Due to their versatility, liquid/liquid interfaces are currently of great interest for a variety of
optical applications, such as variable-focus lenses, microfluidics, optical switches and display
elements. This thesis explores the properties of the electrified interface between two immiscible
electrolytic solutions (ITIES ) in two types of systems.
The ITIES formed between a droplet and the surrounding liquid, supported on an electrode, has
been shown to provide a viable ultra-low-voltage alternative to currently used systems. Due
to the electrowetting effect, significant changes in the contact angle are obtained as the result
of small variations in the applied voltage, 1 V. On real electrodes, chemical and physical
inhomogeneities were found to lead to significant hysteresis of the contact angle variation. Pulsed
voltage was used to reduce hysteresis and increase the interval of angles reached. A theoretical
model of the droplet dynamics is developed by analogy to the harmonic oscillator. The predicted
time-dependent motion of the system rationalises the behaviour observed experimentally, and
helps in the design of viable systems. The developed model could also provide a new framework
for the study of the role of friction in wetting dynamics.
Beside changing its shape, another way to functionalise the ITIES is by allowing nanoparticles to
spontaneously assemble at the interface. Once localised, their arrangement greatly influences the
response of the system to incident light. An external voltage can control the response time and
the structure of this assembly, as well as make it reversible. Such systems are of great interest for
controllable optics and sensing applications. There are few independent characterisation methods
of populated interfaces. A model is developed for the capacitance of an ITIES populated by
metal nanoparticles. Model predictions allow to extract important information from capacitance
measurements on the structure of the adsorbed layer, promoting this method as a quantitative
characterisation tool.
The Faraday rotation from a monolayer of dielectric nanoparticles at an ITIES is calculated in a
dipolar approximation. The particle density is assumed to be reversibly controlled by an applied
potential. The difference between the angle of rotation caused by particles dissolved in the bulk
and that caused by a monolayer arrangement is predicted to be large enough to make low-energy
switchable Faraday isolators possible.