Carbon sphere as a black pigment for an electronic paper

Carbon black, a black material popular for use in electronic paper, could limit the performance of the electronic paper due to its non-uniform structure. Carbon spheres, with spherical shape and relatively narrow size distribution, are expected to overcome this limitation and substitute for carbon black in the electronic paper. Carbon spheres were synthesized through a hydrothermal reaction using glucose as a raw material. By controlling reaction time and glucose concentration, appropriate non-agglomerated carbon spheres with an average diameter of 202.26 (±26.15) nm were fabricated. To increase their dispersibility in dielectric fluid, p-(2-ethylhexyl acrylate) was grafted onto the surface of the carbon spheres. Then, acid and base charge control agents were mixed with the carbon spheres to produce a pigment with higher mobility in the dielectric fluid. The optimized combination of pigment, charge control agent and solvent reveals reasonably fast switching time of about 540 ms.