Dielectric relaxation and electro-optical switching behavior of nematic liquid crystal dispersed in poly(methyl methacrylate)

Investigation of liquid crystal dispersion and dielectric relaxation behavior in polymer dispersed liquid crystal composite films

“…The area of the ITO coated glass electrode was 4.83 cm 2 and surface resistance was 5.59 Ω cm. The dielectric properties of the composite films were determined from the measurement of capacitance (C p ), dissipation factor (tan δ), phase angle (θ) and impedance (Z), and the relative dielectric constant was calculated using the following formula [17][18][19].…”

“…As frequency is inversely proportional to the time, at high frequencies, molecules have less time to cope with an applied electric field. In this case, higher frequencies may lead to a certain blocking in the potential barriers which are created due to interfacial and space charge polarization, and hence the dielectric parameter decreases to a minimum value [17]. When 80 wt.% of LC was added to PMMABA matrix, the relative dielectric constant increased as compared to the LC content of 70 wt.%, because more numbers of LC droplets were available to store energy, thereby increasing the capacity to hold charges which in turn increases the dielectric constant.…”

“…They have concluded that, dopant does not influence the intrinsic identity of LC host in terms of dielectric dispersion till the clearing temperature of nematic LC [30]. But at the higher temperature, thermal agitation becomes more predominant as compared to intermolecular interaction which produces randomization of dipoles [17,31].…”

“…The real part ε′(ω) increases considerably up to 60°C temperature, and thereafter decreases with an increase in temperature. The temperature dependent study of relative dielectric constant (ε r ) contains valuable information regarding the dipole reorientation of liquid crystal [17]. The maximum value of the real part for both the composite films was observed at 60°C and it was found to be minimum at room temperature.…”

“…If the centers of the semicircles lie on x-axis (ε′ axis), the distribution parameter α is zero (Debye type), and if the center is below the ε′ axis then α ≠ 0 (nonDebye type) [36], while if α is more than 0.5 there could be more than one relaxation processes involved. The study of relaxation time reveals that the relaxation process totally depends upon the molecular rotational motion along the long axis [17].…”