Nanocomposites and nanomaterials

Orientational behavior of a lath-like goethite nanoparticle
suspended in a liquid crystal matrix
Burylov S.V., Burylova N.V., Skosar V.Yu., Voroshilov O.C.
Institute of Transport Systems and Technologies of the NAS of Ukraine.
Pisargevskogo Str.,5,Dnipro -49005, Ukraine. 
E-mail: S.Burylov@nas.gov.ua

A main mesoscopic problem of a continuum description of the nematic liquid crystal suspension filled with magnetic lath-like goethite nanoparticles [1] is considered. It is a problem of the orientational behavior of an individual nanoparticle in a uniform liquid crystal matrix including behavior under applying an external magnetic field. At theoretical consideration the individual nanoparticle is modeled by nanorod in the form of long parallelepiped with mean values of length l, width w and thickness t, where l >> w ~ t. The nanorod interacts both with nematic environment and with magnetic field. 
The interaction with nematic matrix describes by the so-called orientational energy which we choose in more general bistable form [2]. The last one allows two possible orientations of long axis of the nanorod – along or perpendicular to anisotropy axis of the liquid crystal matrix. In the absence of a magnetic field, the equilibrium orientation of the nanorod corresponds to a minimum of the free energy of these orientational states. 
The interaction of the nanoparticle with an external field depends on specific magnetic properties of the goethite nanorod which has a remanent magnetic moment and an induced magnetic moment. The last ones are oriented respectively along and perpendicular to the long axis of the nanorod. As a result the nanorod tends to orient parallel and perpendicular to external field in a low or high magnetic field region, respectively. The real orientation of the nanorod with respect to a field direction and a nematic anisotropy axis corresponds to a minimum of the system free energy (sum of orientational and magnetic energies of the nanorod).

1.	Kopčanský P, Gdovinová  V., Burylov S., Burylova N., Voroshilov  A., Majorošová J., Agresti F., Zin V., Barison S., Jadżyn J., Tomašovičová  N. The influence of goethite nanorods on structural transitions in liquid crystal 6CHBT // J. Magn. and Magn. Mater.- 2018. – 459, P 26-32.
2.	Burylov S. V., Zakhlevnykh A. N. Orientational energy of anisometric particles in liquid-crystalline suspensions // Phys. Rev. E. – 2013.- 88, N1. - 012511.