Role of dipole elongation in orientationally ordered liquids

Abstract

A recent study shows that the dipole elongation in the extended dipole model plays a significant role in the phase transitions of liquid crystal phases. In this paper, molecular dynamics (MD) simulations were performed for the dipole model with different distances between the two charges keeping the total dipole moment the same. The potential energy consists of the Lennard-Jones potential and the site-site electrostatic contribution of partial charges. Detailed analyses were made with respect to the average order parameters (P(1)) and (P(2)) as functions of density along with other thermodynamic properties. When the reduced dipole elongations are 0.16 and 0.32, respectively, it is shown that the chainlike structures in the low density regime, liquid phases with columnar and smectic orders, and solid phases are formed; the phase with nematic order is not present anymore. At 0.64, the phases with antiferroelectric order were favored. The transition is found at the reduced elongation 0.55. It shows that the phase transitions are quite sensitive to the molecular charge distribution; this simple system could exhibit rather rich phase behaviors, which represents a significant advance in identifying molecular and state parameters of the future ferroelectric liquids.

Kinetic Theory and Shear Viscosity of Dense Dipolar Hard Sphere Liquids

“…The snapshots are for system with λ ¼ 4 and two different densities ξ Ã ¼ 0.03 and ξ Ã ¼ 0.49. Similar structures are reported by simulations for dipolar fluids (and ferromagnetic particles) [42][43][44][45][46] and also by experiments [47][48][49][50]. )…”

Kinetic theory and shear viscosity of dense dipolar hard sphere liquids

“…The snapshots are for system with λ = 4 and two different densities ξ * = 0.03 and ξ * = 0.49. Similar structures are reported by simulations for dipolar fluids (and ferromagnetic particles) [42][43][44][45][46] and also by experiments [47][48][49][50].…”

Finite-size scaling analysis of isotropic–polar phase transitions in an amphiphilic fluid

“…Depending on the precise form of this distribution higher multipole moments may have to be considered. That this may be necessary at some stage was shown very recently by Wei et al who studied the phase behavior of a dipolar fluid in which point charges are embedded in an otherwise spherical particle [13]. Their model has been suggested earlier by Ballenegger and Hansen [14].…”

“…Their model has been suggested earlier by Ballenegger and Hansen [14]. Employing molecular dynamics simulations Wei et al obtain rich phase diagrams that depend crucially on the length of the embedded dipole [13], that is on the charge distribution.…”