Theory and molecular simulations of the Interface of Two Immiscible Electrolytic Solutions (ITIES)

In this thesis, atomistic simulations of the specific adsorption of tetrabutylammonium tetraphenylborate (TBA+TPB-) have been performed for the first time. Three different systems have been analysed; DCE(TBA+TPB-)/vapour, DCE(TBA+TPB-)/pure water, DCE(TBA+TPB-)/water(Na+Cl-). The ions have been shown to change the bulk properties of the electrolyte but only change the non-electrostatic interfacial properties in the DCE/vapour system. TBA+TPB- has been seen to specifically adsorb at all the interfaces simulated. Due to the more compact nature of the TPB- ion, the TBA+TPB- charge separate in the adsorption equilibrium. For DCE/water and the interface of two immiscible electrolytic solutions (ITIES), the adsorption of the ions recede from the interface engendering the interface resistance to change for properties such as surface tension and interfacial width. The adsorption of salt at the DCE/water interface shows significant charge overscreening beyond 0.08m but no such overscreening is seen at the DCE/vapour interface. Due to the charge separation at the interface, an electric field is generated seen as a shoulder in the electrostatic potential distributions. The presence of salt at the interface also changes the bulk-bulk potential drop. For the ITIES, on charging, the bulk density of DCE was seen to increase. The field also has an effect on the dumbbells and when the field does not support the negative TPB- to be present at the interface, the dumbbells are destroyed which negates the electric field that had been generated by the charge separation. The properties of the solvent, interface and ions (bulk and interfacial) in all cases have been measured. Large errors were seen in the measurement of surface tension and differential capacitance, however, the thesis presents a novel description on the specific adsorption of TBA+TPB- at the ITIES.