Xie Shi-Jie, Qian Hu-Jun, Lu Zhong-Yuan
State Key Laboratory of Supramolecular Structure and Materials, Institute of Theoretical Chemistry, Jilin University, Changchun 130023, China.
J Chem Phys. 2015 Feb 21;142(7):074902. doi: 10.1063/1.4908047.
The effect of confinement on the glass transition temperature Tg of polymeric glass formers with different side chain stiffness is investigated by coarse-grained molecular dynamics simulations. We find that polymer with stiffer side groups exhibits much more pronounced Tg variation in confinement compared to that with relatively flexible side groups, in good agreement with experiments. Our string analysis demonstrates that the polymer species dependence of dynamics can be described by an Adam-Gibbs like relation between the size of cooperatively rearranging regions and relaxation time. However, the primary effect of changing side-group stiffness is to alter the activation barrier for rearrangement, rather than string size. We clarify that free-surface perturbation is the primary factor in determining the magnitude of Tg variation for polymers in confinement: It is more significant for polymers having higher Tg and results in much more pronounced reduction of surface Tg and then the overall Tg of the polymers.
通过粗粒化分子动力学模拟研究了受限条件对具有不同侧链刚度的聚合物玻璃形成剂的玻璃化转变温度Tg的影响。我们发现，与具有相对柔性侧基的聚合物相比，具有更刚性侧基的聚合物在受限条件下表现出更明显的Tg变化，这与实验结果高度一致。我们的弦分析表明，动力学的聚合物种类依赖性可以用协同重排区域的大小与弛豫时间之间类似Adam-Gibbs的关系来描述。然而，改变侧基刚度的主要作用是改变重排的活化能垒，而不是弦的大小。我们阐明，自由表面扰动是决定受限聚合物Tg变化幅度的主要因素：对于具有较高Tg的聚合物，它更为显著，并导致聚合物表面Tg以及整体Tg的更明显降低。
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