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Title: A simulation study of simple ionic liquids near charged walls : the melting of the electric double layers and structural transitions at the interface
Author: Kirchner, Kathleen
Awarding Body: University of Strathclyde
Current Institution: University of Strathclyde
Date of Award: 2013
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The temperature dependence of the electrical double layer (EDL) capacitance of high and low temperature ionic liquids (IL) is under excited debates within experimental, theoretical & computational communities for decades. Using a coarse-grain model of ILs with asymmetric sized ions we studied the EDL behaviour of ILs at an electrified interface to gain understanding in the temperature-effect. We improved the accuracy of the capacitance calculations by increasing the overall simulation time by an order of magnitude compared to former publications and discussed possible error sources. The analysis of different temperatures from 250K to 500K revealed a voltage dependent temperature-effect on the differential capacitance. To our opinion, the temperature dependence can be attributed to the formation of well ordered structures of the EDL at low temperatures, that are ‘melted’ at higher temperatures. The results provide an explanation for the contradicting experimental results published in the past years. By systematically analysing number density profiles, a charge induced structural transition has been revealed. At most surface charge densities under study, the electric double layer forms a multilayered structure. At transition points, a hexatic (also termed as Moiré-like) monolayer structure is formed by the counter-ions. These findings correlate very well with experimental observations on room temperature ionic liquids and metal melts by Freyland and co-workers (Phys. Chem. Chem. Phys., 2008, 10, 923-936). The ions of the hexatic layer screen the electrode charge completely, thereby annihilating the interaction between electrode and subsequent bulk ionic liquid. Moreover we can report the formation of herring-bone structures at higher surface charge densities, that form as the superposition of two hexatic layers.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available