We investigate the effect of film deposition methods on the film properties of layer-by-layer assembled polyelectrolyte multilayers. Multilayered structures of linear polyethylenimine (LPEI) and poly(acrylic acid) (PAA) are prepared by using conventional dipping-based assembly as well as spin-assisted assembly. While the polyelectrolyte interpenetration by the diffusion motion of LPEI species is allowed in dipping-based assembly, an instantaneously and kinetically frozen phase of the film deposition is obtainable from spin-assisted assembly. Being kept from the interdiffusion of LPEI, a stratified internal structure is expected in the spin-assisted assembly, which is completely contrasted to the intermixed phase in the dipping-based assembly. The ability to control the inner structure of the multilayered film enables us to manipulate the physical properties or chemical activity of the functionalized thin films. We also demonstrate that the control over the strength of polyelectrolyte interdiffusion on a very top surface can be utilized for a quantitative manipulation on the degree of macromolecular self-assembly of nanomaterials.

We report a facile means to achieve planarization of nonflat or patterned surfaces by utilizing the layer-by-layer (LbL) assembly of highly diffusive polyelectrolytes. The polyelectrolyte pair of linear polyethylenimine (LPEI) and poly(acrylic acid) (PAA) is known to maintain intrinsic diffusive mobility atop or even inside ionically complexed films prepared by LbL deposition. Under highly hydrated and swollen conditions during the sequential film buildup process, the LbL-assembled film of LPEI/PAA undergoes a topological self-deformation for minimizing surface area to satisfy the minimum-energy state of the surface, which eventually induces surface planarization along with spontaneous filling of surface textures or nonflat structures. This result is clearly different from other cases of applying nondiffusive polyelectrolytes onto patterned surfaces or confined structures, wherein surface roughening or incomplete filling is developed with the LbL assembly. Therefore, the approach proposed in this study can readily allow for surface planarization with the deposition of a relatively thin layer of polyelectrolyte multilayers. In addition, this strategy of planarization was extended to the surface modification of an indium tin oxide (ITO) substrate, where surface smoothing and enhanced optical transmittance were obtained without sacrificing the electronic conductivity. Furthermore, we investigated the potential applicability of surface-treated ITO substrates as photoelectrodes of dye-sensitized solar cells prepared at room temperature. As a result, an enhanced photoconversion efficiency and improved device characteristics were obtained because of the synergistic role of polyelectrolyte deposition in improving the optical properties and acting as a blocking layer to prevent electron recombination with the electrolytes.