Infoscience

Thesis

Preparation and Physical Characterization of Carbon Nanotubes-SU8 Composites

This thesis firstly describes the synthesis and characterisation of carbon nanotubes (CNTs). We focused our research on the growth conditions of CNTs synthesized by chemical vapour deposition (CVD). In particular, the effect of the support surface structure, composition and size of the catalyst precursor, relation of catalyst size with the size of its precursor and the diameter of synthesized CNTs, as well as CNTs diameter distribution were investigated. It was found that the support surface structure strongly influenced the size, shape and chemical composition of the catalyst precursor. Moreover, the size of the catalyst was found to be not always dependent on the size of the catalyst precursor. The best graphitized CVD CNTs were produced from the completely amorphous catalyst precursor in the form of micrometer-sized lumps. Thus, it was found that the growth of CVD CNTs proceeds from the in-situ formed catalyst grains, which were often found unrelated with the support due to the precursor large size and lack of available support's surface sites favourable for the precursor binding. We optimized the CVD CNTs synthesis method towards CNTs diameter controlled growth. Furthermore, well-structured CNTs comparable with arc-discharge CNTs were synthesized for the first time by the CVD method. In particular, catalyst particles were not found in such CNTs which were closed on both ends. CNTs, few-layered graphene and graphene were successfully synthesized by the CVD method without the presence of the transitional metal catalyst. We developed the method of controlled cutting of CNTs to the prescribed length by the planetary ball milling. The second part describes preparation and physical characterisation of the composite made of the SU8 polymer and CVD CNTs previously optimized for this purpose. At first, we have optimized the preparation conditions (including the appropriate solvents, surfactants and all steps of the preparation process). CNTs dispersion in the SU8 matrix was characterized by the transmission electron microscopy (TEM) of the microtome composite and by the impedance measurements. The homogeneous CNTs-SU8 composites have been obtained and the results of the mechanical (hardness and Young's modulus), electrical (four-point measurement and resistivity as a function of temperature) and thermal characterization (thermal conductivity and thermo power) of the prepared composites were measured. The increase in hardness of 122% and in the Young's modulus of 56% (for 0.8 wt% of CNTs in SU8) and thermal conductivity of 3.7 times (for 10wt% of CNTs in SU8) was achieved for composites containing randomly oriented CNTs. Moreover, all prepared composite samples were electrically conductive. In the third part, processing of the obtained composites was successfully optimized for the ink jet printing process, photolithography and screen printing. Especially, photo-patterning was optimized at each processing step in order to minimize their drawbacks.

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