Preparation and characterization of composite LB films of lignin and cadmium stearate

Abstract

We report on studies of composite Langmuir films containing lignin (extracted from sugar cane bagasse) and cadmium stearate and their subsequent transfer as Langmuir–Blodgett (LB) films. Pure lignin was found to form non-monomolecular films at the air-water interface. Composite monolayers of lignin and cadmium stearate with varying compositions have been obtained and characterized by surface pressure and surface potential isotherm studies which essentially indicated the formation of a meta-stable composite monolayer at the air-water interface. Nevertheless, these composite monolayers could be uniformly transferred onto solid substrates under optimized deposition conditions. Transferred multilayer LB films were characterized by UV-vis and Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and surface potential measurements. FTIR studies confirmed the transfer of lignin along with cadmium stearate. UV-vis results revealed a layer-by-layer transfer of the composite monolayer. In the composite film, both cadmium stearate and lignin were present as separate domains and the stacking order in the cadmium stearate domains was found to be influenced by the incorporation of lignin, as evidenced from XRD. Surface potential measurements indicated a good film uniformity.