The electrical charge of colloidal particles plays an important role in applications such as electrophoretic ink displays (Sony e-Reader, Kindle,…) and liquid toner printing. Typically charging additives (surfactants) are added to charge up particles, but the precise mechanism of this charging is not understood. Video microscopy and optical trapping electrophoresis has been used in our group to measure charging processes on a particle-to-particle basis with accuracy high enough to see changes with plus or minus the elementary charge. This method offers a unique way to study the fundamental charging and de-charging processes which are relevant for these applications.
The aim of this Master thesis is to study the electrical charge of particles used in e-ink displays with a precision higher than the elementary charge. To achieve this movies will be made of fluorescent particles using a microscope setup operated in LabView. By applying ac voltages the charge of the particles can be measured in real-time. Therefore the dynamic changes of the charge can be studied with high precision as a function of the particle size and concentration of additives such as surfactants. It is expected that the charge fluctuations will be more rapid when the concentration of surfactant is increased and when the particle size is larger.