Measurements of viscosity in the nematic phase of MBBA are made under an application of an electric field up to 5 kV mm
−1. When the electric field is applied, the viscosity in the nematic phase ...decreases with its amount being saturated at high electric fields. On the basis of the theoretical analysis by Leslie and Ericksen, it is interpreted that the electric field makes the director orient along the flow direction to decrease the viscosity.
ER effects were studied in a suspension composed of starch particles and 5CB (4-n-pentyl-4'-cyanobiphenyl) having liquid crystalline nematic phase. To investigate the effects of dispersant 5CB, ER ...effects of starch/silicone oil and starch/5CB suspensions were explored, finding that the ER effect in starch/5CB suspension is about 3.5 times larger than that of starch/silicone oil suspension. It was also clarified that the magnitude of the ER effect is hardly affected by the difference in the phase, nematic or isotropic phase, of the dispersant 5CB, suggesting that the enhancement of the ER effect is not due to the orientational order of the liquid crystal but to the larger value of the dielectric constant of 5CB. In addition, dielectric properties were measured to make clear the relationships between the relaxation time of the polarization and the magnitude of the ER effect in these suspensions.
In the nematic phase of 5CB, nonlinear dielectric properties induced by a shear flow were measured. The results show that a dielectric dispersion is observed in the shear-modified 3rd order ...dielectric constants and the peak of the imaginary part shifts to higher-frequencies with increasing the shear rate and the temperature. These results will be discussed from the motion of the director under the shear and the electric field.
It has been reported that if a shear flow is applied in the nematic phase of 8CB, some shear-induced structures are formed. To clarify these structures in more detail, temperature dependence of the ...viscosity and dielectric permittivity, transient dielectric response after the application of the shear flow, and frequency dependence of dielectric permittivity were measured. In each shear-induced structural region, characteristic behaviors were observed. These results will be discussed based on the fluctuation of the smectic A structure developed in the nematic phase.
It has been reported that if a shear flow is applied to the nematic phase of 8CB, some dynamical structure are induced. To clarify these structures is more detail, transient dielectric response after ...the application of the shear flow was measured. In the flow alignment region the dielectric permittivity decreased monotonously, while in the precession region a damped-oscillation of the dielectric permittivity was measured with critical increases in the oscillating frequency and damping faster when approaching to the nematic to smectic A phase transition point. These results will be discussed based on the fluctuation of smectic A structure.
Rheological properties, including the electrorheological effect, and the dielectric behaviors under steady shear flow are examined in the chiral smectic C (Sc*), and the chiral nematic (N*) phases of ...4-n-octyloxyphenyl-4-(2"-methylbutyl) biphenyl-4'-carboxylate (8OBE). In the Sc * phase the viscosity decreases almost linearly with increase in temperature, and above the Sc *- N* phase transition point TCN, via an unstable region, it gradually decreases to lower values in the N* phase. The application of the electric field causes a two step increase in the viscosity in the Sc * phase, while a monotonous increase in the N* phase. Based on These rheological and the simultaneously measured dielectric properties, shear-induced structural changes in the Sc * and N* phases are discussed in terms of the orientational changes of the director and the smectic layer.
Simultaneous measurements of rheological and dielectric properties were made to clarify the shear-induced structural changes in the nematic phase of 8CB (4-n-octyl-4'-cyanobiphenyl). Varying the ...shear rate, viscosity and the dielectric permittivity were measured precisely as a function of temperature, finding the shear diagram specifying the stable structural regions of the respective shear-induced structures. In the transient response of the dielectric permittivity after the steady shear flow is applied, different behaviors are observed between the flow-alignment region (b*) and the director-precession regions (a-b, am, as, a(b), ac); a monotonous change is observed in the former region while a damped oscillation in the latter regions. Based on these results, shear-induced structures in the nematic phase will be discussed.
Rheological properties, including the electrorheological effect, and the dielectric behaviors under steady shear flow are examined in the chiral smectic C (SC*) and the chiral nematic (N*) phases of ...4-n-octyloxyphenyl-4-(2"-methylbutyl) biphenyl-4'-carboxylate (8OBE). In the SC* phase the viscosity decreases linearly with increase in temperature, and above the SC*- N* phase transition point TCN, it gradually decreases to lower values in the N* phase. The flow in the SC* phase is non-Newtonian, which is in contrast to the Newtonian behavior in the N* phase. The application of the electric field causes some increase in the viscosity in the SC* phase. These rheological and the simultaneously measured dielectric properties are discussed on the basis of the directional changes of the director and the smectic layer.
When a steady shear flow is applied to the nematic phase of 5CB, nonlinear dielectric properties are observed. In the dielectric spectra, dielectric dispersions are recognized in the nonlinear ...dielectric constants but not in the linear one. These shear-induced nonlinear dielectric properties under the shear flow will be discussed based on the orientational change of the director under the shear and the electric fields.
Simultaneous measurements of rheological and dielectric properties were made to clarify the shear-induced structural changes in the nematic phase of 8CB (4-n-octyl-4'-cyanobiphenyl). Varying the ...shear rate, viscosity and the dielectric permittivity were measured precisely as a function of temperature to find the shear diagram specifying the stable structural regions of the respective shear-induced structures. The dielectric permittivity was also measured as a function of the electric field strength in the respective shear-induced structure regions. With increase in the electric field strength, dielectric permittivity increases monotonously in the flow-alignment region (b*), while in the a-b and director-precession regions (am, as, a(b), ac) it increase in two steps, reflecting the change from the precessional motion to flow alignment of the director. Based on these results, shear-induced structures in the nematic phase will be discussed.
PDF
