Investigation into the Applications of PDMS and TEMs in Thermal Origami Composites

Abstract

The proposed research uses PDMS (Polydimethylsiloxane) and TEMs (Thermally Expandable Microspheres) to synthesize a composite capable of expanding when subjected to heat. When this composite is integrated into a bi-layer structure, it can cause bending upon heating which can be the first step towards making a shape changing polymer. Polymer shape changing composites have been researched heavily where several different materials have been used, and numerous methods have been developed for countless real-life applications. The current research proposes an alternative, less complex, method for creating an all-polymer shape changing composite using inexpensive and available materials. The proposed composite can be made from PDMS and TEMs, where PDMS is the matrix that contains the TEMs. The proposed composite was used previously for its expanding characteristics in other research projects, but it was never used for making a bending/shape-changing application. PDMS was favored as the medium holding the TEMs for its flexible and elastic properties, in addition to being a reliable medium that was available in the university and suggested by one of the supervisors. While TEMs were chosen as the expansion option for causing the overall expansion in the composite. TEMs are micro-sized spheres, or microspheres, having a small volume, in the order of μm3, of liquid hydrocarbon (Iso-Octane) encapsulated in a thermoplastic polymer shell, made from acrylonitrile. The composite synthesized can be activated by temperature, and could expand more than 100% its original volume, which makes it a prime candidate to be used in making shape-changing composites. To understand the capability of the composite to cause bending, the expansion of the composite had to be understood and characterized in relation with the microsphere loading and the activation temperature. The understanding of the expansion of the composite paved the way towards the understanding and predicting of how a bi-layer structure made from pure PDMS and the developed composite will bend and to what angle. The microspheres present in the composites were also viewed under the SEM (Scanning Electron Microscope) before and after expansion to get a more detailed understanding of how different temperatures affect the expansion of the composites. After the proper testing of the expansion and bending capabilities of the composite, a functional hinge structure was designed and tested before making a complex 2D-to-3D shape changing composite. The hinge design outlined how the composite expands, and how to use the composites’ expansion to achieve bending. The results obtained regarding expansion and bending can the user fabricate a working composite. however, with many different microspheres, with each one having its own characteristics and limitations, further research must be done to determine the optimum microsphere to be used. In addition, the design and placement of the hinges in the current research worked, but not as expected, which means that a better design must be perfected to obtain a properly working shapechanging composite.