Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
2002-05-24
2004-11-09
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
47, 47, 47, C252S062520, C252S062620, C252S062540
Reexamination Certificate
active
06815063
ABSTRACT:
This invention relates to a magnetic fluid medium (a ferrofluid) which comprises a suspension of nanoscale ferro- or ferri-magnetic particles dispersed in a carrier liquid. A process for making the ferrofluid is also disclosed.
Ferrofluids are stable suspensions of nanoscale ferro- or ferri-magnetic particles in carrier liquids. The particles are small enough that thermal energy maintains a stable dispersion. However, regardless of the procedure hitherto used for synthesizing ferrofluids, the dispersion is polydisperse (i.e. there is a relatively wide range of particle sizes).
The term “ferromagnetic” is often used in the art to embrace materials which are either “ferromagnetic” or “ferrimagnetic”. The present invention may be utilized to prepare fluids containing ferro- or ferri-magnetic nanoscale particles.
According to a first aspect of the present invention, there is provided a magnetic fluid medium which comprises a plurality of ferro- or ferri-magnetic particles, each of which particles has a largest dimension no greater than 100 nm, said particles having been prepared by a process which includes a step in which the particles are formed within an organic macromolecular shell.
Preferably, the ferro- or ferri-magnetic particles have a largest dimension no greater than 50 nm, more preferably no greater than 15 nm.
Preferably, the magnetic fluid medium is monodisperse, by which we mean that the particles in the fluid do not vary in their largest dimension by more than about 10%, preferably by no more than 5%.
Normally, the nanoparticles will be generally spherical in shape, in which case the largest dimension will refer to the diameter of the particle. In some circumstances, other particle morphologies may be established in which case the size of the particles is referred to in terms of the largest dimension.
As a result of the process by which they are formed, each of the ferro- or ferri-magnetic particles is initially at least partially accommodated within an organic macromolecule. In one embodiment, the magnetic fluid medium of the invention comprises the particles still accommodated within the organic macromolecules within which they are formed. In this embodiment, the organic macromolecular shell may be functionalised (see below). In another embodiment, the organic macromolecular shell is removed to leave the nanoparticle itself and in yet a further embodiment, the organic macromolecular shell may be carbonized to provide a carbon layer surrounding a nanoparticle core.
The term macromolecule here means a molecule, or assembly of molecules, which may have a molecular weight of up to 1500 kD, typically less than 500 kD.
The macromolecule should be capable of accommodating or at least partially accommodating the ferro- or ferri-magnetic particle, and may therefore comprise a suitable cavity capable of containing the particle; such a cavity will normally be fully enclosed within the macromolecule. Alternatively, the macromolecule may include a suitable opening which is not fully surrounded, but which nevertheless is capable of receiving and supporting the magnetic particle; for example, the opening may be that defined by an annulus in the macromolecule.
Suitable organic macromolecules which may be used in the invention are proteins having a suitable cavity or opening for accommodating a nanoscale particle. Presently preferred is the protein apoferritin (which is ferritin in which the cavity is empty). However, other suitable proteins include, for example, flagellar L-P rings and virus capsids.
The ferro- or ferri-magnetic material chosen should be one which is capable of being magnetically ordered. It may be a metal, a metal alloy or an M-type or spinel ferrite. The metal, metal alloy or ferrite may contain one or more of the following: aluminium, barium, bismuth, cerium, chromium, cobalt, copper, dysprosium, erbium, europium, gadolinium, holmium, iron, lanthanum, lutetium, manganese, molybdenum, neodymium, nickel, niobium, palladium, platinum, praseodymium, promethium, samarium, strontium, terbium, thulium, titanium, vanadium, ytterbium, and yttrium. The metal, metal alloy or ferrite preferably contains one or more of the following: cobalt, iron and nickel.
In one embodiment of the magnetic fluid medium of the invention, the particles are accommodated or otherwise encased within the organic macromolecule, preferably protein coating, that inhibits aggregation and oxidation, and which also provides a surface which can be functionalised to allow dispersion in a variety of carrier liquids or attachment to contaminants. For example, the surface may be functionalised to render it hydrophobic, thereby allowing dispersion in a non-polar carrier liquid. Another example is to functionalize the surface with, for example, a metal binding ligand to enable the medium to be used in applications for removing metal contaminants from materials such as waste materials.
In this embodiment, the ferro- or ferri-magnetic material chosen is preferably a metal, such as cobalt, iron, or nickel; or a metal alloy; or an M-type ferrite. More preferably, the ferro- or ferri-magnetic material is a metal or a metal alloy.
The present invention most preferably makes use of the iron storage protein, ferritin, whose internal cavity is used to produce nanoscale magnetic particles. Ferritin has a molecular weight of 400 kD. Ferritin is utilised in iron metabolism throughout living species and its structure is highly conserved among them. It consists of 24 subunits which self-assemble to provide a hollow shell roughly 12 nm in outer diameter. It has an 8 nm diameter cavity which normally stores 4500 iron (III) atoms in the form of paramagnetic ferrihydrite. However, this ferrihydrite can be removed (a ferritin devoid of ferrihydrite is termed “apoferritin”) and other materials may be incorporated. The subunits in ferritin pack tightly; however there are channels into the cavity at the 3-fold and 4-fold axes. The presently preferred macromolecule for use in the invention is the apoferritin protein which has a cavity of the order of 8 nm in diameter. The ferro- or ferri-magnetic particles to be accommodated within this protein will have a diameter up to about 15 nm in diameter, as the protein can stretch to accommodate a larger particle than one 8 nm in diameter.
Ferritin can be found naturally in vertebrates, invertebrates, plants, fungi, yeasts, bacteria. It can also be produced synthetically through recombinant techniques. Such synthetic forms may be identical to the natural forms, although it is also possible to synthesise mutant forms which will still retain the essential characteristic of being able to accommodate a particle within their internal cavity. The use of all such natural and synthetic forms of ferritin is contemplated within the present invention.
Carrier liquids for ferrofluids are known per se. The carrier liquid may be polar or non-polar. Typical polar carrier liquids include water, lower alcohols such as ethanol, synthetic esters. Water is presently preferred. Typical non-polar carrier liquids which may be used are organic solvents such as heptane, xylene, or toluene, other hydrocarbons, polyglycols, polyphenyl ethers, perfluoropolyethers, silahydrocarbons, halocarbons, or styrene.
The nanoparticles may be prepared by a process in which a suspension of the organic macromolecule, typically in an aqueous medium, is combined with a source of ions of the appropriate metal or metals which is to comprise or consist the nanoparticle. Alternatively, but presently less preferred, the source of metal ions may be present in suspension to which a source of organic macromolecule is added.
The mixture of organic macromolecules and metal ions may be agitated to ensure homogenization.
Where the nanoparticle is to comprise the elemental metal, a reduction is effected, preferably under an inert atmosphere, on the suspension whereby nanoscale metal particles form within the organic macromolecule cavity. Where the nanoparticle is a ferrite, an oxidation is effected whereby the ferrite nanoscale particles are f
Kiliman Leszek
NanoMagnetics, Ltd.
Testa Hurwitz & Thibeault LLP
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