The present invention provides a nano-particle comprising a shell and a polar core, their preparation, and their applications in ER fluids, polymeric product, rubber composition, tire product, hard disk drive gasket, matrix composition, and engine mount etc. The shell comprises a polymer formed from formula (I) monomers and the core comprises a polymer formed from formula (II) monomers, in which R1 and R2 are hydrogen; R3, R4, R5, R6, and up to three of R7, R8, R9, and R10 are each independently selected from the group consisting of hydrogen, methyl, ethyl, propyl, and isopropyl; and at least one of R7, R8, R9, and R10 is a polar group that is more polar than any one of R1, R2, R3, R4, R5, and R6 groups.