Nanocomposites and nanomaterials

Ferronematics – liquid crystal nanocomposites
filled with magnetic nanoparticles
Burylov S.V.
Institute of Transport Systems and Technologies of the NAS of Ukraine.
Pisargevskogo Str.,5,Dnipro -49005, Ukraine. 
E-mail: S.Burylov@nas.gov.ua
Ferronematics (FNs) are suspensions of anisotropic monodomain ferri- or ferromagnetic nanoparticles (with length L ~ 100 nm and diameter d ~ (L/10)) in nematic liquid crystals (NLCs). The most essential feature of these systems is an orientational coupling between the nanoparticles and the liquid-crystalline matrix. The volume fraction of the disperse phase is rather small (10−7–10−2), therefore the existence of ferromagnetic nanoparticles does not change the nature of orientational order of nematic matrix but enhances the magnetic susceptibility of FNs, in comparison with pure NLCs, by several orders of magnitude. Due to this, ferronematics are considered as very promising magnetic liquid crystal nanocomposites for technical application.
In this report we discuss the main theoretical investigations devoted to the construction of FN continuum theory, as well as the results of the experiments which influenced the development of theoretical views about the internal structure and behavior of such liquid crystal nanocomposites. We start from «the theory of rigid FNs» [1], then we describe «the theory of soft FNs» [2, 3] and last – «the modified theory of soft FNs» [4]. We show these theories develop on a way of more detailed description of orientational interactions between nanoparticles and liquid crystal environment.

1.	Brochard F., De Gennes P. G. Theory of magnetic suspensions in liquid crystals // Journal de Physique -1970.-31, N7.-P. 691-708.
2.	Burylov S. V., Raikher Y. L. Ferronematics: On the development of the continuum theory approach. // J. Magn. and Magn Mater. – 1990.- 85, N1-3.- P. 74-76.
3.	Burylov S. V., Raikher Yu L. Macroscopic properties of ferronematics caused by orientational interactions on the particle surfaces. I. Extended continuum model // Mol. Cryst. and Liq.Cryst. - 1995.-258, N 1.-P. 107-122.
4.	Burylov S. V., Zakhlevnykh A. N. Orientational energy of anisometric particles in liquid-crystalline suspensions // Phys. Rev. E. – 2013.- 88, N1. - 012511.