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Freestanding films of polyelectrolyte multilayers are expected to be used for applications, such as separation membranes, sensors, catalysts, micromechanical devices [1]. However, it is not easy to control film stress arising during deposition on substrates. Upon film removal the stress can lead to film expansion or contraction altering freestanding film properties. Stress-free membranes after detachment can be fabricated when the origin of stress is clarified and the magnitudes can be reduced during the film formation process. In particular the first few layers of polyelectrolyte adsorption are known to be different from the following ones.
In this study, single and multilayers of polyelectrolytes on a silicon wafer were studied by X-ray photoelectron spectroscopy. (XPS). PAH (polyallylamine hydrochloride) and PSS (polystyrenesulphonate) at a concentration of 3 mM in NaCl solutions were used for film formation on silicon wafers. In the XPS spectra the N1s peak shifts were analyzed in single and multilayers consisting of (PAH/PSS)n where n=1, 2 and 3. The N1s signals allow inferring the ionic state of PAH in PSS. From our XPS measurements significant changes of ionic state for amines from 9 % (n=0.5) to 94 % (n=1.0) were found in the initial growth of polyelectrolyte multiplayer. Our measurements indicate that both, the pH value and the NaCl concentration upon polyelectrolyte adsorption play a role in the stress magnitude of multilayer films which were measured by micromechanical cantilever sensors [2].
[1] S. S. Ono, and G. Decher; Nano Letters 2006, 6, pp592.
[2] M. Toda, A. N. Itakura, K. Buescher,K. Graf, and R. Berger, e-Journal of Surface Science and Nanotechnology 2006, 4, pp96.
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