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 Title: EXPLORING THE SOLID STATE PHASE TRANSITION IN DL-NORVALINE WITH TERAHERTZ SPECTROSCOPY Author(s): Schmuttenmaer, Charles A. Contributor(s): Williams, Michael R. C.; Regan, Kevin P.; Nemes, Coleen T.; Neu, Jens Subject(s): Mini-symposium: Far-Infrared Spectroscopy Abstract: DL-Norvaline is a molecular crystal at room temperature and it undergoes a phase transition when cooled below 190 \textit{K}. This phase transition is believed to be Martensitic. We investigate this phase transition by measuring its terahertz (THz) spectrum over a range of temperatures. Temperature-dependent THz time-domain spectroscopy (THz-TDS) measurements reveal that the transition temperature ($\textit{T}_{\beta \rightarrow \alpha}$) is 190 \textit{K}. The influence of nucleation seeds was analyzed by determining the $\textit{T}_{\beta \rightarrow \alpha}$ of molecular crystals with varying grain size. Grains of 5 $\mu$m or less result in a lower transition temperature ($\textit{T}_{\beta \rightarrow \alpha}$ = 180 \textit{K}) compared to larger grains of 125–250 $\mu$m ($\textit{T}_{\beta \rightarrow \alpha}$ = 190 \textit{K}). Additionally, we gain insight into the physical process of the phase transition \textit{via} temperature-dependent THz-TDS spectra of doped and mixed molecular crystals. The addition of molecular dopants, which differ from DL-norvaline only at the end of the side chain which resides in the hydrophobic layers of the crystal, decreases $\textit{T}_{\beta \rightarrow \alpha}$. This is consistent with a solid-solid phase transition in which the unit cell shifts along this hydrophobic layer, and it leads us to believe that the phase transition in DL-norvaline is Martensitic in nature. Issue Date: 06/20/18 Publisher: International Symposium on Molecular Spectroscopy Citation Info: APS Genre: Conference Paper / Presentation Type: Text Language: English URI: http://hdl.handle.net/2142/100844 DOI: 10.15278/isms.2018.WI05 Other Identifier(s): WI05 Date Available in IDEALS: 2018-08-172018-12-12
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