title: Reversible clustering of pH- and temperature-responsive Janus magnetic nanoparticles.
abstract: Janus nanoparticles have been synthesized consisting of approximately 5 nm magnetite nanoparticles coated on one side with a pH-dependent and temperature-independent polymer (poly(acrylic acid), PAA), and functionalized on the other side by a second (tail) polymer that is either a pH-independent polymer (polystyrene sodium sulfonate, PSSNa) or a temperature-dependent polymer (poly(N-isopropyl acrylamide), PNIPAM). These Janus nanoparticles are dispersed stably as individual particles at high pH values and low temperatures, but can self-assemble at low pH values (PSSNa) or at high temperatures (>31 degrees C) (PNIPAM) to form stable dispersions of clusters of approximately 80-100 nm in hydrodynamic diameter. The Janus nanoparticle compositions were verified using FTIR and XPS, and their structures observed directly by TEM. Their clustering behavior is analyzed by dynamic light scattering and zeta potential measurements.
authors.affiliation: Department of Chemical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.
authors.forename: Tatsushi
authors.initials: T
authors.lastname: Isojima
authors.forename: Marco
authors.initials: M
authors.lastname: Lattuada
authors.forename: John B
authors.initials: JB
authors.lastname: Vander Sande
authors.forename: T Alan
authors.initials: TA
authors.lastname: Hatton
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry*; D003460:Crystallization / Q000379:methods*; D006863:Hydrogen-Ion Concentration; D046911:Macromolecular Substances / Q000737:chemistry; D008280:Magnetics; D008422:Materials Testing; D008968:Molecular Conformation; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure*; D036103:Nanotechnology / Q000379:methods*; D010316:Particle Size; D013499:Surface Properties; D013696:Temperature
chemical_list: D000180:Acrylic Resins; D046911:Macromolecular Substances; C052970:poly-N-isopropylacrylamide