Combining rules for three-component systems molecules

2 Combining rules for three-component systems molecules, particles and surfaces in a third medium 

In Section 7.2 we described combining rules for molecular, particle and surface interactions in a two-component system of (1) and (2). In this section, we will examine the combining rules when the molecules, particles or surfaces of (1) and (2) are placed in a solvent medium (3). 

Then it is possible to estimate which state is preferable in a three-component system from the difference in interaction potential energy, AV, on going from the dispersed to associated states. There are two possibilities the first one 

The difference in interaction potential energy, AV on going from the 12 associated state, to the 11-22 associated state, can also be calculated as 

Equations (585), (587) and (589) are very important for understanding the behavior of two unlike molecules, particles or surfaces in a third (solvent) medium. If (AV, 0), which means that (VAs iOC 12 VDis) in Equation (585), then the molecules tend to disperse and a repulsion occurs between the unlike molecules. This condition can be met only if the value of A3 is intermediate between A, and A2 so that when [A, A3 A ] or [A2 A3 A,] then Equation (585) must give a positive value of AV and two particles or surfaces in a third medium will repel each other. For the other conditions, we may state that unlike particles may attract or repel each other depending on the values of A A2 and A3. The same conclusions apply for the AV2 = VAssoc 11 22 — VDis interaction potential energy difference given by Equation (587). However, when we consider Equation (589) describing the [AV3 = VV iSOC-1. 22 - VAssoc 12] case, it is clear that the most favored final state will be that of particles (1) associated with particles (1) and (2) with (2) and (3) with (3), so that there is always a preferential attraction between like molecules or particles or surfaces in a multi-component mixture, except for the cases where H-bonding and/or Coulombic interactions are operative. 

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