Pyroelectric active coatings in aqueous environmentsTuesday (18.06.2019) 11:30 - 11:45
The poling process of a ferroelectric material causes the dipoles of the spontaneous polarization to orient in the direction of the externally applied field. This poling is stable below the Curie temperature until a large enough electric field of the opposite sign is applied, which enables the application of ferroelectrics for non-volatile memory applications. The incomplete compensation of the spontaneous polarization of the outermost layer of the ferroelectric material by neighbouring atoms results in charged surfaces on the two opposing sides to which the electric field was applied. This surface charge is compensated either by reorganization of the surface atomic structure, by developing a certain domain structure in order to minimize the external electric field or by surrounding charges (such as ions in solutions, dust particles and others) if not in a vacuum environment. The so-called pyroelectric effect is inherent in all ferroelectric materials. It is defined as the change in the spontaneous polarization due to a temperature change multiplied by a factor called the pyroelectric coefficient so that ΔPs=p*ΔT [Lang2005]. The temperature-induced change in the spontaneous polarization perturbs the charge balance at the surface of ferroelectric single crystals, causing a net surface charge of the pyroelectric active material during a temperature change.
It has been suggested that this surface charge influences processes in the electrochemical double layer (EDL) located at the interface between a material and a surrounding aqueous medium [Kakekhani2015]. The applications of pyroelectric active layers in aqueous environments might therefore be desirable to influence processes in the EDL such as adsorption, filtration, anti-fouling or heterogeneous crystallization [Goldberg2018] and to even switch the surface properties by changing the temperature change direction. The co-polymer Polyvinylidenefluorid-Trifluoroethylene P(VDF-TrFE) is a semi-crystalline polymer that can spontaneously crystallize into the ferroelectric phase upon deposition. A beneficial orientation of the polymer chains in thin films between 100 and 500nm on different substrates can be achieved by dip- and spin-coating P(VDF-TrFE) from a solution. The presentation will cover the preparation and characterization of P(VDF-TrFE) thin films and their potential application for anti-ice coatings.