Molecular orientation in Langmuir and Langmuir-Blodgett films of disk-shaped molecules including amphiphilic dendrimers and liquid crystalline perylene diimide derivatives.

摘要

Physical and chemical properties always come from structural features. For the disk shaped macromolecules, face-on and edge-on model are employed to describe the molecular orientation of the discotic molecules in Langmuir and L-B films. Langmuir and Langmuir-Blodgett (L-B) films with different molecular arrangements showed various physical properties, which have wide potential applications in nanoelectronic devices and photovoltaic cells. Two different molecular systems were studied in this thesis. They are the amphiphilic dendrimers and liquid crystalline (LC) perylene diimide derivatives. The interfacial, spectroscopic and topographic properties of these two types of system were studied by Langmuir and L-B techniques. Molecular orientations and the structural differences behind the various molecular arrangements were analyzed.; A series of amphiphilic poly (amido amine) (PAMAM) dendrimers were prepared by attaching different functionalized chains to the PAMAM cores of different generations. The chains included pentacosadiynoic acid (PDA) hydroxydodecanoic acid chains (HA). The amphiphilic dendrimer with PDA chains demonstrated face-on orientation; whereas the dendrimers with HA chains showed edge-on orientation. These various orientations were also supported by topographic studies. Besides dendrimer cores' determining molecular orientations, we proved that the functionalized chains can play an important role in determining the molecular arrangements of amphiphilic dendrimers in Langmuir and L-B films.; For the LC perylene diimide derivatives, surface chemistry properties of three compounds with different chains have been investigated thoroughly. Among them, PPMEEM showed face-on orientation at air/water interface; whereas PPEEB and PPE4CN demonstrated face-on and edge-on orientations under different surface pressures. The two dimensional self-assembly process was first time observed in the presented research accompanying the appearance of the edge-on orientation. The relationship between the edge-on orientation and two dimensional self-assembly property was proved by the different topographic studies including Brewster angle microscopy (BAM), epifluorescence, environmental scanning electron microscopy (ESEM) and atomic force microscopy (AFM) techniques. Well defined correspondence among these techniques has been identified.