论水的无定形多晶性的非均匀性
On the heterogeneous character of water's amorphous polymorphism
摘要：
在这封信中，我们报告{ \it原位}小角中子散射结果的高密度（HDA）和低密度非晶（LDA）冰结构和中间结构，发现在温度诱导的转变HDA到LDA。我们表明，小角度信号的特点是由两个$Q$制度具有不同的属性（$Q$是定义为$Q = 4π\sin{(Θ)}/λ_{\rm i}$与$Θ$是一半的散射角和$λ_{\rm i}$入射中子波长的散射矢量的模量）。极低- $Q$区域（$< 5\times 10^{-2}$-$^{-1}$ $^{-1}$）由Porod-极限散射主导。它的强度降低的过程中的HDA LDA转换后的动力学让人想起在广角衍射实验中观察到的。在$5 \times 10^{-2} < Q < 0.5$、$^{-1}$ HDA和LDA的中间区，小角中子散射形状因子具有相当平坦的平台.然而，HDA信号显示朝向较小的$Q$的强度上升，将该无定形结构标记为异质的。当遵循HDA到LDA的过渡时，形状因子显示出明显的瞬态强度过剩，这标志着所有中间结构在一些纳米的长度尺度上都是强烈异质的。
英文摘要：
In this letter we report {\it in situ} small--angle neutron scattering results on the high--density (HDA) and low-density amorphous (LDA) ice structures and on intermediate structures as found during the temperature induced transformation of HDA into LDA. We show that the small--angle signal is characterised by two $Q$ regimes featuring different properties ($Q$ is the modulus of the scattering vector defined as $Q = 4π\sin{(Θ)}/λ_{\rm i}$ with $Θ$ being half the scattering angle and $λ_{\rm i}$ the incident neutron wavelength). The very low--$Q$ regime ($< 5\times 10^{-2}$ Å$^{-1}$) is dominated by a Porod--limit scattering. Its intensity reduces in the course of the HDA to LDA transformation following a kinetics reminiscent of that observed in wide--angle diffraction experiments. The small--angle neutron scattering formfactor in the intermediate regime of $5 \times 10^{-2} < Q < 0.5$ Å$^{-1}$ HDA and LDA features a rather flat plateau. However, the HDA signal shows an ascending intensity towards smaller $Q$ marking this amorphous structure as heterogeneous. When following the HDA to LDA transition the formfactor shows a pronounced transient excess in intensity marking all intermediate structures as strongly heterogeneous on a length scale of some nano--meters.
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