Electrically enhanced nucleation of liquid water
Objective and task description
The condensation of liquid water from vapor is driven by the gain in free energy of the condensed phase as compared to the vapor phase. In order to form the first small drop of water, a nucleation barrier due to the newly formed interfaces between liquid and vapor (and solids – if involved) needs to be overcome. Generally, the most common pathway to stimulate condensation is to increase the driving force, e.g. by cool the system. This leads effectively to a reduction of free energy of the liquid phase as compared to the vapor due to entropic effects. In case of polar liquids such as water, the condensed phase has a much higher polarizability than the vapor phase. As a consequence, the free energy of the system depends very strongly on the presence of electric fields: the stronger the electric field, the bigger the difference in free energy between liquid and vapor. The goal of this project, is to exploit this effect in order to stimulate condensation of liquid water from vapor.
Your task will be to perform experiments with a so-called Quartz-Crystal-Microbalance (QCM) to monitor the onset of liquid water condensation from vapor. A QCM is an ultrasensitive mass sensor with enough sensitivity to detect the adsorption of a single monolayer of water. The operating principle is based on the shift of the mechanical resonance frequency of quartz crystals upon variations of the mass of adsorbed material. You will be provided with specific QCM sensors that allow to apply electric fields in a specific interdigitated electrode geometry. You will expose these sensors to water vapor of variable degrees of (super)saturation at variable electrical voltage and simultaneously record variations of the resonance frequency and damping of the QCM sensor. A consistent data set should provide a clear overview of the shifts of the liquid-vapor phase boundary as a function of the electric field. (In combination with numerical simulations of the electric field distribution, which is outside the task of the present project, this is expected to lead to a scientific publication.)
What will you learn?
You will learn about the thermodynamics of phase transformations and the operation principle and usage of a quartz-crystal microbalance.
Contact Information & daily supervision
- Dr Igor Siretanu, Meander 160, tel. 1239