Abstract: The aggregation structure of monolayer was discussed by the observations of electron diffraction patterns and bright field images. When 2C_(14)SNa was spread on pure water surface, a homogeneous monolayer was formed before compressing as the result of electrostatic repulsion among hydrophilic anionic groups, the crystallization was occurred in the process of compressing, i.e., it was a compressing crystallized monolayer. When 2C_(14)SNa was spread on PEI solution surface, a crystalline monolayer with an un-oriented domain structure was formed before compressing as the results of anchoring effect of ion complex and the weakened electrostatic repulsion, the orientation was occurred in the process of compressing, i.e., it was a compressing oriented crystalline monolayer. The formation of polyion complex at the air/water interface greatly affected the aggregation state of monolayer.

Key words: Monolayer, Aggregation structure, Anionic amphipile, Polyethyleneimine