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Method of Uniformly Orienting Magnetic Particles in a Dispersion

IP.com Disclosure Number: IPCOM000060537D
Original Publication Date: 1986-Apr-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 2 page(s) / 39K

Publishing Venue

IBM

Related People

Bandara, U: AUTHOR [+3]

Abstract

Magnetic particles are enveloped in a spherical coating by bead polymerization. If dispersed in a liquid and exposed to an outer homogeneous magnetic field, the spherical droplets thus obtained line up, with their magnetic moments pointing essentially in the same direction. There are two stable positions that acicular magnetic particle overlapping magnetic fields may assume relative to each other: a position where the magnetic moments point in opposite directions (twin position; Fig. 1) and a position in which the magnetic moments point in the same direction (chain position; Fig. 2). If the acicular magnetic particles are enveloped in a spherical coating, the twin position is destabilized, i.e., the particles, if freely rotatable, assume the chain position (Fig. 3). The spherical coating is formed as follows.

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Method of Uniformly Orienting Magnetic Particles in a Dispersion

Magnetic particles are enveloped in a spherical coating by bead polymerization. If dispersed in a liquid and exposed to an outer homogeneous magnetic field, the spherical droplets thus obtained line up, with their magnetic moments pointing essentially in the same direction. There are two stable positions that acicular magnetic particle overlapping magnetic fields may assume relative to each other: a position where the magnetic moments point in opposite directions (twin position; Fig. 1) and a position in which the magnetic moments point in the same direction (chain position; Fig. 2). If the acicular magnetic particles are enveloped in a spherical coating, the twin position is destabilized, i.e., the particles, if freely rotatable, assume the chain position (Fig. 3). The spherical coating is formed as follows. The magnetic particles (I) (Fig. 4), having OH-groups on their surface, are made to react with 3-methacrylpropyl-trimethoxysilane(II), forming particles
(III) coated with a thin film of (II). (III), a monomer (IV), such as methylmethacrylate (MMA), insoluble in water, and a polymer initiator, soluble in the monomer but insoluble in water, are dispersed in water by vigorous stirring. An emulsion of spherical MMA droplets (V) is formed, with the droplets preferably containing a magnetic particle (Fig. 5). The droplets' shape is spherical because with that shape the MMA/water interfacial energy is...