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首页> 外文期刊>Physical chemistry chemical physics: PCCP >Exploring the solid state phase transition in DL-norvaline with terahertz spectroscopy
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Exploring the solid state phase transition in DL-norvaline with terahertz spectroscopy

机译：用太赫兹光谱法探索DL-NORVALINE中的固态相转变

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摘要

DL-Norvaline is a molecular crystal at room temperature and it undergoes a phase transition when cooled below 190 K. This phase transition is believed to be Martensitic, thus making it of particular interest for molecular machines. In this paper 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 (T-beta -alpha) is 190 K. The influence of nucleation seeds was analyzed by determining the Tb-a of molecular crystals with varying grain size. Grains of 5 mm or less result in a lower transition temperature (T beta-alpha = 180 K) compared to larger grains of 125-250 mm (T-beta -alpha = 190 K). Additionally, we gain insight into the physical process of the phase transition 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 T-beta -alpha. This is consistent with a solidsolid 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.
机译：DL-NORVALINE是室温下的分子晶体，当冷却在190k低于190k时，它经历相变。认为这种相转变是马氏体的，因此使其特别感兴趣的分子机。在本文中，我们通过在一系列温度范围内测量其太赫兹（THz）光谱来调查该阶段过渡。温度依赖性THz时域光谱（THz-TDS）测量表明，过渡温度（T-β - ＆GT;α）是190k。通过测定具有不同变化的分子晶体的Tb-a来分析成核种子的影响晶粒尺寸。与125-250mm的较大颗粒相比，5mm以下的5mm或更小的晶粒导致较低的过渡温度（tβ-α= 180k）（t-β - ＆α= 190k）。另外，我们通过掺杂和混合分子晶体的温度依赖性Thz-TDS光谱深入了解相转移的物理过程。添加分子掺杂剂，其仅不同于D1-NORVALINE在侧链的末端，该侧链在晶体层的疏水层中，降低T-β - ＆α。这与固溶体相转变一致，其中单位细胞沿着这种疏水层移位，并导致我们相信D1-Norvalinine中的相变是马氏体的。

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