| Summary: | This thesis presents the development of novel stretchable conductors based on gold films magnetron sputtered on polydimethylsiloxane (PDMS). The Thesis starts with an overview of the available state of the art in stretchable conductors and their applications in smart fabrics, biomedicine and consumer goods. It then identifies two novel methods designed to improve these conductors using a/ hydrogenated amorphous carbon (a-C:H) interlayers and b/ carbon nanotube CNT/PDMS composite substrates. The ultra-thin thin a-C:H films were deposited on PDMS by Plasma enhanced chemical vapour deposition (PECVD). Atomic force microscopy (AFM) showed that the a-C:H film buckled, resulting in a linear surface length increase of 6-6.5%, potentially very useful to relieve tensile strains. Electro mechanical tensile cycling measurements showed a 280 fold decrease in electrical resistivity for the gold conductor with a-C:H interlayer when compared to that without interlayer. The electrical resistivity obtained with a-C:H interlayer, 8xlO-6 O.cm, was smaller than the best published v.lues to date (-3x!O"' D.cm). After tensile cycling both samples return to their original position but leaving remarkable differences in their electrical resistance, - 9 0 for the sample with a-C:H interlayer but -3000 n for that without a-C:H interlayers. The SEM micrographs also shows much improvement in terms of crack density and delaminated area for the gold conductor with a-C:H interlayer. Angle resolved XPS and SIMS analysis indicate that the a-C:H is intermixed with the PDMS substrate resulting in a graded interface, because of the energetic carbon ions used in the PECVD process. Hence, the beneficial effect of the a-C:H interlayer is two-fold; it forms a graded layer, which reduces the thermal strain mismatch and it produces an increase in specific surface area which reduces the applied biaxial tensile stress. This latter effect was confirmed by Finite Element Analysis (FEA) of the buckled a-C:H surfaces using the acquired AFM images to define the modelling geometry. The second part of the thesis examines gold coated CNTIPDMS conductors. These composite substrates were prepared by in situ curing. UV -Visible absorbance and Raman measurements showed that sonication treatments can lead to the breakage of tubes but are also efficient in dispersing the tubes within the polymer. Raman analysis of the composites shows that there is an intercalation and chemical reaction that restrict the vibration of CNT characteristic peaks and this leads to higher Raman ID/IG ratio, i.e. more defects in the CNT, reduces the electrical resistivity and lowers the mechanical properties. At rest, the conduction in the gold coated samples depends on the conduction in the composite substrate but also on the crack pattern in the gold layer. As the cracking results from a thermo-mechanical mismatch, it is sometimes more severe for the gold layers deposited on composite substrates. Cyclic tensile testing however shows that the gold layers deposited on composite substrates perfonn better in leon of conduction under load and fatigue resistance. To conclude, this project showed that, while both of these innovative approaches perfooned well, they gave complementary results; the a-C :H interlayer mainly reduce the zero strain resistivity of the conductors while the CNT composite substrate assisted the conduction under loading conditions.
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