Microfabrication of conductive polymer nanocomposite for sensor applications
This dissertation developed novel microfabrication techniques of conductive polymer nanocomposite and utilized this material as a functional element for various physical sensor applications. Microstructures of nanocomposite were realized through novel microcontact printing and laser ablation assisted micropatterning processes. Prototype devices including large-strain strain sensor and highly-sensitive pressure sensor were demonstrated showing distinct advantages over existing technologies. The polymer nanocomposite used in this work comprised elastomer poly(dimexylsiloxane) (PDMS) as polymer matrix and multi-walled carbon nananotubes (MWCNTs) as a conductive nanofiller. To achieve uniform distribution of carbon nanotubes within the polymer, an optimized dispersion process was developed, featuring a strong organic solvent—chloroform, which dissolved PDMS base polymer easily and allowed monodispersion of MWCNTs. Following material preparation, three novel approaches were employed to pattern microstructures of polymer nanocomposite, each of which held respective advantages over previous fabrication techniques. For example, microcontact printing, by using a pre-defined stamp, directly transfers nanocomposite patterns from the ink reservoir to a substrate. Therefore, it eliminates the need of repeated photolithography process for every sample, saving time and cost. For another example, two variations of the laser assisted screen printing technique with micropatterns defined by the programmable laser ablation of a thin polymer film, allowed direct filling of nanocomposite and required only a CAD drawing for each design of sensor sample. Two variations of this fabrication protocol realized both fully embedded nanocomposite structures in a bulk polymer, as well as protruding relief-patterns of the nanocomposite on a polymer surface. The sensing capability of the polymer nanocomposite is attributed to the unique combination of mechanical flexibility and electrical piezoresistivity. To demonstrate feasibility for practical sensor applications, two sensor prototypes were constructed. The strain sensor, for example, showed significant resistive response while sample withheld large range tensile strain of over 45%. Also, the fabricated pressure sensor indicated high sensitivity of differential pressure. Each prototype showed distinctive advantages over conventional technologies. Complex hysteresis effects were observed and analyzed regarding the resistance and stress of the nanocomposite, which was followed by discussions of potential polymeric mechanisms.
Polymer nanocomposite, carbon nanotubes, sensor, microfabrication
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