Chiashi Shohei, Saito Yuta, Kato Takashi, Konabe Satoru, Okada Susumu, Yamamoto Takahiro, Homma Yoshikazu
Department of Mechanical Engineering , The University of Tokyo , Bunkyo, Tokyo 113-8656 , Japan.
Research Institute for Science & Technology , Tokyo University of Science , Shinjuku, Tokyo 162-8601 , Japan.
ACS Nano. 2019 Feb 26;13(2):1177-1182. doi: 10.1021/acsnano.8b06041. Epub 2019 Jan 25.
Melting point is independent of size and shape in bulk materials, but it exhibits a size dependence when the material size is extremely small. In this study, we measured the melting point of water confined in single-walled carbon nanotubes (SWCNTs) with 16 different chiralities, which ranged from 0.95 to 1.26 nm in diameter, and revealed the details of the SWCNT diameter dependence on the melting points. The melting points were probed by utilizing the change of photoluminescence (PL) emission wavelength of SWCNTs, which encapsulated water, and the relation between the emission wavelength, and the water phase was confirmed by first-principles calculations. The periodicity of the melting point variation with SWCNT diameter came from the discrete change of ice-nanotube (ice-NT) diameter, and in addition, even ice-NT with an identical diameter exhibited different melting points due to the slight difference of the inner space size of the encapsulating SWCNTs. The present results agreed with those of the molecular dynamics simulation (Takaiwa, D.; et al., Proc. Natl. Acad. Sci. U.S.A. 2008, 105, 39-43). It was elucidated that the melting point of the nanomaterial changed sensitively to the atomic structure and the confinement space size.
在块状材料中，熔点与尺寸和形状无关，但当材料尺寸极小时，熔点会表现出尺寸依赖性。在本研究中，我们测量了直径在0.95至1.26纳米范围内的16种不同手性的单壁碳纳米管（SWCNT）中受限水的熔点，并揭示了SWCNT直径对熔点的依赖性细节。通过利用封装水的SWCNT的光致发光（PL）发射波长的变化来探测熔点，并且通过第一性原理计算证实了发射波长与水相之间的关系。熔点随SWCNT直径变化的周期性源于冰纳米管（ice-NT）直径的离散变化，此外，即使直径相同的ice-NT由于封装SWCNT内部空间尺寸的细微差异也表现出不同的熔点。本结果与分子动力学模拟结果一致（Takaiwa, D.等人，《美国国家科学院院刊》2008年，105卷，39 - 43页）。结果表明，纳米材料的熔点对原子结构和受限空间尺寸敏感变化。
