Université Nice Sophia Antipolis, Laboratoire de Physique de la Matière Condensée, Equipe Fluides et Matériaux Complexes CNRS UMR 7336, Parc Valrose, 06108 Nice Cedex 2, France.
J Phys Chem B. 2013 Mar 28;117(12):3407-15. doi: 10.1021/jp311196g. Epub 2013 Mar 15.
Compared to other semicrystalline polymers, PTFE demonstrates a very fast crystallization process on cooling. This study explores for the first time the nonisothermal PTFE ultrafast crystallization under tremendously fast cooling rates (up to 800,000 K·s(-1)) achieved by using fast scanning calorimetry (FSC) and ultra-fast scanning calorimetry (UFSC). Regular DSC was also used to get crystallization at slower rates. The data obtained on a wide range of cooling rates (over 8 orders of magnitudes) help to get new knowledge about crystallization kinetics of PTFE. Both FSC and UFSC data show that it is impossible to bypass the crystallization and thus to reach a metastable glassy state even for the fastest cooling rate employed (800,000 K·s(-1)). The crystals formed under such conditions are slightly less stable than those produced under slower cooling rates, as reflected by a shift of the melting peak to lower temperature. The difference in crystal morphologies was confirmed by SEM observations. The variation of the effective activation energy (Eα) with the relative extent of crystallization reveals that PTFE crystallization follows a transition from regime II to regime III around 315-312 °C. Corroborated temperature dependences of Eα obtained respectively for crystallizations under slow and fast cooling rates were combined and fitted to the theoretical dependence of the growth rate derived from the Hoffman-Lauritzen theory.
与其他半结晶聚合物相比，PTFE 在冷却时表现出非常快速的结晶过程。本研究首次探索了在超快冷却速率（高达 800,000 K·s(-1)）下通过使用快速扫描量热法（FSC）和超快扫描量热法（UFSC）实现的 PTFE 超快速非等温结晶。常规 DSC 也用于以较慢的速率进行结晶。在广泛的冷却速率范围内（超过 8 个数量级）获得的数据有助于获得关于 PTFE 结晶动力学的新知识。FSC 和 UFSC 数据均表明，即使采用最快的冷却速率（800,000 K·s(-1)），也不可能绕过结晶从而达到亚稳玻璃态。在这种条件下形成的晶体比在较慢冷却速率下形成的晶体稍微不稳定，这反映在熔融峰向更低温度的偏移。SEM 观察证实了晶体形态的差异。有效活化能 (Eα) 随相对结晶度的变化表明，PTFE 结晶在 315-312°C 左右从 regime II 转变为 regime III。分别对缓慢和快速冷却速率下结晶获得的 Eα 的温度依赖性进行了组合，并拟合到由 Hoffman-Lauritzen 理论推导的生长速率的理论依赖性。
