title: Effect of dipole functionalization on the thermodynamics and dynamics of discotic liquid crystals.
abstract: The effect of dipole substitution on the self-assembly, thermodynamics, and dynamics has been studied in a series of hexa-peri-hexabenzocoronenes (HBCs). The HBCs bear the same number and type of aliphatic chains, but different dipoles directly attached to the cores ranging from ∼0 to ∼3.4 D. Dipole substitution alters the energetics and reduces the transition temperature favoring the columnar hexagonal liquid crystalline phase at the expense of the crystalline phase. The equation of state was obtained by independent pressure-volume-temperature measurements in both phases that resulted in the equilibrium phase diagram. According to the latter, increasing pressure imparts stability to the crystalline phase. The molecular and supramolecular dynamics investigated, respectively, by dielectric spectroscopy and rheology, identified a hierarchy of motions comprising a fast axial motion, a slower process that completely relaxes the dipole moment, and an even slower soliton-like relaxation of structural defects.
authors.affiliation: Max-Planck Institute for Polymer Research, 55128 Mainz, Germany.
authors.forename: Nino
authors.initials: N
authors.lastname: Haase
authors.forename: Christos
authors.initials: C
authors.lastname: Grigoriadis
authors.forename: Hans-Jurgen
authors.initials: HJ
authors.lastname: Butt
authors.forename: Klaus
authors.initials: K
authors.lastname: Müllen
authors.forename: George
authors.initials: G
authors.lastname: Floudas
mesh_terms: D003460:Crystallization; D050866:Liquid Crystals / Q000737:chemistry*; D044367:Phase Transition; D011083:Polycyclic Compounds / Q000737:chemistry*; D013816:Thermodynamics; D044366:Transition Temperature
chemical_list: D011083:Polycyclic Compounds; C507240:hexa-peri-hexabenzocoronene