Yang Ho Na

Viscoelastic Properties of Nematic Liquid Crystals in an Electric Field

We have investigated the electro-rheological (ER) effect of nematic liquid crystals in an oscillatory shear flow. The linear complex viscosity under a constant electric field was derived from the Ericksen–Leslie theory, which was in the same form as that empirically obtained by Narumi et al. Since our viscosity formula was expressed in terms of the Leslie viscosity coefficients, its validity was readily confirmed through the viscoelastic measurements of a nematic liquid crystal, the coefficients of which are already known.

Electric-field-induced deformation of a chiral liquid-crystal elastomer in smectic A phase

Mechanical response to electrical stimulus has been investigated in a chiral smectic A elastomer. During the application of electric field, the two-dimensional strain tensor was precisely measured by tracking fluorescent beads dispersed on the film. It was found that the shear strain is dominantly induced by the electric field and proportional to the applied electric field.

Scaling Properties of Immiscible Fluid Blends in Electric and Shear Flow Fields

We have investigated the scaling properties of immiscible fluid blends in shear flow and electric fields. Scaling relations were derived by dimensional analysis. For example, when they are subjected to a step electric field at a constant shear rate, transient apparent viscosity depends only on strain, as long as \(\dot{\gamma}/E^{2}\) is constant, where \(\dot{\gamma}\) and E are, respectively, the shear rate and electric field. Another scaling property was derived for the characteristic length of the domain structure. These scaling relations were experimentally proved.