The use of carbon nanotubes (CNTs) as a material for construction of sensors is a promising effort. This is due to some unique characteristics of CNTs. In recent years, strain sensors built from CNT composite films have been developed. This thesis study first proposed that the piezoresistive sensitivity of CNT composite films can be limited due to the presence of one of the constituent elements in the CNT composite films, that is, surfactant. CNT films free of surfactants were thus hypothesized to have a great promise to improve piezoresistive sensitivity. The motivation of this thesis study was to explore this promise.<p> This thesis presents an experimental study on Single-Wall CNT (SWNT) films free of surfactants. Such SWNT films are called pure SWNT films. The study has concluded: (1) the gauge factor of one layer SWNT film is much higher than that of CNT composite film; (2) the fabrication of multilayered pure CNT films is highly possible; (3) the gauge factor of multilayered pure SWNT films (10 layers and 0.8mg/ml concentration) can reach as high as 2.59 with non-linearity of 0.89% and repeatability of 0.1%, which outperforms the strain sensor built from CNT composite films; (4) the role of surfactants is indeed restrictive to piezoresistive response, and (5) the junction theory is likely applicable to pure SWNT film sensors.<p> The main contributions of this thesis study are: (1) the finding of a new type of strain sensors built from pure CNT films and (2) the development of a fabrication process for multilayered pure SWNT films.

The use of carbon nanotubes (CNTs) as a material for construction of sensors is a promising effort. This is due to some unique characteristics of CNTs. In recent years, strain sensors built from CNT composite films have been developed. This thesis study first proposed that the piezoresistive sensitivity of CNT composite films can be limited due to the presence of one of the constituent elements in the CNT composite films, that is, surfactant. CNT films free of surfactants were thus hypothesized to have a great promise to improve piezoresistive sensitivity. The motivation of this thesis study was to explore this promise.<p> This thesis presents an experimental study on Single-Wall CNT (SWNT) films free of surfactants. Such SWNT films are called pure SWNT films. The study has concluded: (1) the gauge factor of one layer SWNT film is much higher than that of CNT composite film; (2) the fabrication of multilayered pure CNT films is highly possible; (3) the gauge factor of multilayered pure SWNT films (10 layers and 0.8mg/ml concentration) can reach as high as 2.59 with non-linearity of 0.89% and repeatability of 0.1%, which outperforms the strain sensor built from CNT composite films; (4) the role of surfactants is indeed restrictive to piezoresistive response, and (5) the junction theory is likely applicable to pure SWNT film sensors.<p> The main contributions of this thesis study are: (1) the finding of a new type of strain sensors built from pure CNT films and (2) the development of a fabrication process for multilayered pure SWNT films.

Strain detecting with carbon nanotube (CNT) networks is one of the encouraging findings in sensor technologies. Two types of CNT based films are available for strain detection, namely CNT composite films and CNT films. Configurations of the CNT networks in these films can be made into random and aligned distributions. Understanding of fundamental knowledge regarding piezoresistive response in CNT networks in particular of the CNT film is not quite available, and this is the motivation of the present thesis. In this thesis, piezoresistive response of CNT networks under in-plane straining was studies in details first. Based on the stick percolation model, the relation between the density and conductance in CNT networks (with randomly distributed) was established and then the models which describe the relation between the density and piezoresistive sensitivity and the relation between density and piezoresistive linearity, respectively, were developed. After that, fabrication of CNT networks with aligned distributions was studied. Likewise, the models as developed for CNT network with random distributions were developed for ones with aligned distributions. Finally, modeling of the stress transfer between the nanotubes and polymer matrix was studied. This study has led to the following conclusions: (1) piezoresistive response in CNT networks of the CNT film follows the stick percolation model with the critical exponent coefficient (α) in the model being 1.938; (2) it is feasible to fabricate aligned CNT networks of varying densities with the technique which combines the spray deposition and externally applied magnetic field; (3) the configuration of CNT networks, in addition to their density, was a primary factor governing their piezoresistive response; (4) slipping occurs at the interface between the nanotube and polymer matrix when the films are subject to in-plane straining. The contributions of this study are: (1) the knowledge along with a percolation model for piezoresistive response of CNT networks of the CNT film, (2) a fabrication technique to align CNT networks of the CNT film, and (3) the knowledge along with a model for interaction between the CNT and polymer substrate in the CNT film.