Hydrogen-bonded liquid crystalline polymers have emerged as promising "smart" supramolecular functional materials with stimuli-responsive, self-healing, and recyclable properties. The hydrogen bonds can either be used as chemically responsive (i.e., pH-responsive) or as dynamic structural (i.e., temperature-responsive) moieties. Responsiveness can be manifested as changes in shape, color, or porosity and as selective binding. The liquid crystalline self-organization gives the materials their unique responsive nanostructures. Typically, the materials used for actuators or optical materials are constructed using linear calamitic (rod-shaped) hydrogen-bonded complexes, while nanoporous materials are constructed from either calamitic or discotic (disk-shaped) complexes. The dynamic structural character of the hydrogen bond moieties can be used to construct self-healing and recyclable supramolecular materials. In this review, recent findings are summarized, and potential future applications are discussed.

Hydrogen-Bonded Supramolecular Liquid Crystal Polymers: Smart Materials with Stimuli-Responsive, Self-Healing, and Recyclable Properties.

Developing self-oscillating soft actuators that enable autonomous, continuous, and directional locomotion is significant in biomimetic soft robotics fields, but remains great challenging. Here, an untethered soft photoactuators based on covalently-bridged black phosphorus-carbon nanotubes heterostructure with self-oscillation and phototactic locomotion under constant light irradiation is designed. Owing to the good photothermal effect of black phosphorus heterostructure and thermal deformation of the actuator components, the new actuator assembled by heterostructured black phosphorus, polymer and paper produces light-driven reversible deformation with fast and large response. By using this actuator as mechanical power and designing a robot configuration with self-feedback loop to generate self-oscillation, an inchworm-like actuator that can crawl autonomously towards the light source is constructed. Moreover, due to the anisotropy and tailorability of the actuator, an artificial crab robot that can simulate the sideways locomotion of crabs and simultaneously change color under light irradiation is also realized.

Light-Driven Self-Oscillating Actuators with Phototactic Locomotion Based on Black Phosphorus Heterostructure.

Significance Autonomy is crucial for soft robotics that are constructed of soft materials. It remains challenging to create autonomous soft robots that can intelligently interact with and adapt to changing environments without external controls. To do so, it often requires an analogical soft “brain” that integrates on-board sensing, control, computation, and decision-making. Here, we report an autonomous soft robot embodied with physical intelligence for decision-making via adaptive soft body-environment interactions and snap-through instability, without integrated sensing and external controls. This study harnesses physical intelligence as a new paradigm for designing autonomous soft robots that can interact intelligently with their environments, thus potentially reducing the burdens on the conventional integrated sensing, control, computations, and decision-making systems in designing intelligent soft robots.

Twisting for soft intelligent autonomous robot in unstructured environments

Dynamic Liquid Crystalline Networks for Twisted Fiber and Spring Actuators Capable of Fast Light-Driven Movement with Enhanced Environment Adaptability

Recent years have witnessed the rapid development of sustainable materials. Along this line, developing biodegradable or recyclable soft electronics is challenging yet important due to their versatile applications in biomedical devices, soft robots, and wearables. Although some degradable bulk hydrogels are directly used as the soft electronics, the sensing performances are usually limited due to the absence of distributed conducting circuits. Here, sustainable hydrogel-based soft electronics (HSE) are reported that integrate sensing elements and patterned liquid metal (LM) in the gelatin-alginate hybrid hydrogel. The biopolymer hydrogel is transparent, robust, resilient, and recyclable. The HSE is multifunctional; it can sense strain, temperature, heart rate (electrocardiogram), and pH. The strain sensing is sufficiently sensitive to detect a human pulse. In addition, the device serves as a model system for iontophoretic drug delivery by using patterned LM as the soft conductor and electrode. Noncontact detection of nearby objects is also achieved based on electrostatic-field-induced voltage. The LM and biopolymer hydrogel are healable, recyclable, and degradable, favoring sustainable applications and reconstruction of the device with new functions. Such HSE with multiple functions and favorable attributes should open opportunities in next-generation electronic skins and hydrogel machines.

https://rss.onlinelibrary.wiley.com/doi/am-pdf/10.1002/smll.202201643

Healable, Recyclable, and Multifunctional Soft Electronics Based on Biopolymer Hydrogel and Patterned Liquid Metal.

Twisted toroidal ribbons such as the one-sided Mobius strip have inspired scientists, engineers and artists for many centuries. A physical Mobius strip exhibits interesting mechanical properties deriving from a tendency to redistribute the torsional strain away from the twist region. This leads to the interesting possibility of building topological actuators with continuous deformations. Here we report on a series of corresponding bi-layered stripe actuators using a photothermally responsive liquid crystal elastomer as the fundamental polymeric material. Employing a special procedure, even Mobius strips with an odd number of twists can be fabricated exhibiting a seamless homeotropic and homogeneous morphology. Imposing a suitable contraction gradient under near-infrared light irradiation, these ribbons can realize continuous anticlockwise/clockwise in-situ rotation. Our work could pave the way for developing actuators and shape morphing materials that need not rely on switching between distinct states.

/pdf/light-driven-continuous-rotating-mobius-strip-actuators-222i01azk3.pdf

Light-driven continuous rotating Möbius strip actuators.

The development of controllable artificial light-harvesting systems based on liquid crystal (LC) materials, i.e., anisotropic fluids, remains a challenge. Herein, an annulene-based discotic LC compound 6 with a saddle-shaped cyclooctatetrathiophene core has been synthesized to construct a tunable light-harvesting platform. The LC material shows typical aggregation-induced emission, which can act as a suitable light-harvesting donor. By loading Nile red (NiR) as an acceptor, an artificial light-harvesting system is achieved. Relying on the thermal-responsive self-assembling ability of 6 with variable molecular order, the efficiency of such 6 -NiR system can be controlled by temperature. This light-harvesting system works sensitively at a high donor/acceptor ratio as 1000:1, and exhibits a high antenna effect (39.1) at a 100:1 donor/acceptor ratio. This thermochromic artificial light-harvesting LC system could find potential applications in smart devices employing soft materials.

An Artificial Light-Harvesting System with Controllable Efficiency Enabled by an Annulene-Based Anisotropic Fluid.

Nanoporous materials derived from hydrogen-bonded supramolecular liquid crystal complexes present a promising and prevalent perspective in selective adsorption, water desalination, ion conductivity...

Nanoporous Supramolecular Liquid Crystal Polymeric Material for Specific and Selective Uptake of Melamine

Light Harvesting In their Research Article (e202200466), Xu-Man Chen, Hong Yang, Quan Li et al. report an artificial light-harvesting system with controllable efficiency enabled by an annulene-based anisotropic fluid. 

Frontispiece: An Artificial Light‐Harvesting System with Controllable Efficiency Enabled by an Annulene‐Based Anisotropic Fluid

The low crosslink density characteristic of liquid crystal elastomer (LCE) materials causes poor fatigue resistance performance, which has seriously plagued their prospects in industrial applications. Here we report that the introduction of 5 wt% liquid metal nanodroplets (average diameter: ca. 195 nm) into the LCE network can dramatically reinforce the corresponding composite’s mechanical properties, in particular ultrahigh fatigue resistance, capable of bearing unprecedented 10,000 tensile cycles within a large range of strain amplitude up to 70% and 2000 times of continuous actuating deformations. Furthermore, this liquid metal-incorporated LCE composite material exhibits large actuation stroke (maximum actuation strain: 55%), high actuation stress (blocking stress: 1.13 MPa), fully reversible thermal/photo-actuation functions, and self-healing ability at moderate temperatures, which qualifies the composite material for high-load actuators. 

/pdf/an-ultrahigh-fatigue-resistant-liquid-crystal-elastomer-1zhfeb76.pdf

Zhen-Zhou Nie

Papers

Light-driven continuous rotating Möbius strip actuators.

An Artificial Light-Harvesting System with Controllable Efficiency Enabled by an Annulene-Based Anisotropic Fluid.

Nanoporous Supramolecular Liquid Crystal Polymeric Material for Specific and Selective Uptake of Melamine

Frontispiece: An Artificial Light‐Harvesting System with Controllable Efficiency Enabled by an Annulene‐Based Anisotropic Fluid

An ultrahigh fatigue resistant liquid crystal elastomer-based material enabled by liquid metal