Magnetically-responsive microparticles with improved response times

A magnetically responsive particle having substantially no residual magnetism and a faster 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 first heterocoagulant intermingled with the ferrofluid of the first magnetically responsive layer as to heterocoagulate the magnetically responsive grains on the core;
• a first dispersant covering the first magnetically responsive layer and cross-linked with the first heterocoagulant so as to form a first cross-linked polymeric layer that encapsulates the first magnetically responsive layer on the core;
• a second magnetically responsive layer bound to the first cross-linked polymeric layer, said second magnetically responsive layer comprising a ferrofluid that includes a plurality of magnetically responsive grains, which may be identical to or different from the ferrofluid of the first magnetically responsive layer, 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 second heterocoagulant intermingled with the ferrofluid of the second magnetically responsive layer so as to heterocoagulate said second magnetically responsive grains on the first cross-linked polymeric layer;
• and
• a second dispersant covering the second magnetically responsive layer and cross-linked with the second heterocoagulant so as to form a second cross-linked polymeric layer that encapsulates the second magnetically responsive layer on the first cross-linked polymeric layer,
• 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 the first magnetically responsive layer and the first cross-linked polymeric layer that encapsulates the first magnetically responsive layer.

A method of preparing a magnetically responsive particle having substantially no residual magnetism and a faster magnetic response time, the method comprising

• preparing a first aqueous dispersion comprising an electrically charged core layer and a ferrofluid that includes a plurality of magnetically responsive grains in a manner such that the magnetically responsive particles agglutinate to the core to form a first magnetically responsive layer, 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;
• adding at least one of a first dispersant or first heterocoagulant to the first magnetically responsive layer so as to form a second aqueous dispersion therewith;
• encapsulating the first magnetically responsive layer with at least one of the first dispersant or first heterocoagulant so as to form a cross-linked first polymeric layer;
• adding additional ferrofluid that includes a plurality of magnetically responsive grains to the first polymeric layer so as to form a second magnetically responsive layer on the first polymeric layer, wherein the magnetically responsive particles are attached to the first polymeric layer, 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;
• adding at least one of a second dispersant or second heterocoagulant to the second magnetically responsive layer so as to form a third aqueous dispersion therewith;
• and
• encapsulating the second magnetically responsive layer with at least one of the second dispersant or second heterocoagulant so as to form a cross-linked second polymeric layer,
• 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 the first magnetically responsive layer and the first cross-linked polymeric layer that encapsulates the first magnetically responsive layer.