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A Smectic A Liquid Single Crystal Elastomer (LSCE): Phase Behavior and Mechanical Anisotropy
Author(s) -
Aßfalg Nicole,
Finkelmann Heino
Publication year - 2001
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 - 10.1002/1521-3935(20010301)202:6<794::aid-macp794>3.0.co;2-c
Subject(s) - liquid crystal , materials science , isotropy , phase (matter) , elastomer , condensed matter physics , anisotropy , phase transition , composite material , optics , chemistry , physics , optoelectronics , organic chemistry
The analysis of the phase behavior of a smectic A (S A ) elastomer reveals a nematic phase existing within a small temperature range below the isotropic state. Stress‐optical measurements in the pretransformational regime of the isotropic state indicate smectic as well as nematic fluctuations yielding a critical exponent of γ = 0.65. The formation of the liquid single crystal elastomer (LSCE) at the isotropic to liquid crystalline phase transformation equals a nematic LSCE. At the nematic to S A phase transformation, the orientation of the director remains constant while the tendency of the network strands towards an oblate equilibrium conformation is suppressed by the high modulus parallel to the smectic layer normal. The mechanical anisotropy of the S A ‐LSCE as a function of the temperature is characterized by entropy elasticity perpendicular to the smectic layer normal. Parallel to the layer normal the mechanical response is determined by the enthalpy elastic response of the smectic layers having a modulus larger by about two orders of magnitude. In this direction the modulus decreases linearly with increasing temperature and reflects the falling stability of the layers. Accordingly, above a deformation of about 2% the homogeneous layered structure breaks down at a threshold stress that also falls linearly with increasing temperature while the threshold strain remains constant at about 2% elongation.