Tunable structures of mixtures of magnetic particles in liquid-crystalline matrices

Abstract

We investigate the self-organization of a binary mixture of similar sized rods and dipolar soft spheres by means of Monte-Carlo simulations. We model interparticle interactions by employing anisotropic Gay-Berne, dipolar and soft-sphere interactions. In the limit of vanishing magnetic moments we obtain a variety of fully miscible liquid crystalline phases including nematic, smectic and lamellar phases. For the magnetic mixture, we find that the liquid crystalline matrix supports the formation of orientationally ordered ferromagnetic chains. Depending on the relative size of the species the chains align parallel or perpendicular to the director of the rods forming uniaxial or biaxial nematic, smectic and lamellar phases. As an exemplary external perturbation we apply a homogeneous magnetic field causing uniaxial or biaxial ordering to an otherwise isotropic state.

Orientational order and translational dynamics of magnetic particle assemblies in liquid crystals

“…Furthermore, the self-organization and assembly of the magnetic particles can be tuned by external fields giving rise to (infinite or finite) ferromagnetic chains in homogeneous magnetic fields, 47 formation of synchronized ferromagnetic layers in rotational fields, 48 cave structures in triaxial fields 49 with potential applications in biomedicine 50,51 and magneto-rheology. 52 Even though, an enormous effort has been devoted in mono-dispersed dipolar sphere systems, as it is shown above, there are a few simulation studies 22,23 that take into account explicitly the presence of an anisotropic medium (e.g. a LC matrix) in dipolar spheres suspensions.…”

“…To the best of our knowledge, the study both of structure and dynamics of magnetic particle assemblies (clusters) in LC matrices using simulations is missing from the research literature. In earlier Monte Carlo simulations 22,23 we have focused on systems in which the diameter of spheres is equal or greater than the width of the rods; consequently, the magnetic particles form infinite or fragmented chains that organize into uniaxial and biaxial states. In the present work, we scrutinise the opposite direction, by studying both the structure and dynamics in mixtures of rods and relative small magnetic spheres (i.e.…”

“…19,20 The DSS particles interact via a soft repulsive potential and a dipole-dipole interaction. 22,23 The diameter of the DSS particles is set s s * = s s /s 0 = 0.25 (i.e. it is four times smaller than the width of the rods comparable with that in corresponding experimental systems 19,20 ).…”

“…Here we provide a brief description of the parametrization of the model that is used; a more detailed presentation is given elsewhere. 22,23 The rods interact via an anisotropic (orientational dependent) attractiverepulsive GB potential. 32 The GB potential is of Lennard-Jones form incorporating an orientation dependent range; it depends both on the orientation and interparticle distance of two anisotropic particles.…”

“…A systematic examination of mixtures with spheres diameter equal or greater than the width of the rods has been reported elsewhere. 22,23 The long range interactions are handled by the implementation of the three dimensional Ewald sum. 54 The reduced permanent point dipole moment is set to m à ¼ m .…”