Room temperature ionic liquids: A simple model. Effect of chain length and size of intermolecular potential on critical temperature

Abstract

A model of a room temperature ionic liquid can be represented as an ion attached to an aliphatic chain mixed with a counter ion. The simple model used in this work is based on a short rigid tangent square well chain with an ion, represented by a hard sphere interacting with a Yukawa potential at the head of the chain, mixed with a counter ion represented as well by a hard sphere interacting with a Yukawa potential of the opposite sign. The length of the chain and the depth of the intermolecular forces are investigated in order to understand which of these factors are responsible for the lowering of the critical temperature. It is the large difference between the ionic and the dispersion potentials which explains this lowering of the critical temperature. Calculation of liquid-vapor equilibrium orthobaric curves is used to estimate the critical points of the model. Vapor pressures are used to obtain an estimate of the triple point of the different models in order to calculate the span of temperatures where they remain a liquid. Surface tensions and interfacial thicknesses are also reported.

Charge ordering and scattering pre-peaks in ionic liquids and alcohols

“…Conversely, complex ionic disorder is characterised by a scattering pre-peak [6,8,11,23], which is present in room temperature ionic liquids and absent from the high temperature ionic melts [3,4]. This pre-peak has been associated to the segregated domains, as observed in early computer simulations of these systems [42], as well in models [43,44]. In Ref.…”

Multiscale response of ionic systems to a spatially varying electric field

“…Of course, this comparison is equivalent to test the linear response, Eq. (15). The case of m = 0 is also shown, however, the agreement is less satisfactory for low wavevectors, which is due to the diverging amplitude in the limit of zero wavevector causing a non-linear response and failure of the constitutive relation, Eq.…”

“…The response is evaluated for two simple models: (i) one model for molten salt proposed by Hansen and McDonald [1] and (ii) one modified model for ionic liquids used by Chapela et al [15]. For the molten salt the ions are simple spherical particles with same mass and point charges ±q.…”

“…The particles in the cation are linearly connected using a simple spring force F = −k(r − 1)r/r, where k = 100 is the spring constant. Anions are simple spherical point charge particles [15]. Rather than a hard-sphere type potential in the original model, the van der Waals interactions are here given through the Weeks-Chandler-Andersen potential [22] V (r) = 4((1/r) 12…”