Conductive Polymers and Polymer Nanocomposites for Flexible Thermoelectrics.

PhD ThesisWith the development of fields like soft (micro-) robotics, wearable devices and internet-of-things, there is a growing demand for new materials with combinations of functional properties, ranging from electrical conductivity, sensing and energy storage/harvesting, together with mechanical properties like large elastic deformations and toughness. Organic thermoelectric (OTE) materials and their composites are excellent candidates for self-powered sensors, due to their ability to harvest waste heat energy in a robust and reliable manner, combined with mechanical properties (e.g. high strain at break) and additional functionalities. This thesis focuses on the application of OTE as multi-functional self-powered sensors. Three types of representative OTE materials have been mainly investigated to explore different characteristics and potential applications. Three different processing methods have been explored for achieving the different structures aiming at various functions and potential applications in fields like wearable electronics and self-powered sensors. Poly nickel-ethenetetrathiolates (Nax(Ni-ett)n) has been selected as the n-type OTE material. Highly stretchable n-type composite films are obtained by blending with polyurethane. When subjected to a small temperature difference (< 20 oC), the films generated sufficient thermopower to be used for sensing strain and visible light, independently of humidity. Poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) has also been selected as the most widely investigated p-type OTE material. A novel self-powered ultrasensitive deformation sensor has been demonstrated based on PEDOT:PSS being Abstract vii coated on Lycra® yarns. By controlling the crack induced patterns of the conductive PEDOT:PSS coating, the strain sensitivity could be tuned in a wide range. Finally, carbon nanotube (CNT) has also been studied. A self-folding method has been used to create 3D structures by fixing CNT veils between patterned polycarbonate and biaxial stretched polystyrene films. The obtained honey-comb shaped OTE device has been utilised as a structural composite as a self-powered integrated sensor