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Model phase diagrams of binary nematic mixtures. A comparative study between linear and crosslinked polymers
Author(s) -
Benmouna Farida,
Maschke Ulrich,
Coqueret Xavier,
Benmouna Mustapha
Publication year - 1999
Publication title -
macromolecular theory and simulations
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.37
H-Index - 56
eISSN - 1521-3919
pISSN - 1022-1344
DOI - 10.1002/(sici)1521-3919(19990901)8:5<479::aid-mats479>3.0.co;2-9
Subject(s) - liquid crystal , phase diagram , polymer , thermodynamics , materials science , phase (matter) , mesogen , phase transition , binary number , side chain , isotropy , polymer chemistry , chemistry , organic chemistry , mathematics , composite material , physics , optics , liquid crystalline , optoelectronics , arithmetic
Model calculations of phase diagrams of side chain liquid crystal polymers (SCLCP) and low molecular weight liquid crystals (LMWLC) are presented. The polymer is assumed to have grafted side chain units characterized by a nematic‐isotropic transition temperature T NI 2 , and the LMWLC presents also a similar transition at a temperature T NI 1 . The model calculations can accommodate for the cases where the latter two temperatures are comparable or widely different. For the sake of illustration, the case T NI 1 = 60°C and T NI 2 = 80°C is adopted here. The main point of interest here is to perform a comparative study of the equilibrium phase diagrams of SCLCP made either of linear free chains or crosslinked chains forming a single network. To our knowledge this is the first comparative study of the phase behavior of binary nematic mixtures involving linear and crosslinked polymer matrices which permits to clearly identify the effects of crosslinks present in the polymer matrix. The crosslinks attribute elasticity to the polymer constituent which induces important distortions in the phase diagram. To highlight these distortions, examples of hypothetical binary nematic mixtures are chosen involving both linear and crosslinked polymers with side chain mesogen units. The quadrupole interaction parameter between the two nematogens is related to individual parameters via a geometric average ν 2 12 = κν 11 ν 22 with a coupling parameter κ . Different values of this parameter are considered and the impact of coupling strength on the phase diagram is discussed for crosslinked and linear polymers.