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——Ⅰ.硬脂酸镉盐膜系

Studies of SAXS on the Microstructure and Superstructure of Finite-Layer Langmuir-Blodgett Crystal-Like Films——Ⅰ.Cadmium Salt Film System of Stearate Acid

本文应用小角 X-射线散射,参考方介石与硬脂酸结晶结构,为硬脂酸镉盐膜系设计了七种可能的分子链模型,在微机上进行拟合研究.结果指出:链倾角也 A_(ch)～24—27°,与β-硬脂酸结晶相近;碳链键角 A_(cc)～115°,比正四面体模型有所扩张;链端羧酸镉属离子键结构,而非文献习用的共价键结构;堆砌缺陷 d 约0.156nm,小于文献值约0.1nm;酸/皂剂量比 x=0.8—1.0,因制膜条件变化而不同;界面对链堆砌有明显影响.总之,小角 X-射线散射可对超薄 L-B 薄膜(<10 nm)的精细结构进行有效的研究.

Cadmium stearate is a traditional molecular system of L-B films and most ofamphiphiles molecules used to prepare L-B films include various hydrocarbon chains,sothe study of cadmium stearate,including hydrocarbon chain,is still an important andfundamental problem.But so far X-ray investigation of microstructure and superstructureof cadmium stearate in L-B films was the matter only last decade.Among which,thereare many problems unsolved,such as the tilt-angle of the chain Ach;the bond-angle ofCarbon-Carbon in the fatty chain A_(cc);the relative positions of Cd^(2+) and—CO_2^-;thepacking-defect of a unit-cell of a reverse bilayer (in Y-type L-B film) d;the acid/soapstoichiometry x;the effect of interface on the chain packing etc.In present work,SANSwere applied to study above problems.In reference with trigonal-system of calcite andmonoclinic-system of stearate acid,seven possible models M-1 to M-7 were used forfitting study.The conclusion is that M-4 is the optimum fitting model,i.e.A_(ch)～24°—27°,larger than that in references about 10°,somewhat like the inclination-angle of β-crystal of stearate acid (29.9°);A_(cc)～115°,greater than 109°28＇,somewhat extended inthe parallel packing-chains;the structural configuration of Cd^(2+) and—CO_2^- belongs toion-bond type,not to covalent type as quoted in reference everywhere;d～0.156nm,lessthan that estimated in referenes about 0.1nm;acid/soap stoichiometry x～0.8—1.0,which changes as the preparation condition of the films changes;the interface affects themolecular packing in the films.In short,SANS is a powerful method to investigate themicrostructure and superstructure of finite-layer(<10nm) or ultrathin L-B films.