Strengthening,Toughening And Self-Healing Of Biomimetic Intelligent Materials Based On Multi-Scale Structure Design

Biomimetic intelligent material is a kind of new material with biological intelligence which is inspired by the structure or function of the organism.It can sense environment stimulation and take measures to response.The research of biomimetic intelligent materials has developed rapidly since the 1990s,and has become a frontier research field involving materials science,chemistry,biology,mechanical engineering,electronic and electrical engineering and other disciplines.Due to the unique self-adaptive characteristic of biomimetic intelligent material,and with the rapid development of advanced manufacturing technology and computer technology,the deep integration of biomimetic intelligent materials and artificial intelligence has become one of the research hotspots in academia and industry.So,it is expected to expand its applications in the soft robotics,tactile perception,precision medical,Internet-of-things and so on.Smart actuators and flexible electronic skin are two important application fields of biomimetic intelligent materials.In recent years,there have been a lot of research reports related with actuators and sensors.Although these smart devices have achieved good performance,the mechanical property of most smart actuation materials is low.So,it is difficult to meet the device long-term use requirement.In addition,even if the mechanical strength of smart materials has been improved,the mechanical enhancement cannot satisfy the multi-functional application of intelligent composites.To realize the multi-scenarios application of intelligent materials,a wide range of mechanical property tunable composites are required,which can be adjusted arbitrarily between high strength and high toughness.At the same time,many intelligent materials with high mechanical properties are difficult to possess mechanical and functional self-healing ability due to their stable chemical structure,which leads to poor structural and functional reliability.Moreover,due to the stable structure of most intelligent materials,its geometric structure is hard to be changed.As a result,different bionic 3D structures cannot be rapidly processed,which leads to the single motion form of actuators,greatly limiting the demand of diversified application scenarios of smart actuators.To address the problems above,this paper proposes the multiple length-scale structural design strategy,from molecular scale,micro/nano scale to macroscopic scale.Through the design and construction of mesoscale gradient structure,interfacial supramolecular interactions,micro/nano-scale assembly structure and crystalline structure,the bionic intelligent composite materials demonstrate high mechanical properties and excellent self-healing performance.Futhermore,we implement the biomimetic intelligent material in the smart actuators and artificial electronic skin to achieve stable and reliable applications.The main research contents and conclusions are as follows:1.To study the influences of mesoscale assembly and supramolecular hydrogen bonding interaction on the morphology,structure,mechanical properties and driving properties of intelligent composites.By selecting two-dimensional MXene nanosheets,one-dimensional cellulose nanofiber（CNF）nanofibers and polydopamine（PDA）molecules,the gradient structured G-MXCP composites were prepared through layer-by-layer assembly.The G-MXCP composite showed high mechanical strength（237.1±20.1 MPa）,elastic modulus（8.5±0.5 GPa）and excellent mechanical toughness（10.9±1.0 MJ m-3）,which realizes the synergistic strengthen of strength and toughness of MXene-based composites.This work solves the problem that the existing MXene composites possess low toughness and are easy to break.Furthermore,the G-MXCP composite material was applied to the robust actuator,and showed excellent actuating stability,even after being trampled by an adult weighing 7.5 million times its own weight.2.To investigate the influence of interfacial supramolecular interaction and two-dimensional nano-fillers on mechanical properties of polymer composite.By introducing calcium chloride and tannic acid-assisted exfoliated WS₂ nanosheets into the silk fibroin matrix,a reversible supramolecular interaction and nano-filler-reinforced skeleton network was constructed at the interface of the composites,which realized the mechanical tunability of the composites.At ambient humidity,the tensile strength of the composites can reach 72.5 MPa,which is much higher than that of other silk proteins and their composites.When the composite is hydrated,the tensile strength,Young’s modulus,tensile strength and toughness of the composite can reach11.0 MPa,6.89 MPa,360%and 12.52 MJ/m³,respectively.It solves the problem that the traditional intelligen materials can not realize arbitrary adjustment between the two states of high mechanical strength and high flexibility,and lays the foundation for the multi-functional applications of biomimetic intelligent materials.3.To study the effects of reversible supramolecular interactions on mechanical self- healing properties of composites,and explore their applications in actuation and sensing fields.Due to the reversible interfacial supramolecular interaction of the silk protein-based composites prepared above,the composites show excellent self-healing properties:The self-healing efficiency of tensile strength can reach 96.1%in the environment humidity,and the self-healing efficiency of mechanical toughness can reach 100%in the hydration state,addressing the problem that high mechanical properties and self-repairing properties of intelligent composite materials can not be realized synergically.Therefore,the mechanical properties of composites can be adjusted to meet the requirements of practical applications.In this paper,we conceptually demonstrate the stable use of the composite material for actuators and artificial electronic skin,expanding the application of intelligent materials.4.To study the influence of covalent and non-covalent dual network structure on the phase transformation behavior,processing properties of the synthesized intelligent materials and its actuating functions for diverse scenarios.This polyester with covalent and non-covalent double network structure were prepared by emulsion polymerization and crosslinking of crystal prepolymer molecules.As a result,the 3D shape configuration processing of the polyester at room temperature（≤35 ℃）,rapid humidity actuating performance and excellent mechanical and functional self-healing properties were realized.It breaks through the technical problem that it is difficult for intelligent actuating materials to be processed into different 3D structures at room temperature and it is difficult to realize a variety of actuation forms.At last,we conceptually demonstrated the various actuation forms of smart robots with different3D structures and their potential applications.