Characterization and patterned polymer films from a novel self-assembly process

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Virginia Tech


The layer-by-layer molecular-level manipulation of ionic polymer have been utilized to fabricate ultrathin multilayer films (SAMp). In this process, monolayers of polycations and polyanions are sequentially adsorbed onto a substrate surface by alternately dipping the substrate into aqueous solutions of poly(vinylamine) backbone azo (PDYE), poly(sodium 4-styrenesulfonate) (PSS), and poly(al1ylamine hydrochloride) (PAH). The ionic attractions developed between the oppositely charged polymers promote strong interlayer adhesion and a uniform and linear multilayer deposition process. UV/Vis absorbance, contact angle, and ellipsometry measurements revealed that in all cases the bilayer deposition process was linear and highly producible from layer to layer and film thickness of up to 1 µm can be easily obtained by repeating the deposition process. The typical thickness of bilayer film depend on the solution concentration. Contact angle and UV/Vis spectroscopy measurements demonstrated that the deposition time for a full monolayer coverage of azo dye and PAH was about 20 seconds. Our results showed that the mechanical stability of these SAMp films was remarkable, and SAMp films can only be removed from the substrate by scraping. SAMp films are stable in the common organic solvents and even in the high acidic media (6M HCl aqueous solution). The conformation of these films are thermally stable at high temperature.

In an attempt to develop patterned surfaces of sulfonate and thiol functionality, close-packed, well-ordered (3-mercaptopropyl)trimethoxysilane (MPS) monolayer were formed on the surfaces of single crystal silicon, quartz, and glass by allowing hydrolyzed silane to self-assemble from a dilute hydrocarbon solution. The films of MPS were irradiated with an ozone-producing UV light source results in efficient conversion of the surface-localized thiol groups to sulfonated groups, a complete photo-oxidation of the thiol surface was obtained and characterized by x-ray photoelectron spectroscopy (XPS) and contact angle measurements. Sulfonated self-assembled films can be used as good organic templates for the deposition of SAMp films and for micropatterning of organic surfaces based on our results. Such results significantly extend the application of SAMp films since the sulfonate-functionalized surface can be introduced into the surfaces of aromatic polymers, metals, ceramics, semiconductors, and plastics. So that the process of SAMp deposition can be carried out onto many different substrate surfaces.

The novel self-assembly technique combined with photolithography was used to develop three different methods of micropatterning fabrication in an attempt to achieve the goal of full-color flat-panel display. The characteristic of distinguishing our methods from the existed ones is that the patterning is done first and then the vertical multilayers were built-up on the patterned areas. Moreover, in this process, SAMp films were used as active species. Scanning Electron Microscopy (SEM) was employed to confirm the patterning technique. In order to block the further growth of the second film type on the sites of first film type, several molecules with inert function groups were tried. UV/Vis absorbance and contact angle measurements revealed that dodecyltrimethylammonium bromide (DTAB) atop the PAH/PSS SAMp film could prevent further adsorption of the ionic polymers.



Self-Assembly, Photolithography, Organic Thin Films, Muitilayers, Pattern