Rotational fluctuations of water confined to layered oxide materials: nonmonotonous temperature dependence of relaxation times.
Rotational fluctuations of water confined to layered oxide materials: nonmonotonous temperature dependence of relaxation times.
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水的旋转波动仅限于层状氧化物材料：弛豫时间的非单调温度依赖性。
DOI：
10.1021/jp0717140
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发表时间：
2007
期刊：
影响因子：
--
通讯作者：
V. Rives
中科院分区：
文献类型：
--
作者：
L. Frunza;A. Schönhals;Ş. Frunzǎ;V. Pârvulescu;B. Cojocaru;D. Carriazo;Cristina Martín;V. Rives
本文用介电谱方法研究了水镁石结构层状氧化物材料中水的转动分子动力学，频率范围为10（-2）~ 10（7）Hz，温度范围较宽。层状双氢氧化物样品显示一个弛豫过程，这是分配给波动的水分子形成一个层，强烈吸附到氧化物表面。的弛豫速率的温度依赖性有一个不寻常的鞍状形状的特点是由一个最大值。Ryabov等人（J. Phys. Chem. B 2001，105，1845）最近应用于描述多孔玻璃中水分子的动力学的模型也用于层状材料。这个模型假设两个相互竞争的影响：旋转波动的水分子，同时发生的缺陷形成，允许创建必要的重新取向的自由体积。的激活能的旋转波动，缺陷形成的能量，一个指前因子，和缺陷浓度的主要参数，从这个模型的数据拟合。这些参数的值进行了比较与那些被发现的水局限于纳米多孔分子筛，多孔玻璃，或散装冰。详细讨论了缺陷形成能越低，缺陷数越多的关系。指前因子随着活化能的增加而增加，作为补偿定律的表达，并指示运动过程的合作性质。进一步讨论了表面OH基团和层间阴离子氧原子参与氢键形成的问题。对于水钠锰矿样品，弛豫过程可能是由一个占主导地位的电导率的贡献，这是在其频率和温度的依赖性进行了分析。发现水钠锰矿的电导率服从半导体无序材料的特性。尤其是巴顿/中岛/并川的关系得到了满足。详细分析了直流电导率σ 0的温度依赖性，给出了一些暗示，σ 0（T）也有一个不寻常的鞍形。
The rotational molecular dynamics of water confined to layered oxide materials with brucite structure was studied by dielectric spectroscopy in the frequency range from 10(-2) to 10(7) Hz and in a broad temperature interval. The layered double hydroxide samples show one relaxation process, which was assigned to fluctuations of water molecules forming a layer, strongly adsorbed to the oxide surface. The temperature dependence of the relaxation rates has an unusual saddlelike shape characterized by a maximum. The model of Ryabov et al. (J. Phys. Chem. B 2001, 105, 1845) recently applied to describe the dynamics of water molecules in porous glasses is employed also for the layered materials. This model assumes two competing effects: rotational fluctuations of water molecules that take place simultaneously with defect formation, allowing the creation of free volume necessary for reorientation. The activation energy of rotational fluctuations, the energy of defect formation, a pre-exponential factor, and the defect concentration are obtained as main parameters from a fit of this model to the data. The values of these parameters were compared with those found for water confined to nanoporous molecular sieves, porous glasses, or bulk ice. Several correlations were discussed in detail, such as the lower the value of the energy of defect formation, the higher the number of defects. The pre-exponential factor increases with increasing activation energy, as an expression of the compensation law, and indicates the cooperative nature of the motional process. The involvement of the surface OH groups and of the oxygen atoms of the interlayer anions in the formation of hydrogen bonds was further discussed. For the birnessite sample, the relaxation processes are probably overlaid by a dominating conductivity contribution, which is analyzed in its frequency and temperature dependence. It is found that the conductivity of birnessite obeys the characteristics of semiconducting disordered materials. Especially the Barton/Nakajima/Namikawa relationship is fulfilled. Analyzing the temperature dependence of the direct current (dc) conductivity sigma0 in detail gives some hint that sigma0(T) has also an unusual saddlelike form.