Investigation On The Influence Of Extrusion Process Parameter On The Morphing Mechanism Of 4D Printed LCEs

4D printing is a 3D printed object that can produce changes in geometric shapes or physical and chemical properties;this change is spontaneously generated under appropriate external excitation,such as temperature,humidity,and light,etc.;the way of change is pre-designed and programmable.4D printing has advantages over traditional automation systems such as high volume and high-quality efficiency,self-deformation,self-driving,and multi-function.It can be applied to software robots,biomedicine,drug-controlled release,and aerospace intelligent structures.4D printing needs to produce programmable changes.How to "bury" the design logic that you want to program in the material through printing is the difficulty and core technology of 4D printing.That is,how to program the deformation control instructions in the material through the design of the material and its structure so that it produces a specific response behavior.Some plant tissues and organs can deform.For example,pine cone scales can open and close according to changes in humidity.Pine cones use the orientation of the cellulose fibers in the scales to achieve bending and straightening deformation.The pine cone scales bury the control instructions in the material so that when it is separated from its parent body,it still has the control function to achieve specific deformation or movement.Pineta's deformation control method inspires 4D printing programming design.We can use 3D printing to make materials with different structures in different positions to realize 4D printing programming.When the liquid crystal elastomer material with an ordered structure is heated to the phase transition temperature,and when the temperature is cooled from the phase transition temperature to room temperature,the order-disorder mutual conversion of the mesogenic arrangement will occur,resulting in macroscopic deformation,deformation mode and The degree of mesogenic orientation is related to the orientation direction.The sheer force generated by extrusion 3D printing can make the mesogenic orientation of the liquid crystal elastomer material,and the degree and direction of the orientation are related to the 3D printing parameters.In this paper,a liquid crystal elastomer material is prepared as a smart material for 4D printing,and the material formula and preparation process is designed.Thermal,dynamic thermomechanical,and rheological tests and analysis of the prepared liquid crystal elastomer material were carried out,and the printability and excitation response characteristics of the prepared material were studied,and the feasibility of the material as an extrusion 4D printing material was confirmed.Designed a variable parameter extrusion 3D process,and developed an extrusion printing device with variable process parameters.The developed extrusion printing process was used to print the liquid crystal elastomer material,which verified the rationality of the process design and the practicability of the printing device.The process parameters such as the moving speed of the extrusion head,extrusion air pressure,ultraviolet light measurement,printing temperature,substrate temperature,printing path,and extrusion head height,as well as the influence of external excitation temperature on the deformation characteristics of liquid crystal elastomers,are studied.According to the corresponding relationship between the obtained process parameters and the deformation characteristics,the stimulus-response deformation behavior of the liquid crystal elastomer smart component was programmed and designed through the printing parameter settings,and the feasibility of the process parameter programming 4D printing was verified.The glass transition temperature Tg of the prepared precursor ink is-10°C,and the phase transition temperature is about 90°C.The phase transition temperature of the liquid crystal elastomer completely cured by ultraviolet light is about 155°C.The rheological test results show that the prepared material has shear thinning characteristics,and the viscosity decreases with increasing temperature,indicating that the material is suitable for direct writing 3D printing.The results of the dynamic thermomechanical analysis show that the prepared material has temperature-controlled deformation characteristics,and its reversible cycle performance is good.Printing speed,extrusion pressure,needle diameter,the distance between the extrusion head and the substrate,substrate temperature,and extrusion head temperature can all affect the orientation of the liquid crystal mesogen along the printing path,which can make the liquid crystal elastomer produce 10-45%Deformation can be controlled.The phase transition temperature can be adjusted by controlling the degree of UV crosslinking so that the phase transition temperature of the liquid crystal elastomer can be adjusted in the range of 90°C to 155°C.By setting the phase transition temperature in different regions of the same piece,it can produce a staged controllable deformation.By using differentiated process parameters in different areas of the print,the deformation characteristics of the printed liquid crystal elastomer can be designed,and controllable deformation such as bending and torsion can be generated.Utilizing the regulation of ultraviolet light measurement,the stimulus-response temperature can be regulated,and the deformation behavior of 4D printing can be realized through external stimulus control.