Institut für Festkörperphysik, Technische Universität Darmstadt, 64289 Darmstadt, Germany.
J Chem Phys. 2010 Jun 14;132(22):224505. doi: 10.1063/1.3431537.
We investigate structure and dynamics of concentration fluctuations in the binary glass former methyl-tetrahydrofuran and oligomeric methyl metacrylate by photon correlation spectroscopy with partially coherent x-rays from a synchrotron source. Although the system is macroscopically well miscible and optically clear in the full temperature range, calorimetric and dielectric measurements reveal two distinct glass transition temperatures. The relaxation of long range concentration fluctuations turns out to be diffusive and exponential only well above the upper glass transition temperature. As the characteristic time tau(cf) for concentration fluctuations shows a much weaker temperature dependence than the alpha-relaxation both traces finally intersect upon lowering the temperature. Thus, close to T(g), the concentration fluctuations show pronounced features of out-of-equilibrium dynamics such as compressed relaxation functions and a crossover to a ballistic wave vector dependence of tau(cf), like previously observed in various soft matter systems. Moreover, the analysis of time-resolved correlation functions reveals that the relaxation of concentration fluctuations around T(g) involves pronounced dynamic heterogeneities.
我们通过使用同步加速器源的部分相干 X 射线研究了二元玻璃形成体甲基四氢呋喃和低聚物甲基丙烯酸甲酯中浓度涨落的结构和动力学。尽管该系统在整个温度范围内宏观上具有良好的混溶性和光学透明性，但量热法和介电测量显示出两个不同的玻璃化转变温度。只有在较高的玻璃化转变温度以上，长程浓度涨落的弛豫才表现为扩散和指数。由于特征时间 tau(cf) 对于浓度涨落的温度依赖性比 α 弛豫弱得多，因此这两个轨迹最终在降低温度时相交。因此，在接近 T(g)时，浓度涨落表现出明显的非平衡动力学特征，如压缩弛豫函数以及 tau(cf)对弹道波矢的依赖性的转变，如先前在各种软物质系统中观察到的那样。此外，对时间分辨相关函数的分析表明，在 T(g)附近浓度涨落的弛豫涉及明显的动态不均匀性。
