Synthesis of ellipsoidal hematite/silica/polymer hybrid materials and the corresponding hollow polymer ellipsoids

Ellipsoidal trilayer hematite/silica/poly(divinylbenzene) hybrid particles were prepared by distillation precipitation polymerization of divinyl benzene (DVB) in the presence of hematite/3-(methacryloxy)propyl trimethoxysilane (MPS)modified silica (SiO2) core-shell particles as,the seeds. The polymerization of DVB was performed in neat acetonitrile with 2,2'-azobisisobtyronitrilc. (AIBN) as initiator to coat the hematite/MPS-modified SiO2 seeds through the capture of DVB oligomer radicals with the aid of a vinyl group on the surface of the hematite/MPS-modified silica core-shell particles in the absence of any stabilizer or surfactant. The other hem atite/silica/polymer trilayer hybrid particles with different polarity and various functionality, such as hematite/silica/poly(ethylene glycol dimethacrylate) and hematite/ silica/poly(divinyl benzene-co-methacrylic acid) could also be prepared by this procedure. Hematite/silicalpoly(N,N'-methylenebisacrylamide) composite particles could be prepared with unmodified hematite/silica particles as seeds. Hollow poly(divinyl benzene) (PDVB) and poly(N,N'-methylenebisacrylamide) (PMBAAm) ellipsoids with movable hematite cores were subsequently developed after the selective etching of the silica midlayer in diluted hydrofluoric acid from hematite/silica/PDVB and hematite/silica/PMBAAm trilayer hybrids. Hollow PDVB ellipsoids were obtained by removal of the silica midlayer and hematite core of the trilayer hybrids with concentrated HF solution. The resultant trilayer hybrid particles and hollow polymer ellipsoids were characterized by transmission electron microscopy and vibrating sample magnetometer.