Stilbazium iodide (symboled as S) has high b values and was used to prepare LB films, but the deposition properties of S and the stabilities of S-LB films are very poor. The mixed systems of stilbazium salt and cadmium arachidate (symboled as SA, the mol. ratio RM = S/A = 0 to 1) can improve the deposition property, but the stability of SA-LB films are still poor. The present work is to investigate the microstructure and superstructure of S-LB and SA-LB films, and the reason of unstability of these films by SAXS and MCMI. The results are as follows. First, the fatty chains of both stilbazium salt and cadmium arachidate can form a crystal-like structure of two-dimension as same as the usual fatty acid. Second, the phase-inversion of S and A from dispersed phase to continuous phase occurs as Rm changes from 0 to 1. Third, in the crystal-like of two-dimension S-mols. are in high energy and full-straighten conformation, but the stilbazium group of dumbbell-shape tends to pile up in the oblique and close packing form two fatty chains of S tend to extend in the lower energy trans-form and swallow tail conformation; the length of the fatty chains (C16) is about 2/3 length of S-mol., so the mol. forces between SS or S-AS are less than of usual fatty acid and Y-type LB films of S continuous phase are unstable. Fourth, a lot of lattice defect exist in two-dimension crystal-like of SA-systems as mentioned above, so only 4 to 6 layers unstable and less regular Y-type SA-LB films could be prepared and these layers' structure collapse after 1 mo.

Key words: X-RAY SMALL ANGLE SCATTERING ANALYSIS, SUPERMOLECULAR STRUCTURE, NON LINEAR OPTICS, MICRO-STRUCTURE, L-B MEMBRANE