Electrophoresis is the movement of electrically charged particles through electric fields. The principle of electrophoresis is used, among other things, in bistable displays such as e-paper.
The technical implementation of electrophoresis in displays involves the use of tiny beads, microcapsules or microparticles that are located in a liquid and whose position can be influenced by electric fields. The beads can be made of polyethylene (PE) and have a diameter of 20 µm to 100 µm.
In later developments, these were replaced by tiny titanium oxide particles with one side positively charged and the other negatively charged. These tiny particles have a diameter of only one micrometer (µm) and, like the beads, lie between two electrode arrays, the upper of which is made of induim tin oxide (ITO) and is transparent, the lower reflective.
The beads contain positively and negatively charged pigments, one white, the other black. When an electric field is applied to the electrodes, the beads or the charged microparticles rotate depending on the polarity of the electric field. Positive charges repel the positively charged white particles, causing the corresponding particle to rotate, while negative charges cause the positively charged particles to be attracted.