Saturation Phenomena in ElectrowettingResearch funded by the General Secretariat for Research and Technology through the "ΕΝΤΕΡ" Program (2003 2005) 
By
applying a voltage between the base electrode and the conducting liquid,
charges accumulate at the dielectric solid / liquid interface. Charges
repel each other enhancing wetting. The dependence of the contact
angle on the applied voltage, V, is well predicted
by the Lippmann equation at low voltages. However, wetting
enhancement levels off when voltage exceeds a critical value. The contact
angle reaches a lower limit and the associated phenomenon, which
is not predicted by the Lippmann equation, is commonly called contact
angle saturation. 


Lippmann equation fails at high voltages 

Lippmann equation: 

The electrostatic energy stored in the ideal capacitor is equal to solid / liquid interfacial energy change  
ε_{r } : relative dielectric
permittivity
ε_{0 }: electric permittivity of vacuum γ_{lg}: liquid surface tension 

Connection between breakdown strength and contact angle saturation  
The capillary
electrohydrostatics problem is solved by the Galerkin/Finite
Element method (see a sample of the computational
mesh); it is found that contact angle saturation sets in when the field
strength, in the vicinity of the three phase contact line, exceeds the
breakdown strength of the dielectric coating of the base electrode  cf.
Papathanasiou
and Boudouvis "Manifestation of the connection between dielectric breakdown
strength and contact angle saturation in electrowetting." Applied Physics
Letters 86, 164102 (2005). 
