Bistability, Remanence, Read/Write-Memory, and Logic Gate Function via a Stimuli-Responsive Polymer

Double layered asymmetrical hydrogels enhanced by thermosensitive microgels for high-performance mechanosensors and actuators

Thermosensitive hydrogels have found extensive applications in soft devices, but they often suffer from limited functionalities, low response rate and small response amplitude. In this work, double layered asymmetrical hydrogels composed of a thermosensitive layer and a non-thermosensitive layer are developed to simultaneously achieve high-performance mechanosensing and actuating properties in a single hydrogel. In thermosensitive layer, thermosensitive microgels are introduced to construct hierarchical structure, which accounts for the enhanced thermosensitive behaviors by cooperative responsiveness. In non-thermosensitive layer, poly(acrylamide-co-acrylic acid) (P(AM-co-AA)) hydrogel is constructed. KCl is introduced as conductive component. Mechanosensors for monitoring various mechanical stimuli in daily life have been fabricated utilizing such hydrogels and high gauge factors (GF) have been achieved, 0.38 for resistive strain sensors, 9.40 kPa-1 for piezoresistive pressure sensors and 3.92 kPa-1 for capacitive pressure sensors. Because of the asymmetrical structure, such hydrogels also exhibit outstanding actuating properties with a fast response rate of 863°/min and a bending amplitude about 360°. Interestingly, grasping-releasing of target objects utilizing an octopus-shaped hydrogel actuator and temperature alerting based on hydrogel actuator are also demonstrated. Overall, the double layered asymmetrical ionic hydrogels have provided a new clue to construct hydrogel devices with multiple functionalities and enhanced response properties.

Light, Heat, and Force-Responsive Polyolefins

Stimuli-responsive polymers have found applications as shape-memory materials, optical switches, and sensors, but the installation of these responsive properties in non-polar and inert polyolefins is challenging. In this contribution, a series of spiropyran (SP)-based comonomers are synthesized and copolymerized with ethylene or ethylene/cyclic monomers. In addition to great mechanical and surface properties, these functionalized polyolefins responded to light, heat, and force, which induced changes in the polymer structure to transmit color or mechanical signals. These interesting responsive properties are also installed in a series of commercial polyolefin materials through reactive extrusion, making the scalable production of these materials possible.

Photo-Responsive Dynamic Organic Room-Temperature Phosphorescence Materials Based on a Functional Unit Combination Strategy

A rational molecular design strategy facilitates the development of a purely organic room-temperature phosphorescence (RTP) material system with precisely regulated luminescence properties, which surely promotes its functional integration and intelligent application. Here, a functional unit combination strategy is proposed to design novel RTP molecules combining a folding unit with diverse luminescent cores. The different luminescent cores are mainly responsible for tunable RTP properties, while the folding unit contributes to the spin-orbit coupling (SOC) enhancement, which makes the RTP material design as workable as the building block principle. By this strategy, a series of color/lifetime-tunable RTP materials is achieved with unique photo-responsive RTP enhancement when subjected to UV irradiation, which expands their application scenarios in reusable privacy tags, advanced "4D" encryption, and phase separation analysis of blended polymers. This work suggests a simple and effective strategy to design purely organic RTP materials with tunable color and lifetime, and also provides new application options for photo-responsive dynamic RTP materials.

Programmable and Self-Healable Liquid Crystal Elastomer Actuators Based on Halogen Bonding

Shape-changing polymeric materials have gained significant attention in the field of bioinspired soft robotics. However, challenges remain in versatilizing the shape-morphing process to suit different tasks and environments, and in designing systems that combine reversible actuation and self-healing ability. Here, we report halogen-bonded liquid crystal elastomers (LCEs) that can be arbitrarily shape-programmed and that self-heal under mild thermal or photothermal stimulation. We incorporate halogen-bond-donating diiodotetrafluorobenzene molecules as dynamic supramolecular crosslinks into the LCEs and show that these relatively weak crosslinks are pertinent for their mechanical programming and self-healing. Utilizing the halogen-bonded LCEs, we demonstrate proof-of-concept soft robotic motions such as crawling and rolling with programmed velocities. Our results showcase halogen bonding as a promising, yet unexplored tool for the preparation of smart supramolecular constructs for the development of advanced soft actuators.

Cellulose-Based Intelligent Responsive Materials: A Review

Due to the rapid development of intelligent technology and the pursuit of green environmental protection, responsive materials with single response and actuation can no longer meet the requirements of modern technology for intelligence, diversification, and environmental friendliness. Therefore, intelligent responsive materials have received much attention. In recent years, with the development of new materials and technologies, cellulose materials have become increasingly used as responsive materials due to their advantages of sustainability and renewability. This review summarizes the relevant research on cellulose-based intelligent responsive materials in recent years. According to the stimuli responses, they are divided into temperature-, light-, electrical-, magnetic-, and humidity-responsive types. The response mechanism, application status, and development trend of cellulose-based intelligent responsive materials are summarized. Finally, the future perspectives on the preparation and applications of cellulose-based intelligent responsive materials are presented for future research directions.

Investigating Fundamental Principles of Nonequilibrium Assembly Using Temperature-Sensitive Copolymers

Both natural biomaterials and synthetic materials benefit from complex energy landscapes that provide the foundation for structure-function relationships and environmental sensitivity. Understanding these nonequilibrium dynamics is important for the development of design principles to harness this behavior. Using a model system of poly(ethylene glycol) methacrylate-based thermoresponsive lower critical solution temperature (LCST) copolymers, we explored the impact of composition and stimulus path on nonequilibrium thermal hysteretic behavior. Through turbidimetry analysis of nonsuperimposable heat-cool cycles, we observe that LCST copolymers show clear hysteresis that varies as a function of pendent side chain length and hydrophobicity. Hysteresis is further impacted by the temperature ramp rate, as insoluble states can be kinetically trapped under optimized temperature protocols. This systematic study brings to light fundamental principles that can enable the harnessing of out-of-equilibrium effects in synthetic soft materials.

Multicompartment polymeric colloids from functional precursor Microgel: Synthesis in continuous process

Raspberry-like poly(oligoethylene methacrylate-b-N-vinylcaprolactam)/polystyrene (POEGMA-b-PVCL/PS) patchy particles (PPs) and complex colloidal particle clusters (CCPCs) were fabricated in two-, and one-step (cascade) flow process. Surfactant-free, photo-initiated reversible addition-fragmentation transfer (RAFT) precipitation polymerization (Photo-RPP) was used to develop internally cross-linked POEGMA-b-PVCL microgels with narrow size distribution. Resulting microgel particles were then used to stabilize styrene seed droplets in water, producing raspberry-like PPs. In the cascade process, different hydrophobicity between microgel and PS induced the self-assembly of the first formed raspberry particles that then polymerized continuously in a Pickering emulsion to form the CCPCs. The internal structure as well as the surface morphology of PPs and CCPCs were studied as a function of polymerization conditions such as flow rate/retention time (Rt), temperature and the amount of used cross-linker. By performing Photo-RPP in tubular flow reactor we were able to gained advantages over heat dissipation and homogeneous light distribution in relation to thermally-, and photo-initiated bulk polymerizations. Tubular reactor also enabled detailed studies over morphological evolution of formed particles as a function of flow rate/Rt.

A Tissue Paper/Hydrogel Composite Light-Responsive Biomimetic Actuator Fabricated by In Situ Polymerization

Stimulus-responsive hydrogels are an important member of smart materials owing to their reversibility, soft/wet properties, and biocompatibility, which have a wide range of applications in the field of intelligent actuations. However, poor mechanical property and complicated fabrication process limit their further applications. Herein, we report a light-responsive tissue paper/hydrogel composite actuator which was developed by combining inkjet-printed tissue paper with poly(N-isopropylacrylamide) (PNIPAM) hydrogel through simple in situ polymerization. Due to the high strength of natural tissue paper and the strong interaction within the interface of the bilayer structure, the mechanical property of the composite actuator was highly enhanced, reaching 1.2 MPa of tensile strength. Furthermore, the light-responsive actuation of remote manipulation can be achieved because of the stamping graphite with high efficiency of photothermal conversion. Most importantly, we also made a few remotely controlled biomimetic actuating devices based on the near-infrared (NIR) light response of this composite actuator. This work provides a simple strategy for the construction of biomimetic anisotropic actuators and will inspire the exploration of new intelligent materials.

Memory Effect in Thermoresponsive Proline-based Polymers

We report that synthetic polymers consisting of L-proline monomer units exhibit temperature-driven aggregation in water with unprecedented hysteresis. This protein-like behavior is robust and governed by the chirality of the proline units. It paves the way to new processes, driven by either temperature or ionic strength changes, such as a simple "with memory" thermometer.