SGER: Collaborative Research: Terahertz Dynamics of Polymer Crystallization

合成聚合物的结晶，尽管具有重要的工业意义，但仍然是聚合物科学和凝聚态物理的主要挑战。尽管聚合物结晶的动力学理论已被广泛接受，但聚合物结晶的潜在动力学仍然是未知的。因此，人类通过结晶控制聚合物结构的能力是有限的，特别是在其早期阶段和纳米尺度上。在这个SGER提案中，我们提议开始对聚合物结晶的太赫兹（THz）动力学进行研究。太赫兹动力学起源于链间和链内运动的集体模式，预计在成核和生长两个阶段都是活跃的。集体模式的光谱指纹位于远红外区域，从几个波数到大约300厘米-1。在能量上，它们驻留在太赫兹区（1太赫兹= 1012赫兹）。这一建议的目的是建立太赫兹动力学在结晶过程中的结构形成的作用。努力将集中在初级成核阶段。具体目的是建立具体的显微证据，证明太赫兹能量输入能够控制成核行为。实验将采用能量具有成核活化特征的明亮单色太赫兹自由电子激光器（FEL）。用原位显微镜观察了在FEL照射下亚稳聚合物熔体的成核行为变化。目标不仅是建立太赫兹动力学在聚合物结晶中的作用，而且还引入太赫兹动力学的概念来研究聚合物体系的结构相变。本提案中采用的实验策略也为分子工程中突破性纳米技术的发展打开了大门。

The crystallization of synthetic polymers, in spite of its significant industrial importance,continues to represent a primary challenge of polymer science and condensed matter physics.Although kinetic theories on polymer crystallization enjoyed widespread acceptance, theunderlying dynamics of polymer crystallization is still unknown. Consequently, man's ability tocontrol polymer structure via crystallization is limited, particularly during its early stages and atthe nanoscale. In this SGER proposal, we propose to initiate research on the Terahertz (THz) dynamicsof polymer crystallization. THz dynamics originates from the collective modes of inter- andintra-chain motions and is expected to be active during both stages of nucleation and growth. Thespectral fingerprints of the collective modes lie in the far-IR region, from a few wavenumbers tosome 300 cm-1. Energetically, they reside in the THz regime (1 THz = 1012 Hz). It is the objective of this proposal to establish the role of THz dynamics in structuralformation during crystallization. Efforts will be focused on the stage of primary nucleation. Thespecific aim is to establish concrete microscopy evidence that THz energy input is capable ofcontrolling nucleation behavior. Experimentally, brilliant monochromatic THz free-electronlaser (FEL), whose energy is characteristic of nucleation activation, will be used. In-situmicroscopy is employed to follow changes in nucleation behavior upon FEL illumination onmetastable polymer melts. The goal is not only to establish the role of THz dynamics in polymer crystallization, butalso to introduce the concept of THz dynamics to study structural phase transformations inpolymer systems. The experimental strategy adopted in this proposal also opens the door for thedevelopment of a groundbreaking nanotechnology for molecular engineering.