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A novel approach to fabricate bioinspired programmable composite materials : the 3D Printing way

Abstract : This thesis work deals with 4D printing. That is to say the manufacturing of 3D printed objects whose shape and/or properties vary in a controlled way in time by the application of external stimuli. In particular, the use of magnetic fields is very promising because they can be easily applied, are not dangerous for health and allow the printed object to be remotely controlled.During our thesis work, we have incorporated magnetic charges (Fe3O4) in photocurable formulations in order to print magneto-active objects. For the 3D printing process, we used the digital light processing (DLP).In a first step, we modified the reactivity of the photo-curable formulations by varying the amount of reactive diluent (butyl acrylate, BA) in the acrylic resin (Ebecryl 8232). In particular, by varying the amount of BA reagent, we were able to control the stiffness of the polymers. We then showed that the maximum charge of magnetic particles that can be dispersed in the resin was 6% by weight, which allowed us to obtain printed parts with a resolution of about 400 µm. By varying the mechanical properties of the printed composites, we exploited different movements of the printed objects: rolling and translation for rigid matrices and folding and unfolding for softer polymers.To improve the remote control of printed materials, we have exploited the self-assembly process of magnetic particles to program their microstructure. Indeed, when magnetic charges are dispersed in a liquid medium and exposed to a uniform magnetic field, they spontaneously assemble into wire structures oriented along the field lines. By dispersing the magnetic particles in a photosensitive formulation, once the desired spatial arrangement was obtained, we irradiated the formulation to "freeze" the chains of magnetic particles in the host matrix.The self-assembly process as well as the rotation of the magnetic particle chains was studied by optical microscopy. In addition, a simplified theoretical model was proposed to describe both phenomena, and numerical simulations were performed to characterize the system. The self-assembly process and the rotation of the chains were also observed in situ and at the nanometer scale by scanning X-ray microscopy on the Hermes line of the SOLEIL synchrotron. This gave us detailed information on the evolution of the microstructure in a liquid film (in 2D) as a function of the applied magnetic field.To control the microstructure of a 3D printed object, our strategy consisted in reproducing the 2D control on the magnetic chains in each printed layer of the object. This was done by modifying a DLP printer to be able to apply magnetic fields of variable intensity and direction during the printing process. By optical microscopy, we demonstrated that the proposed DLP device is effective in programming the microstructure of the composites printed in 3D.Magnetic characterizations showed that samples incorporating oriented magnetic chains have an easy magnetic axis that coincides with the orientation of the microstructure. Thanks to this property, we were able to program the macroscopic magnetic behavior of the manufactured materials.Magneto-sensitive polymers containing oriented microstructures behave like magnetic compasses. Therefore, when a uniform magnetic field is applied, the objects are rotated to align their axis of easy magnetization along the field lines. Exploiting this phenomenon, we produced objects, which depending on their mechanical properties can undergo rotation or bending. In addition, we have printed gears composed of toothed wheels or magneto-active clamps that undergo a programmed rotation by the remote application of a magnetic field.
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Submitted on : Thursday, July 15, 2021 - 3:51:10 PM
Last modification on : Saturday, July 17, 2021 - 3:34:43 AM
Long-term archiving on: : Saturday, October 16, 2021 - 6:46:05 PM

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  • HAL Id : tel-03287405, version 1

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Simone Lantean. A novel approach to fabricate bioinspired programmable composite materials : the 3D Printing way. Polymers. Institut Polytechnique de Paris; Politecnico di Torino, 2021. English. ⟨NNT : 2021IPPAX024⟩. ⟨tel-03287405⟩

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