| abstract |
An electrophoretic medium (200) comprising a plurality of particles (108, 218)suspended in a suspending fluid (206), the particles (108, 218) being capable of movingthrough the fluid (206) upon application of an electric field to the medium (200).The fluid has dissolved or dispersed therein a polymer having a numberaverage molecular weight in excess of 20,000, the polymer being essentiallynon-absorbing on the particles. The polymer improves the bistability of the display(i.e., the period for which a written image persist without the display being refreshed)but does not greatly increase the viscosity of the suspending fluid, thus keeping theswitching time of the display within reasonable limits. The medium may be encapsulated,or may be in the form a polymer-dispersed electrophoretic medium. |