Programming Orientation in Liquid Crystalline Elastomers Prepared with Intra-Mesogenic Supramolecular Bonds

Abstract

The large, directional stimuli-response of aligned liquid crystalline elastomers (LCEs) could enable functional utility in robotics, medicine, consumer goods, and photonics. The alignment of LCEs has historically been realized via mechanical alignment of a two-stage reaction. Recent reports widely utilize chain extension reactions of liquid crystal monomers (LCM) to form LCEs that are subject to either surface-enforced or mechanical alignment. Here, we prepare LCEs that contain intra-mesogenic supramolecular bonds synthesized via direct free-radical chain transfer photopolymerization processible by a distinctive mechanical alignment mechanism. The LCEs were prepared by the polymerization of a benzoic acid monomer (11OBA), which dimerized to form a liquid crystal monomer, with a diacrylate LCM (C6M). The incorporation of the intra-mesogenic hydrogen bonds increases the achievable nematic order from mechanical programming. Accordingly, LCEs prepared with larger 11OBA concentration exhibit higher magnitude thermomechanical strain values when compared to a LCE containing only covalent bonds. These LCEs can be reprogrammed with heat to return the aligned film to the polydomain state. The LCE can then be subsequently programmed to orient in a different direction. The facile preparation of (re)programmable LCEs with supramolecular bonds opens new avenues for the implementation of these materials as shape deployable elements.

Large Range Thermochromism in Liquid Crystalline Elastomers Prepared with Intra‐Mesogenic Supramolecular Bonds

“…We hypothesized that the integration of the supramolecular mesogenic monomer 6‐OBA into these compositions would shift the thermochromic response to lower temperatures. [ 19 ] Mixtures were heated into the isotropic phase and subsequently filled into alignment cells with 20 µm spacers. The filled cells were carefully cooled into the cholesteric phase, just below the observed cholesteric to isotropic phase transition temperature ( T N*I ).…”

“…[ 20 ] Our recent report details that these systems, like LCE prepared with covalent adaptable networks, can be subject to shape‐memory processing. [ 19 ] The shape memory behavior of these materials is attributable to the mechanochemical disruption of the dimers upon deformation. As shown in the stress‐strain curves in Figure a, increasing 6‐OBA content in a 0.9:1 CLCE substantially increases the strain‐at‐break.…”

“…When polymerized into a network these OBA dimers incorporate reversible supramolecular bonds which can be disrupted thermally or mechanically, allowing further network disruption and actuation. Recent reports have incorporated OBA monomers into liquid crystalline elastomer networks retaining the nematic phase, utilizing this thermal responsivity to enable improved actuation stroke, [ 19 ] shape memory and recyclability. [ 20 ] Others have utilized the chemical reactivity of the oxy‐benzoic acids to sensitize materials to biological stimuli.…”

Defect-Engineered Charge Transfer in a PtCu/PrxCe1–xO2 Carbon-Free Catalyst for Promoting the Methanol Oxidation and Oxygen Reduction Reactions

“…Carbon materials are commonly studied as the supports of Pt-based catalysts for the homogeneous dispersion of metal nanoparticles and improving the activity. − However, the number of unpaired electrons in the surface of carbon is almost zero and the valence band is saturated. Metal nanoparticles can only be bounded by the weak van der Waals forces .…”

A dimensionally-reduced nonlinear elasticity model for liquid crystal elastomer strips with transverse curvature

“…Because the nematic director is highly programmable in the manufacturing of LCEs, a wide range of controlled deformations is possible. 8,11,12…”