Commodity polymers are produced in large volumes, providing robust mechanical properties at relatively low costs. The products made from these commodity polymers typically offer only static ...functionalities. Over the past decade, however, in the scientific literature, stimuli-responsive additives and/or polymer coatings have been introduced to commodity polymers, yielding composites and bilayers that change shape in response to light, temperature, and/or humidity. These stimuli responsive commodity polymers allow the marketing and sales of these otherwise bulk products as “high-end” smart materials for applications spanning from soft actuators to adaptive textiles. This Spotlight on Applications presents an overview of recent intriguing works on how shape changing commodity polymer composite and bilayer actuators based on polyamide 6, poly(ethylene terephthalate), polyethylene, and polypropylene have been fabricated that respond to environmental stimuli and discusses their potential applications.
In recent years, light‐responsive liquid crystal (LC) polymers have been studied as promising materials for the fabrication of untethered soft actuators. The underwater behavior of these advanced ...materials has, however, been rarely investigated. This paper reports on the fabrication of light‐responsive amphibious LC‐actuators via direct ink writing (DIW). The actuators present two underwater deformation modes triggered by different stimuli. Temperature induces contraction/expansion and light induces bending/unbending. Unexpectedly, temperature can regulate the bending directionality, giving the material additional versatility to its deformation modes. These findings serve as a toolbox for the fabrication of light‐responsive actuators via DIW that operate in air and underwater.
A liquid crystalline‐ink suitable for direct ink writing is reported. The ink results in a stimuli‐responding polymer network that bends upon light illumination in which the directionality is temperature controlled. Using this ink, an amphibious light‐responsive liquid crystalline film isfabricated via direct ink writing. The results serve as an inspiration to develop novel light‐fueled 4D actuators.
Liquid crystal networks doped with azobenzene molecular photo-switches have been commonly used as responsive polymers in untethered soft/micro robots. Understanding the underlying actuation mechanism ...of azobenzene chromophores in aqueous and ambient environments is crucial for the control of deformation speed and amplitude of the photo responsive actuators. Here, a systematic study is presented that clarifies the outstanding uncertainty in the mechanistic contributions of azobenzene powered actuation. The photothermal and photomechanical contributions in the mechanism are elucidated and the mechanistic dependence on azobenzene chemistry is demonstrated. By connecting mechanical, thermal, isomerization and actuation analysis in both dry and aqueous environments, this study reveals design guidelines for light-responsive amphibious soft robots.
Design guidelines to aid the choice of azobenzene derivatives for light responsive polymer actuators in dry and wet environments.
Cuttlefish can modify their body shape and both their pigmentary and structural colors for protection. This adaptability has inspired the development of appearance-changing polymers such as ...structural color actuators, although in most cases, the original shape has been confined to being flat, and pigmented structural color actuators have not yet been reported. Here, we have successfully created a pigmented structural color actuator using a cholesteric liquid crystal elastomer with a lower actuation temperature where both actuation and coloration (structural and pigmental) are tunable with temperature and NIR light. The shape, structural color, and absorption of the NIR-absorbing dye pigment of the actuator all change with temperature. Light can be used to trigger local in-plane bending actuation in flat films and local shape changes in a variety of 3D-shaped objects. A cuttlefish mimic that can sense light and respond by locally changing its appearance was also made to demonstrate the potential of pigmented structural color actuators for signaling and camouflage in soft robotics.
Achieving oscillatory motion in polymers without requiring on/off switching of stimuli is a current challenge. Hereby, a free‐standing liquid crystal polymer (LCP) is demonstrated to undergo a ...sustained oscillatory motion when triggered by light, moving back and forth, resembling the motion of a rocking‐chair. Two polymer films having different azobenzene photo‐switches have been studied, revealing photoswitch requirements as well as illumination conditions necessary to sustain oscillations. The motion presented here shows how feedback loops involving light‐triggered actuation, self‐shadowing and a shifting center of gravity can be utilized to achieve self‐sustained motion in free‐standing polymers.
Sustained oscillations in stimuli‐responsive actuators will increase the autonomy of future devices. Here, a liquid crystal polymer is shown to undergo continuous light‐driven oscillation without requiring on/off switching of the light source.
A new principle is developed to fabricate temperature-responsive, multicolor photonic coatings that are capable of switching color. The coating is composed of a non-cross-linked liquid crystal ...siloxane-based elastomer that is interpenetrated through an acrylate-based liquid crystal network. Discrete temperature changes induce phase separation and mixing between the siloxane and the acrylate polymers and change the reflective colors correspondingly. The temperature-responsive color change of the coatings can be programmed by the processing conditions and coating formulation, which allows for the fabrication of photopatterned multicolor images. The photonic ink can be coated on flexible poly(ethylene terephthalate) films using roll-to-roll flexographic printing, making these temperature-responsive, multicolor-changing polymers appealing for applications such as responsive color decors, optical sensors, and anticounterfeit labels.
Here, a remotely controlled dual magneto‐ and photoresponsive soft robotic gripper is reported, capable of loading, transport, rotation, and release of cargo. The untethered soft actuator consists of ...a magnetically responsive polydimethylsiloxane layer containing magnetic iron powder coated onto the central region of a light‐responsive liquid crystal polymer film hosting photochromic azobenzene dyes. Light is used to trigger the actuator to autonomously grab and pick up cargo with a high degree of control. Magnetic response is employed to conduct the locomotion as magnetic guidance, allowing the gripper to have both translational freedom and rotational freedom in its locomotion, differentiating the device from other soft robotic grippers. Control can be attained even in enclosed and/or confined spaces, through solely remote actuation. Through combined video, mechanical, and thermal analyses, the actuation mechanism of the light‐responsive liquid crystal network is investigated, shedding light on the decisive role of the temperature evolution in governing both rate of motion and deformation amplitude of the light‐responsive soft actuator.
A remotely controlled dual magneto‐ and photoresponsive soft robotic gripper based on a liquid crystal network is shown to perform loading, transport, rotation, and release of cargo. Light is used to trigger the actuator to autonomouslygrab and pickup cargo, and magnetic response allows for transportation and rotational freedom. A detailed understanding of the light‐triggered actuation is presented.
Narrowly dispersed, 10 micron-sized, liquid crystalline elastomer polymer actuators were first prepared via thiol-ene dispersion polymerization and then embedded and stretched in a polyvinyl alcohol ...film, followed by photopolymerization of the residual acrylate groups. Prolate micro spheroids in which the mesogens are aligned parallel to the long axis were obtained and showed reversible thermally driven actuation owing to nematic to isotropic transition of the liquid crystal molecules. The particles were also compressed to form disk-shaped oblate microactuators in which the mesogens are aligned perpendicular to the short axis, demonstrating that the reported method is a versatile method to fabricate liquid crystal elastomer microactuators with programmable properties.
Cholesteric liquid crystals (CLCs) are chiral photonic materials reflecting only circularly polarized light with the same handedness as the helical polymer structure. Concurrent shape and color ...changes can be achieved using CLCs, but the fabrication of CLCs with switchable 3D shape, structural color, and hyper‐reflectivity, that is, reflecting both left‐ and right‐handed circularly polarized light simultaneously, has not yet been achieved. Here, CLC elastomer (CLCE) actuators are reported to reflect equal amounts of left‐ and right‐handed circularly polarized light. Hyper‐reflectivity is achieved by uniaxially stretching the partially crosslinked film to induce helix deformation which is then fully crosslinked to fix the deformed helical structure. The shape, structural color, and hyper‐reflectivity of the polymer film are switchable with temperature. At high temperatures, only right‐handed circularly polarized light is reflected and the color is redshifted. The film can be shaped in three dimensions: a structural colored 3D shaped beetle is fabricated using molding, which reflects both left‐ and right‐handed circularly polarized light and shows reversible, temperature responsive structural color and 3D shape changes. Hence, 4D engineered bioinspired multifunctional materials are fabricated, which are interesting for applications ranging from sensing actuators to switchable hyper‐reflective films and objects.
Cholesteric liquid crystal elastomer (CLCE) actuators with a switchable shape, structural color, and hyper‐reflectivity are reported. The film can be shaped in 3D using molding, after which it shows reversible, temperature responsive structural color, 3D shape, and reflectivity changes. The fabricated 4D engineered multifunctional materials are interesting for applications ranging from sensing actuators to switchable hyper‐reflective films and objects.
The fabrication of reversible and robust thermochromic coatings remains challenging. In this work, a temperature-responsive photonic coating with a protective topcoat is fabricated. A cholesteric ...oligosiloxane liquid crystal possessing a smectic-to-cholesteric phase-transition temperature response is synthesized. A planar alignment of its cholesteric phase is possible with blade coating. By stabilizing with 3 wt % of a crosslinked liquid crystal network, the photonic coating shows a color change ranging from red to blue upon heating. High transparency is retained, and the structural color changes are fully reversible. A transparent polysiloxane layer can be directly applied on top of the cholesteric layer to protect it against damage without affecting its optical properties. This approach satisfies the basic requirements of thermochromic polymer coatings, as it combines easy processability, coating robustness, and a reversible temperature response.
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