Dendritic and branched macromolecules on liquid and solid surfaces
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Abstract
Several generations of five dendritic molecular systems are studied to discern the optimum balance in amphiphilic behavior at the air/water interface. Monomolecular layers fabricated at the air-water and air-solid interface by the Langmuir-Blodgett technique are characterized using atomic force microscopy, ellipsomety, X-ray reflectivity, X-ray diffraction and UV-vis spectrometry. Rod, discotic, and random hyperbranched cores are balanced with hydrophilic and hydrophobic tails to create an appropriate amphiphilic balance suitable for the formation of stable monolayers at the air/water interface. The chemical composition and shape of cores and pheripherial branches is shown to greatly affect the molecular packing structure of a variety of molecular compounds. A flexible hydrophilic core balanced with hydrophobic tails along with monodendron shape is found to facilitate organized monolayer formation more completely than a rigid hydrophobic core terminated with flexible hydrophilic tails. Unlike the traditional amphiphilic molecules based on hydrophilic cores terminated with hydrophobic branches, the molecules based on hydrophobic cores balanced with flexible hydrophilic tails exhibit appealing phase transitions of the intralayer structures. The shape of the rigid core greatly affects the stability of the molecules at the air/water interface.