在中,冷却速度依赖的结晶和玻璃过渡在n-中
1The Fritz Haber Research Center, Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem 9190401, Israel. agmon@fh.huji.ac.il.
Physical chemistry chemical physics : PCCP
|April 11, 2025
概括
这项研究探讨了n-基中的分子形状如何影响它们过渡到玻璃状状态. 较长的n-基 (n ≥18) 形成发针形状,影响玻璃过渡温度 (Tg),并揭示了玻璃化关键链的长度.
科学领域:
- 材料科学 材料科学 材料科学
- 物理化学 物理化学
- 计算化学计算化学
背景情况:
- n-基是线性化合物,具有作为有机相变材料 (PCM) 的应用.
- 冷却速度会影响n-基是否形成晶状或玻璃状状态,后者以玻璃过渡温度 (Tg) 为特征.
- 分子构成在n-的玻璃化中的作用在很大程度上仍未被探索.
研究的目的:
- 研究分子构成对中长度n-基的玻璃化过程的影响.
- 为了确定链条长度 (n) 和n-的玻璃化过渡温度 (Tg) 之间的关系.
- 探索分子端到端距离 (Ree) 在n-的结晶和玻璃化中的相关性.
主要方法:
- 用全原子分子动力学模拟来研究n-基.
- 模拟涉及以七种不同的速度冷却中间长度基 (n=12,16).
- 对14个n-基 (4 ≤ n ≤ 50) 进行了快速冷却,以确定Tg.
主要成果:
- 端到端的距离 (Ree) 是至关重要的;晶体状态由完全拉伸的分子 (最大Ree) 组成.
- 对于n ≥18出现一个毛旋转形状,与液态n-的Rg/Ree (n) 中的最小相对应.
- Tg对n的依赖是由两个交叉的Ueberreiter和Kanig方程描述的,其中Tg∞ = 250 K的非对称极限.
结论:
- 分子构造,特别是超出n=18的发针结构的出现,显著影响了n-的玻璃化.
- 该研究提供了基于Ree分布的"结晶度"的新定义.
- 导出的Tg(n) 关系及其不对称极限为对n-烯玻璃过渡的理论理解提供了宝贵的见解.
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