Bottom-up self-assembly of nanofibers in the surfactant mixture of CTAB and Pluronics

Abstract

Bottom-up self-assembly of nanofibers in a chemical method is presented using the surfactant mixture of cetyltrimethylammonium bromide (CTAB) and Pluronics as the anisotropic micellar templates. Fully fluorinated perfluorooctanoic acids with highly hydrophobic C–F chains are imported for constructing exceptionally long nanofibers. Ag(I) provides robustness of the materials by the complexation with ethylene oxides in Pluronic copolymers. Fluorocarbons reside in the PPO (polypropylene oxide) blocks in Pluronic polymers and accordingly in reverse Pluronics, they are placed in the surrounding regions of nanofibers. During the segregation of water from hydrophobic cores, self-assembly is assumed to be driven by hydrophobic interactions among alkyl chains of CTAB, fluoroalkyl chains of perfluorooctanoic acids, and dehydrated methyl groups of PPO blocks in Pluronics. Nanofibers with relatively high aspect ratios were obtained when Pluronic copolymers with low number average molecular weights (Mn), such as L-31 (Mn ∼ 1100) and L-64 (Mn ∼ 2900), were used. Heterogeneous catalytic activities were monitored in the reduction reactions of 4-nitrophenol, and the nanorods prepared from Pluronic 31R1 show the best catalytic performances with a rate constant of 0.002 35 s−1. The roles of fluorine or C–F groups in perfluorooctanoic acids are believed to be the disruption of hydrogen bonding between water and polyethylene oxide groups, and the phase separation of nanofibers from the aqueous environment by the dehydration of hydrophobic cores.