Fabrication and characterization of optically active multilayer thin films based on polyaniline colloids

In this paper, we report the fabrication and characterization of polyaniline colloid (PANIC) multilayer thin films prepared from PANIC aqueous dispersion and a polyelectrolyte solution. Both chiral and achiral PANICs were used to fabricate multilayer thin films of up to 30 bilayers. Transmission electron microscopy, atomic force microscopy (AFM), UV-visible spectroscopy, circular dichroism, and cyclic voltammetry (CV) were used to characterize the PANICs and their multilayer thin films. CV suggests that these PANICs are more stable electrochemically than pure polyaniline (PANI). In the case of the optically active PANIC, we observe a linear increase of both the amount of the PANICs deposited and the optical activity in these thin films. Our results show that the periphery of the PANIC is mainly poly(acrylic acid), PAA, and the inner core is a mixture of PANI and PAA. Spin assembly introduces additional centrifugal forces that allow the alignment of elongated colloids parallel to the substrate surface. The AFM micrographs of a film composed of 20 PANIC/poly(diallyldimethylammonium chloride) bilayers reveal a roughness of 300 nm, equivalent to the depth of three-four colloids. This roughness level suggests that spin assembly is an ideal method for constructing colloid multilayer thin films.