Dispersion and stability of nanoparticles in electrophoretic displays

This work is focused on investigating the influence of morphologies and composition of polymer coating layers on the dispersion stability of the hybrid particles dispersed in non-aqueous solvent for use in electrophoretic displays. Black copper chromite/polymer core-shell nanoparticles are synthesized through radical grafting polymerization. A series of methylacrylate monomers containing a plurality of alkyl side chains with different length, methyl methacrylate (MMA), tert-butylmethacrylate (TBMA), 2-ethylhexyl methacrylate (EHMA) and lauryl methacrylate (LMA), are employed for polymer encapsulation. The morphologies and composition of Black 1G/polymer core-shell nanoparticles are characterized by a combination of TEM and FTIR measurements. The UV–vis transmittance results demonstrate that the longer or more branching the monomers used in polymer modification, the more stable the particle suspension. For homopolymer encapsulation, monomer with an alkyl chain containing more than about four carbon atoms will impart good dispersibility to particles. Moreover, incorporation of a second monomer into polymer backbone can adjust the dispersion stability of particle suspension. When 15 mol% of MMA or 5 mol% of TBMA is added into PLMA backbone, the particles will gain better dispersibility than particles coated with 100 mol% LMA. If EHMA acts as main monomer, addition of a second monomer will decrease the dispersibility instead. These findings may be a guideline to tune electrophoretic medium stability and improve life of EPDs. Within this study, A dual-particle electrophoretic dispersion of P (4-VP-co-LMA) anchored Black 1G particles and white TiO₂ was prepared to show black/white image under a bias voltage of 5 V.