Premium
Nematic and smectic liquid single crystal elastomers: Influence of external stress parallel and perpendicular to the director
Author(s) -
Kundler Isabel,
Nishikawa Etsushi,
Finkelmann Heino
Publication year - 1997
Publication title -
macromolecular symposia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.257
H-Index - 76
eISSN - 1521-3900
pISSN - 1022-1360
DOI - 10.1002/masy.19971170105
Subject(s) - liquid crystal , perpendicular , materials science , elastomer , rubber elasticity , anisotropy , condensed matter physics , phase (matter) , composite material , deformation (meteorology) , elastic modulus , elasticity (physics) , optical axis , optics , natural rubber , crystallography , physics , geometry , chemistry , optoelectronics , lens (geology) , mathematics , quantum mechanics
The influence of uniaxial mechanical stress applied parallel or perpendicular to the director axis (optical axis) of nematic and smectic‐A elastomers having a permanent macroscopically ordered monodomain structure is investigated. Due to the different phase structures applying an external mechanical stress leads to completely different responses with respect to the young moduli and reorientation processes of the director. Nematic elastomers exhibit a weak anisotropy of the moduli parallel (μ 11 and perpendicular (μ) to the optical axis with μ 11 / μ = 1.5. The moduli are mainly determined by the rubber elasticity of the poly(siloxane) network. Applying the mechanical stress perpendicular to the initial director axis causes a rotation of the director axis that is connected with a periodic pattern formation and a ‘soft elastic’ response. For smectic‐A elastomers μ 11 /μ is in the order of 10 2 . While μ reflects a rubber elastic response similar to that of the nematic system, μ 11 indicates an enthalpy‐elastic behaviour of the one‐dimensional long range order of the smectic layers. In this direction reorientation of the phase structure with a deformation of the smectic layers occurs above a threshold elongation. In contrast to the nematic networks, a deformation perpendicular to the optical axis causes no director reorientation, displaying the liquid‐like properties within the smectic layers.