Roles of individual and cooperative motions of molecules in glass-liquid transition and crystallization of toluene.
Roles of individual and cooperative motions of molecules in glass-liquid transition and crystallization of toluene.
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分子的单独运动和协同运动在甲苯玻璃液转变和结晶中的作用。
DOI：
10.1021/jp104520f
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发表时间：
2010
期刊：
影响因子：
--
通讯作者：
R. Souda
中科院分区：
文献类型：
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作者：
R. Souda
众所周知，深度过冷的脆性液体是动态非均质的，其中剪切粘度以及α和β弛豫过程的超阿伦尼乌斯行为已经被观察到。为了阐明这些行为的起源，我们通过使用飞行时间二次离子质谱法研究了气相沉积甲苯薄膜的微观分子扩散和宏观流体动力学之间的相关性。在 15 K 沉积的薄膜上，分子在 70 K 左右逐渐混合，随后在 117 K 的量热玻璃化转变温度 (T(g)) 附近薄膜形态发生突然变化。对于在 100 K 沉积的薄膜，分子的混合发生在温度超过 100-130 K 的情况下，但在 T(g) 下没有观察到扩散率的突然增加。这一结果可以解释为动力学异质性或平移扩散与粘度之间的解耦。自扩散被认为发生在亚 T(g) 区域，作为玻璃-液体转变的前体状态；也就是说，类固体状态下的个体运动在T(g)时演化为类液体状态的协同运动。过冷液体在 147 K 时成核，但只要原子核预先存在，晶体甚至可以在 117 K 下生长。还与该标准进行比较，讨论了非晶固体水异常玻璃化转变行为的起源。
Deeply supercooled fragile liquid is known to be dynamically heterogeneous, where super Arrhenius behavior of shear viscosity and alpha and beta relaxation processes have been observed. To clarify origins of these behaviors, we have investigated correlations between microscopic molecular diffusion and macroscopic hydrodynamics of vapor-deposited toluene films by using time-of-flight secondary ion mass spectrometry. The molecules are intermixed gradually at around 70 K on the film deposited at 15 K, which is followed by an abrupt film morphology change at around the calorimetric glass-transition temperature (T(g)) of 117 K. For the film deposited at 100 K, intermixing of the molecules occurs at temperatures over 100-130 K, but no abrupt increase in diffusivity is recognizable at T(g). This result can be explained as dynamical heterogeneity or decoupling between translational diffusion and viscosity. The self-diffusion is thought to occur in a sub-T(g) region as a precursor state of the glass-liquid transition; that is, individual motion in the solid-like state evolves into cooperative motion of liquid-like state at T(g). The supercooled liquid nucleates at 147 K, although the crystal can grow even at 117 K provided that nuclei preexist. The origins of unusual glass transition behaviors of amorphous solid water are also discussed in comparison with this standard.