Institut für Festkörperphysik, Technische Universität Darmstadt, 64289 Darmstadt, Germany.
Phys Rev Lett. 2012 Jul 20;109(3):035702. doi: 10.1103/PhysRevLett.109.035702.
We study dynamically highly asymmetric binary mixtures comprised of small methyl tetrahydrofuran (MTHF) molecules and polystyrene. Combined use of dielectric spectroscopy, 2H nuclear magnetic resonance, incoherent quasielastic neutron scattering, and depolarized dynamic light scattering allows us to selectively probe the dynamics of the components in a broad dynamic range. It turns out that the mixtures exhibit two glass transitions in a wide concentration range although being fully miscible on a macroscopic scale. In between both glass transition temperatures, the dynamics of the small molecules show strong confinement effects, e.g., a crossover from Vogel-Fulcher to Arrhenius behavior of the time constants. Moreover, the dynamical behavior of small molecules close to the slow matrix is consistent with mode coupling theory predictions for a type-A glass transition, which was expected from recent theoretical and simulation studies in comparable systems.
我们研究了由小甲基四氢呋喃（MTHF）分子和聚苯乙烯组成的动态高度不对称二元混合物。介电光谱学、2H 核磁共振、非相干准弹性中子散射和去偏振动态光散射的综合应用使我们能够在广泛的动态范围内选择性地探测各组分的动力学。结果表明，尽管在宏观尺度上完全混溶，但混合物在很宽的浓度范围内表现出两个玻璃化转变。在这两个玻璃化转变温度之间，小分子的动力学表现出强烈的受限效应，例如，时间常数从沃格尔-富勒尔行为转变为阿雷尼乌斯行为。此外，接近慢基质的小分子的动力学行为与模式耦合理论对 A 型玻璃化转变的预测一致，这是从最近在可比系统中的理论和模拟研究中预期的。
