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Identification of a Charging Mechanism using Infrared Spectroscopy

Volume 33, Number 2 (April 1979) Page 107-110

Fitzhenry, B.

The working medium in an electrophoretic image display (EPID) is a colloidal dispersion of charged organic pigment particles in a dyed organic medium. This suspension is sandwiched between two transparent electrodes. The display utilizes the movement of these charged particles in an electric field. Displacement of the negatively charged particles toward the front electrode allows the viewer to see the color of the particles, whereas the dyed medium is seen when the particles are moved to the rear electrode. The particles are charged through the addition of an organic dispersant, which serves the additional function of providing steric stabilization for the particles. Creating a stable charge on the pigment particles is essential to the operation of the display. With the use of infrared spectroscopy, the mechanism through which the dispersant reacts with surface of the pigment particles to generate a charge was identified. One of the charged species resulting from an acid/base type interaction between pigment and dispersant was identified with a Perkin-Elmer infrared spectrophotometer. Simpler models of both the acidic pigment and the basic dispersant were also reacted in the same manner in the same solvent system and analyzed using infrared spectroscopy. Results from the model systems support the analysis of the data on the more complicated pigment/dispersant system.