Solvation effect, polymer aggregation

Rgure 1. Scenarios depicting the possible solvation or aggregation states of a polymer-bound peptide sequence, (a) Peptide and polymer chains (bold) are fully solvated, (b) Peptide chains are intramolecularly aggregated whilst polymer is solvated, (c) Peptide chains are well solvated whilst the polymer backbone is poorly solvated, (d) Peptide chains are intermolecularly aggregated whilst polymer is solvated, effectively increasing the overall level of cross-linking in the matrix. (Reproduced from ref. 7 with permission.)... 

Because the above MEH-PPV solutions were made from the same batch of polymer, the different surface tension values observed in Table 6.1 should be due to the different aggregation states (or packing) styles of the polymer chains, resulting from the different solvation effects. 

Polymerization of acrylonitrile adsorbed on polyacrylonitrile" An intimate mixture of polyacrylonitrile solvated by its monomer is obtained if one melts acrylonitrile crystals which have been subjected to high energy radiation at low temperatures. The polymer forms under irradiation within the crystal lattice and upon melting, a gel-like phase is obtained in which the individual polymer molecules do not aggregate, presumably because most of the CN groups are then associated in pairs with the -CN groups of the monomer. Such a polyacrylonitrile solvated by its monomer should indeed be an ideal medium for the matrix effect to operate. 

As mentioned above, to prevent aggregation of the formed polymer particles one needs a dispersant (polymer surfactant) that must satisfy several criteria. The most effective dispersants are those of the block (A-B or A-B-A) or graft (BA ) type. The B chain is chosen to be insoluble in the medium and has high affinity to the surface of the polymer particles (or becomes incorporated within its matrix) (Chapter 5). This is usually referred to as the anchor chain. A chain(s) are chosen to be highly soluble in the medium and strongly solvated with its molecules. It should give a Flory-Huggins interaction parameter (/) < 0.5 to ensure effective steric stabilisation. 

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