title: Monodisperse magnetizable composite silica spheres with tunable dipolar interactions.
abstract: We demonstrate that magnetic particles of maghemite (gamma-Fe(2)O(3)) and cobalt ferrite (CoFe(2)O(4)) can be irreversibly attached to colloidal silica that is grafted with 3-mercaptopropyl(trimethoxy)silane (followed by the controlled growth of a silica layer) to obtain stable dispersions of monodisperse colloidal silica spheres that contain a dense shell of ferrite particles at an adjustable distance from the sphere surface. Magnetization of the ferrite shell induces a large dipole moment, and adjusting the thickness of the outer silica layer enables one to tune the contact attraction. This novel type of magnetizable silica colloid exhibits structure formation in a homogeneous field that varies from isotropic distributions to elongated dipolar chains.
authors.affiliation: Van't Hoff Laboratory for Physical and Colloid Chemistry, Debye Institute, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands.
authors.forename: E M
authors.initials: EM
authors.lastname: Claesson
authors.forename: A P
authors.initials: AP
authors.lastname: Philipse