Engineering the microfabrication of layer-by-layer polyelectrolyte assembly

• Main Author: Clark, Sarah L. (Sarah Louise), 1972-
• Other Authors: Paula T. Hammond.
• Format: Others
• Language: English
• Published: Massachusetts Institute of Technology 2005
• Subjects: Chemical Engineering.
• Online Access: http://hdl.handle.net/1721.1/9509

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1999. === Includes bibliographical references. === The feasibility of microstructuring polyelectrolyte multilayers has been established by using the layer-by-layer assembly technique in combination with patterned self-assembled monolayers (SAMs). SAMs of a carboxylic acid surface (COOH) and a triethylene glycol surface (EG) were used to promote and resist polyelectrolyte adsorption. respectively. Processing conditions necessary for the selective deposition of both weak and strong polyelectrolytes were established as a function of polyelectrolyte molecular weight. ionic content, ion type. and pH. Low molecular weight polyelectrolytes adsorbed more selectively on patterned SAM surfaces than high molecular weight polyelectrolytes. Strong polyelectrolytes multilayers of sulfonated poly(styrene) (SPS) and polydiallyldimethyl ammonium chloride (PDAC) required the addition of 0.1 M NaCl to the polyelectrolyte dipping solutions to optimize selective deposition. Adding 1.0 M NaCl to each polyelectrolyte solution and including a periodic drying step in the multilayer fabrication process reversed the templating ability of the COOH and EG SAMs for the SPS/PDAC multilayers. Weak polyelectrolytes such as linear (polyethylenimine) (LPEI), branched (polyethylenimine) (BPEI), poly(allylamine hydrochloride (PAH), poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMAA) were adsorbed at pH 2.5. 4.8, 7, and IO on patterned COOH and EG SAMs to determine optimal patterned deposition conditions. Each polyacid and polyamine had a secondary interaction that changed the affinity of the multi layers for the COOH and EG surfaces. The technique was also extended to include an optically active dye in the multilayers. Imaging the patterned dye multilaycrs under a fluorescence microscope produced light emission from the selectively adsorbed dye molecules. The different conditions and interactions that produced selective deposition of polyelectrolyte multilayers were combined to build complex multilayer structures. A cladding structure was produced by depositing a blanketing layer of strong polyelectrolytes on preformed patterned multilayers. A different complex structure of polyelectrolytes was fabricated by selectively adsorbing a second polyelectrolyte system within the patterned structure of strong polyelectrolyte multilayers. This assembly was accomplished by utilizing secondary interactions of weak polyelectrolyte multilayers with the EG surface. === by Sarah L. Clark. === Ph.D.