| 摘要 |
PURPOSE:To obtain a magnetic fluid which uses oils as a liquid medium, where a solid phase is not separated from a liquid phase and whose dispersion stability is excellent by a method wherein a nonionic surface-active agent and an anionic surface-active agent are adsorbed to the surface of fine particles of a magnetic oxide and, furthermore, a cationic surface-active agent is adsorbed. CONSTITUTION:A nonionic surface-active agent is added to a water suspension containing fine particles of a magnetic oxide; the mixture is ripened at a temperature of higher than a cloud point; the surface of the fine particles of the magnetic oxide is covered with the nonionic surface-active agent which does not display a hydrophile property because a hydrogen bond in a polyethylene oxide chain (a hydrophile part) at an anionic interface has been cut due to a heating operation and water bonded to oxygen has been removed; the water adsorbed to the surface of the particles is taken away. In succession, an anionic surface-active agent and a cationic surface-active agent are oriented and adsorbed easily and firmly to the surface of the fine particles of this magnetic oxide while a hydrophobic group has been directed to the outside. Because the fine particles of the magnetic oxide displaying a hydrophobic property are used as a raw material, they become a magnetic fluid where a solid phase is not separated from a liquid phase in a liquid medium composed of oils and whose dispersion stability is excellent. |
