Design And Preparation Of Bionic Intelligent Soft Materials And Investigation Of Their Self-Driven Mechanisms

《Made in China 2025》clearly proposes that intellectualization is the strategic focus area of the new materials and devices development,which has been the current international hot frontier of engineering science.Intelligent soft material is a kind of material with integration of “perception”,“feedback” and “response”,which can receive driving information(such as light,temperature,electricity,magnetism,humidity,pH and so on)and output control action or mechanical motions.Compared with the traditional rigid materials,intelligent soft materials can realize “small stimulation and large responses” with the of external environment change.The characteristics of dynamic precise sensing deformation result in the wide application of intelligent soft materials in intelligent actuators and equipment.The design and preparation of intelligent soft materials has been an emerging and important development direction of intellectualization.As one of typical intelligent soft materials,intelligent hydrogels own properties of abundant stimulation models,linear driving force output and high biocompatibility,which has been widely used in soft actuators,artificial muscle,electron device,medical instrument and so on.But,in the widespread application,intelligent hydrogels are faced with the complex application environment requirements including high capacity and various stimulations.Therefore,intelligent hydrogels should own high mechanical strength,high response rate,multiple response pattern,various self-driven function and so on.The combination of mechanical property,intelligent property and functional property is the bottleneck problem of intelligent hydrogel design and preparation.The wild wheat awn in nature owned high mechanical property and the self-driven deformation and movement under stimulation of humidity variation via the combination of layered structure,gradient micropore structure and fiber distribution pattern,which provided an important bionic inspiration for the researches of intelligent soft materials.The wild wheat awn was treated as the biological model.Based on microstructure characteristics of wild wheat awn,the bionic layered micropore structure model,bionic 90°/0° bilayer network structure model and bionic layered gradient micropore structure model were built to guide the design of bionic intelligent soft materials.Based on three bionic structure models,nanofibrillated cellulose was the reinforcement,graphene oxide was the photothermal conversion agent,the poly N-isopropyl acrylamide temperature response intelligent hydrogels were treated as the basic material system.The bionic intelligent soft materials with high mechanical strength,high response rate,multiple response pattern,efficient self-driven deformation and movement,were successfully fabricated via molding technology,3D printing technology and hydrothermal synthesis technology.Moreover,various series of bionic intelligent self-driven samples were also design and fabricated successfully.The self-driven mechanism of static deformations and dynamic movements of bionic intelligent soft materials were explained via mechanical analysis.The bionic intelligent soft materials successfully realized the integration of structure-material-perception-driving-function,which provided a new effective bionic method for the solution of bottleneck problem of intelligent soft materials.The main research contents and conclusions are listed as follows.(1)Based on the difference expansion deformation mechanism of layered porous structure in deformation part of wild wheat awn,the bionic layered micropore structure model with layered porous structure was designed.The poly N-isopropyl acrylamide temperature response intelligent hydrogels were fabricated via molding technology successfully.With the increase of nanofibrillated cellulose and graphene oxide contents,the crosslink density of intelligent hydrogels was enhanced.The intelligent hydrogels exhibited high mechanical strength on the base of intelligent perception and self-driven deformation.The self-driven mechanisms of bionic bilayer intelligent soft materials fabricated via “one-step” molding technology was the swelling/deswelling anisotropy of the two layers.The nanofibrillated cellulose and graphene oxide content and sample dimensions significantly affected intellectualization and function characteristics of bionic bilayer intelligent soft materials.The small sample dimension(relatively small thickness)owned the relative high response rate and deformation degree.The graphene oxide realized temperature and near infrared laser responses of bionic bilayer intelligent soft materials,which realized simple functional applications of “capture” and “transportation” abilities.(2)Based on the fiber distribution pattern of cap and ridge of wild wheat awn,the bionic 90°/0° bilayer network structure model was built.The solidification of poly N-isopropyl acrylamide temperature response intelligent hydrogel with graphene oxide was solved via the in situ free radical polymerization under vacuum innovatively,which realized the precise molding of 3D printing of bionic intelligent soft materials.The nanofibrillated cellulose content was the important parameter for the effective control of apparent viscosity,storage modulus and loss modulus,which affected the printable and structure maintaining abilities directly.The nanofibrillated cellulose content of 10 mg/mL was the optimal concentration for 3D printing.The relatively small thickness and precise bilayer network structure built via 3D printing can realize high response rate under temperature and near infrared laser stimulations.Compared with molding technology,the anisotropy of swelling and deswelling in precise structure of same materials was self-driven mechanism of bionic intelligent soft materials fabricated via 3D printing under temperature and near infrared laser stimulations.Different 3D printing structure models can realize different self-driven intelligent deformation characteristics.(3)Based on the layered structure and gradient micropore structure of wild wheat awn,the bionic layered gradient micropore structure was built,which decreased the adverse influence of micropore size of layered structure.The N-isopropyl acrylamide and 4-hydroxy butyl acrylate were treated as monomer and crosslinker,respectively.The poly N-isopropyl acrylamide intelligent hydrogel with gradient structure was fabricated via hydrothermal synthesis technology.The controllable distribution of graphene oxide in gradient hydrogels was innovatively realized by graphene oxide infiltration method including the entirety infiltration method and the locality infiltration method,which controlled the heat transfer models and deformation scale effectively.Based on high response rate and structure design,the static deformations and dynamic movements including bionic origami,bionic palm,bionic chrysanthemum and bionic inchworm were realized successfully.(4)The nanofibrillated cellulose enhanced the crosslink density and weakened gradient structure pattern of gradient structure intelligent hydrogels.The graphene oxide infiltration ability was still maintained.The nanofibrillated cellulose reinforced gradient structure intelligent hydrogels still owned high mechanical strength and relative high swelling/deswelling rate.With the increase of nanofibrillated cellulose content,the Young’s modulus scales of gradient structure intelligent hydrogels increased first and then decreased,which was the important material parameter of response rate of gradient structure bionic intelligent soft materials.The gradient structure bionic intelligent soft material with nanofibrillated cellulose content of 2 mg/mL own the highest Young’s modulus and steadiest intelligent response process.With the increase of power density,the response rate of gradient structure bionic intelligent soft materials increased within limits.(5)The gradient structure intelligent hydrogels with nanofibrillated cellulose enhanced the mechanical strength and realized the combination of intelligent property and functional property.Under near infrared laser stimulation,the nanofibrillated cellulose reinforced gradient structure bionic intelligent soft materials realized many kinds of typical controllable,repeatable and highly efficient typical static deformations and dynamic movements including bending deformation,curling deformation,folding deformation,switching movement and forward/turn movement.The “Polymer” static deformation,the bionic octopus “swimming” movement,the 90° cyclic switching with low power density,the syntropy cyclic switching with high power density and the “8” obstacle avoidance movement was realized by controlling the nanofibrillated cellulose content,power density and irradiation patterns of near infrared laser.The congruent relationships of curvature change,deformation angle,deformation displacement,material properties and excitation intensity were built via mechanical analysis,which effectively revealed the self-driven mechanisms of typical static deformations and dynamic movements of gradient structure bionic intelligent soft materials.