Self-Assembly of Perfluorooctanoic Acid (PFOA) and PS- b -P4VP in Chloroform and the Encapsulation of PFOA in the Formed Aggregates as the Nanocrystallites

The complexation of perfluorooctanoic acid (PFOA) and pyridine (as the model for the complexation of PFOA and polystyrene- b -poly(4-vinyl pyridine) (PS- b -P4VP)) in deuterated chloroform leads to an unusual low field shift of the 13 C NMR signal of the carbon atoms in the carboxyl groups of PFOA. Unlike the complexes of block copolymers with other small molecular surfactants in low-polarity organic solvents, the complexes of PFOA/PS- b -P4VP self-assemble in chloroform, forming vesicles when the molar ratio of PFOA to the pyridine units is greater than or equal to 1/5 and less than or equal to 1/1. When the molar ratio is 2/1, the PFOA molecules that are unconnected to P4VP chains are encapsulated in the aggregates rather than solubilized in the solvent, leading to a solid spherical morphology of the resultant aggregates. Moreover, the PFOA molecules both connected and unconnected to the P4VP chains are crystallized within the aggregates and melt at different temperatures.