Electrophoretic media comprising electrophoretic particles and a combination of charge control agents

An electrophoretic medium comprising:

• a non-polar fluid;
• a first type of particles comprising a first type of pigment, the first type of pigment being inorganic and having a first color, the first type of particles having a first charge polarity;
• a second type of particles comprising a second type of pigment, the second type of pigment having a second color, the second color being different from the first color, the second type of particles having a second charge polarity, the second charge polarity being the opposite of the first charge polarity;
• a third type of particles comprising a third type of pigment having a third color, the third color being different from the first and second colors, the third type of particles having the second charge polarity;
• and
• a fourth type of particles comprising a fourth type of pigment having a fourth color, the fourth color being different from the first, second, and third colors, the fourth type of particles having the first charge polarity or the second charge polarity;
• a first charge control agent having a molecular structure, the molecular structure of the first charge control agent including at least one quaternary ammonium group and a non-polar tail;
• a second charge control agent having a molecular structure, the molecular structure of the second charge control agent including two or more polar groups, and a non-polar tail, the two or more polar groups being selected from the group consisting of amino group, sulfonate group, sulfate group, sulfinate group, carboxylic acid group, phosphonic acid group, phosphinate group, phosphate group, hydroxyl group, thiol group, alpha diketone group, beta diketone group, ethylene oxide group, and propylene oxide group, the non-polar tail comprising a polymeric group, the polymeric group being formed by a monomer comprising an alkyl or alkenyl group having at least ten carbon atoms, and
• a water-soluble ether, the water-soluble ether having molecular weight from 75 to 5,000 Dalton.