SGER: Collaborative Research: Terahertz Dynamics of Polymer Crystallization

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, the

underlying dynamics of polymer crystallization is still unknown. Consequently, man's ability to

control polymer structure via crystallization is limited, particularly during its early stages and at

the nanoscale.

In this SGER proposal, the PIs propose to initiate research on the Terahertz (THz) dynamics

of polymer crystallization. THz dynamics originates from the collective modes of inter- and

intra-chain motions and is expected to be active during both stages of nucleation and growth. The

spectral fingerprints of the collective modes lie in the far-IR region, from a few wavenumbers to

some 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 structural

formation during crystallization. Efforts will be focused on the stage of primary nucleation. The

specific aim is to establish concrete microscopy evidence that THz energy input is capable of

controlling nucleation behavior. Experimentally, brilliant monochromatic THz free-electron

laser (FEL), whose energy is characteristic of nucleation activation, will be used. In-situ

microscopy is employed to follow changes in nucleation behavior upon FEL illumination on

metastable polymer melts.

The goal is not only to establish the role of THz dynamics in polymer crystallization, but

also to introduce the concept of THz dynamics to study structural phase transformations in

polymer systems. The experimental strategy adopted in this proposal may also open the door for the

development of a groundbreaking nanotechnology for molecular engineering.