Mittleman, Daniel M.2016-02-052016-02-052015-052015-02-25May 2015Nickel, Daniel Vincent. "Terahertz Spectroscopy of Soft Condensed Matter: Single Methyl Branched n-Alkanes and Plastic-Crystals." (2015) Diss., Rice University. <a href="https://hdl.handle.net/1911/88377">https://hdl.handle.net/1911/88377</a>.https://hdl.handle.net/1911/88377Terahertz time-domain spectroscopy has long been recognized as a valuable tool for characterizing the far-IR range (0.1 THz to 10 THz) properties of innumerable condensed phase materials. Soft condensed matter, a broad subcategory of condensed matter, encompasses thermally and/or mechanically deformable phases such as liquids, liquid-crystals, plastic-crystals, and polymers. With comparatively more internal degrees of freedom and weaker atomic/molecular interactions, complex phase behavior and dynamics often emerge in these materials, which generally have not been explored in the THz range. Here, temperature-dependent THz-TDS is applied to three soft condensed matter systems. Using a custom designed reflection geometry spectrometer and a novel variable path length liquid sample cell, the isotropic polarizabilities of liquid phase methyl-branched n-alkanes and their linear structural isomers are characterized and compared in the THz range. In addition, the plastic-crystal’s succinonitrile and camphor are studied using transmission geometry THz-TDS. The THz range properties and dynamics characterized in these studies, from the structure-dependent isotropic polarizabilities of prototypical liquid hydrocarbons to the complex disorder/order transitions and correlated molecular dynamics of plastic-crystals, provide valuable fundamental insight into the behavior of soft condensed matter systems.application/pdfengCopyright is held by the author, unless otherwise indicated. Permission to reuse, publish, or reproduce the work beyond the bounds of fair use or other exemptions to copyright law must be obtained from the copyright holder.TerahertzSpectroscopySoft condensed matterPlastic-crystal phasesliquid phasespolarizabilitiesphononsThesis2016-02-05