Layer-by-Layer Assembly of Charged Particles in Nonpolar Media

Layer-by-layer (LbL) assembly of charged species such as nanoparticles and polymers has been widely used to generate functional thin films with unique wetting, optical, catalytic, and biological properties. Although LbL assembly is a versatile tool for creating functional thin films on a variety of substrates, it is generally restricted to aqueous media, in which electrolytes ionize readily due to the large dielectric constant of water. LbL assembly of non-water-soluble materials would expand the range of film properties and functionalities that are attainable. In this study, we have successfully performed LbL deposition of charged particles in a nonpolar solvent, toluene. In toluene, carbon black (CB) and alumina acquired negative and positive surface charge, respectively, in the presence of a charge-inducing agent, Aerosol OT (AOT). The dependence of particle surface charge on the concentration of AOT in toluene was probed by electrophoretic mobility analysis. The two oppositely charged particles were sequentially deposited onto glass slides to form CB/Al2O3 nanocomposite thin films. UV-vis spectroscopy, optical profilometry, and thermogravimetric analysis (TGA) were used to investigate the effect of assembly conditions (i.e., the concentration of AOT in each suspension) on the composition and growth behavior of CB/Al2O3 nanocomposite films. Our results demonstrate that LbL assembly can indeed be performed using charged particles in nonpolar media. Such possibility will widen the library of materials that can be incorporated into thin films based on the LbL, technique, which can ultimately lead to the generation of multifunctional nanocomposite thin films.