| Biological materials,through long periods of natural selection,have evolved intricate macrostructures and microstructures,acquiring advanced properties such as lightweight yet strong,tough,multifunctional,and adaptive,which artificial materials struggle to replicate.Adaptation,a unique characteristic of biological materials,refers to their ability to dynamically change their properties and structural shapes in response to environmental changes,allowing them to better adapt to their surroundings.For instance,pine cone scales exhibit bending deformation in response to humidity changes due to their oriented fibrous structure,enabling the opening and closing of the scales.During bird flight,wing feather structures are adjusted based on flight conditions to achieve better aerodynamics.Compared to traditional static material structures,dynamic biological material structures possess stronger interactivity and environmental adaptability,enabling organisms to flexibly respond to changing environments,ensuring their survival and successful reproduction.However,due to limitations in manufacturing techniques and materials,traditional processing methods struggle to accurately replicate the complex macro and microstructures of biological materials.Additionally,half of engineering materials lack responsive properties to external stimuli,unable to exhibit intelligent behaviors akin to biological organisms.These limitations pose significant challenges to the development of biomimetic dynamic materials.Understanding and elucidating the construction principles of dynamic biological materials,designing and manufacturing biomimetic dynamic materials and structures,represent important directions for the development of next-generation advanced materials.Biomimetic dynamic materials research mainly focuses on two aspects:(1)Revealing the relationship between the macrostructure,microstructure,and dynamic performance of biological dynamic materials,analyzing their dynamic deformation mechanisms to provide a basis for the design of biomimetic dynamic structural materials.(2)Developing manufacturing methods to control the internal structure of materials,such as additive manufacturing and 3D printing technologies,to produce intelligent material structures with special internal organizations,utilizing the stimulusresponse properties of smart materials to create programmable dynamic properties in biomimetic adaptive materials.Liquid crystal elastomers(LCEs),as liquid crystal-based elastic materials,combine the characteristics of liquid crystals and elastomers,making them an ideal choice for biomimetic dynamic biological materials.4D printing refers to the capability of structures and materials printed using 3D printing technology to undergo programmable changes in shape,physical,chemical properties,and functionality under external stimuli.This bears similarity to the self-driven deformation mechanism of biological materials.Utilizing the adaptive dynamic deformation concept of biomimetic materials and employing 3D and 4D printing additive manufacturing technologies present unprecedented opportunities for creating biomimetic intelligent materials with controllable dynamic properties.However,4D printing of biomimetic dynamic materials faces several challenges: the internal structure of materials,such as molecular arrangement and fiber orientation,is crucial for controlling the intelligent behavior of materials.Understanding how printing processes affect the structure of materials remains difficult and requires elucidating the influence mechanism of process parameters on material structure.The relationship between the dynamic properties of materials and their internal structure is not yet clear and requires revealing the structureproperty relationship.The dynamic behavior of materials is closely related to external stimuli and requires clarifying the intrinsic relationship between external stimuli and material property changes.Although there is extensive research on the deformation and motion of LCEs,studies on the mechanical properties of these phase-change materials under dynamic loads and changing temperatures are limited.LCE materials undergo phase transitions under dynamic loads and changing temperatures,leading to dynamic changes in their mechanical properties.However,the mechanisms underlying these dynamic properties are not fully understood,and the application of dynamic performance remains unexplored.Research on composite materials based on LCEs as matrices or reinforcement phases is limited,failing to unleash the potential of these phase-change materials,requiring increased research efforts.To address these issues,this study primarily conducted research in the following four aspects:(1)To address the challenge of predicting,controlling,and utilizing stimulusresponse deformation during 4D printing,a liquid crystal elastomer 4D printing method encoding multiple process parameters was proposed.By studying the influence of coupling changes between printing parameters on liquid crystal interdigitation orientation during extrusion printing,a correspondence between process parameters and interdigitation orientation was established.Based on the deformation control strategy of biomimetic material,a "theoretical calculation-simulation analysisexperimental verification" deformation control strategy for 4D printing LCEs was established to meet the requirements of predictable and designable stimulus-response deformation in 4D printing.During direct extrusion,the coupling changes of process parameters(printing speed,extrusion pressure,printing height,and photocuring intensity)significantly affect the interdigitation orientation of LCEs and the thermally responsive driven strain.By adjusting these process parameters,the driven strain of liquid crystal elastomers can be adjusted within the range of 10-45%.The mechanism of the influence of process parameters on liquid crystal orientation and driven strain was analyzed,and a biomimetic multi-parameter encoding LCE deformation control strategy inspired by plant deformation was proposed.By applying the multi-parameter encoding strategy,including programming based on printing speed,extrusion pressure programming,printing height programming,photocuring agent programming,and multi-parameter combination programming,LCE actuators were successfully printed.The actual deformation of printed LCE specimens under thermal stimulation was highly consistent with theoretical calculations and simulation analysis results,demonstrating the feasibility and precision of the multi-parameter encoding biomimetic microstructure4 D printing deformation control strategy.(2)Inspired by the non-uniform strain strategy of caterpillars,a dynamic printing parameter 4D printing method was applied to design and prepare liquid crystal elastomer self-propelled biomimetic soft robots.LCE soft robots can generate caterpillar-like autonomous rhythmic crawling motion in non-uniform temperature fields.Through mechanical and thermodynamic analysis,the self-rhythmic deformation and motion mechanism in non-uniform temperature fields were analyzed,and kinematic and thermodynamic models of self-rhythmic robots in thermal gradient fields were established to clarify the influence of design parameters and environmental stimulus changes on their motion characteristics.By using printing speed to design regional orientation of internal interdigitation and controlling the external stimulus field,control over the motion path,step length,and period of LCE robots was achieved.Utilizing intelligent LCE materials to produce reversible deformation effects in thermal fields,combined with 4D printing process parameter programming methods,programmable continuous motion of robots in gradient thermal fields,including crawling,rolling,and self-oscillation,was achieved.(3)Short-cut glass fibers were added to liquid crystal elastomers as reinforcement phases to prepare glass fiber/liquid crystal elastomer(GF/LCE)composite materials.Based on printing processes,quasi-zero stiffness structures were manufactured,and the energy transmission and absorption properties under dynamic loads(vibration excitation)were studied.Firstly,the relationship between process parameters during printing and the formation of material structures and mechanical properties was analyzed.Experimental results showed that adjusting the printing speed could effectively control the mechanical properties of glass fiber structures and composite materials.Utilizing the printed composite materials,quasi-zero stiffness structural units were designed and manufactured.Quasi-zero stiffness units were used to construct metamaterial arrays for programming custom quasi-zero stiffness isolators.Customization of load weight and quasi-zero interval bandwidth was achieved through horizontal,vertical,and combined array designs.By incorporating carbon black(CB)particles into the material,quasi-zero isolators with light-stimulated response characteristics were developed.Quasi-zero stiffness isolators,stimulated by nearinfrared light,could change their isolation load and damping characteristics,achieving on-demand adjustments to low-frequency isolation characteristics.This study provides important theoretical and experimental foundations for the development of intelligent,controllable isolation material structures.(4)Liquid crystal elastomer freeze-crushed into particles(LCEP)were used as reinforcement particles,with acrylic elastomer(FPUA)as the matrix,to prepare LCEP/FPUA composite materials,which were applied to direct-write 4D printing,successfully preparing dynamically adjustable quasi-zero stiffness isolation structures.LCEP/FPUA composite materials possess shape memory characteristics compared to pure FPUA materials,while also retaining the characteristics of viscoelastic damping materials,enabling them to exhibit high damping performance over a wide frequency and temperature range.The effects of LCEP particle size and content in LCE/FPUA composites on shape memory characteristics and damping performance were explored.Using LCEP/FPUA as printing ink,flexural beam quasi-zero stiffness isolators were printed using direct-write technology.By programming shape memory characteristics,adjustable temporary shapes were obtained,thereby achieving adjustments to the load and low-frequency isolation properties of quasi-zero stiffness isolators.The dynamic performance of isolators at different vibration frequencies and amplitudes,including vibration transmission and energy absorption characteristics,was systematically studied.Based on shape memory programming,control over load weight and quasi-zero interval bandwidth was achieved,maintaining good low-frequency isolation characteristics under different loads.Isolation characteristics could also be adjusted by temperature,maintaining good vibration isolation performance at different temperatures and under different loads.Through shape memory programming of quasi-zero stiffness isolators,precise control of temporary shapes was achieved.Under impact loading,using shape memory characteristics,strain distribution and deformation modes of the material could be adjusted,thereby controlling its energy absorption performance.By designing shape memory programming reasonably,the material could effectively absorb and dissipate energy under impact loading,improving its impact energy absorption performance. |
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