Thermally and Optically Fixable Shape Memory in Azobenzene-Functionalized Glassy Liquid Crystalline Polymer Networks

Abstract

Thermally and optically fixed shape memory is examined in glassy, azobenzene-functionalized liquid crystalline polymer networks (azo-LCN) in the twisted nematic (TN) geometry. The thermal and optical responses of two materials with a large difference in crosslink density are contrasted. The crosslink density was reduced through the inclusion of a monoacrylate liquid crystal monomer RM23. Reducing the crosslink density decreases the threshold temperature of the thermally-induced shape change and increases the magnitude of the deflection. Surprisingly, samples containing RM23 also allows for retention of a complex permanent shape, potentially due to differentiated thermal response of the pendant and main chain mesogenic units of the azo-LCN material.

Photomotility of polymers

“…The photomotility is a spontaneous mechanical response of these anisotropic materials where the intrinsic granularity of the actuation mechanisms is at the molecular level ( trans-cis isomerization) and offers refined levels of modularity for tuning mechanical adaptivity. Due to the hierarchical (through thickness) variation in the director profile (twisted nematic orientation) offsetting the alignment of the director to the principal axes of the strips results in the formation of spiralled shapes1516171819. We demonstrate that irradiation of these materials can result in seemingly perpetual photomotility.…”

Light‐Fueled Climbing of Monolithic Torsional Soft Robots via Molecular Engineering

“…The photomechanical deformation of polymers has been demonstrated by embedding an azobenzene moiety into a light‐responsive molecular switch that can perform both reversible trans (9 Å)– cis (5.5 Å) photoisomerization and cis – trans back‐isomerization. [ 1 ] In polymeric form, these molecular‐level contractile and tensile stresses can be transferred into various macroscopic strain responses, such as bending, [ 2–7 ] twisting, [ 8–15 ] and three dimensional (3D) shape‐morphing, [ 16–18 ] according to their preprogrammed molecular alignment. Current research literatures report azobenzene‐functionalized liquid crystalline polymer networks (azo‐LCNs) and elastomers (azo‐LCEs) have mostly achieved passive‐type photomotility through beam patterning or localized beam scanning.…”

Liquid Crystal Networks on Thermoplastics: Reprogrammable Photo‐Responsive Actuators

“…Recently, 3D printing has allowed for the construction of LC‐based actuators having pre‐designed initial shapes . The ability to shape fix the starting geometry into any arbitrary shape and subsequently trigger reversible actuation through exposure to light, as done for temperature‐driven actuators through shape memory or by using dynamic covalent bonds, remains largely unexplored. Light encoding has been employed by Priimagi and co‐workers as an approach towards photo‐rewritable programming of light‐driven actuation in LCNs .…”