Electrophoretic media including charge control agents comprising quartenary amines and unsaturated polymeric tails

An electrophoretic medium comprising:

• (a) a non-polar fluid;
• (b) a plurality of first charged particles having a first charge polarity;
• (c) a plurality of second charged particles having a second charge polarity;
• and
• (d) a charge control agent comprising a quaternary amine and an unsaturated polymeric tail having at least one carbon-carbon double bond comprising monomers of at least 10 carbon atoms in length, wherein the polymeric tail comprises a polyester, and wherein the charge control agent is adsorbed on the first and second charged particle;
• wherein the conductivity of the electrophoretic medium is higher than 300 pS/m, when the content of the charge control agent in mg per gram of pigment is 15 or higher;
• and
• wherein the viscosity of the electrophoretic medium is less than 5×10−2 Pa·s at −30° C., measured with a rheometer having a recessed concentric cylinder using a temperature ramp of 2° C. per minute method.