Dipole dynamics and macroscopic alignment in molecular and polymeric liquid crystals by broad-band dielectric relaxation spectroscopy

A liquid crystal monomer (LCM) was synthesized and attached as a side chain to a siloxane polymer (SCLCP). The molecular dynamics of LCM and SCLCP wer e investigated by broad-band dielectric relaxation spectroscopy (DRS) over 10 decades of frequency. The surface treatment of the electrodes was found to have a pronounced effect on the macroscopic alignment and dynamics. In t he isotropic state the relaxations in LCM and SCLCP are well-described by t he Kohlrausch-Williams-Watts (KWW) functional form. In the LC state, the ov erall dielectric response is a weighted sum of two dispersions that depend on the macroscopic alignment. The hometropic (H) alignment is dominated by the (slower) delta process, while the planar (P) alignment is dominated by the (faster) alpha (m) process. Both processes are symmetric and can be des cribed by Cole-Cole (CC) or Fuoss-Kirkwood (FK) functional forms. The delta process governs the dynamics in the SCLCP near the glass transition, simil ar to the segmental a process in non-LC glass formers. Excellent agreement was observed with the various aspects of the seminal work by Attard and Wil liams.