When an elastomer is in equilibrium with a nonideal solution, activity coefficients based upon the constituent volume fractions are introduced.
For example, consider a moderately nonideal solution of reformulated gasoline containing methyl tertiary-butyl ether (MTBE).
If nonideal solution behavior originates only from spatial and/or physical considerations among the solvents, nonideal solution activity coefficient models will adequately account for excess swelling observed in elastomers.
This generalization is accomplished by incorporating concepts taught by Chemical Theory for nonideal solutions .
Now consider highly nonideal solutions exhibiting chemical association.
Theoretical treatments of activity coefficients in nonideal solutions have been discussed for a century.
Complicating the equilibrium condition further is the fact that aromatic and aliphatic hydrocarbons form slightly nonideal solutions themselves.
A partition coefficient model can be applied generally to ideal solutions and also to various forms of nonideal solutions exhibiting both positive and negative deviations.
This accounting can be accomplished through the use of Chemical Theory of nonideal solutions, often without adjustable parameters.