Liquid Crystal Elastomers with Mechanical Properties of a Muscle

Abstract

Free-standing anisotropic side chain liquid crystalline elastomer films have been prepared using mesogens with laterally affixed polymerizable side chains. We present data on two networks: one containing the monomer of 4‘-acryloyloxybutyl 2,5-(4‘-butyloxybenzoyloxy)benzoate and another from a 50/50 mol % mixture of the above with 4‘-acryloyloxybutyl 2,5-di(4‘-pentylcyclohexyloyloxy)benzoate. The cross-linking was achieved using 10 mol % of 1,6-hexanediol diacrylate. The calculated cross-linking density, as determined from the Young's modulus, was in the 10 -5 mol/cm3 range. Thermoelastic responses show strain changes through the nematic−isotropic phase transition to be 30−45%. The order parameters of the oriented films were determined from the dichroic ratio of IR absorption at 3343 cm-1 to the in-plane aromatic stretching overtone of the LC mesogen core. The variation of the order parameter with temperature scales similar to the strain changes at constant stress. Isostrain studies, conducted through the nematic to isotropic phase transition, show that the two networks behave as true elastomers with significant differences in the force developed. Dynamic shear measurements near the nematic to isotropic phase transition region show that the mechanical relaxation peak appears above 100 Hz, and that viscoelastic relaxations are minimal in the nematic to isotropic phase transition region below 5−10 Hz.

One-piece micropumps from liquid crystalline core-shell particles

“…Attached to the rigid mesogenic unit are three flexible side chains, one of which comprises a polymerizable acrylate group. The monomer exhibits a nematic phase between 72 1C and 98 1C 15 . By addition of the non-mesogenic photoinitiator (3 wt% Lucirin TPO) and crosslinker (10 mol% 1,6-hexanedioldiacrylate), a crystalline-isotropic phase transition is observed on heating (80 1C), without any intermediate liquid crystalline regime.…”

“…29 and for the Young's modulus of a comparable film (0.4 MPa) see ref. 15. They were characterized by light microscopy, some example images are shown in Fig.…”

“…The LC side-chain monomer (4 00 -acryloyloxybutyl) 2,5-di(4 0 -butyloxybenzoyloxy)benzoate was synthesized according to literature 15 . Glycerol was obtained from Fluka.…”

“…The microscopic transition from the ordered but soft mesophase to the isotropic state can be triggered by temperature, light or electric fields 13 , and results in a directed macroscopic change of shape that can reach up to 400%, matching the performance of skeletal muscles 14,15 . Crucial to the preparation of LCEs is the uniform orientation of the anisotropic structural units, the so-called mesogens, along a common axis, the director.…”

Effects of structural imperfections on the dynamic mechanical response of main‐chain smectic elastomers

“…Several studies of the dynamic mechanical properties of SCLCE 3,5,8,[21][22][23][24][25][26][27][28][29][30][31] and MCLCE 6,7,[32][33][34] have appeared in recent years. MCLCE have a more direct coupling between backbone conformation and mesogen orientation compared with SCLCE, and the elasticity of MCLCE is significantly affected by the presence of hairpin folds.…”