Study On External Field Assisted Direct Writing 3D Printing Of Porous Elastomeric Material

In recent years,porous materials have shown great potential for drug delivery and engineering applications due to their low density and high specific surface area.While the properties of porous materials prepared by conventional methods are difficult to be controlled precisely because of the inconsistent shape and non-uniform distribution of internal cells.Direct Ink Writing（DIW）in 3D printing can fabricate regular and ordered porous structures.In DIW,the influence of sample structure on the final performance of the sample cannot be ignored.And the poor manufacturing process and structural design in the conventional DIW process will lead to distortion of the sample structure and degradation of the performance.In this paper,porous silicone elastomers are fabricated by external field-assisted DIW,in which the external fields include thermal field and laser field.Finally,silicone foams with high fabrication accuracy and high structural fidelity are obtained,which is expected to play an important role in energy absorption and vibration damping.The main research contents of this subject are as follows:（1）SE1700 is used as the experimental material to prepare silicone foams and the fabrication process is investigated with the assistance of a high-temperature platform.The feasibility of the high-temperature platform-assisted DIW process is first analyzed by characterizing the rheological and thermodynamic properties of SE1700.The fluid behavior inside the syringe and at the tip during the DIW printing process is analyzed in ANSYS Polyflow.The simulation results show that the paste maintains an almost quasi-static flow process inside the syringe,while the flow rate,pressure,and shear rate have a large gradient change at the tip.In addition,the effects of printing speed,extrusion pressure,and substrate temperature on the deposited filament diameter（d）are investigated by the controlled variable method.Based on the above experiments,the optimal printing parameters at each temperature substrate are obtained.The silicone foams with different filament span（s）are prepared to characterize the interlayer collapse and compressive mechanical properties.The results show that 1)the addition of a high-temperature platform can significantly reduce the interlayer collapse in the foams with a large filament span.The collapse of the foams with s/d=10decreases from 1000μm on the ambient substrate to 100μm on the 150°C substrate;2)the addition of a high-temperature platform can remarkably improve the fabrication stability and compressive mechanical properties of the foams.The working range of the stress plateau is improved by nearly 100%for the samples with s/d=5 on the 150°C substrate compared to the sample on the ambient substrate.Finally,the extensions and limitations of the high-temperature platform-assisted DIW process are illustrated by a combination of experiments and simulations.（2）Instant curing DIW printing of SE1700 is achieved with the help of CO₂ laser,and its fabrication process is investigated.Firstly,the FT-IR spectrum of SE1700 is analyzed,which shows that it maintains a very high absorption in the infrared range.Therefore,a CO₂ laser with a wavelength of 10.6μm is selected.The extrusion process is decoupled from the curing process to explore the effects of different extrusion parameters and laser power on silicone curing.The surface morphology and mechanical properties of silicone filaments under different curing conditions are characterized by Atomic Force Microscope（AFM）.The temperature distribution inside the filament when the laser irradiates on the surface of the silicone is simulated in COMSOL Multiphysics.The results show that the temperature inside the filament decreases gradually with the increasing laser scanning speed,and the average temperature inside the area can reach about 150℃when the laser scanning speed is set to 3 mm/s.Finally,combining the results of the above experiments and simulations,silicone rubber foam is prepared by laser-assisted DIW printing.The problem of difficulty in curing the materials near the substrate due to the difference in thermal conductivity is successfully achieved by combining the high-temperature platform and the CO₂ laser to prepare silicone foams instantly.