Mechanical Deformations in Smectic-C Main-Chain Liquid-Crystalline Elastomers

Abstract

A novel crosslinked smectic-C Main-Chain Liquid-Crystalline Elastomer (MCLCE) has been synthesized by polycondensation of vinyloxy-terminated mesogens, tetramethyldisiloxane and pentamethylpentaoxapentasilecane. The introduction of the functional vinyloxy group allows the synthesis of well-defined networks having low soluble content and good mechanical properties. Networks having a macroscopic uniformly ordered director and a conical distribution of the smectic layer normal with respect to the director are mechanically deformed by uniaxial and shear deformations. Under uniaxial deformations two processes were observed: parallel to the director the mechanical field directly couples to the smectic tilt angle while perpendicular to the director a reorientation process takes place. A shear deformation parallel and perpendicular to the director causes a uniform layer orientation and the network exhibits a smectic-C monodomain phase having a macroscopic uniform director and layer orientation. This process is reversible for shear deformation perpendicular and irreversible by applying the shear force parallel to the director.

Influence of strain rate and temperature on necking transition in a polydomain smectic main chain elastomer

“…Varying either r or ρ in MCLCE alters the effective crosslink density, judging by equilibrium swelling measurements 3. The crosslink density is an important parameter affecting mechanical response in MCLCE 15…”

“…Smectic main‐chain liquid crystalline elastomers (MCLCE) exhibit strong deviations from ordinary rubber‐elastic mechanical behavior due to the conformational constraints imposed on the polymer backbone by strong, segment‐level positional correlations. Recent studies of smectic MCLCE focused on their synthesis and phase behavior,1, 2 on the molecular factors influencing their static and dynamic mechanical response,3–8 and on basic understanding of smectic rubber elasticity 9–15. Smectic MCLCE have also attracted interest due to the capability of globally oriented specimens to change shape in response to temperature change,11 or in the case of the S C * type, to exhibit electromechanical effects 16–19…”

Polydomain–Monodomain Orientational Process in Smectic‐C Main‐Chain Liquid‐Crystalline Elastomers

“…In previous communications, [1,35] parallel and perpendicular deformations were applied to a monodomain of SmC MCLCE, showing a great difference between both uniaxial stretchings, but coupling between the applied mechanical field and the director, as well as between the field and the layers, was always observed.…”

“…All synthetic and characterisation details can be found in the literature, as well as the structures of the chemicals used for the synthesis of the SmC MCLCES (Scheme 1). [1,34,35] Results and Discussion…”

Influence of thermal history on mesoscale ordering in polydomain smectic networks

“…Smectic liquid crystalline elastomers, especially those with mesogenic units in the main chain, have attracted attention as shape‐memory materials,1 as soft actuators,2–4 as energy‐dissipative coatings,5 and as model anisotropic soft materials. Recent studies of smectic elastomers focused on their synthesis and phase behavior,6, 7 on the molecular factors influencing their static and dynamic mechanical response,5, 8–13 and on basic understanding of smectic ordering11, 14, 15 and rubber elasticity 1, 16–22. Smectic elastomers have also attracted interest due to the ability of globally oriented specimens to change shape in response to temperature change,18 or in the case of the S type, to exhibit electromechanical effects 3, 4, 23, 24.…”