A rotation mechanism for bichromal balls in a twisting ball display is based
on
electrostatic induction. A bichromal ball with hemispherically differentiated electrical
time constants is immersed in a dielectric liquid containing a charge director
solution. The liquid is contained within an encapsulant. The charge director solution
has positive and negative ions with substantially different mobilities. Space charge
clouds created in this fluid upon application of an electric field act so as to
induce polarization differently in each hemisphere, leading to a net dynamic polarization.
Interaction between the space charge and the induced polarization serves to rotate
the ball. Ions are subsequently trapped at the fluid/encapsulant interface due
to greater polarizability of the encapsulant. A threshold is obtained by the excess
field needed to release the ions and so reverse the ion motion.
