Patent ID: 7989065

Claim:
A magnetically responsive particle having substantially no residual magnetism and an improved magnetic response time, comprising: an electrically charged core layer; a first magnetically responsive layer on the core layer, said first magnetically responsive layer comprising a ferrofluid that includes a plurality of magnetically responsive grains, wherein each of the plurality of magnetically responsive grains in the ferrofluid has a size in a range of about 10 nm to about 120 nm, a portion of the magnetically responsive grains being agglutinated to the core layer; a first polymeric layer encapsulating the first magnetically responsive layer, said first polymeric layer formed by cross-linking a first monomer having a first reactive group and a second monomer having a second reactive group; a second magnetically responsive layer on the first polymeric layer, said second magnetically responsive layer comprising a ferrofluid that includes a plurality of magnetically responsive grains, wherein each of the plurality of magnetically responsive grains in the ferrofluid has a size in a range of about 10 nm to about 120 nm, which may be identical to or different from the ferrofluid of the first magnetically responsive layer, attached to the first or second reactive groups of the first polymeric layer; and a second polymeric layer encapsulating the second magnetically responsive layer, said second polymeric layer formed by cross-linking a third monomer having a third reactive group and a fourth monomer having a fourth reactive group, wherein the magnetically responsive particle has a magnetic response time that is at least about 50% faster as compared to a magnetically responsive particle having only one magnetically responsive layer.