Nonequilibrium steady-state response of a nematic liquid crystal under simple shear flow and electric fields

Abstract

The effect of a dc electric field on the response of a nematic liquid crystal under shear flow has been investigated by measuring the shear stress response to an ac electric field used as a probe. It was found that both the first-and second-order responses do not vanish at high frequencies, but have constant nonzero values. The experimental results are in good agreement with calculations based on the Ericksen-Leslie theory. The role of the Parodi relation (which is derived from the Onsager reciprocal relation) in the stress response is discussed.

Electric-field-induced flow-aligning state in a nematic liquid crystal

“…(11), and the dashed line is 1/τ calculated from Eq. (9). A slowing down of the relaxation time is observed in the FAS, as is expected from Eqs.…”

“…the FAS even in the absence of a dc electric field [9]. In 5CB we have already observed a characteristic behavior under shear flow and dc electric fields: The real part of the frequency dispersion has a plateau at high frequencies.…”

“…A slowing down of the relaxation time is observed in the FAS, as is expected from Eqs. (5) and (9). At around 100 V mm −1 the solid line disappears because the peak changes to the dip in the imaginary part there, and so it is difficult to obtain the peak or dip position.…”

“…In this simple case, the shear stress response has been calculated on the basis of the Ericksen-Leslie theory [9]. We briefly summarize the results and note some additional considerations regarding the electric-field-induced FAS in the following.…”

“…Although the electric-field dependence of shear stress in 8CB at a constant shear rate, in which an NFAS appears without electric field, was also reported by Negita [7] and Patricio et al [8]; the change in the shear stress was too small for the transition to be clearly detected. In this study, we measured the shear stress response to an ac electric field as a probe under both shear flow and dc electric fields [9]. These measurements are more sensitive to the change in director orientation and demonstrate that different frequency dispersion curves in the stress response can be clearly observed and the transition from NFAS to FAS can be detected by changing the dc electric field at a constant shear rate.…”