US Patent 7236290 Electrophoretic medium with improved stability

An electrophoretic medium comprises a liquid and at least one particle disposed within the liquid and capable of moving therethrough on application of an electric field to the medium. The medium further comprises a free radical scavenger selected from the group consisting of (a) stable free radicals; and (b) polymeric free radical scavengers comprising a plurality of free radical scavenging groups attached to a polymeric chain. The medium is desirably encapsulated.