Hybrid self-assembly and fractal dimension dependence of a carboxyl-ended hyperbranched polyester/ferric complex

Controlled self-assembly of non-amphiphilic hyperbranched polymers (HBPs) has attracted increasing interest because of their potential application in catalysis and the much easier synthetic procedure than that for amphiphilic HBPs. In this paper, we present the surface self-assembly of a carboxyl-ended hyperbranched polyester/ferric complex (HTD-2-Fe) on glass substrate. The HTD-2-Fe complex was obtained by a coordination between HTD-2 and ferric chloride hexahydrate. The appearance of a new peak at 1619 cm−1 in FT-IR spectra, and the shift of Fe2p peaks from 710.8 eV (Fe2p3/2) and 724.5 eV (Fe2p1/2) to 712.0 eV and 724.9 eV in XPS spectra indicate the formation of coordinate bond (–COOFe), respectively. Factors affecting the morphology of self-assembly, including temperature, time, relative humidity, organic solvent and concentration of the complex, were studied using polarizing optical microscope (POM) and SEM. Both ordered 1D ruler-like and 2D tree-like self-assemblies with crystal and fractal behaviors are observed. The fractal dimension decreases with increase of the complex concentration. The self-assembly mechanism is accounted by diffusion-limited aggregation (DLA) theory, being attributable to the synergy of ferric ion coordination, micelles formation and DLA of micelle particles.