Layer-by-layer Assembled Chiral Polyelectrollyte Multilayer Films

The LBL self-assembling method has shown some obvious advantages such as powerful, versatile, operational simplicity, high controllability in the thickness and structure, and has applied to the ranges from drug delivery, sensor, solid-state-based batteries, photovoltaic devices, membranes separation. In this paper, we synthesized a chiral polyelectrolyte, a R-1-(4-methoxyphenyl) ethylamine derivative of poly(ethylene-alt-maleic acid) (PEMA- PMEA) and constructed an optically active multilayer film with poly(allylamine hydrochloride) (PAH ) and PEMA- PMEA by LbL assembly method. The influences of deposition conditions on the fabrication of the (PAH/PEMA-PMEA)n multilayer films has been investigated in detail. The development of this functional multilayer film is of benefit to expanding the application areas of layer-by-layer technology.First, PEMA-PMEA were prepared from poly(ethylene-alt-maleic anhydride) and R-1-(4-methoxyphenyl) ethylamine. By controlling the reaction conditions, different degree of substitution (DS) of optically active polyelectrolyte were prepared and characterized by the FTIR, UV-Vis, 1HNMR, fluorescence and circular dichroism(CD) analysis. Then, (PEMA-PMEA)/PAH multilayer were fabricated by the electrostatic layer-by-layer self-assembly method and characterized by UV-Vis, fluorescence, circular dichroism analysis. The surface morphology of the (PEMA-PMEA)/PAH multilayer was measured with an AFM instrument. Finally, the (PEMA-PMEA)/PAH multilayer was studied based on an expression describing the growth regime of the multilayer films. The model parameters q and m, which represents the growth rates of the exponiential and linear multilayers, respectively, applied to study the influences of the deposition conditions on the (PEMA-PMEA)/PAH multilayer. In low polyelectrolyte concentration (0.1mmol/L, 0.2mmol/L, 0.5mmol/L), the absorbance at 225nm of the PAH/PEMA-PMEA multilayer increases with the number of bilayers. In high polyelectrolyte concentration (1mmol/L, 2mmol/L, 5mmol/L, 10mmol/L), the absorbance at 225nm of multilayer films increases exponentially with the number of bilayers at the first few deposition circles and then increases linearly. Parameters q m are increasing with the concentration of polyelectrolyte. With increasing the NaCl concentration, parameters q and m increases, indicating that the higher the NaCl concentration is, the faster the growth rate of the multilayer is. When the pH value of the deposition solution is near pKa of PAH, parameters m and q of the multilayer increase with the increase of the pH value.