Molecular dynamics of a siloxane liquid-crystalline polymer as studied by dielectric relaxation spectroscopy

Dielectric and orientational properties of nematogenic 4-n-octyl(4′-cyanophenyl)benzoate

“…The temperature of the cells was regulated and controlled by means of a Scientific Instruments temper− ature controller, model 9700, with an accuracy of ±0.01 K. These two groups contribute to the resultant value of the permanent dipole moment μ and its direction does not corre− spond to the molecular long axis. Therefore, in the dielectric spectrum at least two dispersion regions, related to the lon− gitudinal μ l and transverse μ t components of the dipole mo− ment, should appear [16]. In principle, in the nematic phase, the relaxation process connected with the molecular rotation on the cone around the director n occurs additionally, but in the parallel component of e * it is observed rather rarely [3,4,17].…”

Dynamic and photochemical behavior of amorphous comb-like copolymers with photochromic azobenzene side groups

“…The a -relaxation is a cooperative molecular process which is mainly connected with the segmental motion of the chain backbone and, therefore, the temperature dependence of its relaxation rate can be described by the Vogel-Fulcher-Tammann (VFT) equation 9) , and at low relaxation rates it correlates with the glass temperature. It should also be noted that Williams and coworkers 10,11) have assigned the a -relaxation for liquid crystalline polymers to rotational fluctuation of the transversal dipole moment of the mesogenic unit. The d -relaxation at higher temperatures than the a -relaxation seems to be characteristic for side group liquid crystalline polymers.…”

“…The d -relaxation at higher temperatures than the a -relaxation seems to be characteristic for side group liquid crystalline polymers. Detailed investigations have shown that this relaxation process is related to rotational fluctuations of the mesogenic units around its short axis [10][11][12][13] . The photoisomerization of azobenzene is an important and very convenient model reaction to study photoinduced reversible changes of physical properties of polymers 14) .…”

“…-relaxation: For liquid crystalline polymers the d -relaxation is related to rotational fluctuations of the mesogenic units around its short axis 3,8,[10][11][12] . There are many experimental results which support that conclusion but the actual molecular mechanism remains unclear up to now.…”

Molecular mobility in halogen-containing side-chain liquid-crystalline polymers studied by dielectric spectroscopy

“…Dielectric investigations on side-chain liquid-crystalline polymers (SCLCPs), in particular by Kresse et al, 1 Haase et al, 2 Borisova and co-workers, 3 and Williams and co-workers, 4 have provided signi®cant information on dynamics in relation to structure and micromorphology. Zentel et al 5 classi®ed the different relaxation processes present in SCLCPs.…”