Polymer Ultrathin Films Via Alternate Self-Assembly Adsorption of Polyelectrolyte and Azo-Dye Molecules: Photo-Induced A
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EXPERIMENT The experiments involved the preparation of the ultrathin films, analysis of layer ordering, photo-induced alignment studies, and fabrication and characterization of the hybrid LC cell. A complete description of the experimental details will be described in a forthcoming publication.[7] ACTIVE DYES Materials. The water-soluble SO3- Na SO3 - NHe dyes used for these experiments include N /, _\ NH-d NH \ (Scheme 1): Direct Red 80 (DR80), Acid Blue (ABI), Chicago Sky Blue (CSB), S0,- Na' 13-N+L' Direct Yellow 50 (DY50). All where "Direct Yellow 50 (DY50). X.max = 390 nm commercially available from Aldrich aO Chemical Co. Further purification of the 0- N N 83 dyes involved recrystallization using solvent mixtures (DMF and Ethanol), followed by extensive washing. The MDirected80 (DR80). X max = 560 nm oppositely charged polyelectrolytes used to alternately adsorb with the dyes include: Poly(diallyldimethyl ammonium / \N. NH \ chloride) (PDADMAC) MW= 100,000; SAcid Blue (AB1) Xmax = 56 nm (PAH) amine,HCl) Poly(allyl MW=28,000; Poly(ethylenimine) (PEI) OH NH2 NH2 OH MW=70,000, All were commercially S--3-Na÷ S0 N NN. I +No-So. were available (Aldrich). The solutions prepared using Milli-Q quality water. 80 3 -Na. -Noa'+
W
Chicago Sky Blue (CSB)
X.max = 618 nm
Scheme 1.
Layer-by-layer adsorption. The layer-by-layer adsorption of the azobenzene dye and polycation species was performed as follows: aqueous solutions of the dyes and polymers were prepared with a concentration of 0.01-0.001 M or M/repeat unit and deposited alternately (sequentially) until the desired layer number is reached. This was carried out using an HMS Series Programmable Slide Stainer apparatus (Carl Zeiss, Inc) with 15 min. immersion time involving rinsing steps in-between. Initial surface functionalization of glass or silicon involved treatment with 3-aminopropyltriethoxysilane (Aldrich Co.). An alternative procedure is the initial deposition of 5 pair-layers of PAH and PSS. For QCM measurements, quartz crystals with a gold patterned electrode was initially functionalized with 3-mercapto-l-propanesulfonic sodium salt (0.001M in ethanol). Instrumentation. UV-visible absorption spectra (Perkin Elmer Lambda20 and Ocean Optics 2000); QCM (PM-740, Maxtek Sytem); Ellipsometry (Microphotonics SE400); Irradiation with polarized light (Oriel, Hg Lamp 150 Watts with band pass filter (430 nm and sheet polarizer): LC Cell Fabrication (glass substrates with stearic acid monolayer, mylar spacers and 5CB liquid crystal); birefringence monitor (linearly polarized He-Ne laser,20 mW / LC cell/crossed polarizer (analyzer)/Detector). X-ray reflectometry was done on a Rigaku 0-0 difractometer, 18 Kw with a rotating anode source. Instrumentation and measurement details for SPS, XPS and AFM will be described in a forthcoming publication.[8]
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RESULTS AND DISCUSSION We initially employed UV-vis spectroscopy, ellipsometry and QCM to investigate the adsorption properties of the dye/polyelctrolyte pair layers and the mode of dye aggregation. The ellipsometric
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