This dissertation details results of using terahertz (THz) radiation to investigate material properties. Progress in instrumentation has allowed researchers to work in this frequency region, yet most of the effort has been in hardware design and not directly in application. Here, select studies of foam drainage, alcohol absorption and dielectric properties, and amino acid spectral features are presented.
Foam drainage has been investigated with THz spectroscopy to characterize various aqueous-based surfactant solutions. Anionic, cationic, nonionic, mixed ionic, and protein surfactant systems were studied. Nitrogen gas was bubbled into the respective aqueous systems to create a wet foam, which then drained characteristically based on interacting forces between the surfactant molecules with both water and each other. THz radiation, readily absorbed by water, was then used to identify the water content throughout the foam at various positions and times, yielding static and kinetic absorption data. In addition, basic imaging was attempted using an x-y translation stage to raster across a longer-lasting foam.
Absorption and dielectric data of alcohols were collected by passing THz radiation through a high-density polyethylene cell containing the liquids. Octanol down to ethanol were investigated, and material properties were calculated from the time-domain waveforms collected. Pure alcohols were studied along with dilutions in hexane, as hexane has negligible absorption in the THz region. These data extend the available resources from the microwave region regarding dielectric properties of polar molecules.
Amino acids, important in body function, have also been investigated using THz spectroscopy. Pure powders were "diluted" in polyethylene and pressed into pellets that were probed in transmission mode. Mixed amino acid pellets were also created to use as a basic polypeptide study. Attenuated total reflectance modules, included with the instrument purchased from TeraView, were incorporated to collect spectra of the pure amino acid powders and compared to the transmission results.