different 

When two chemicals are mixed, an ideal solution is defined when the properties of the mixture are a linear function of the properties of the two chemicals. The simplest relation is in the form of linear relations  

This is certainly true of the simple properties, such as the molecular weight of a mixture. For the van der Waals equation of state, the parameter b stands for the excluded volume due to the molecule, which suggests that the linear additive relation, or the arithmetic mean, may be appropriate for an ideal mixture  

However, parameter a, which stands for the interaction energy between two molecules, is proportional to the product of their polarizabilities and to the product of their dipole moments, and would not be linearly additive. 

When there is only a slight deviation from the linear, it may be appropriate to use a quadratic equation to fit the data. An interaction energy Qy can be introduced for each pair of molecules i and j, and the interaction energy so generated to be XiXj Qy. The total quadratic contributions would sum to 

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Dulnev, G.N., Zarichnjak, Yu. P. Heat Conductivity of Mixtures and Composite Materials. Leningra Energy 1974. 

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