| dc.description.abstract | Over the past decade, two-dimensional (2D) programmable polymeric materials have attracted a great interest due to their ability to self-transform their flat shape into a complex three-dimensional (3D) geometry, in response to external stimuli. Despite the expectations created by 3D programmed structures in the academic and industrial communities, their success so far has been limited. This can be attributed to a combination of factors ranging from the complexity of the programmable 3D structures, the ability to achieve a fast and accurate folding at low energy constrained by a number of physical properties and functionalities. This thesis aims to develop a novel concept to fabricate complex 3D programmed multi-functional structures inspired by origami/kirigami. In this thesis, all the aspects above will be tackled, by studying a fast and controlled sequential folding, incorporating several physical properties of the 3D structures, such as mechanical, electrical, thermal, and functionalities such as sensing and actuating. After an extensive literature review in chapter 2, the experimental part of this thesis starts with the characterisation of the main materials used for the project, including oriented polymers, epoxy resin and graphene in chapter 3. Thermal and mechanical properties of several oriented polymers are evaluated, and the graphene network formation process is investigated, under two different (medium and high shear) Three Roll Mill (TRM) processing conditions (chapter 4). Chapter 5 focuses on the mechanism of simultaneous self-folding and exposes the limitations of such a method for 3D structures. In order to overcome these limitations, a controlled sequential folding is designed by combining three simple actuating multilayer units, during actuation. As proof of concept, three demonstrators obtained by sequential folding have been developed, with three different possible applications, ranging from a deployment device to a vascular filter. A finite element method (FEM) model, developed to better understand the main underlying physical mechanism, as well as to feedback into materials and structure design, is discussed in this chapter. After showing the use of sequential folding to create complex 3D structures, chapter 6 demonstrates how bespoke physical properties and functions can also be incorporated. Inspired by the Japanese art of kirigami, a self-programming Carbon Nanotubes (CNTs) veil-based honeycomb structure has been developed, in order to go beyond the typical sensing/actuation dichotomy, with capabilities to both actuate and to sense. Chapter 6 shows that this kirigami-engineered honeycomb pattern allows to drive the positioning of nanoparticles (hence providing high electrical and thermal conductivity) from the in-plane direction initially, to the out-of-plane direction once actuated. A self-folded one-cell honeycomb structure has been developed using an epoxy resin/graphene system and bi-oriented polymer. Ultra-low electrical percolation thresholds have been obtained for reduced graphene oxide (rGO)/epoxy nanocomposites with good levels of electrical conductivity at low filler loadings, while flexural modulus was improved. The strain sensing capability of the composites has been examined under flexural loadings with high sensitivity. A Joule heating with a potential application to de-icing, was also successfully integrated. | en_US |
