Investigations On The Microstructure Of Composite LB Films

The Langmuir-Blodgett (LB) technique has been shown to be a powerful and convenient method for molecular assembly and also been found wide application in fabricating ordered functional structures at nanometer scale to get some new type devices with fine properties. In order to study the interplay between the control of special structure and the modulation of the special functions, scientists recently have paid much attention to the microstructure of the films and have made some great progress in this field. Based on this, the abstract of my work is shown following:1. X-ray diffraction (XRD) technique was used to investigate the phase-separation and microstructure of the BA/SA mixed multilayers. The results showed that the interplanar spacing D values and relative X-ray diffraction intensity of the mixed LB films change with the ratio of BA/ SA in a step- and W- shaped curve respectively, which indicates that only three kinds of longitudinal periodic structures can form in the mixed multilayer LB films of all ratios and each microstructure can be maintained in a certain ratio range. Furthermore the mixed system always goes through a process of the longitudinal regularity decreasing when the ratio of BA/SA is out of the intermediate ratio range (BA/SA: 1/5 ~ 1/1). Tilted BA clusters are embedded in SA when BA/SA is below 1/9. Longer and shorter chain domains mesh with each other when BA/SA = 1/7 ~ 1/1, especially when BA/SA = 1/5 ~ 1/1, this "meshed structures" are much ordered and stable, therefore they may have fine mechanical property. When BA/SA = 3/1 -9/1, longer domains (BA) are in majority, and some hydrophobic "holes" (caused by the difference in height between BA and SA) formed in the alkyl layer which can be used to fabricate special functional nanostructures. Those conclusions may be meaningful for us to determine mixture ratio when fabricating composite films with special structures.2. We study the phase-separation and microstructure of the pure binary and trinary mixed LB and LS films of Dimyristoyl phosphatidyicholine (DMPC) cholesterol(Chol )and sphingomylin(Sph) deposited from pure water subphase by π-A isotherms and tapping mode Atomic Force Microscopy.3. Polyethylenimine(PEI),a water-soluble cationic polyelectrolyte , has been extensively used as a deformable and mobile substrate for a biomembrane for it high transfection efficiency of chemical-based delivery systems. What's more, PEI is good buffer in physiological environment (PH<9). We used this water-soluble cationic polyelectrolyte PEI as a soft cushion for biomimetic membranes in this chapter, and studied the microstructure of polymer-cushioned pure binary and trinary mixed LB and LS films of Dimyristoyl phosphatidyicholine (DMPC) . cholesterol(Chol )and sphingomylin(Sph) ( that is to say study the influence of PEI cushion on the microstructure of the monolayers) deposited from lOOppm PEI water solution subphase by π-A isotherms and tapping mode Atomic Force Microscopy. Results revealed that there are strong interactions between spreading molecules and PEI soft cushion, and PEI's existing made the microstructure of the monolayers very different from that of the films deposited from pure water subphase, and surface patterned topography formed. But when the mixure ratio of the film is similar to that of actual biomembrane, their topographies are almost the same as that of the special films deposited from pure water subphase, so such mixed films deposited from the 100ppm PEI water solution subphase, can be used to study their thermodynamic properties.