Functional Multilayer Organic Thin Films Fabricated by Layer- by-Layer Sequential Adsorption Technique

A novel layer-by-layer sequential adsorption technique based on electrostatic interaction is a powerful way to fabricate multilayer organic thin films. The advantages of this technique include control over the number of layers, the architecture of the multilayers, and their ease of fabrication. By controlling the conditions of the polyion dipping solutions, such as salt concentration, solution pH, and polymer concentration, the thickness of an individual layer in the multilayer can be systematically manipulated. Solution pH and salt content affect the degree of ionization and the repulsive forces between the same charged segments of the polyion, respectively. The technique has been used to modify surface properties of various substrates on a molecular level. Contact angle measurements show that the surface wettability can be manipulated in a layer-by-layer manner to produce very stable surfaces with characteristics ranging from hydrophobic to hydrophilic. The sequential adsorption of a number of different functional dye molecules has been accomplished via the alternate spontaneous adsorption of polyelectrolytes and ionic dyes from dilute solutions. Multilayer thin films containing such functional dyes as pH indicator dyes, infrared absorbing dyes, porphyrin dyes, and various fluorescent dyes have been successfully fabricated and their electrical and optical properties examined. Newly synthesized ionic ruthenium based polypyridyl dye and polymer have been utilized to fabricate light emitting devices with high brightness (ca. 100 cd/m 2) at voltages in the range of 5 7 volts. Multilayers containing the synthesized ruthenium based polypyridyl polymer produce highly efficient (ca. 2 % quantum efficiency) and reversible electrochemiluminescent devices. The fabrication and device evaluation of new heterostructure thin films based on this new light emitting dye and polymer are presented. The bilayer thickness and composition as well as the total thickness of the heterostructure strongly affect the functional properties of these multilayer films. Thesis Supervisor: Michael F. Rubner Title : TDK Professor of Polymer Science