Abstract
Ionic liquid crystals (ILCs) are anisotropic mesogenic molecules which additionally carry charges. This combination gives rise to a complex interplay of the underlying (anisotropic) contributions to the pair interactions. It promises interesting and distinctive structural and orientational properties to arise in systems of ILCs, combining properties of liquid crystals and ionic liquids. While previous theoretical studies have focused on the phase behavior of ILCs and the structure of the respective bulk phases, in the present study we provide new results, obtained within density functional theory, concerning (planar) free interfaces between an isotropic liquid L and two types of smectic-A phases (SA or SAW). We discuss the structural and orientational properties of these interfaces in terms of the packing fraction profile η(r) and the orientational order parameter profile S2(r) concerning the tilt angle α between the (bulk) smectic layer normal and the interface normal. The asymptotic decay of η(r) and of S2(r) towards their values in the isotropic bulk is discussed, too.
Highlights
Ionic liquid crystals (ILCs) are pure ionic systems, solely composed of cations (+) and anions (À)
The discussion focuses on two kinds of ionic liquid crystals (ILCs) which are described by the pair interaction potential U(r12,x1,x2) (eqn (1)), introduced in Section 2.1: first, ILCs with charges in the center, i.e., D = 0 (see Fig. 1 and eqn (5)), and second, ILCs with charges at the tips, i.e., D/R = 1.8
For the case of an ionic liquid crystal with L/R = 4, eR/eL = 2, g/(Re0) = 0.045, lD/R = 5, and D = 0, i.e., the charges are localized in the center of the molecule, the bulk phase behavior is shown in the T*–Z0-phase diagrams of Fig. 4(a) where T* = kT/e0 and Z0 = Q0LR2p/6 are the reduced temperature and the mean packing fraction, respectively
Summary
Ionic liquid crystals (ILCs) are pure ionic systems, solely composed of cations (+) and anions (À). 7 and 8, is composed of cations with long alkyl-chains attached (1-dodecyl-3-methylimidazolium) and significantly smaller anions (iodide) For such an ILC system, one observes a liquid crystalline structure, in particular the smectic-A phase SA. This is done by investigating how the structural and orientational properties of ILC systems are affected by the presence of a free interface between coexisting bulk states Both smectic-A phases, SA and SAW, observed in ref. Ionic systems are often analyzed assuming a simple geometry of the particles, such as a spherical shape of the particles like in the restricted primitive model.[28,29,30] In this regard, the present study attempts to analyze the aforementioned type of interface between an isotropic and a smectic phase by accounting for an anisotropic particle shape combined with the presence of charges.
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