arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 0709.4404cond-mat.softcond-mat.stat-mech
收藏

玻璃形成氢键液体的弛豫动力学理论

Theory of Relaxation Dynamics in Glass-Forming Hydrogen-Bonded Liquids

H. G. E. Hentschel, Itamar Procaccia

备注：
submitted to Phys. Rev. E., 11 pages, 11 figures
阅读 PDF
arXiv 页面 ↗HTML 原文 ↗

摘要：

我们解决了氢键过冷液体的玻璃化转变附近的弛豫动力学，通过宽带介电谱（BDS）测量。我们提出了一个理论的基础上分解的宏观偶极矩从氢键聚簇的$s$分子的贡献，与$s_{min}\le s \le s_{max}$的松弛。$s_{max}$的存在是由于动力学停滞，其值可能取决于冷却方案和老化时间。$s_{max}$的存在被转化为大小为$s$的簇的浓度的求和规则。我们构建的统计力学的过冷液体受此求和规则作为约束，估计大小$s$的集群的温度依赖的密度。与理论估计的每个集群的弛豫时间，我们提供的频率依赖的介电响应的实部和虚部的预测。预测的光谱和它们的温度依赖性与测量结果一致，解释了许多唯象拟合，如Vogel-Fulcher拟合和拉伸指数拟合。使用甘油作为一个特定的例子，我们证明定量理论和实验之间的对应关系。该理论还表明，在这种材料中，$α$峰和“多余翼”源于相同的物理。该理论还表明，在其他氢键玻璃形成剂中，“多余的翼”可以发展成$β$峰，这取决于分子材料参数（主要是簇的表面能）.因此，我们认为，$α$和$β$峰可以源于相同的物理。最后，我们解决的BDS在约束的几何形状（孔），并解释为什么最近的实验甘油没有显示出偏离散装光谱。

英文摘要：

We address the relaxation dynamics in hydrogen-bonded super-cooled liquids near the glass transition, measured via Broad-Band Dielectric Spectroscopy (BDS). We propose a theory based on decomposing the relaxation of the macroscopic dipole moment into contributions from hydrogen bonded clusters of $s$ molecules, with $s_{min}\le s \le s_{max}$. The existence of $s_{max}$ is due to dynamical arrest and its value may depend on the cooling protocol and on the aging time. The existence of $s_{max}$ is translated into a sum-rule on the concentrations of clusters of size $s$. We construct the statistical mechanics of the super-cooled liquid subject to this sum-rule as a constraint, to estimate the temperature-dependent density of clusters of size $s$. With a theoretical estimate of the relaxation time of each cluster we provide predictions for the real and imaginary part of the frequency dependent dielectric response. The predicted spectra and their temperature dependence are in accord with measurements, explaining a host of phenomenological fits like the Vogel-Fulcher fit and the stretched exponential fit. Using glycerol as a particular example we demonstrate quantitative correspondence between theory and experiments. The theory also demonstrates that the $α$ peak and the "excess wing" stem from the same physics in this material. The theory also shows that in other hydrogen -bonded glass formers the "excess wing" can develop into a $β$ peak, depending on the molecular material parameters (predominantly the surface energy of the clusters). We thus argue that $α$ and $β$ peaks can stem from the same physics. Finally we address the BDS in constrained geometries (pores) and explain why recent experiments on glycerol did not show a deviation from bul k spectra.

机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。

↑