Infrared Studies of Novel Optically Responsive Materials: Orientation Characteristics of Sulfonated Polystyrene/Poly(Diallyldimethylammonium Chloride) Ionic Polymer Multilayers on Patterned Self-Assembled Monolayers

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Abstract
Polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) is utilized in the characterization of a new class of polymeric materials that exhibit unique optical properties. The differential nature of PM-IRRAS, coupled with the fact that the experiment was performed on a commercially available hardware setup, makes the technique ideal for studying selectively deposited polyion multilayers on metal surfaces. The system under study was a polymeric thin film of alternating bilayers of sulfonated polystyrene/poly(diallyldimethylammonium chloride) (SPS/PDAC) fabricated by ionic multilayer assembly. Specifically, patterned self-assembled monolayers (SAMs) of (Ω-functionalized alkane thiolates were used as the molecular template. Alternating layers of polyanion and polycation were then selectively adsorbed onto specific regions of the surface to form a patterned films of thicknesses from 150 to 400 Å. The total thickness of the film was measured at 150 Å with the use of ellipsometry. Polyion conformation plays a crucial role in the selectivity of the patterned film, film surface characteristics, and ultimately, the ability of these systems to function as optical devices. The infrared spectroscopic data give insight into chemical composition and conformation and show that the molecular orientation of polyions in these polymeric multilayer structures depends on the ionic content of the initial solutions.

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