Dynamics of liquid-crystalline magnetic suspensions in a rotating magnetic field

Abstract

We theoretically study the dynamics of the orientational structure of a ferronematic liquid crystal with soft planar coupling between the director and the magnetization in a rotating magnetic field. We determine critical parameters characterizing the boundary between synchronous and asynchronous rotation regimes. We show that the magnetic impurity increases the stability threshold of an asynchronous rotation regime. The critical angular velocity, the angles of the director and the magnetization rotation in each regime of orientational structure rotation are found for rigid planar coupling. We obtain that in weak magnetic fields when the main mechanism of the field influence on a ferronematic liquid crystal is associated with the effect on the magnetic particles, the critical angular velocity is linearly dependent on the field strength, while in strong magnetic fields, when the influence of a field is determined by a diamagnetic mechanism, the critical velocity is quadratically dependent on the field strength.

Dissipative versus reversible contributions to macroscopic dynamics: the role of time-reversal symmetry and entropy production

“…Even if one disregards flow, the couplings number 3: to 5: are still missing. This clearly contradicts the recent claim by Boychuk et al (2016), that the two approaches, namely, the one by Raikher and Stepanov on the one hand and by Jarkova et al on the other would be equivalent without flow field.…”

Soft Ferrocholesteric in a Rotating Magnetic Field: Phase Diagrams

“…Подставляя теперь выражение (18) в соотношение (14), получаем интегральное уравнение -поле раскручивания беспримесного холестерика в постоянном магнитном поле. Пунктирной линией на рисунке обозначена граница между синхронным и асинхронным режимами вращения суспензии, определяемая согласно работе [14] системой уравнений:…”

“…В синхронном режиме директор вращается с угловой скоростью поля, отставая от него на некоторый постоянный угол, а в асинхронном режиме вращение за магнитным полем происходит с фазовой задержкой, которая сложным образом зависит от времени. Теоретически эффект Цветкова в ферронематических жидких кристаллах был изучен ранее в [14]. Впервые поведение ориентационной структуры ФХ во вращающемся магнитном поле при жестком сцеплении между жидкокристаллической матрицей и магнитной примесью было проанализировано в работе [15].…”

A ferronematic slab in external magnetic fields

“…Ferronematics, i.e., suspensions of anisotropic ferromagnetic particles dispersed in a nematic liquid crystal (NLC), attract both theoretical [1][2][3][4][5][6][7][8] and experimental [9][10][11][12][13][14] interest due to their ability to exhibit fluidity due to the solvent, and macroscopic magnetization, due to colloidal inclusions. The anisotropic nature of the solvent implies broken rotational symmetry as compared to a simple isotropic liquid.…”