有限层Langmuir-Blodgett类晶型薄膜微观结构与超分子结构的小角X射线散射研究——Ⅱ.(艹氐)唑盐/花生酸镉混合膜系

Studies of SAXS on the Microstructure and Superstructure of Finite-Layer Langmuir-Blodgett Crystal-Like Films Ⅱ. The Mixed Film Systems of Stilbazium Salt and Cadmium Arachidate

本文应用SAXS与微机模型拟合(MCMI)研究了S-LB(S为芪唑盐)薄膜与SA-LB(SA为芪唑盐/花生酸镉)薄膜的微观结构与超分子结构,以及这类LB薄膜凝聚态不稳定的原因.结果指出;第一,从π-A.曲线可知,S与A的脂肪链可以类似于脂肪酸晶胞形成二维类晶系结构;第二,随着分子比R_M=S/A=0到l,S和A之间发生了从分散相至连续相的相逆转;第三,S在二维类晶系中处于不稳定的近似伸直型的高能态构象,然而,哑铃形的芪唑基类似于芪趋向于作倾斜状密堆砌,S的两条脂肪链则倾向于转变为稳定的全反式燕尾形的低能态构象,仅占S分子长约2/3的脂肪链亦降低子S分子间与S-A分子间的凝聚力,这就导致了S连续相的二维类晶系存在大量晶格缺陷,故只能形成4～6层不稳定的Y型LB薄膜;第四,存放一月后,这种不稳定的S连续相的层状超分子结构极易破坏和崩塌.

Stilbazium iodic (symboled as S) has high BBBBBBBB value and has been 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 aa SA, the molecular 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 MOMI. The results are as follows. First, the fatty chains of both stilbazium salt and cadmium arachi date can form thecrystal-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-molecules are in high energy and full-straighten conformation, but the stilbazium group of dumbbell-shape tends to pile up in the oblique and close packingform; two fatty chains of S tend to extend in the lower energy trans-form and swallowtail conformation; the lengh of the fatty chains (C16) is about 2/3 lengh of S-molecule, so the molecular forces between SSor S-AS are less than that 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. month