Association schemes

The association term is used in PC-SAFT and copolymer PC-SAFT. It allows the model to handle more complex mixtures since it will take cross association into account.

Nr	Scheme	Description
1	1A	1 neutral site
2	1C	1 negative site (active only when mixed with a molecule with at least one positive site)
3	1D	1 positive site (active only when mixed with a molecule with at least one negative site)
4	2A	2 neutral site
5	2B	1 negative site and 1 positive site
6	2C	2 negative sites (active only when mixed with a molecule with at least one positive site)
7	2D	2 positive sites (active only when mixed with a molecule with at least one negative site)
8	3A	3 neutral sites
9	3B	2 positive sites and 1 negative site
10	4A	4 neutral sites
11	4B	3 positive sites and one negative site
12	4C	2 positive sites and 2 negative sites
13	User	User can define a scheme. The maximum number of sites allowed is 4

The schemes 1C, 1D, 2C and 2D are for components that does not self-associate but is able to associate with other components like water or methanol.

However this pose the problem of obtaining the parameters needed for e.g. acetone since it cannot be determined by fitting to pure component data.

To solve this problem the "Consortium of complex fluid" has suggested that the kappa parameter is taken from the other component while the epsilon is set to zero.

This method may not always give the best result and VLXE therefore support user given parameters where no mixing rules are used.

If "Automatic" is selected the standard mixing rules are used and the user has to give AssociationkappaAB and epsilonAB for each component.

If "User" is selected no mixing rules are used and the user has to give both the kappaAB and epsilonAB matrix.