We shall try to sort out to what extent these factors are important in various cases. In co-operation with a Japanese scientist, Prof. Asakawa from Kanazawa Univ. The fluorinated surfactants behave mainly as normal surfactants, with similar sequences of phases and aggregate structures, but they also show interesting differences. The main reason is the bulkiness of the fluorocarbon tail. The tail cross-sectional area is more similar to the effective headgroup area than for hydrocarbon surfactants, which results in structures of less curvature.
Fluorocarbons have much smaller cohesive energy density than hydrocarbons, but are more hydrophobic.
The hydrophobicity is mainly due to the larger volume and the large cohesive energy of the water that is displaced. The stiffness is probably a strongly contributing factor to the abundance of intermediate phases, in particular between the lamellar and the hexagonal phase. While the intermediate phases are known also from meticulously studied phase diagrams of normal ionic surfactants such as SDS in water, they seem to occur much more commonly with fluorosurfactants, and also exist over a much larger composition range. The occurrence of the intermediate structures indicates that the fluorocarbon surfactants can withstand much less of frustration than the corresponding hydrocarbon surfactants, which evidently remain satisfied in either one or the other of the end-structures, even when the spontaneous curvature corresponds to something between a cylinder and planar layer. A most intriguing phenomenon is the phase separation that occurs in mixtures of hydrocarbons and fluorocarbons.