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Effects of nematic coupling on the phase behaviour of nematogen mixtures
Author(s) -
Benmouna Farida,
Maschke Ulrich,
Coqueret Xavier,
Benmouna Mustapha
Publication year - 2001
Publication title -
polymer international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.592
H-Index - 105
eISSN - 1097-0126
pISSN - 0959-8103
DOI - 10.1002/pi.659
Subject(s) - liquid crystal , miscibility , materials science , phase diagram , thermodynamics , isotropy , phase (matter) , phase transition , polymer , biaxial nematic , thermotropic crystal , condensed matter physics , chemistry , organic chemistry , optics , composite material , physics , liquid crystalline , optoelectronics
The phase behaviour of binary nematogen mixtures of side‐chain liquid crystal crosslinked polymers and low molecular weight liquid crystals is investigated with particular emphasis on the effects of nematic coupling. The cross nematic quadrupole parameter ν 12 is assumed to be proportional to the geometric average of ν 11 and ν 22 characteristic of single nematogens. In the weak coupling limit, the proportionality constant is lower than 1, and the phase diagram exhibits a reduced miscibility of the nematogens. In the case of strong coupling, the proportionality constant exceeds 1 resulting in higher miscibility. This is characterized by a nematic order that extends to temperatures above the upper nematic–isotropic transition temperature. A wide region of miscibility emerges showing a single nematic phase. Nematogens having similar nematic–isotropic transition temperatures exhibit different phase properties from systems with widely separated transition temperatures. Effects of the polymer volume fraction at crosslinking, rubber elasticity parameters of the network, and the Flory–Huggins interaction parameter on the equilibrium phase diagram of these systems are discussed. © 2001 Society of Chemical Industry