Hybrids of Magnetic Nanoparticles with Double-Hydrophilic Core/Shell Cylindrical Polymer Brushes and Their Alignment in a Magnetic Field

The synthesis of double-hydrophilic core/shell cylindrical polymer brushes (CPBs), their hybrids with magnetite nanoparticles, and the directed alignment of these magnetic hybrid cylinders by a magnetic field are demonstrated. Consecutive grafting from a polyinitiator poly(2( 2-bromoisobutyryloxy) ethyl methacrylate) (PBIEM) of tert-butyl methacrylate (tBMA) and oligo(ethylene glycol) methacrylate (OEGMA) using atom-transfer radical polymerization (ATRP) and further de-protection yields core/shell CPBs with poly(methacrylic acid) (PMAA) as the core and POEGMA as the shell, which is evidenced by H-1 NMR, gel permeation chromatography (GPC), and dynamic and static light scattering (DLS and SLS). The resulting core/shell brush is well soluble in water and shows a pH responsiveness because of its weak polyelectrolyte core. Pearl-necklace structures are observed by cryogenic transmission electron microscopy (cryo-TEM) at pH 4, while at pH 7, these structures disappear owing to the ionization of the core. A similar morphology is also found for the polychelate of the core/shell CPBs with Fe3+ ions. Superparamagnetic magnetite nanoparticles have also been prepared and introduced into the core of the brushes. The hybrid material retains the superparamagnetic property of the magnetite nanoparticles, which is verified by superconducting quantum interference device (SQUID) magnetization measurements. Large-scale alignment of the hybrid cylinders in relatively low magnetic fields (40-300 mT) can easily be performed when deposited on a surface. which is clearly revealed by the atomic force microscopy (AFM) and TEM measurements.