Hierarchically assembled nanofibers created by a layer-by-layer self-assembly

We report the hierarchically assembled nanofibers created by LbL self-assembly depending on the PSS-PAA fraction in the blend solutions and pH during bulid-up of the PAH/(PSS-PAA) multilayer films. The multilayer [(PEI/blend)/(PAH/blend)₄] films with ρ_PAA (PSS-PAA fraction in the blend solutions) = 0.0 in the blend solution exhibited surface morphologies of randomly isolated globular clusters, while at ρ_PAA = 0.75, worm-like morphologies were observed. Interestingly, the multilayer [(PEI/blend)/(PAH/blend)₄] films with ρ_PAA = 0.9 exhibited unique fibrous morphologies with the diameter of about 50 nm at narrower pH range from 3.5 to 4.2, but also the fiber diameter distribution was narrower. Based on the thickness from the X-ray reflectivity, the thickness of the one bilayer multilayer film seemed to be 8.6 nm. The 3 bilayers multilayer film seemed to be formed as islands with very large roughness. The crystal sizes of the 3 bilayers and 5 bilayers multilayer films were about 71 nm and 123 nm, respectively. The resultant films were characterized using atomic force microscopy (AFM) and real-time in situ X-ray scattering measurements.