Characterizing the Structure and Phase Transformation of Poly(ethylene Oxide)-Urea Complexes Using Terahertz Time-Domain Spectroscopy.

Terahertz time-domain spectroscopy (THz-TDS) was employed to characterize the structure and α→β phase transformation of poly(ethylene oxide) (PEO)-urea complexes. While the THz responses of α- and β-form complexes are both originated from hydrogen bonding interactions, they possess different THz absorption bands. The α-form PEO-urea complex shows two bands at 1.12 and 1.24 THz, which are vibration modes due to the hydrogen bonding among urea and between PEO and urea, respectively; the β-form PEO-urea complex shows a band at 1.48 THz, which is a vibration mode due to the hydrogen bonding among urea. A polarized THz-TDS study demonstrates that the urea-urea hydrogen bonding direction rotates 90° during the β→α transformation process. This study reveals the great potential of THz-TDS for investigating polymer-small molecule complexes. [ABSTRACT FROM AUTHOR]