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Cooperative modes of molecular mobility in liquid crystalline comb‐like oligoacrylates and oligomethacrylates with 4‐cyanoazobenzene side groups
Author(s) -
Nikonorova Natalia A.,
Borisova Tamara I.,
Shibaev Valeriy P.
Publication year - 2000
Publication title -
macromolecular chemistry and physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.57
H-Index - 112
eISSN - 1521-3935
pISSN - 1022-1352
DOI - 10.1002/(sici)1521-3935(20000201)201:2<226::aid-macp226>3.0.co;2-m
Subject(s) - mesogen , homeotropic alignment , rigidity (electromagnetism) , liquid crystal , side chain , crystallography , materials science , relaxation (psychology) , dielectric , chemical physics , chemistry , polymer chemistry , liquid crystalline , composite material , polymer , psychology , social psychology , optoelectronics
Cooperative modes of molecular mobility in comb‐like liquid crystalline oligoacrylates and oligomethacrylates containing mesogenic 4‐cyanoazobenzene side groups and spacers of 3, 5, 7, 9, 10, and 11 CH 2 groups were studied by means of dielectric spectroscopy. Near T g the existence of two cooperative relaxation processes denoted as α and δ was revealed. The δ ‐relaxation is connected to the motion of mesogenic groups with respect to the short mesogenic axis and the α‐relaxation is connected to the motion of mesogenic groups with respect to the long axis and with the segmental mobility of the main chains. The temperatures of α‐ and δ‐transitions decrease with increasing spacer length. The liquid‐crystalline structure formation increases main chain rigidity and temperatures of the α‐ and δ‐transitions. For these oligomers aligned by an external electric field or by mechanical shear, the planar or homeotropic orientation of mesogenic groups is established. The choice of orientation conditions makes it possible to obtain the predetermined order parameters.