Browsing by Author "Minofar, B"

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    Studying electrical double layers in ionic liquids using neutron and x-ray reflectometry
    (Australian Institute of Physics, 2010-02-05) Lauw, Y; Nelson, A; Horne, MD; Rodopoulos, T; Minofar, B; Webster, NAS; Hamilton, WA
    Ionic liquids are typically defined as salts that exist in a liquid state at, or near, room temperature. Due to their favourable properties (e.g., good thermal stability, low volatility, and wide electrochemical window), ionic liquids have potential use in many industrial applications, such as catalysis, lubrication, batteries, and metal electrodeposition. Despite recent advances in the field, ionic liquid research is still in its infancy. Additional fundamental studies are needed to explore the properties of ionic liquids and to allow the full potential of these properties in particular applications to be exploited. Electrical double layers (EDL) are well known in aqueous colloidal systems where the potential field from a charged surface affects many properties of the particle. The structure of the EDL at a conductive surface is of prime importance to electrochemistry because it strongly affects the transport of reactants and products within the region where electrochemical reactions take place. The understanding of the EDL in ionic liquids is not nearly as advanced as aqueous systems and even a description of how it responds to changes in the conductor potential is yet to be agreed. Here we present some recent results from simulation and Neutron/X-ray reflectometry measurements that explore the electrical double layer in ionic liquids at the air-liquid and solid-liquid interfaces. The effect of water impurities within the (EDL) of an ionic liquid is of particular interest since they are known to reduce the electrochemical window of ionic liquids, decrease their density and viscosity, and anomalously decrease their surface tension.
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    X-ray reflectometry studies on the effect of water on the surface structure of [C(4)mpyr][NTf2] ionic liquid
    (Royal Society of Chemistry, 2009-10-21) Lauw, Y; Horne, MD; Rodopoulos, T; Webster, NAS; Minofar, B; Nelson, A
    The effect of water on the surface structure of 1-butyl-1-methylpyrrolidinium trifluoromethylsulfonylimide [C(4)mpyr][NTf2] ionic liquid was investigated using X-ray reflectometry. The measured reflectivity data suggests a significant amount of water is adsorbed at the surface, with the first layer from the gas (nitrogen)-liquid phase boundary mainly occupied by a mixture of cations and water. Beyond the cation + water layer, the scattering length density increases towards the bulk value, indicating a decreasing amount of water and cations, and/or an increasing amount of anions. The orientation of the butyl chain of cation at the phase boundary and the population of water at the surface were described based on results from an independent molecular dynamics (MD) simulation. We show that the presence of water in the ionic liquid has a non-monotonic effect on the overall thickness of the surface. At low water content, the addition of water does not change the surface thickness since water is mainly present in the bulk. As the water content increases, the surface swells before eventually shrinking down close to the solubility limit of water. The non-monotonic surface thickness is used to explain the anomalous trend of surface tension in ionic liquid-water mixtures reported in the literature. © 2009, Royal Society of Chemistry