Ion-Exchange Enabled Dual-Functional Swarms with Reconfigurability and Magnetic Controllability.

In nature, many organisms are capable of self-organizing into collective groups through local communications to perform complex tasks that individuals cannot complete. To date, the reported artificial microswarms either rely on toxic chemical reactions for communication or lack the hierarchical controllability and functionality, which is unfavorable for practical applications. To this end, this exploits the ion-exchange reaction enabled hierarchical swarm composed of cationic ion exchange resin and magnetic microspheres of internal information exchange. The swarm is reconfigurable under magnetic fields, generating ordered structures of controllable mobilities and even reversed hierarchy, able to navigate in confined and complex environments. Moreover, the swarm shows interesting communications among each other, such as merging, splitting, and member exchange, forming multi-leader groups, living crystals, and complex vortices. Furthermore, the swarm functions as a dual-functional microreactor, which can load, transport, and release drugs in a pH-enhanced manner, as well as effectively degrade antibiotics via light-enhanced Fenton-like reaction in polluted water. The organized structure of the swarm greatly improves the drug loading/transport efficiency and the local concentration of catalysts for fast pollutant removal. This design lays the foundation for the design of dual-functional micro/nanorobots for intelligent drug delivery and advanced environmental remediation.

Weak Ion-Exchange Based Magnetic Swarm for Targeted Drug Delivery and Chemotherapy.

Swimming microrobots that are actuated by multiple stimuli/fields display various intriguing collective behaviors, ranging from phase separation to clustering and giant number fluctuation; however, it is still chanllenging to achieve multiple responses and functionalities within one colloidal system to emulate high environmental adaptability and improved tasking capability of natural swarms. In this work, a weak ion-exchange based swarm is presented that can self-organize and reconfigure by chemical, light, and magnetic fields, showing living crystal, amorphous glass, liquid, chain, and wheel-like structures. By changing the frequency and strength of the rotating magnetic field, various well-controlled and fast transformations are obtained. Experiments show the high adaptability and functionality of the microrobot swarm in delivering drugs in confined spaces, such as narrow channels with turns or obstacles. The drug-carrying swarm exhibits excellent chemtherapy for Hela and CT26 cells due to the pH-enhanced drug release and locomotion. This reconfigurable microswarm provides a new platform for biomedical and environmental applications.

Efficient Fabrication of Micro/Nanostructured Polyethylene/Carbon Nanotubes Foam with Robust Superhydrophobicity, Excellent Photothermality, and Sufficient Adaptability for All-Weather Freshwater Harvesting.

The integration of fog collection and solar-driven evaporation has great significance in addressing the challenge of the global freshwater crisis. Herein, a micro/nanostructured polyethylene/carbon nanotubes foam with interconnected open-cell structure (MN-PCG) is fabricated using an industrialized micro extrusion compression molding technology. The 3D surface micro/nanostructure provides sufficient nucleation points for tiny water droplets to harvest moisture from humid air and a fog harvesting efficiency of 1451 mg cm-2 h-1 is achieved at night. The homogeneously dispersed carbon nanotubes and the graphite oxide@carbon nanotubes coating endow the MN-PCG foam with excellent photothermal properties. Benefitting from the excellent photothermal property and sufficient steam escape channels, the MN-PCG foam attains a superior evaporation rate of 2.42 kg m-2 h-1 under 1 Sun illumination. Consequently, a daily yield of ≈35 kg m-2 is realized by the integration of fog collection and solar-driven evaporation. Moreover, the robust superhydrophobicity, acid/alkali tolerance, thermal resistance, and passive/active de-icing properties provide a guarantee for the long-term work of the MN-PCG foam during practical outdoor applications. The large-scale fabrication method for an all-weather freshwater harvester offers an excellent solution to address the global water scarcity.

Cost-Effective Fabrication of Micro-Nanostructured Superhydrophobic Polyethylene/Graphene Foam with Self-Floating, Optical Trapping, Acid-/Alkali Resistance for Efficient Photothermal Deicing and Interfacial Evaporation.

Solar evaporation is one of the most attractive and sustainable approaches to address worldwide freshwater scarcity. Unfortunately, it is still a crucial challenge that needs to be confronted when the solar evaporator faces harsh application environments. Herein, a promising polymer molding method that combines melt blending and compression molding, namely micro extrusion compression molding, is proposed for the cost-effective fabrication of lightweight polyethylene/graphene nanosheets (PE/GNs) foam with interconnected vapor escape channels and surface micro-nanostructures. A contact angle of 155 ± 2°, a rolling angle of 5 ± 1° and reflectance of ≈1.6% in the wavelength range of 300-2500 nm appears on the micro-nanostructured PE/GNs foam surface. More interestingly, the micro-nanostructured PE/GNs foam surface can maintain a robust superhydrophobic state under dynamic impacting, high temperature and acid-/alkali solutions. These results mean that the micro-nanostructured PE/GNs foam surface possesses self-cleaning, anti-icing and photothermal deicing properties at the same time. Importantly, the foam exhibits an evaporation rate of 1.83 kg m-2 h-1 under 1 Sun illumination and excellent salt rejecting performance when it is used as a self-floating solar evaporator. The proposed method provides an ideal and industrialized approach for the mass production of solar evaporators suitable for practical application environments.

One-step laser etching of a bionic hierarchical structure on a silicone rubber surface with thermal and acid/alkali resistance and tunable wettability.

Superhydrophobic silicone rubbers with robust physical and chemical stability have promising application potential in the field of flexible electronics. A one-step laser etching strategy is proposed for successfully fabricating superhydrophobic silicone rubbers with bioinspired hierarchical micro/nanostructures. Regular and dense micro/nano spheres gradually accumulate on the modified silicone rubber surface with the increase of laser etching cycles. Owing to the bioinspired hierarchical micro/nano spheres, a 5 µL water droplet on the modified silicone rubber surface exhibits a contact angle of 158 ± 3° and a sliding angle of 5 ± 1°. Moreover, the modified silicone rubber can maintain a stable superhydrophobic state in acid/alkali (pH = 2, 4, 6, 8, and 10) and thermal environments (50-90 °C). Importantly, the contact angle and sliding angle are adjustable depending on the number of laser etching cycles, which is beneficial for the different application requirements. The proposed method for the fast fabrication of superhydrophobic silicone rubbers with tunable wettability can provide an excellent candidate for the protection of flexible electronics in rainy and acid/alkali environments.

Layer-by-Layer Assembly of Multifunctional NR/MXene/CNTs Composite Films with Exceptional Electromagnetic Interference Shielding Performances and Excellent Mechanical Properties.

With the rapid advance of electronics, the light, flexible, and multifunctional composite films with high electromagnetic interference (EMI) shielding effectiveness and excellent thermal management are highly desirable for next-generation portable and wearable electronic devices. Herein, a series of flexible and ultrathin natural rubber/MXene/carbon nanotubes (NR/MXene/CNTs) composite films with sandwich structure are constructed layer by layer through a facile vacuum-assisted filtration method for EMI shielding and Joule heating application. The fabricated NR/MXene/CNTs-50 composite film, with NR/MXene as inner layer and NR/CNTs as out layers, not only has high EMI shielding efficiency, but also has excellent comprehensive mechanical properties at the thickness of only 200 µm. In addition, the superior environmental durability, high electrothermal conversion efficiency, hydrophobicity, and fine performance stability after periodic cyclic bending make the film possess more value in practical application.

Ultrafast Fabrication of Graphene-Reinforced Nanocomposites via Synergy of Steam Explosion and Alternating Convergent-Divergent Flow.

Producing high-quality graphene and polymer/graphene nanocomposite is facing the problems of complex procedure, low efficiency, and serious resource waste. To explore a new fabrication approach with high efficiency and low cost is crucial for solving these technical issues, which becomes a current research hotspot and also a great challenge. Herein, a one-step melt mixing strategy based on the synergy of steam explosion and alternating convergent-divergent flow, is innovatively developed to fabricate high-density polyethylene (HDPE)/graphene nanocomposites using industrial-grade expanded graphite (EG) without chemical agents and complex procedures. The co-action of the external force derived from elongational melts and the internal force generated by steam explosion make EG ultrafastly exfoliate into few-layer graphene nanosheets (GNS) and simultaneously disperse in melts within 4 min. The as-produced GNS have a lateral size of over 5 µm and a minimum thickness of 1.4 nm, can introduce super heterogeneous nucleation to HDPE macromolecules and greatly increases nanocomposite crystallinity up to 86.5%. Moreover, plentiful HDPE crystallites and well-dispersed GNS jointly form an improved thermally-conductive network, making nanocomposites with a rapid-respond ability in solar-to-thermal conversion and heat dissipation. This facile strategy will facilitate the development of scalable production and wide application of high-performance graphene and highly-filled nanocomposites.

Dual-functional metal-organic frameworks-based hydrogel micromotor for uranium detection and removal.

Self-propelled micro/nanomotors have attracted great attention for environmental remediation, however, their use for radioactive waste detection and removal has not been addressed. Engineered micromotors that are able to combine fast detection and highly adsorptive capability are promising tools for radioactive waste management but remain challenging. Herein, we design self-propelled micromotors based on zeolite imidazolate framework (ZIF-8)-hydrogel composites via inverse emulsion polymerization and show their potential for efficient uranium detection and removal. The incorporation of magnetic ferroferric oxide nanoparticles enables the magnetic recycling and actuation of the single micromotors as well as formation of swarms of worm-like or tank-treading structure. Benefited from the enhanced motion, the micromotors show fast and high-capacity uranium adsorption (747.3 mg g-1), as well as fast uranium detection based on fluorescence quenching. DFT calculation confirms the strong binding between carboxyl groups and uranyl ions. The combination of poly(acrylic acid-co-acrylamide) with ZIF-8 greatly enhances the fluorescence of the micromotor, facilitating the high-resolution fluorescence detection. A low detection limit of 250 ppb is reached by the micromotors. Such self-propelled micromotors provide a new strategy for the design of smart materials in remediation of radioactive wastewater.

Highly Tribo-Positive Nylon-11 Film Fabricated by Multiscale Structural Regulation through a Roll-to-Roll Processing.

Triboelectric polymers have attracted extensive attention due to their great electron-accepting and electron-donating properties in contact electrification as well as their flexible and low-cost merits and have become promising electrode materials in triboelectric nanogenerators (TENGs). However, most research has exclusively focused on improving the electron capture capability of the triboelectric layer, neglecting to enhance the electron-donating capability, which leads to a low output performance of TENG and limits its practical application. In this study, we developed a method to fabricate highly tribo-positive Nylon-11 film through roll-to-roll processing. Paired with the poly(tetrafluoroethylene) triboelectric layer, the transferred charge density of contact-separation TENG based on Nylon-11 film prepared by this method reaches 291.1 µC/m2, which has been improved by 12.4% compared with the conventional compression molding sample. The novel fabricating method can regulate the surface functional groups to achieve higher surface potential and obtain a favorable pseudohexagonal crystal phase, leading to an increasing transferred charge density in triboelectrification. Additionally, it has been analyzed that higher chemical potential of materials can facilitate the transfer of electrons from the triboelectric polymer surface. This study provides a nonadditive, simple, and effective strategy to fabricate excellent tribo-positive material, which can significantly enhance the performance of TENG.

In situ MIL-101 growth on cotton cloth to fabricate multifunctional phase change composites driven by solar and magneto-thermal for all-day desalination.

It is certainly one of the most feasible ways to extract fresh water from seawater in the face of the current depletion of fresh water resources. Although solar energy as a heat source for desalination is the cleanest and most abundant way, its intermittent and seasonal also poses an obstacle to its practical application. In order to solve the above-mentioned issues, we prepared a series of phase change composites (PCCs) with excellent light-absorbing and magnetic properties by growing MIL-101(Fe) in situ on cotton fabric. All-day desalination through the synergistic action of phase change material (PCM) and magnetic particles. The evaporation rate of PCC can reach 2.76 kg m-2h-1 with an evaporation efficiency of 90.19 % under one sunlight condition. The evaporation rate of sea water under the synergistic effect of magnetic particles and PCM reached 4.53 kg m-2h-1 in the absence of sunlight. This paper provides a new approach to all-day desalination without contact heating.

High transparency, degradable and UV-protective poly(lactic acid) composites based on elongational rheology and chain extender assisted melt blending.

Conventional polylactic acid (PLA) melt plasticization and toughening processes are typically achieved at the expense of PLA strength and transparency, which is clearly detrimental to its application in areas such as smart home and food packaging. Herein, an ultraviolet (UV)-protective PLA-based composite (PP6) that simultaneously achieves high strength (63.3 MPa), high plasticity (125.3 %), and enhanced toughness (4.3 kJ/m2) by adding only 6 wt% poly(3-hydroxybutyrate-4-hydroxybutyrate) (P34HB) under the assist of 1 wt% chain extender was prepared using melt blending technique. Benefiting from the cross-linking effect of the chain extender and the elongational flow during processing, the compatibility between P34HB and PLA, as well as the thermomechanical properties, heat resistance, and biodegradable properties of the composite, have been enhanced significantly. The extremely low melt enthalpy (1.9 J/g) and the low crystallinity PLA phase contribute to an appropriate transparency (78.3 % of glass in 400-1100 nm). The prepared composites display mid- and long-wave UV-protective performance, which is superior to conventional industrial glasses. Through the superior elongational rheology technology, PP6 maintains favorable overall properties even after six thermomechanical cycles. Collectively, the composite fabricated in this work is an attractive candidate for future applications such as smart windows, food packaging, agricultural films, and biomedical applications.

Acid-Doped Pyridine-Based Polybenzimidazole as a Positive Triboelectric Material with Superior Charge Retention Capability.

The energy conversion efficiency of a triboelectric nanogenerator (TENG) is severely limited by the charge density of triboelectric materials, while drastic and unavoidable charge decay happens during contact due to the insufficient charge retention capacity of positive triboelectric materials. Here, elaborately synthesized acid-ion-doped pyridine-based polybenzimidazole processing with strong charge retention capability is demonstrated to couple with negatively corona-polarized electrets. As illustrated by thermal stimulation and an ion mass spectrometer, the formation of acid-ion chimerism processes high activation energy for stored charges, and the selective anion migration can compensate the escape of polarized charge. Accordingly, the charge density can reach up to 596 µC m-2 and the charge retention rate reaches 49.7%, which is so far the highest intrinsic charge density obtained in the open air. Thus, the ionic chimerism strategy provides an effective way to suppress the charge escaping in the open air and gives a great expandable avenue for the material challenges of TENG's practical deployment.

High-Safety Lithium-Ion Battery Separator with Adjustable Temperature Function Inspired by the Sugar Gourd Structure.

As the power core of an electric vehicle, the performance of lithium-ion batteries (LIBs) is directly related to the vehicle quality and driving range. However, the charge-discharge performance and cycling performance are affected by the temperature. Excessive temperature can cause internal short circuits and even lead to safety issues, such as thermal runaway. The separator plays a crucial role in protecting the battery from regular operation, preventing direct touch between the cathode and the anode while allowing the transport of lithium ions. In this study, we have designed a thermoregulating separator in the shape of calabash, which uses melamine-encapsulated paraffin phase change material (PCM) with a wide enthalpy (0-168.52 J g-1) to dissipate the heat generated inside the battery promptly. Under extra-long-use conditions, the heat emitted by the battery is absorbed by the PCM without causing a significant temperature rise that triggers thermal runaway. The PCM separator can effectively suppress the temperature increase caused by battery penetration. Due to the unique structure of the PCM, the battery is short-circuited; it can significantly delay the internal temperature rise of the battery and quickly dissipate the heat, which is consistent with the characteristics of natural calabash in nutrient absorption and water diffusion, improving the melting and heat storage efficiency of the PCM. The design of the phase change separator provides an effective reference for overheat protection and improved safety in lithium-ion batteries.

Harnessing Synchronous Photothermal and Photocatalytic Effects of Substoichiometric MoO3-x Nanoparticle-Decorated Membranes for Clean Water Generation.

Solar-driven interfacial evaporation provides a promising pathway for sustainable freshwater and energy generation. However, developing highly efficient photothermal and photocatalytic nanomaterials is challenging. Herein, substoichiometric molybdenum oxide (MoO3-x) nanoparticles are synthesized via step-by-step reduction treatment of l-cysteine under mild conditions for simultaneous photothermal conversion and photocatalytic reactions. The MoO3-x nanoparticles of low reduction degree are decorated on hydrophilic cotton cloth to prepare a MCML evaporator toward rapid water production, pollutant degradation, as well as electricity generation. The obtained MCML evaporator has a strong local light-to-heat effect, which can be attributed to excellent photothermal conversion via the local surface plasmon resonance effect in MoO3-x nanoparticles and the low heat loss of the evaporator. Meanwhile, the rich surface area of MoO3-x nanoparticles and the localized photothermal effect together effectively accelerate the photocatalytic degradation reaction of the antibiotic tetracycline. With the benefit of these advantages, the MCML evaporator attains a superior evaporation rate of 4.14 kg m-2 h-1, admirable conversion efficiency of 90.7%, and adequate degradation efficiency of 96.2% under 1 sun irradiation. Furthermore, after being rationally assembled with a thermoelectric module, the hybrid device can be employed to generate 1.0 W m-2 of electric power density. This work presents an effective complementary strategy for freshwater production and sewage treatment as well as electricity generation in remote and off-grid regions.

Self-poled piezoelectric polymer composites via melt-state energy implantation.

Lightweight flexible piezoelectric polymers are demanded for various applications. However, the low instinctively piezoelectric coefficient (i.e. d33) and complex poling process greatly resist their applications. Herein, we show that introducing dynamic pressure during fabrication is capable for poling polyvinylidene difluoride/barium titanate (PVDF/BTO) composites with d33 of ~51.20 pC/N at low density of ~0.64 g/cm3. The melt-state dynamic pressure driven energy implantation induces structure evolutions of both PVDF and BTO are demonstrated as reasons for self-poling. Then, the porous material is employed as pressure sensor with a high output of ~20.0 V and sensitivity of ~132.87 mV/kPa. Besides, the energy harvesting experiment suggests power density of ~58.7 mW/m2 can be achieved for 10 N pressure with a long-term durability. In summary, we not only provide a high performance lightweight, flexible piezoelectric polymer composite towards sustainable self-powered sensing and energy harvesting, but also pave an avenue for electrical-free fabrication of piezoelectric polymers.

Novel dynamic elongational flow procedure for reinforcing strong, tough, thermally stable polypropylene/thermoplastic polyurethane blends.

Thermoplastic polyurethane (TPU)/polypropylene (PP) blends of different weight ratios were prepared with a self-made vane extruder (VE), which generates global dynamic elongational flow, and a traditional twin-screw extruder (TSE), which generates shear flow. High-resolution scanning electron microscopy and polarizing microscopy showed a structure feature of fiber morphology and a clear interlocking structure of spherulites of PP/TPU blends prepared with a VE. The wide-angle X-ray diffraction results showed that the TPU/PP blend based on dynamic elongational flow had evident crystalline structure of the ß form as a function of PP (90 wt %), compared to that of the conventional shear flow processing techniques. A significant improvement of the mechanical properties was obtained; the samples prepared with a VE had superior mechanical properties compared to those of the samples prepared with a TSE. Interestingly, differential scanning calorimetry curves showed that dynamic elongational flow could successfully improve the crystallinity of the PP/TPU blends. Furthermore, dynamic thermomechanical and thermogravimetric analysis curves revealed the apparent partial miscibility and strong interaction of the PP/TPU blends influenced by dynamic elongational flow, compared to that of TSE-extruded. Further research will provide significant understanding of the spherulite interface and high-performance manipulation of PP/TPU blends under dynamic elongational flow, achieving superior PP/TPU blends.

Collective Behaviors of Isotropic Micromotors: From Assembly to Reconstruction and Motion Control under External Fields.

Swarms of self-propelled micromotors can mimic the processes of natural systems and construct artificial intelligent materials to perform complex collective behaviors. Compared to self-propelled Janus micromotors, the isotropic colloid motors, also called micromotors or microswimmers, have advantages in self-assembly to form micromotor swarms, which are efficient in resistance to external disturbance and the delivery of large quantity of cargos. In this minireview, we summarize the fundamental principles and interactions for the assembly of isotropic active particles to generate micromotor swarms. Recent discoveries based on either catalytic or external physical field-stimulated micromotor swarms are also presented. Then, the strategy for the reconstruction and motion control of micromotor swarms in complex environments, including narrow channels, maze, raised obstacles, and high steps/low gaps, is summarized. Finally, we outline the future directions of micromotor swarms and the remaining challenges and opportunities.

Strengthening-toughening pure poly(lactic acid) with ultra-transparency through increasing mesophase promoted by elongational flow field.

Poly(lactic acid) (PLA), as a biodegradable material, finds wide applications in packaging, automotive, and biological industries. However, achieving high strength, toughness, ultra-transparency, and heat resistance simultaneously in pure PLA through continuous one-step manufacturing remains a significant challenge. In this study, we addressed this challenge by utilizing the eccentric rotor extruder (ERE) in combination with cooling rolls to manufacture PLA sheets with outstanding mechanical performance. The ERE's elongational flow field combined with the cooling roller's weak stretching action induced orientation in the PLA molecular chains and promoted the formation of more mesophase, significantly improving mechanical properties. When the extrusion-stretch ratio (λ) value was 3.5, the tensile yield strength, Young's modulus, and elongation at break of ERE-fabricated samples ER-3.5 reached 86.2 MPa, 1777 MPa, and 57.9 %, respectively. Compared to the SE-3.5 samples manufactured with traditional methods, the increases were 38.8 %, 25.8 %, and 9.4 times, respectively. Additionally, the ERE manufactured samples maintained ultra-transparency and high heat resistance, making them suitable for food packaging, biomedicine, and other related fields. This methodology provides an efficient industrial-scale approach for manufacturing neat, biodegradable PLA with outstanding mechanical performance and ultra-transparency.

Cicada Wing-Inspired Transparent Polystyrene Film Integrating Self-Cleaning, Antifogging, and Antibacterial Properties.

A transparent film integrating antifouling, antifogging, and antibacterial properties is crucial for its application as a protective mask, goggles, or lens. Herein, applying dynamic injection molding coupled with a bionic gradient template, a fast and efficient method is proposed for the preparation of the bionic polystyrene surface (BNPPS) with a cicada wing-inspired nanopillar structure. The contact angle of the BNPPS film increases continuously along the wing vein, while the sliding angle decreases continuously, mimicking the gradient wetting state of a cicada wing and providing excellent self-propelled removal properties for tiny water droplets. Notably, the BNPPS film has a transmittance higher than 90% and a reflectivity lower than 5% in the visible light range. Dyeing water, milk, juice, cola, and ink can slide smoothly from the BNPPS film surface without leaving any residue. Importantly, the nanopillars on the BNPPS film surface can penetrate and kill most of the Escherichia coli within 20 min. Therefore, the prepared BNPPS film with sufficient mechanical strength gathers the unique properties of the cicada wing together. The proposed research is expected to offer valuable guidance for fabricating self-cleaning, antifogging, and antibacterial optical devices that could be utilized in medical and vision systems operating in harsh environments.

Water evaporation induced in-situ interfacial compatibilization for all-natural and high-strength straw-fiber/starch composites.

In this paper, we proposed a novel and green strategy based on water evaporation induced in-situ interfacial compatibilization (WEIC) mechanism for fabricating high-strength and all-natural lignocellulose/starch composites. This mechanism exploits the natural compatibility of the lignocellulose and starch and was tested through an internal mixing process with regulated water evaporation. Specifically, we revealed that a restrained layer was in-situ formed at the interface of the lignocellulose and starch during the internal mixing process; a faster water evaporation rate thickens this restrained layer, restricts the starch's molecular movement and significantly increases the composite's mechanical properties. The highest tensile strength and Young's modulus of the composites achieved are 21.7 ± 0.8 MPa and 2.2 ± 0.1 GPa, respectively, superior to many existing starch/lignocellulose composites. Thus, this work provides new insight into the compatibilization of various hydrophilic polysaccharides and paves new avenues for developing greener and more facile methods to fabricate all-polysaccharide composites.