Huanjun Li

Nanocomposite hydrogels with high strength cross-linked by titania

A new type of nanocomposite hydrogel with excellent mechanical properties, good water-stability, as well as unique water-activated shape memory behavior were successfully prepared by in situ free-radical polymerization using titania nanoparticles as the cross-linking agent.

High strength nanocomposite hydrogel bilayer with bidirectional bending and shape switching behaviors for soft actuators

We report on a type of TiO2 cross-linked nanocomposite hydrogel bilayer with bidirectional bending and shape switching behaviors that could be used as a soft actuator.

Thermal and water dual-responsive shape memory poly(vinyl alcohol)/Al2O3 nanocomposite

We report a new type of poly(vinyl alcohol) (PVA)/Al2O3 nanocomposite with fast thermal and water activated shape memory behavior via a cyclic freezing/thawing method.

Bio-inspired layered chitosan/graphene oxide nanocomposite hydrogels with high strength and pH-driven shape memory effect

The layered nanocomposite hydrogel films containing chitosan (CS) and graphene oxide (GO) have been prepared by water evaporation induced self-assembly and subsequent physical cross-linking in alkaline solution. The layered CS/GO hydrogel films obtained have a nacre-like brick-and-mortar microstructure, which contributes to their excellent mechanical properties. The tensile strength and elongation at break of the hydrogel films with 5wt% GO are 5.35MPa and 193.5%, respectively, which are comparable to natural costal cartilage. Furthermore, the CS/GO hydrogel films exhibited pH-driven shape memory effect, and this unique phenomenon is mainly attributed to the reversible transition of partial physically cross-linking corresponding to hydrogen bondings and hydrophobic interactions between CS polymer chains due to pH changing.

Fe3O4-decorated single-walled carbon nanohorns with extraordinary microwave absorption property

Single-walled carbon nanohorns (SWCNHs) are seldom used as electromagnetic (EM) wave absorption materials due to their inferior impedance matching resulting from their high dielectric constant. In this work, decorated with 35.6 wt% Fe3O4 nanoparticles, the as-prepared composite displays a significantly enhanced EM wave absorption ability because of the improved impedance matching, electric polarization and interfacial polarization. Specifically, the maximum reflection loss of this composite with a thickness of 5.8 mm is −38.84 dB at 3.72 GHz in the S-band. The bandwidth of absorption exceeding −10 dB is 9.2 GHz (from 3.2 GHz to 12.4 GHz) with an absorber thickness of 2–6 mm. What is more, a second absorption peak with a reflection loss no less than −10 dB appears when the absorber thickness is over 4 mm.

Graphene oxide based moisture-responsive biomimetic film actuators with nacre-like layered structures

Hygroresponsive biomimetic actuators that convert chemical potential energy contained within the humidity gradient into mechanical deformation are of particular significance for realizing a sustainable society. Here, we report the preparation of nanocomposite films containing chitosan (CS) and graphene oxide (GO) with nacre-like brick-and-mortar microstructures by combination of water evaporation induced self-assembly and subsequent physical crosslinking in alkaline solution. The resulting hybrid films exhibit strong mechanical properties in both hydrated and anhydrous states, and the changes in physical properties between the two states likely result in perpetual mechanical reconfiguration. Whats more, these films are capable of autonomous and continuous locomotion due to water exchange with the environment. The film actuator can lift objects 50 times heavier and transport cargos 10 times heavier than itself. Furthermore, we have assembled a motor that can move forward in response to humidity gradients, which provides proof of the utilization of this hybrid material in bio-inspired applications.

Self-healing elastomer assembly towards three-dimensional shape memory devices

The superior self-healing elastomers were readily prepared by free-radical copolymerization of methoxyethyl acrylate (MEA) and N,N-dimethylacrylamide (DMAA). The synergistic interaction between the shape memory effect and the reversible weak hydrogen bonds lead to the excellent self-healing properties and high mechanical strength of the elastomers. By taking advantage of the two outstanding performances, we demonstrated that various novel two-dimensional (2D) and three-dimensional (3D) shape memory devices can be precisely designed on the basis of the self-healing mediated assembly of the elastomers as building blocks. This assembly method to combine self-healing and shape memory properties might open up a promising avenue for the design and fabrication of 3D complex-shape smart devices.

Multiple shape memory polymers for self-deployable device

In this study, novel multiple shape memory polymers (MSMPs) are successfully prepared using the facile, inexpensive, and effective approach of multistage polymerization procedures. The resultant samples comprising three copolymers with well-separated glass transition temperatures can change their shapes in a pre-defined way over a broad temperature range with almost full recovery of all temporary shapes. We anticipate that a similar approach can be broadly applicable to other stimuli-responsive materials for the design and fabrication of diverse triple- or multiple-SMPs.

Thermosensitive antibacterial Ag nanocomposite hydrogels made by a one-step green synthesis strategy

We developed a simple one-step synthesis route to prepare silver nanoparticles containing nanocomposite hydrogels by in situ free-radical copolymerization of N-isopropylacrylamide and N-(hydroxymethyl) acrylamide. In this synthesis, the hydrogels and nanoparticles are formed simultaneously without any additional reducing agent at room temperature, thus demonstrating the synergetic effect between reductive monomer HMAm and catalytic clay nanosheets in promoting the reduction of silver ions. The in situ generated silver nanoparticles within the hydrogel matrix were highly stable and the hydrogels showed sustained release of silver for periods of at least ten days in aqueous solution. Interestingly, the mechanical properties of the hydrogels showed remarkable improvement upon addition of a small amount of AgNPs. Furthermore, the resulting gels exhibited thermosensitive antibacterial activity, which was enhanced with an increase in the N-isopropylacrylamide content of the copolymers. Our work provides a facile and convenient green approach to preparing antibacterial tough hydrogels, which may find potential applications in wound dressings, tissue engineering and catalysis.

Rapid room-temperature self-healing conductive nanocomposites based on naturally dried graphene aerogels

Recent progress on flexible electronics has inspired remarkable efforts in the design and fabrication of novel conductive soft materials. However, the combination of room-temperature self-healing and highly conductive properties in flexible composite materials remains a great challenge. Herein, we describe the construction of conductive nanocomposites through an in situ copolymerization of N-isopropylacrylamide and 2-methoxyethyl acrylate in naturally dried graphene-based aerogels, which show ultralow density below 10 mg cm−3, superelasticity, and high conductivity up to 120 S m−1. The resulting nanocomposites with less than 1 wt% graphene loading achieve superior conductivity of 70 S m−1 and rapid room-temperature self-healing properties. On rupture, the mechanical properties recover to more than 98% of the virgin sample within 2 h and the electrical properties recover to above 80% of their original conductivity within 15 minutes. The high room-temperature healing efficiency is attributed to the reversible hydrogen bonding and sufficient chain entanglement enabled by the low glass transition temperature of the copolymer. It is further demonstrated that the graphene-based conductive nanocomposites can be used as strain sensors for human motion detection. We believe that the flexible conductive nanocomposites could find numerous applications in wearable electronic devices, sensors, and soft robotics.