Unravelling the photothermal and photomechanical contributions to actuation of azobenzene-doped liquid crystal polymers in air and water

Abstract

Design guidelines to aid the choice of azobenzene derivatives for light responsive polymer actuators in dry and wet environments.

Liquid Crystal Networks on Thermoplastics: Reprogrammable Photo‐Responsive Actuators

“…It is remarkable to observe that by depositing a 4 μm thin LCN, a 12 μm PET substrate was bent so easily attaining bending speeds similar to single layer >20 μm thick LCN films . Upon removal of the UV irradiation, the bilayer retains its bent state; this shape persists due to the slow (hours) back isomerization of the cis azobenzene isomer . The macroscopic bending deformation of the pre‐bent bilayer in Figure C is independent of the incident UV illumination direction, always resulting in the LCN on the interior of the bent strip.…”

“…Tracking of the bilayer temperature during irradiation revealed the surface remains around 33 °C under 170 mW cm −2 UV irradiation (Figure S6). Hence, the actuation is primarily photomechanical in nature, driven by the exerted network pull‐effect derived from cis isomers, leading to an anisotropic contraction along the molecular axis . When the actuator is submerged in water, the bilayer displays bending similar to the dry environment when illuminated, Movie S2.…”

Liquid Crystal Networks on Thermoplastics: Reprogrammable Photo‐Responsive Actuators

“…[39] Upon removal of the UV irradiation, the bilayer retains its bent state; this shape persists due to the slow (hours) back isomerization of the cis azobenzene isomer. [40,41] The macroscopic bending deformation of the pre-bent bilayer in Figure 1 C is independent of the incident UV illumination direction, always resulting in the LCN on the interior of the bent strip. The direction of bending is commonly found in uniaxial aligned bilayer systems, indicating that actuation is dictated by the dominant planar section in the splay LCN.…”

“…Hence, the actuation is primarily photomechanical in nature, driven by the exerted network pull-effect derived from cis isomers, leading to an anisotropic contraction along the molecular axis. [40,41] When the actuator is submerged in water, the bilayer displays bending similar to the dry environment when illuminated, Movie S2. Since, the thermal contribution to the back isomerization of the azobenzene moieties (cis-trans) is absent, as water acts as a heat sink, this results in an overall higher cis isomer population, hence in a marginally larger actuation upon irradiation underwater.…”

A Soft Transporter Robot Fueled by Light

“…[27] In recent years, a variety of centimeter-sized light-driven soft robots based on LCNs have been demonstrated, [6] yet design and locomotion freedoms in dry environment remain limited to one dimension, either forward [28][29][30] or forward and backward. [31][32][33][34][35][36] Unidirectional locomotion strategies such as inchworm, [28,37] snail, [34] and Mobile organisms with ability for locomotion and transportation, such as humans and other animals, utilize orchestrated actuation to perform actions. Mimicking these functionalities in synthetic, light-responsive untethered soft-bodied devices remains a challenge.…”