SGER: Collaborative Research: Terahertz Dynamics of Polymer Crystallization

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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.