Tomoyuki Nagaya

A MODEL OF POLARIZATION REVERSAL IN FERROELECTRICS

The ferroelectric switching process has been studied on the basis of a one-dimensional discrete lattice model. The characteristics of the model is discussed in the relationship with the Kolmogorov-Avrami(KA) model. It has turned out that the features in the early stage of the polarization reversal in the present model coincides with what described by the KA model.

Electrorheological effect in immiscible polymer blends

A new model of the electrorheological (ER) effect for immiscible polymer blends is proposed on the basis of microscopic observations. In the absence of an electric field the polymer with high viscosity is dispersed as droplets in the other polymer with low viscosity, while in the presence of an electric field, the droplets stretch and coalesce to form bridges between electrodes, resulting in the increase of the macroscopic viscosity. A few experimental results are given to confirm the validity of this model.

Observation of annihilation process of disclinations emerging from bubble domains

Dynamics of interacting disclinations is investigated by utilizing bubble domains. A pair of wedge disclinations with strength of +1 and -1 emerge from bubble domains when a suitable electric field is applied, and the density of disclinations can be controlled by adjusting the field. To investigate the interaction between the disclinations, the time evolution is analyzed on the basis of the equation of motion for the disclinations.

Dynamics of One-Dimensional Periodic Pattern Formation on the Electro-Hydrodynamic Convection of a Nematic Liquid Crystal

The formation processes of a one-dimensional periodic pattern were investigated on the electro-hydrodynamic convection of a nematic liquid crystal. Two kinds of processes for different initial conditions were observed. In the first initial condition the system was set to be the no-flow state in the absence of the applied field, and in the second the turbulent state under a strong field. The temporal change of the one-dimensional image intensity was measured after the amplitude of an ac electric field was jumped from these initial values to a value slightly above the critical one. The power spectrum function and the locally varying phase were calculated from the image intensity. The obtained results were compared with the numerical simulations of the diffusion equation.

Experimental Study of the Coarsening Dynamics of +1 and -1 Disclinations

Dynamics of interactive disclinations in a nematic liquid crystal cell, which can be regarded as the two-dimensional XY-system, has been investigated. We made numerous wedge disclinations of the strength ±1 and observed the annihilation process by means of a polarizing microscope. By analyzing the image, it is found that the number of disclinations N ( t ) decreases as N ( t )∼ t -1 and the dynamical scaling law holds. Furthermore, the correlation function obtained by experiments is discussed by applying the theory of the two-dimensional XY-model.

Collective Motion of an Assembly of Disclinations in the Non-Orthogonally Twisted Nematics Quenched below the Clearing Point

The disclination pattern, emerging in the ordering process after the non-orthogonally twisted nematics is quenched, showed quite different features from that of orthogonally twisted nematics. Dynamical scaling law found in the orthogonally twisted nematics does not hold. By introducing, however, the characteristic time and characteristic length from the equation of motion of single disclination line, we have found a scaling property in these systems.

Localized structures and their dynamics in a liquid crystal light valve with optical feedback

In this article we review the conditions for the appearance of localized states in a nonlinear optical system, with particular reference to the liquid crystal light valve (LCLV) experiment. The localized structures here described are of dissipative type; that is, they represent the localized solutions of a pattern-forming system. We discuss their features of stable addressable localized states, and we show that they dispose themselves on the nodes of highly symmetric lattices, as obtained by the introduction of an N-order rotation angle in the optical feedback loop. The stability is lost either on increase of the input light intensity or by the introduction of an extra small angle of rotation. The complex spatio-temporal dynamics that follows is characterized by oscillations in the position of the localized states. We discuss the origin of this permanent dynamics in relation to the non-variational character of the LCLV system, underlining the general character of such complex behaviours of localized states.

Direct Observation of the Orientational Fluctuations in a Tilted Smectic Liquid Crystal with a High-Speed TV Camera

The orientational fluctuations in a smectic liquid crystal were successfully observed with a high-speed video camera. From the series of images obtained, first the spatial Fourier transformation of each image was computed and then the time correlation function at each wave number was calculated. It was found that the time correlation function shows an exponential decay and the inverse of the relaxation time is proportional to the square of the wave number. The ratio of the elastic constant to the viscosity was also obtained in this experiment.

Dynamics of Disclinations in the Non-Orthogonally Twisted Nematics

The equation of motion of disclinations in the non-orthogonally twisted nematic cell is derived. The experimental results on a liquid crystal MBBA are presented and discussed.

Observation of Phase Separation Process in the Binary Mixture of Nematic and Isotropic Polymers

We investigated the phase separation process in the binary mixture of the semi-rigid thermotropic liquid crystalline polymer and the flexible polymer. By raising temperature, an initially homogeneous mixture undergoes the phase separation. Utilizing the nematic property of one component, we were able to observe this segregation process by means of a polarizing microscope under crossed polarizers. We found a new mechanism to explain the coalescence of droplets in the latest stage.