Forces between elongated particles in a nematic colloid

Using molecular dynamics simulations we study the interactions between elongated colloidal particles (length to breath ratio ≫1) in a nematic host. The simulation results are compared to the results of a Landau–de Gennes elastic free energy. We find that depletion forces dominate for the sizes of the colloidal particles studied. The tangential component of the force, however, allows us to resolve the elastic contribution to the total interaction. We find that this contribution differs from the quadrupolar interaction predicted at large separations. The difference is due to the presence of nonlinear effects, namely, the change in the positions and structure of the defects and their annihilation at small separations

Defect structures and torque on an elongated colloidal particle immersed in a liquid crystal host

Combining molecular dynamics and Monte Carlo simulation we study defect structures around an elongated colloidal particle embedded in a nematic liquid crystal host. By studying nematic ordering near the particle and the disclination core region we are able to examine the defect core structure and the difference between two simulation techniques. In addition, we also study the torque on a particle tilted with respect to the director, and modification of this torque when the particle is close to the cell wall

Inhomogeneous States in a Small Magnetic Disk with Single-Ion Surface Anisotropy

We investigate analytically and numerically the ground and metastable states for easy-plane Heisenberg magnets with single-ion surface anisotropy and disk geometry. The configurations with two half-vortices at the opposite points of the border are shown to be preferable for strong anisotropy. We propose a simple analytical description of the spin configurations for all values of a surface anisotropy. The effects of lattice pinning leads to appearance of a set of metastable configurations.Comment: 10 pages, 7 figures; submitted to Phys. Rev.

Magnetic field induced orientational bistability in a ferronematic cell

The equilibrium states of a suspension of single-domain ferroparticles in a nematic liquid-crystalline homeotropic cell subject to an external magnetic field are studied. We predict the existence of magnetic field induced orientational bistability in such a system in a magnetic field ?102 Oe. The existence of the bistability phenomenon is governed by conditions on the cell thickness and on the director anchoring energy. The effect can be controlled using a small bias magnetic field normal to the unperturbed director. The director reorientation in a magnetic field causes an effective change in refraction index, which enables the orientational bistability to be exploited in optical devices

Weak anchoring effects in ferronematic systems

We study the magnetically induced behaviour of a ferronematic cell with finite anchoring energy at the cell surfaces. We calculate the dependence of orientational and concentration profiles on the magnetic field, the director anchoring energy, and the cell thickness. We find a new intermediate thickness high field state, in which there is no ferroparticle segregation and a highly ordered director field. This contrasts with previous work in which only a restricted set of system parameters and strong anchoring at the cell surfaces were considered

Adsorption phenomena and macroscopic properties of ferronematics caused by orientational interactions

We have studied the effect of adsorption and desorption of rod-like magnetic grains on the macroscopic properties of ferronematics in a ferronematic cell. An external magnetic field controls the equilibrium between ferroparticles in the bulk and those adsorbed on the cell surfaces. The magnetic field can thus influence the anchoring and the nematic orientational texture. In the presence of ferroparticle adsorption, the segregation effect is diminished, and the system becomes less susceptible to bulk ferroparticle coagulation