过量构型熵对脆性的影响：polymer /低聚物共混物的情况
The consequence of excess configurational entropy on fragility: the case of a polymer/oligomer blend
摘要：
通过利用聚合物的玻璃化转变的分子量依赖性及其形成完全可混溶的共混物的能力，我们提出了一种方法来修改系统的脆弱性，从脆弱到强大，保持相同的玻璃性质，即振动态密度，均方位移和局部结构。通过量热法和中子散射法研究了非热聚苯乙烯/低聚物共混物的慢动力学和快动力学，并与被认为是参考的纯17-mer聚苯乙烯的动力学进行了比较。尽管共混物和纯17-mer在玻璃和液体中具有相同的热容，但它们的脆性差异很大。这种脆弱性的差异与混合过程产生的额外构型熵有关，其作用范围远大于链间距离，而不会影响玻璃的快速动力学和结构。
英文摘要：
By taking advantage of the molecular weight dependence of the glass transition of polymers and their ability to form perfectly miscible blends, we propose a way to modify the fragility of a system, from fragile to strong, keeping the same glass properties, i.e. vibrational density of states, mean-square displacement and local structure. Both slow and fast dynamics are investigated by calorimetry and neutron scattering in an athermal polystyrene/oligomer blend, and compared to those of a pure 17-mer polystyrene considered to be a reference, of same Tg. Whereas the blend and the pure 17-mer have the same heat capacity in the glass and in the liquid, their fragilities differ strongly. This difference in fragility is related to an extra configurational entropy created by the mixing process and acting at a scale much larger than the interchain distance, without affecting the fast dynamics and the structure of the glass.
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