Insights into the design and optimization of fast displays
Mohammad Khorsand Ahmadi defended his PhD thesis at the Department of Mechanical Engineering on December 20th.
Electronic paper displays replicate the appearance of conventional ink on paper, creating a low-power, paper-like display. They have gained significant importance as a display technology due to their low power consumption, wide viewing angles, and suitability for outdoor readability. The PhD research of Mohammad Khorsand Ahmadi will most likely contribute valuable insights into the design and optimization of fast displays and other applications utilizing the combined effects of electrophoresis and electro-osmosis. In addition, this study contributes to the broader understanding of particle manipulation and fluid dynamics in complex electrokinetic systems.
Current conventional electronic paper displays use microcapsules filled with a nonpolar liquid containing black and white (or colored) pigment particles that can be moved to the top or bottom of the capsule. These devices rely on electrophoresis (EP), the migration of charged particles in a liquid under the influence of an applied electric field; their switching speed is thus limited by the mobility of the charged pigment particles. To address this limitation, we propose a display principle that, in addition to EP, also makes use of electro-osmosis (EO), an effect that drives a flow of the fluid itself.
Reduction in switching time
The aim of the PhD project of Khorsand Ahmadi was to create a model system that enables to investigate the interplay of electro-osmosis and electrophoresis in a system of colloidal particles, surfactants, and nonpolar solvents in the presence of an external electric field. The main goal was to exploit electro-osmosis to enhance the efficiency of electrokinetic displays. By achieving this, a reduction in the display’s switching time is expected, potentially expanding the use of electrokinetic displays for future use in video applications.
Faster particle transport
By tracking the 3D motion of particles within our fluidic cells, it was found that in optimized geometries, EO can contribute to a significantly faster particle transport across a fluidic cell. Through measurements aimed at quantifying the governing physical parameters, such as the effective charge of the particles, the density of charge carriers in the fluid, or the surface charges on the outer walls of the fluidic cells, the experimental results can be rationalized using numerical simulations that incorporate the governing physical mechanisms.
Title of PhD thesis: Experimental Study of the Interplay between Electrokinetic Effects for Electronic Paper Displays. Supervisors: Dr. Hans Wyss, Prof. Jaap den Toonder and Prof. Alex Henzen.