Patsalidis Nikolaos, Papamokos George, Floudas George, Harmandaris Vagelis
Computation-Based Science and Technology Research Center, The Cyprus Institute, Aglantzia 2121, Nicosia Cyprus.
Department of Physics, University of Ioannina, 45110 Ioannina, Greece.
J Chem Phys. 2024 Mar 14;160(10). doi: 10.1063/5.0189652.
We present a detailed computational study on the temperature effect of the dynamics and the interfacial width of unentangled cis-1,4 polybutadiene linear chains confined between strongly attractive alumina layers via long, several μs, atomistic molecular dynamics simulations for a wide range of temperatures (143-473 K). We examine the spatial gradient of the translational segmental dynamics and of an effective local glass temperature (TgL). The latter is found to be much higher than the bulk Tg for the adsorbed layer. It gradually reduces to the bulk Tg at about 2 nm away from the substrate. For distant regions (more than ≈1.2nm), a bulk-like behavior is observed; relaxation times follow a typical Vogel-Fulcher-Tammann dependence for temperatures higher than Tg and an Arrhenius dependence for temperatures below the bulk Tg. On the contrary, the polymer chains at the vicinity of the substrate follow piecewise Arrhenius processes. For temperatures below about the adsorbed layer's TgL, the translational dynamics follows a bulk-like (same activation energy) Arrhenius process. At higher temperatures, there is a low activation energy Arrhenius process, caused by high interfacial friction forces. Finally, we compute the interfacial width, based on both structural and dynamical definitions, as a function of temperature. The absolute value of the interfacial width depends on the actual definition, but, regardless, the qualitative behavior is consistent. The interfacial width peaks around the bulk Tg and contracts for lower and higher temperatures. At bulk Tg, the estimated length of the interfacial width, computed via the various definitions, ranges between 1.0 and 2.7 nm.
我们通过长时间（数微秒）的原子分子动力学模拟，对温度范围为143 - 473K的情况下，被强吸引性氧化铝层限制的非缠结顺式1,4 - 聚丁二烯线性链的动力学和界面宽度的温度效应进行了详细的计算研究。我们研究了平移链段动力学和有效局部玻璃化温度（TgL）的空间梯度。发现后者对于吸附层而言远高于本体玻璃化转变温度（Tg）。在距基底约2nm处，它逐渐降至本体Tg。对于较远区域（大于≈1.2nm），观察到类似本体的行为；对于高于Tg的温度，弛豫时间遵循典型的Vogel - Fulcher - Tammann依赖关系，而对于低于本体Tg的温度，则遵循Arrhenius依赖关系。相反，基底附近的聚合物链遵循分段Arrhenius过程。对于低于吸附层TgL的温度，平移动力学遵循类似本体（相同活化能）的Arrhenius过程。在较高温度下，由于高界面摩擦力，存在低活化能的Arrhenius过程。最后，我们根据结构和动力学定义计算了界面宽度作为温度的函数。界面宽度的绝对值取决于实际定义，但无论如何，定性行为是一致的。界面宽度在本体Tg附近达到峰值，并在较低和较高温度下收缩。在本体Tg时，通过各种定义计算得到的界面宽度估计长度在1.0至2.7nm之间。
